Schema-2-Java is the process of compiling one or more schema files into generated Java classes. Here are some of the basic steps for developing an app:

Java-2-Schema is the process of augmenting existing Java classes with the annotations defined in the javax.xml.bind.annotation package so that the JAXB runtime binding framework is capable of performing the (un)marshal operations. Here are the basic steps for developing an app:

For more information about this process, see the the Java WSDP Tutorial and the extensive Sample Apps documentation.

To run the sample applications, just go into each sample directory, and run ant without any option.

A few sample applications do not use Ant. For those samples, refer to the included readme.txt files for instructions.

Because XML Schema is so complicated, and because there are a lot of tools out there do not implement the spec correctly, it is often the case that a schema you are trying to compile has some real errors in it. When this is the case, you'll see XJC reporting somewhat cryptic errors such as rcase-RecurseLax.2: There is not a complete functional mapping between the particles.

The JAXB RI uses the schema correctness checker from the underlying JAXP implementation, which is the JAXP RI in a typical setup. The JAXP RI is one of the most conformant schema validators, and therefore most likely correct. So the first course of action usually is to fix problems in the schema.

However, in some situations, you might not have an authority to make changes to the schema. If that is the case and you really need to compile the schema, you can bypass the correctness check by using the -nv option in XJC. When you do this, keep in mind that you are possibly feeding "garbage" in, so you may see XJC choke with some random exception.

One of the typical errors you'll see when compiling a complex schema is:

parsing a schema...
[ERROR] Property "MiOrMoOrMn" is already defined.
  line 132 of
file:/C:/kohsuke/Sun/JAXB/jaxb-unit/schemas/individual/MathML2/presentation/scripts.xsd

[ERROR] The following location is relevant to the above error
  line 138 of
file:/C:/kohsuke/Sun/JAXB/jaxb-unit/schemas/individual/MathML2/presentation/scripts.xsd

This is an actual example of the offending part of a schema, taken from MathML. If you go to line 132 of scripts.xsd, you'll see that it has a somewhat complicated content model definition:

<xs:group name="mmultiscripts.content">
    <xs:sequence>
        <xs:group ref="Presentation-expr.class"/>
        <xs:sequence minOccurs="0" maxOccurs="unbounded">      <!-- line 132 -->
            <xs:group ref="Presentation-expr-or-none.class"/>
            <xs:group ref="Presentation-expr-or-none.class"/>
        </xs:sequence>
        <xs:sequence minOccurs="0">
            <xs:element ref="mprescripts"/>
            <xs:sequence maxOccurs="unbounded">                 <!-- line 138 -->
                <xs:group ref="Presentation-expr-or-none.class"/>
                <xs:group ref="Presentation-expr-or-none.class"/>
            </xs:sequence>
        </xs:sequence>
    </xs:sequence>
</xs:group>

This is a standard technique in designing a schema. When you want to say "in this element, B can occur arbitrary times, but C can occur only up to once", you write this as B*,(C,B*)?. This, however, confuses JAXB, because it tries to bind the first B to its own property, then C to its own property, then the second B to its own property, and so we end up having a collision again.

In this particular case, B isn't a single element but it's a choice of large number of elements abstracted away in <xs:group>s, so they are hard to see. But if you see the same content model referring to the same element/group twice in a different place, you can suspect this.

In this case, you'd probably want the whole thing to map to a single list so that you can retain the order those elements show up in the document. You can do this by putting the same <jaxb:property> customization on the whole "mmultiscripts.content" model group, like this (or you can do it externally with XPath):

<xs:groupname="mmultiscripts.content">
<xs:annotation>
    <xs:appinfo>
        <jaxb:propertyname="content"/>
    </xs:appinfo>
</xs:annotation>
<xs:sequence>
<xs:groupref="Presentation-expr.class"/>

Another way to fix this problem is to use the simpler and better binding mode in XJC, which is a JAXB RI vendor extension.

When schemas contain similar looking element/type names, they can result in "Two declarations cause a collision in the ObjectFactory class" errors. To be more precise, for each of all types and many elements (exactly what elements get a factory and what doesn't is bit tricky to explain), XJC produces one method on the ObjectFactory class in the same package. The ObjectFactory class is created for each package that XJC generates some files into. The name of the method is derived from XML element/type names, and the error is reported if two elements/types try to generate the same method name.

There are two approaches to fix this problem. If the collision is coming from two different schemas with different target namespaces, then you can easily avoid the collision by compiling them into different Java packages. To do this, use <schemabindings> customization on two schemas and specify the package name.

Another way to fix this problem is to use <factoryMethod> customization on two conflicting elements/types to specify different factory method names. This can be used in all cases, but if you have a large number of conflicts, you'll have to specify this customization one by one.

Notice that <class> customization doesn't affect the ObjectFactory method name by itself.

The catalog resolver supports many different formats, but the easiest one is a line based *.cat format. Other than comments and empty lines, the file mainly consists of two kinds of declarations, SYSTEM, and PUBLIC.

--
  sample catalog file.

  double hyphens are used to begin and end a comment section.
--

SYSTEM "http://www.w3.org/2001/xml.xsd" "xml.xsd"

PUBLIC "-//W3C//DTD XMLSCHEMA 200102//EN" "s4s/XMLSchema.dtd"

The SYSTEM entry has the format of "SYSTEM REFERENCE ACTUAL-LOCATION", which defines a simple redirection. Every time XJC loads any resource (be it schemas, DTDs, any entities referenced within), it will first resolve relative paths to absolute paths, then looks for a matching REFERENCE line. If it is found, the specified actual location is read instead. Otherwise XJC will attempt to resolve the absolutepath.

ACTUAL-LOCATION above accepts relative paths, and those are resolved against the catalog file itself (so in the above example, xml.xsd is assumed to be in the same directory with sample-catalog.cat.

What you need to be careful is the fact that the REFERENCE portion must be absolute, and when XJC finds a reference in schema, it will first convert that to the absolute path before checking the catalog. So what this means is that if your schema is written like this:

<xs:import namespace="http://www.w3.org/1999/xlink" schemaLocation="xlink.xsd" />

Then your catalog entry would have to look like this:

-- this doesn't work because xlink.xsd will be turned into absolute path --
SYSTEM "xlink.xsd" "http://www.w3.org/2001/xlink.xsd"

-- this will work, assuming that the above schema is in /path/to/my/test.xsd --
SYSTEM "/path/to/my/xlink.xsd" "http://www.w3.org/2001/xlink.xsd"

Another kind of entry has the format of "PUBLIC PUBLICID ACTUAL-LOCATION" or "PUBLIC NAMESPACEURI ACTUAL-LOCATION".

The "PUBLICID" version is used to resolve DTDs and entities in DTDs. But this type of entry is also used to resolve <xs:import> statements. XJC will match the value of the namespace attribute and see if there's any matching entry. So given a schema like this:

<xs:import namespace="http://www.w3.org/1999/xlink" schemaLocation="xlink.xsd" />
<xs:import namespace="http://www.w3.org/1998/Math/MathML" />

The following catalog entries will match them.

PUBLIC "http://www.w3.org/1999/xlink" "http://www.w3.org/2001/xlink.xsd"
PUBLIC "http://www.w3.org/1998/Math/MathML" "/path/to/my/mathml.xsd"

As you can see, XJC will check the PUBLIC entries regardless of whether <xs:import> has the schemaLocation attribute or not. As with the case with the SYSTEM entry, the ACTUAL-LOCATION part can be relative to the location of the catalog file.

Once you write a catalog file, you'd need to specify that when you invoke XJC.

If you are trying to write a catalog file and banging your head against a wall because it's not working, you should enable the verbose option of the catalog resolver. How you do this depends on what interface you use:

If you are otherwise invoking XJC programmatically, you can set the above system property before invoking XJC.

<xs:any /> with processContents=skip means any well-formed XML elements can be placed. Therefore, XJC binds this to DOM Element interface.

<xs:element name="person">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="name" type="xs:string" />
      <xs:any processContents="skip" maxOccurs="unbounded" minOccurs="0" />
    </xs:sequence>
  </xs:complexType>
</xs:element>

import org.w3c.dom.Element;

@XmlRootElement
class Person {
  public String getName();
  public void setName(String);

  @XmlAnyElement
  public List<Element> getAny();
}

<xs:any /> with processContents=strict (or <xs:any /> without any processContents attribute, since it defaults to "strict") means any XML elements placed here must have corresponding schema definitions. This mode is not what people typically expect as "wildcard", but this is the default. The following shows this binding. (lax=true is unintuitive, but it's not an error in this document):

<xs:element name="person">
  <xs:complexType>
    <xs:sequence>
      <xs:element name="name" type="xs:string" />
      <xs:any maxOccurs="unbounded" minOccurs="0" />
    </xs:sequence>
  </xs:complexType>
</xs:element>

@XmlRootElement
class Person {
  public String getName();
  public void setName(String);

  @XmlAnyElement(lax=true)
  public List<Object> getAny();
}

JAXB binds any such element to an Object, and during unmarshalling, all elements encountered are unmarshalled into corresponding JAXB objects (including JAXBElements if necessary) and placed in this field. If it encounters elements that cannot be unmarshalled, DOM elements are produced instead.

At runtime, you can place either DOM elements or some JAXB objects that map to elements. A typical mistake is to put a String that contains XML fragment, but this won't work; you'd have to first read that into a DOM.

<xs:any /> with processContents=lax means any XML elements can be placed here, but if their element names match those defined in the schema, they have to be valid. XJC actually handles this exactly like processContents='strict', since the strict binding allows unknown elements anyway.

Chameleon schema" (read more, in particular this) is a technique used to define multiple almost-identical sets of definitions into multiple namespaces from a single schema document.

For example, with this technique, you can write just one "foo" complex type and define it into namespace X and Y. In this case, one tends to hope that XJC will only give you one Foo class for this, but unfortunately because it's actually defined in two namespaces, JAXB needs two Java classes to distinguish X:foo and Y:foo, so you'll get multiple copies.

If you find this to be problematic, there are a few ways to work around the problem.

If you have a type hierarchy and would like to insert your class in the middle, you can use the combination of XmlTransient and @implClass of <class> customization. See the following example:

<xs:schema ...>
  <xs:complexType name="vehicle">
    <xs:annotation><xs:appinfo>
      <jaxb:class implClass="MyVehicle" />
    </xs:appinfo></xs:annotation>
  </xs:complexType>

  <xs:complexType name="car">
    <xs:complexContent>
      <xs:extension base="vehicle" />
    </xs:complexContent>
  </xs:complexType>

  <xs:complexType name="bicycle">
    <xs:complexContent>
      <xs:extension base="vehicle" />
    </xs:complexContent>
  </xs:complexType>
</xs:schema>

            Vehicle
               ^
               |
            MyVehicle
               ^
          _____|______
         |            |
        Car          Bicycle

You'll then manually write MyVehicle class that extends from Vehicle. Annotate this class with XmlTransient to achieve the desired effect.

The following customization will stop binding a simple type to a type-safe enum. This can be convenient when number of constants is too large to be an useful enum (by default, the JAXB spec won't generate enum with more than 256 constants, but even 100 might be too large for you.)

<xs:simpleType name="foo">
  <xs:annotation><xs:appinfo>
    <jaxb:typesafeEnumClass map="false" />
  </xs:appinfo></xs:annotation>
  <xs:restriction base="xs:string">
    <xs:enumeration value="x" />
    <xs:enumeration value="y" />
    <xs:enumeration value="z" />
  </xs:restriction>
</xs:simpleType>

To disable such type-safe enum binding altogether for the entire schema, use a global binding setting like this (this is actually telling XJC not to generate enums if a simple type has more than 0 constants --- the net effect is no enum generation):

<xs:schema ...>
  <xs:annotation><xs:appinfo>
    <jaxb:globalBindings typesafeEnumMaxMembers="0" />
  </xs:appinfo></xs:annotation>
  ...
</xs:schema>

The <jaxb:dom>customization allows you to map a certain part of the schema into a DOM tree. This customization can be attached to the following schema components:

In the following example, a wildcard is mapped to a DOM node. Each element that matches to the wildcard will be turned into a DOM tree.

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
               xmlns:jaxb="http://java.sun.com/xml/ns/jaxb"
               jaxb:version="2.0">

        <xs:element>
           <xs:complexType>
              <xs:sequence>
                 <xs:any maxOccurs="unbounded" processContents="skip">
                    <xs:annotation><xs:appinfo>
                      <jaxb:dom/>
                    </xs:appinfo></xs:annotation>
                 </xs:any>
              </xs:sequence>
           </xs:complexType>
        </xs:element>
    .
    .
    .
    </xs:schema>

This extension can be used to access wildcard content or can be used to process a part of a document by using other technologies that require "raw" XML. By default, JAXB generates a getContent() method for accessing wildcard content, but it only supports "lax" handling which means that unknown content is discarded. You may find more information in 7.12 chapter of JAXB 2 specification.

The generated beans (and in particular the JAXBElement class) do not support the clone operation. There was a suggestion by another user that beanlib has been used successfully to clone JAXB objects.

Under some rare circumstances, XJC will generate some Java classes into a package called org.w3._2001.xmlschema. This happens when XJC decides that it needs some Java artifacts for the XML Schema built-in namespace of http://www.w3.org/2001/XMLSchema.

Since this package name is most often problematic, you can rename this by simply saving the following text in an .xsd file and submitting it to XJC along with the other schemas you have:

<schema xmlns="http://www.w3.org/2001/XMLSchema"
  targetNamespace="http://www.w3.org/2001/XMLSchema"
  xmlns:jaxb="http://java.sun.com/xml/ns/jaxb"
  jaxb:version="2.0">
  <annotation><appinfo>
    <jaxb:schemaBindings>
      <jaxb:package name="org.acme.foo"/>
    </jaxb:schemaBindings>
  </appinfo></annotation>
</schema>

This is bit tricky, but the idea is that since you can define a schema for one namespace in multiple schema documents, this makes XJC think that this schema is a part of the built-in "XML Schema for XML Schema".

JAXB (or any other databinding engine, for that matter) is for binding strongly-typed POJO-like objects to XML, such as AddressBook class, PurchaseOrder class, and so on, where you have fields and methods that shape a class.

There are other kinds of classes that are more close to reflection. Those classes don't have methods like getAddress, and instead you'd do get("Address"). JDBC ResultSet is one of those classes. It's one class that represents million different data structures, be it a customer table or a product table. Generally speaking, these classes does not allow JAXB to statically determine what the XML representation should look like. Instead, you almost always need to look at an instance to determine the shape of XML.

These classes are not really suitable for binding in JAXB. If this is the only object that you'd want to write out, then you'd be better off using XMLStreamWriter or some such XML infoset writing API. There are a few online articles that cover this topic. Also, many modern database offers a native ability to export a query into XML, which is supposed to work a lot faster than you'd do in Java (and saves your time of writing code.)

If you are using ResultSet as a part of your object tree that you want to marshal to JAXB, then you can use XmlJavaTypeAdapter.

JAXB spec defines a special handling for Map when it's used as a propety of a bean. For example, the following bean would produce XMLs like the following:

@XmlRootElement
class Foo {
  public HashMap<String,Integer> map;
}

<foo>
  <map>
    <entry>
      <key>a</key>
      <value>1</value>
    </entry>
    <entry>
      <key>b</key>
      <value>2</value>
    </entry>
  </map>
</foo>

Unfortunately, as of 2.1, this processing is only defined for bean properties and not when you marshal HashMap as a top-level object (such as a value in JAXBElement.) In such case, HashMap will be treated as a Java bean, and when you look at HashMap as a bean it defines no getter/setter property pair, so the following code would produce the following XML:

m = new HashMap();
m.put("abc",1);
marshaller.marshal(new JAXBElement(new QName("root"),HashMap.class,m),System.out);

<root />

This issue has been recorded as #223 and the fix needs to happen in later versions of the JAXB spec.

In the mean time, such top-level objects have to be first adapted to a bean that JAXB can process. This has added benefit of being able to control XML representation better. The following code illustrates how to do this:

public class MyHashMapType {
    public List<MyHashMapEntryType> entry = new ArrayList<MyHashMapEntryType>();
    public MyHashMapType(Map<String,Integer> map) {
        for( Map.Entry<String,Integer> e : map.entrySet() )
            entry.add(new MyHashMapEntryType(e));
    }
    public MyHashMapType() {}
}

public class MyHashMapEntryType {
    @XmlAttribute // @XmlElement and @XmlValue are also fine
    public String key;

    @XmlAttribute // @XmlElement and @XmlValue are also fine
    public int value;

    public MyHashMapEntryType() {}
    public MyHashMapEntryType(Map.Entry<String,Integer> e) {
       key = e.getKey();
       value = e.getValue();
    }
}

marshaller.marshal(new JAXBElement(new QName("root"),MyHashMapType.class,new MyHashMapType(m)),System.out);

If you have a lot of difference kinds of Map, you can instead use Object as the key and the value type. In that way, you'll be able to use maps with different type parameters, at the expense of seeing xsi:type attribute on the instance document.

When your interface is implemented by a large number of sub-classes, consider using XmlRootElement annotation like this:

@XmlRootElement
class Zoo {
  @XmlAnyElement
  public List<Animal> animals;
}

interface Animal {
  void sleep();
  void eat();
  ...
}

@XmlRootElement
class Dog implements Animal { ... }

@XmlRootElement
class Lion implements Animal { ... }

This will produce XML documents like this:

<zoo>
    <lion> ... </lion>
    <dog> ... </dog>
</zoo>

The key characteristics of this approach is:

@XmlElementWrapper is often useful with this, as it allows you need to group them. Such as:

@XmlRootElement
class Zoo {
  @XmlElementWrapper
  @XmlAnyElement
  public List<Animal> onExhibit;
  @XmlElementWrapper
  @XmlAnyElement
  public List<Animal> resting;
}

<zoo>
    <onExhibit>
        <lion> ... </lion>
        <dog> ... </dog>
    </onExhibit>
    <resting>
        <lion> ... </lion>
        <dog> ... </dog>
    </resting>
</zoo>

When you use interfaces just to hide your implementation classes from exposure, and when there's 1-to-1 (or close to 1-on-1) relationship between a class and an interface, XmlJavaTypeAdapter can be used like below.

@XmlJavaTypeAdapter(FooImpl.Adapter.class)
interface IFoo {
  ...
}
class FooImpl implements IFoo {
  @XmlAttribute
  private String name;
  @XmlElement
  private int x;

  ...

  static class Adapter extends XmlAdapter<FooImpl,IFoo> {
    IFoo unmarshal(FooImpl v) { return v; }
    FooImpl marshal(IFoo v) { return (FooImpl)v; }
  }
}

class Somewhere {
  public IFoo lhs;
  public IFoo rhs;
}

<somewhere>
  <lhs name="...">
    <x>5</x>
  </lhs>
  <rhs name="...">
    <x>5</x>
  </rhs>
</somewhere>

The key characteristics of this approach is:

A variation of this technique is when you have a few implementations for interface, not just one.

@XmlJavaTypeAdapter(AbstractFooImpl.Adapter.class)
interface IFoo {
  ...
}
abstract class AbstractFooImpl implements IFoo {
  ...

  static class Adapter extends XmlAdapter<AbstractFooImpl,IFoo> {
    IFoo unmarshal(AbstractFooImpl v) { return v; }
    AbstractFooImpl marshal(IFoo v) { return (AbstractFooImpl)v; }
  }
}

class SomeFooImpl extends AbstractFooImpl {
  @XmlAttribute String name;
  ...
}

class AnotherFooImpl extends AbstractFooImpl {
  @XmlAttribute int id;
  ...
}

class Somewhere {
  public IFoo lhs;
  public IFoo rhs;
}

<somewhere>
  <lhs xsi:type="someFooImpl" name="...">
  </lhs>
  <rhs xsi:type="anotherFooImpl" id="3" />
</somewhere>

Note that SomeFooImpl and AnotherFooImpl must be submitted to JAXBContext.newInstance one way or the other.

To take this example a bit further, you can use Object instead of AbstractFooImpl. The following example illustarates this:

@XmlJavaTypeAdapter(AnyTypeAdapter.class)
interface IFoo {
  ...
}
public class AnyTypeAdapter extends XmlAdapter<Object,Object> {
  Object unmarshal(Object v) { return v; }
  Object marshal(Object v) { return v; }
}

class SomeFooImpl implements IFoo {
  @XmlAttribute String name;
  ...
}

class Somewhere {
  public IFoo lhs;
  public IFoo rhs;
}

<xs:complexType name="somewhere">
  <xs:sequence>
    <xs:element name="lhs" type="xs:anyType" minOccurs="0"/>
    <xs:element name="rhs" type="xs:anyType" minOccurs="0"/>
  </xs:sequence>
</xs:complexType>

As you can see, the schema will generated to accept xs:anyType which is more relaxed than what the Java code actually demands. The instance will be the same as the above example. Starting from JAXB RI 2.1, we bundle the com.sun.xml.bind.AnyTypeAdapter class in the runtime that defines this adapter. So you won't have to write this adapter in your code.

If the use of interface is very little and there's 1-to-1 (or close to) relationship between interfaces and implementations, then you might find XmlElement to be the least amount of work.

interface IFoo {
  ...
}
class FooImpl implements IFoo {
  ...
}

class Somewhere {
  @XmlElement(type=FooImpl.class)
  public IFoo lhs;
}

<somewhere>
  <lhs> ... </lhs>
</somewhere>

This effectively tells JAXB runtime that "even though the field is IFoo, it's really just FooImpl.

In this approach, a reference to an interface has to have knowledge of the actual implementation class. So while this requires the least amount of typing, it probably wouldn't work very well if this crosses module boundaries.

Like the XmlJavaTypeAdapter approach, this can be used even when there are multiple implementations, provided that they share the common ancestor.

The extreme of this case is to specify @XmlElement(type=Object.class).

Occasionally the above approaches cause the generated schema to become somewhat ugly, even though it does make the JAXB runtime work correctly. In such case you can choose not to use the generated schema and instead manually modify/author schemas tht better match your needs.

With sufficient knowlege, one can also use <jaxb:class ref="..."/> annotation so that you can cause XJC to use the classes you already wrote. See this thread for an example. TODO: more details and perhaps an example.

Some users attempted to use the "generateValueClass" customization and see if they can completely replace the generated implementations with other implementations. Unfortunately, this does not work.

Even with the interface/implementation mode, JAXB runtime still requires that the implementation classes have all the JAXB annotations. So just implementing interfaces is not sufficient. (This mode is mainly added to simplify the migration from JAXB 1.0 to JAXB 2.0, and that's a part of the reason why things are done this way.)

There are two directions in the runtime compatibility. One is whether v1 can still read what v2 write (forward compatible), and the other is whether v2 can read what v1 wrote (backward compatible).

JAXB can read XML documents that don't exactly match what's expected. This is the default behavior of the JAXB unmarshaller, yet you can change it to a more draconian behavior (TODO: pointer to the unmarshalling section.)

When we are talking about evolving classes, it's often convenient to leave it in the default behavior, as that would allow JAXB to nicely ignore elements/attributes newly added in v2. So we call it backward semi-compatible if v2 can read what v1 wrote in this default unmarshalling mode, and similarly forward semi-compatible if v1 can read what v2 wrote in this default unmarshalling mode.

Technically, these are weaker than true backward/forward compatibility (since you can't do a draconian error detection), yet in practice it works just fine.

You can add, remove, or change any non-annotated fields, methods, inner/nested types, constructors, interfaces. Those changes are both backward and forward compatible, as they don't cause any change to the XML representation.

Adding super class is backward compatible and forward semi-compatible. Similarly, removing super class is forward compatible and backward semi-compatible.

Adding new annotated fields or methods is backward compatible and forward semi-compatible. Similarly, removing them is forward compatible and backward semi-compatible.

Changing a property is bit more tricky.

XmlType and XmlRootElement allows you to change a class name without affecting XML.

// BEFORE
@XmlRootElement
public class Foo { ... }

// AFTER: no XML change
@XmlRootElement(name="foo")
@XmlType(name="foo")
public class Bar { ... }

// BEFORE
public class Foo { ... }

// AFTER: no XML change
@XmlType(name="foo")
public class Bar { ... }

TODO.

XmlJavaTypeAdapter allows you to de-couple the in-memory representation and the XML representation by introducing an intermediate representation. The basic model is as follows:

In-memory objects  <===>  Intermediate objects   <===>
XML
                  adapter                         JAXB

Your adapter code will be responsible for converting in-memory objects to/from intermediate objects. Intermediate objects are then bound to XML by following the standard JAXB rules. See XmlAdapter for a general description of how adapters works.

Adapters extend from the XmlAdapter class and provide two methods "unmarshal" and "marshal" that converts values in both directions, and then the XmlJavaTypeAdapter annotation is used to tell JAXB where and what adapters kick in.

(TODO: more info about XmlJavaTypeAdapter needed)

One of the common use cases of XmlJavaTypeAdapter is to map a "value object" to a string in XML. The following example illustrates how to do this, by using java.awt.Color as an example.

@XmlRootElement
class Box {
  @XmlJavaTypeAdapter(ColorAdapter.class)
  @XmlElement
  Color fill;
}

class ColorAdapter extends XmlAdapter<String,Color> {
  public Color unmarshal(String s) {
    return Color.decode(s);
  }
  public String marshal(Color c) {
    return "#"+Integer.toHexString(c.getRGB());
  }
}

This maps to the following XML representation:

<box>
  <fill>#112233</fill>
</box>

Since XmlJavaTypeAdapter is on a field, this adapter only kicks in for this particular field. If you have many Color fields and would like them all to use the same adapter, you can move the annotation to a package:

@XmlJavaTypeAdapter(type=Color.class,value=ColorAdapter.class)
package foo;

@XmlRootElement
class Box {
  @XmlElement Color fill;
  @XmlElement Color border;
}

This causes all the fields in the classes in the foo package to use the same specified adapter.

Also see the DatatypeConverter class that defines a series of basic conversion routines that you may find useful.

Another useful technique is to define two properties, one for JAXB and the other for your application. See the following example:

@XmlRootElement
class Person {
  private int age;

  // This public property is for users
  @XmlTransient
  public int getAge() {
    return age;
  }
  public void setAge(int age) {
    this.age = age;
  }

  // This property is for JAXB
  @XmlAttribute(name="age")
  private String getAge_() {
    if(age==-1)  return "dead";
    else         return String.valueOf(age);
  }
  private void setAge_(String v) throws NumberFormatException {
    if(v.equals("dead"))   this.age=-1;
    else                   this.age=Integer.parseInt(age);
}

The main "age" property is public, but marked as XmlTransient, so it's exposed in your program, but JAXB will not map this to XML. There's another private "age_" property. Since this is marked with XmlAttribute, this is what JAXB is going to use to map to the attribute. The getter and setter methods on this property will handle the conversion between the in-memory representation and the XML representation.

One of the very common forms of cycle is a parent pointer. The following example illustrates a typical parent pointer, and how this can be turned into "natural" XML:

@XmlRootElement
class Department {
  @XmlAttribute
  String name;
  @XmlElement(name="employee")
  List<Employee> employees;
}

class Employee {
  @XmlTransient
  Department department;  // parent pointer
  @XmlAttribute
  String name;

  public void afterUnmarshal(Unmarshaller u, Object parent) {
    this.department = (Department)parent;
  }
}

This will produce the following XML:

<department name="accounting">
  <employee name="Joe Chin" />
  <employee name="Adam Smith" />
  ...
</department>

And reading this document back into Java objects will produce the expected tree with all the proper parent pointers set up correctly.

The first technique here is the use of XmlTransient on the parent pointer. This tells JAXB that you don't need this parent pointer to be represented explicitly in XML, because the fact that employee is always contained inside department implies the parent/child relationship. This causes the marshaller to produce the expected XML. However, when you unmarshal it, since this field is not bound, the Employee.department field will be left null.

That's where the second technique comes in, which is the use of the afterUnmarshal callback. This method is invoked by the JAXB implementation on each instance when the unmarshalling of a Employee object completes. Furthermore, the second parameter to the method is the parent object, which in this case is a Department object. So in this example, this sets up the parent pointer correctly.

This callback can be also used to perform other post-unmarshalling set up work.

TBD

When a reference to another object is annotated with XmlIDREF, its corresponding XML it will be referenced by xs:IDREF, instead of containment. See below for an example:

Example of @XmlID and @XmlIDREF

@XmlRootElement
class Root {
  List<Foo> foos;
  List<Bar> bars;
}
class Foo {
  // you don't have to make it an attribute, but that's more common
  @XmlAttribute @XmlIDREF Bar bar;
}
class Bar {
  // you don't have to make it an attribute, but that's more common
  @XmlAttribute @XmlID String id;
}

<xs:complexType name="foo">
  <xs:sequence/>
  <xs:attribute name="bar" type="xs:IDREF"/>
  </xs:sequence>
</xs:complexType>
<xs:complexType name="bar">
  <xs:sequence/>
  <xs:attribute name="id" type="xs:ID"/>
</xs:complexType>

<root>
  <foo bar="x"/>
  <foo bar="y"/>
  <bar id="x"/>
  <bar id="y"/>
</root>

There are a few things to consider when you do this. First, the object to be referenced must have an ID that is unique within the whole document. You'd also need to ensure that the referenced objects are contained somewhere else (like in the Root class in this case), or else Bar objects will never be marshalled. This technique can be used to remove the cyclic references, but it's only possible when your object model has an easy cut point.

Starting 2.1 EA2, the JAXB RI exposes CycleRecoverable interface. Applications can choose to implement this interface in some of its objects. When a cyclic reference is detected during marshalling, and if the object that formed a cycle implements this interface, then the method on this interface is called to allow an application to nominate its replacement to be written to XML. In this way, the application can recover from a cycle gracefully.

This technique allows you to cope with a situation where you cannot easily determine upfront as to where a cycle might happen. On the other hand, this feature is a JAXB RI feature. Another downside of this is that unless you nominate your replacement carefully, you can make the marshalling output invalid with respect to the schema, and thus you might hit another problem when you try to read it back later.

First, use an independent schema validator to check if your document is really valid with respect to the schema you compiled. When the root element of a document is invalid, then the unmarshaller will issue "unexpected element" errors. When a portion of a document is invalid, JAXB skips that portion, so the end result is that the unmarshalling returns normally, yet you notice that a part of the content tree is missing. This is often the desirable behavior, but it sometimes ends up masking a problem.

Also, try to install ValidationEventHandler on the unmarshaller. When a portion of a document is skipped, the unmarshaller notifies a ValidationEventHandler, so it allows you to see what's going on.

Unmarshaller u = ...;
// this implementation is a part of the API and convenient for trouble-shooting,
// as it prints out errors to System.out
u.setEventHandler(new javax.xml.bind.helpers.DefaultValidationEventHandler());

u.unmarshal(new File("foo.xml"));

Also consider installing a Schema object to the unmarshaller, so that the unmarshaller performs a schema validation while unmarshalling. Earlier I suggested that you try an independent schema validator, but for various reasons (not all tools are reliable, you might have made an error and used a different schema/instance), using validating unmarshalling is a better way to guarantee the validity of your instance document being unmarshalled. Please follow the JAXP tutorial for more about how to construct a Schema object from your schema.

If you are unmarshalling from XML parser APIs (such as DOM, SAX, StAX), then also make sure that the parser/DOM is configured with the namespace enabled.

(TODO: This also applies to the marshaller. Think about moving it.)

The other possibility is that JAXBContext is not set up correctly. JAXBContext "knows" a set of classes, and if it doesn't know a class that it's supposed to know, then the unmarshaller may fail to perform as you expected.

To verify that you created JAXBContext correctly, call JAXBContext.toString(). It will output the list of classes it knows. If a class is not in this list, the unmarshaller will never return an instance of that class. Make you see all the classes you expect to be returned from the unmarshaller in the list. When dealing with a large schema that spans across a large number of classes and packages, this is one possible cause of a problem.

If you noticed that a class is missing, explicitly specify that to JAXBContext.newInstance. If you are binding classes that are generated from XJC, then the easiest way to include all the classes is to specify the generated ObjectFactory class(es).

When a document is large, it's usually because there's repetitive parts in it. Perhaps it's a purchase order with a large list of line items, or perhaps it's an XML log file with large number of log entries.

This kind of XML is suitable for chunk-processing; the main idea is to use the StAX API, run a loop, and unmarshal individual chunks separately. Your program acts on a single chunk, and then throws it away. In this way, you'll be only keeping at most one chunk in memory, which allows you to process large documents.

See the streaming-unmarshalling example and the partial-unmarshalling example in the JAXB RI distribution for more about how to do this. The streaming-unmarshalling example has an advantage that it can handle chunks at arbitrary nest level, yet it requires you to deal with the push model --- JAXB unmarshaller will "push" new chunk to you and you'll need to process them right there.

In contrast, the partial-unmarshalling example works in a pull model (which usually makes the processing easier), but this approach has some limitations in databinding portions other than the repeated part.

The techniques discussed above can be used to handle this case as well, since they let you unmarshal chunks one by one. See the xml-channel example in the JAXB RI distribution for more about how to do this.

For further advanced cases, one could always run a streaming infoset conversion outside JAXB API and basically curve just the portion of the infoset you want to data-bind, and feed it as a complete infoset into JAXB API. JAXB API accepts XML infoset in many different forms (DOM, SAX, StAX), so there's a fair amount of flexibility in choosing the right trade off between the development effort in doing this and the runtime performance.

For more about this, refer to the respective XML infoset API.

The most basic notion of the marshalling is to take a JAXB-bound object that has @XmlRootElement, and write it out as a whole XML document. So perhaps you have a class like this:

class Point {
  @XmlElement
  public int x;
  @XmlElement
  public int y;
  Point(...) { ... }
}

Then you can do:

marshaller.marshal( new Point(1,3), System.out );
marshaller.marshal( new Point(1,3), new File("out.xml") );

.. and so on. There're seven Marshaller.marshal methods that takes different output media as the second parameter. If you are writing to a file, a socket, or memory, then you should use the version that takes OutputStream. Unless you change the target encoding to something else (default is UTF-8), there's a special marshaller codepath for OutputStream, which makes it run really fast. You also don't have to use BufferedOutputStream, since the JAXB RI does the adequate buffering.

You can also write to Writer, but in this case you'll be responsible for encoding characters, so in general you need to be careful. If you want to marshal XML into an encoding other than UTF-8, it's best to use the JAXB_ENCODING property and then write to OutputStream, as it escapes characters to things like ᠤ correctly.

The next medium we support is W3C DOM. This is bit unintuitive, but you'll do it like this:

DocumentBuilderFactory dbf = DocumentBuilderFactory.newInstance();
dbf.setNamespaceAware(true);
Document doc = dbf.newDocumentBuilder().newDocument();

marshaller.marshal( new Point(1,3), doc );

And after the method invocation you get a complete DOM tree that represents the marshalled document.

The other versions of the marshal methods are there to write XML documents in terms of other XML APIs, such as SAX and StAX. The version that takes ContentHandler is useful when you need a custom formatting needs (like you want each attribute to be in new line, etc), but otherwise they are not very interesting if you are writing a whole document.

Another common use of JAXB is where you are writing a bigger document, and you use JAXB to generate part(s) of it. The JAX-WS RI is the prime example. It produces a SOAP message, and JAXB is only used to produce the body. When you are doing this, you first set JAXB_FRAGMENT property on the marshaller. This changes the behaviors of the marshaller so that it works better in this situation.

If you are writing to an OutputStream or Writer and generally sending it to someone else, you can do something like this:

System.out.println("<envelope>");
marshaller.marshal( object, System.out );
System.out.println("</envelope>");

Like I mentioned, this is probably the fastest, even though println isn't very pretty. JAXB_FRAGMENT prevents the marshaller from producing an XML declaration, so the above works just fine. The downside of this approach is that if the ancestor elements declare the namespaces, JAXB won't be able to take advantage of them.

You can also marshal an object as a subtree of an existing DOM tree. To do this, you pass the Element object as the second parameter, and the marshaller will marshal an object as a child of this node.

StAX is also very convenient for doing this sort of things. You can create XMLStreamWriter, write some stuff, and then pass that to the marshaller. JAXB_FRAGMENT prevents the marshaller from producing startDocument and endDocument token. When doing this sub-tree marshaling to DOM and StAX, JAXB can take advantage of available in-scope namespace bindings.

Finally, you can marshal an object as a subtree into ContentHandler, but it requires a fair amount of SAX programming experience, and it goes beyond the scope of this entry.

Another common use case is where you have an object that doesn't have @XmlRootElement on it. JAXB allows you to marshal it like this:

marshaller.marshal( new JAXBElement(
  new QName("","rootTag"),Point.class,new Point(...)));

This puts the <rootTag> element as the root element, followed by the contents of the object, then </rootTag>. You can actually use it with a class that has @XmlRootElement, and that simply renames the root element name.

At the first glance the second Point.class parameter may look redundant, but it's actually necessary to determine if the marshaller will produce (infamous) @xsi:type. In this example, both the class and the instance are Point, so you won't see @xsi:type. But if they are different, you'll see it.

This can be also used to marshal a simple object, like String or an integer.

Marshalling a non-element with @xsi:type

marshaller.marshal( new JAXBElement(
  new QName("","rootTag"),String.class,"foo bar"));

But unfortunately it cannot be used to marshal objects like List or Map, as they aren't handled as the first-class citizen in the JAXB world.

Because of the Source and Result support, JAXB objects can be easily marshalled into other XML APIs that are not mentioned here. For example, dom4j has DocumentResult that extends Result, so you can do:

DocumentResult dr = new DocumentResult();
marshaller.marshal( object, dr );
o = dr.getDocument();

Similar mechanism is available for JDOM and XOM. This conversion is much more efficient than first marshalling to ByteArrayOutputStream and then read it back into these DOMs. The same mechanism can be used to marshal to FastInfoset or send the marshaled document to an XSLT engine (TransformerHandler.)

The other interesting connector is JAXBSource, which wraps a marshaller and allows a JAXB object to be used as a "source" of XML. Many XML APIs take Source as an input, and now JAXB object can be passed to them directly.

For example, you can marshal a JAXB object and unmarshal it into another JAXBContext like this:

JAXBContext context1 = ... ;
JAXBContext context2 = ... ;

context1.createUnmarshaller().unmarshal( new JAXBSource(context2,object) );

This amounts to looking at the same XML by using different schema, and again this is much more efficient than going through ByteArrayOutputStream.

The #1 cause of extra namespace declarations is due to the DOM mapping. This mainly happens because of a schema construct that forces XJC to generate a property with DOM. This includes the use of wildcard <xs:any/> (see more about this Mapping of <xs:any />), as well as xs:anyType (which can also happen by omission, such as <xs:element name="foo"/>, which is interpreted as <xs:element name="foo" type="xs:anyType" />.

During unmarshalling, when a subtree of the input XML is converted into XML, JAXB copies all the in-scope namespace bindings active at that time to the root of the DOM element. So for example, given the following Java class and XML, the DOM tree that the child field will get will look like the following:

@XmlRootElement
class Foo {
  @XmlAnyElement
  public Element child;
}

<foo xmlns:a="a" xmlns:b="b" xmlns:c="c">
  <subtree xmlns:c="cc">
    <data>a:xyz</data>
  </subtree>
</foo>

<subtree xmlns:a="a" xmlns:b="b" xmlns:c="cc">
    <data>a:xyz</data>
  </subtree>

Note that the two namespace declarations are copied over, but c is not because it's overridden. Also not that JAXB is not touching the whitespace in document. This copying of namespace declarations is necessary to preserve the infoset in the input document. For example, if the <data> is a QName, its meaning would change if JAXB unmarshaller doesn't copy it.

Now, imagine what happens when you marshal this back to XML. Despite the fact that in this example neither b nor c prefixes are in use, JAXB cannot delete them, because it doesn't know if those attributes are significant to the application or not. Therefore, this could end up producing XML with "extra namespace declarations" like:

<foo>
  <subtree xmlns:a="a" xmlns:b="b" xmlns:c="cc">
    <data>a:xyz</data>
  </subtree>
</foo>

Resolving this problem is not possible in the general case, but sometimes one of the following strategy works:

If the classes you'd like to generate schema from are already available as java.lang.Class objects (meaning they are already loaded and resolved in the current JVM), then the easiest way to generate a schema is to use the JAXB API:

File baseDir = new File(".");

class MySchemaOutputResolver extends SchemaOutputResolver {
    public Result createOutput( String namespaceUri, String suggestedFileName ) throws IOException {
        return new StreamResult(new File(baseDir,suggestedFileName));
    }
}

JAXBContext context = JAXBContext.newInstance(Foo.class, Bar.class, ...);
context.generateSchema(new MySchemaOutputResolver());

The CLI interface (public static int com.sun.tools.jxc.SchemaGenerator.run(String[])) is the easiest API to access. You can pass in all the schemagen command-line arguments as a string array, and get the exit code as an int value. Messages are sent to System.err and System.out.

Ant task can be invoked very easily from a non-Ant program. The schemagen ant task is defined in the SchemaGenTask class,

The above two interfaces are built on top of externally committed contracts, so they'll evolve only in a compatibile way. The downside is that the amount of control you can exercise over them would be limited.

So yet another approach to invoke schemagen is to use JAXB RI's internal interfaces. But be warned that those interfaces are subject to change in the future versions, despite our best effort to preserve them. This is the API that the JAX-WS RI uses to generate schema inside WSDL when they generate WSDL, so does some other web services toolkits that work with the JAXB RI.

Most of those interfaces are defined and well-documented in the com.sun.tools.xjc.api package. You can see how the schemagen tools are eventually calling into this API at the implementaion of SchemaGenerator class.

As of JAXB 2.1.4, currently no support for this, although there has been several discussions in the users alias.

The JAXB project is currently lacking resources to attack this problem, and therefore looking for volunteers to work on this project. The basic idea would be to define enough annotations to cover the basic constraint facets (such as length, enumerations, pattern, etc.) The schema generator would have to be then extended to honor those annotations and generate schemas accordingly.

Some users pointed out relevance of this to JSR 303: Bean Validation. If you are interested in picking up this task, let us know!

Minimum requirement to compile is jaxb-api. If a client application is running on an environment where JAXB runtime is provided, jaxb-api is all that is needed.

                <!-- API -->
                <dependency>
                    <groupId>javax.xml.bind</groupId>
                    <artifactId>jaxb-api</artifactId>
                    <version>${jaxb.version}</version>
                </dependency>
             

If client application needs to include the runtime, e.g. running standalone on JavaSE jaxb-runtime should be also included.

                <!-- API -->
                <dependency>
                    <groupId>javax.xml.bind</groupId>
                    <artifactId>jaxb-api</artifactId>
                    <version>${jaxb.version}</version>
                </dependency>

                <!-- Runtime -->
                <dependency>
                    <groupId>org.glassfish.jaxb</groupId>
                    <artifactId>jaxb-runtime</artifactId>
                    <version>${jaxb.version}</version>
                </dependency>
    

To generate JAXB classes from schema community maven-jaxb2-plugin can be used.

                <build>
                    <plugins>
                        <plugin>
                            <groupId>org.jvnet.jaxb2.maven2</groupId>
                            <artifactId>maven-jaxb2-plugin</artifactId>
                            <executions>
                                <execution>
                                    <id>generate</id>
                                    <goals>
                                        <goal>generate</goal>
                                    </goals>
                                </execution>
                            </executions>
                        </plugin>
                    </plugins>
                </build>
    

Alternatively to community plugins, there are tooling artifacts jaxb-xjc and jaxb-jxc, which can be used for java from XML schema generation and vice versa.

            <!-- Tooling dependencies -->
            <dependency>
                <groupId>org.glassfish.jaxb</groupId>
                <artifactId>jaxb-xjc</artifactId>
                <version>${jaxb.version}</version>
            </dependency>
            <dependency>
                <groupId>org.glassfish.jaxb</groupId>
                <artifactId>jaxb-jxc</artifactId>
                <version>${jaxb.version}</version>
            </dependency>

            <!-- Invoke tooling API (Java 11) -->
            <plugin>
                <groupId>org.codehaus.mojo</groupId>
                <artifactId>exec-maven-plugin</artifactId>
                    <!-- Generate java sources from schema -->
                    <execution>
                        <id>xjc</id>
                        <goals>
                            <goal>exec</goal>
                        </goals>
                        <configuration>
                            <executable>java</executable>
                            <arguments>
                                <argument>--module-path</argument>
                                <modulepath/>
                                <argument>-m</argument>
                                <argument>com.sun.tools.xjc/com.sun.tools.xjc.XJCFacade</argument>
                                <argument>-p</argument>
                                <argument>com.example</argument>
                                <argument>-d</argument>
                                <argument>${project.build.directory}/generated-sources</argument>
                                <argument>${project.build.directory}/classes/schema.xsd</argument>
                            </arguments>
                        </configuration>
                    </execution>

                    <!-- Generate XML Schema from sources -->
                    <execution>
                        <id>jxc</id>
                        <goals>
                            <goal>exec</goal>
                        </goals>
                        <configuration>
                            <executable>java</executable>
                            <arguments>
                                <argument>--module-path</argument> <!-- or -p  -->
                                <modulepath/>
                                <argument>-m</argument>
                                <argument>com.sun.tools.jxc/com.sun.tools.jxc.SchemaGeneratorFacade</argument>
                                <argument>-d</argument>
                                <argument>${project.build.directory}/generated-sources</argument>
                                <argument>${project.build.directory}/classes/com/example/Author.java</argument>
                                <argument>${project.build.directory}/classes/com/example/Book.java</argument>
                            </arguments>
                            <longModulepath>false</longModulepath>
                        </configuration>
                    </execution>
                </executions>
            </plugin>

See also xml schema compiler usage.

Where are schemagen and xjc command line scripts available in JavaSE prior to 11? These are included only in the zip distribution.

JAXB does reflectively access private members of the class, so client application if loaded from module path needs to "open" packages containing jaxb classes to JAXB. There are alternative JAXB implementations, which will have different module names, JAXB requires pojo classes to be open only to API module.

                //JPMS module descriptor
                module com.example.jaxbclasses {

                //jaxb-api module name
                requires java.xml.bind;

                //open jaxb pojo package to make accessing private members possible for JAXB.
                opens com.example.jaxbclasses.pojos to java.xml.bind;

             

JAXB API will delegate openness to implementation module after resolving it with service discovery mechanism.

Prior to Java 11, JavaSE contains JAXB bundled inside JDK. Module java.xml.bind contains JAXB API and runtime.

Similar to endorsed mechanism prior to Java 9, starting from 9 there is an "upgrade module" mechanism which can replace content of JDK module. JavaSE bundled java.xml.bind module contains both API and Runtime classes and should be replaced with JAXB API module, which has the same java.xml.bind module name.

                    # Using JAXB standalone jars
                    # Replace JavaSE bundled java.xml.bind with standalone API jar
                    user@host: java com.example.jaxb.Main -cp jaxbclient.jar --upgrade-module-path path/to/jaxb-api.jar
                    --module-path path/to/jaxb-runtime.jar --add-modules com.sun.xml.bind

                    #Same as above with client on module path
                    user@host: java -m com.example.jaxbclasses/com.example.jaxb.Main --upgrade-module-path path/to/jaxb-api.jar
                    --module-path path/to/jaxb-runtime.jar:jaxbclient.jar --add-modules com.sun.xml.bind

             

--upgrade-module-path will replace JavaSE java.xml.bind (runtime and API) with jaxb-api.jar contents.

Since java.xml.bind module is removed starting from Java 11, there is no need to upgrade this module on 11 and later.

                    # Using JAXB bundled in JDK
                    # No need for standalone jars here
                    user@host: java com.example.jaxb.Main -cp jaxbclient.jar

                    user@host: java -m com.example.jaxbclasses/com.example.jaxb.Main
                    --module-path jaxbclient.jar

             

If you'd like to reduce the footprint of your application by taking advantage of a JAXB implementation in JavaSE, you can take the following steps:

JavaSE comes with JAXB 2.x API/implementation in rt.jar. Each version of JavaSE (6, 7, 8, ...) contains different version of JAXB 2.x API. Therefore, if you want to use different version of JAXB API/implementation than the one present in your version of JDK, you are required to override a portion of rt.jar with the new API. There are several ways to achieve this:

No matter which approach you take, make sure not to include jar files other than jaxb-api.jar. Doing so, for example including jaxb-xjc.jar, may result in classloading related errors such as "taskdef A class needed by class com.sun.tools.xjc.XJCTask cannot be found: org/apache/tools/ant/...."

See the endorsed directory mechanism for more details.

JavaSE has never shipped an Ant task implementation, so we are just following that tradition. There's an (process-wise) overhead of adding additional dependencies during the JavaSE build, and there would likely be some runtime dependency issues in having a class in tools.jar that would require the ant classes, due to class loader delegation.

We are thinking about perhaps releasing a small jar that only contains the ant task for JDK6.

Please also note that the syntax of <xjc> task is neither defined in the JAXB spec nor in the JavaSE spec. Therefore other JavaSE vendors may not implement that at all, or do so in a different class name, etc. Therefore, from a portability perspective, if you choose to depend on the <xjc> task you should bundle the JAXB RI.

When you compile your sources files with JDK from Java6 and try to run it on Java5 JVMs, you may see a ClassFormatError at runtime like this:

main" java.lang.ClassFormatError: Illegal class modifiers in class
com/alu/parentalcontrol/jaxb/package-info: 0x1600
at java.lang.ClassLoader.defineClass1(Native Method)
at java.lang.ClassLoader.defineClass(ClassLoader.java:620)
at java.security.SecureClassLoader.defineClass(SecureClassLoader.java:124)
at java.net.URLClassLoader.defineClass(URLClassLoader.java:260)
at java.net.URLClassLoader.access$100(URLClassLoader.java:56)
at java.net.URLClassLoader$1.run(URLClassLoader.java:195)
at java.security.AccessController.doPrivileged(Native Method)
at java.net.URLClassLoader.findClass(URLClassLoader.java:188)
at java.lang.ClassLoader.loadClass(ClassLoader.java:306)
at sun.misc.Launcher$AppClassLoader.loadClass(Launcher.java:268)
at java.lang.ClassLoader.loadClass(ClassLoader.java:251)
at java.lang.ClassLoader.loadClassInternal(ClassLoader.java:319)
at java.lang.Class.forName0(Native Method)
at java.lang.Class.forName(Class.java:242)
at java.lang.Package.getPackageInfo(Package.java:350)
at java.lang.Package.getAnnotation(Package.java:361)
at com.sun.xml.bind.v2.model.annotation.RuntimeInlineAnnotationReader.getPackageAnnotation(RuntimeInlineAnnotationReader.java:125)
at com.sun.xml.bind.v2.model.annotation.RuntimeInlineAnnotationReader.getPackageAnnotation(RuntimeInlineAnnotationReader.java:53)
at com.sun.xml.bind.v2.model.impl.TypeInfoImpl.parseElementName(TypeInfoImpl.java:122)
at com.sun.xml.bind.v2.model.impl.ClassInfoImpl.<init>(ClassInfoImpl.java:166)

This is due to a bug, and so far the only way to fix this is to compile your project with JavaSE 5.

Here is what's happening. Java5 added a new class file modifier attribute called ACC_SYNTHETIC, whose bit value is 0x1000. This attribute marks types and methods that are not present in the source file but generated by the compiler. When package-info.java is compiled into package-info.class, javac in Java5 apparently only put 0x0600 (= ACC_ABSTRACT|ACC_INTERFACE.) Some time during Java6 development, someone filed a bug, saying it should also include ACC_SYNTHETIC bit, since it was a synthesized class.

Later it is discovered that the corresponding VM change needs to be made to allow this 0x1600 combination, but apparently no one realized the real implication of this --- namely, 0x1600 will break all the past JVMs. Of course, this problem is eventually discovered, but as of this writing there's still no fix for this.

So as you see, this is why the only workaround is to use javac from Java5.

The customization syntax for DTD is roughly based on the ver.0.21 working draft of the JAXB specification, which is available at xml.coverpages.org. The deviations from this document are:

If all else fails, you should be able to execute the jaxb-xjc.jar file:

This is equivalent of running xjc.sh or xjc.bat, and it allows you to set the JVM parameters.

xjc supports the following parameter attributes.

xjc supports the following nested element parameters.

schemagen supports most of the attributes defined by the javac task, plus the following parameter attributes.

xjc supports all the nested elements defined by the javac task, the following nested element parameters.

The JAXB RI provides a mechanism for users to control declarations of namespace URIs and what prefixes they will be bound to. This is the general procedure:

The com.sun.xml.bind.marshaller.NamespacePrefixMapper class has the following method that you need to implement:

/**
 * Implemented by the user application to determine URI -> prefix
 * mapping.
 * 
 * This is considered as an interface, though it's implemented
 * as an abstract class to make it easy to add new methods in
 * a future. 
 * 
 * @author
 *     Kohsuke Kawaguchi (kohsuke.kawaguchi@sun.com)
 */
public abstract class NamespacePrefixMapper {

    private static final String[] EMPTY_STRING = new String[0];

    /**
     * Returns a preferred prefix for the given namespace URI.
     * 
     * This method is intended to be overrided by a derived class.
     *
     * <p>
     * As noted in the return value portion of the javadoc, there
     * are several cases where the preference cannot be honored.
     * Specifically, as of JAXB RI 2.0 and onward:
     *
     * <ol>
     * <li>
     * If the prefix returned is already in use as one of the in-scope
     * namespace bindings. This is partly necessary for correctness
     * (so that we don't unexpectedly change the meaning of QNames
     * bound to {@link String}), partly to simplify the marshaller.
     * <li>
     * If the prefix returned is "" yet the current {@link JAXBContext}
     * includes classes that use the empty namespace URI. This allows
     * the JAXB RI to reserve the "" prefix for the empty namespace URI,
     * which is the only possible prefix for the URI.
     * This restriction is also to simplify the marshaller.
     * </ol>
     *
     * @param namespaceUri
     *      The namespace URI for which the prefix needs to be found.
     *      Never be null. "" is used to denote the default namespace.
     * @param suggestion
     *      When the content tree has a suggestion for the prefix
     *      to the given namespaceUri, that suggestion is passed as a
     *      parameter. Typicall this value comes from the QName.getPrefix
     *      to show the preference of the content tree. This parameter
     *      may be null, and this parameter may represent an already
     *      occupied prefix. 
     * @param requirePrefix
     *      If this method is expected to return non-empty prefix.
     *      When this flag is true, it means that the given namespace URI
     *      cannot be set as the default namespace.
     * 
     * @return
     *      null if there's no prefered prefix for the namespace URI.
     *      In this case, the system will generate a prefix for you.
     * 
     *      Otherwise the system will try to use the returned prefix,
     *      but generally there's no guarantee if the prefix will be
     *      actually used or not.
     * 
     *      return "" to map this namespace URI to the default namespace.
     *      Again, there's no guarantee that this preference will be
     *      honored.
     * 
     *      If this method returns "" when requirePrefix=true, the return
     *      value will be ignored and the system will generate one.
     * 
     * @since JAXB 1.0.1
     */
    public abstract String getPreferredPrefix(String namespaceUri, String suggestion, boolean requirePrefix);

    /**
     * Returns a list of namespace URIs that should be declared
     * at the root element.
     *
     * <p>
     * By default, the JAXB RI 1.0.x produces namespace declarations only when
     * they are necessary, only at where they are used. Because of this
     * lack of look-ahead, sometimes the marshaller produces a lot of
     * namespace declarations that look redundant to human eyes. For example,
     * <pre><xmp>
     * <?xml version="1.0"?>
     * <root>
     *   <ns1:child xmlns:ns1="urn:foo"> ... </ns1:child>
     *   <ns2:child xmlns:ns2="urn:foo"> ... </ns2:child>
     *   <ns3:child xmlns:ns3="urn:foo"> ... </ns3:child>
     *   ...
     * </root>
     * </xmp></pre>
     *
     * <p>
     * The JAXB RI 2.x mostly doesn't exhibit this behavior any more,
     * as it declares all statically known namespace URIs (those URIs
     * that are used as element/attribute names in JAXB annotations),
     * but it may still declare additional namespaces in the middle of
     * a document, for example when (i) a QName as an attribute/element value
     * requires a new namespace URI, or (ii) DOM nodes as a portion of an object
     * tree requires a new namespace URI.
     *
     * <p>
     * If you know in advance that you are going to use a certain set of
     * namespace URIs, you can override this method and have the marshaller
     * declare those namespace URIs at the root element.
     *
     * <p>
     * For example, by returning <code>new String[]{"urn:foo"}</code>,
     * the marshaller will produce:
     * <pre><xmp>
     * <?xml version="1.0"?>
     * <root xmlns:ns1="urn:foo">
     *   <ns1:child> ... </ns1:child>
     *   <ns1:child> ... </ns1:child>
     *   <ns1:child> ... </ns1:child>
     *   ...
     * </root>
     * </xmp></pre>
     * <p>
     * To control prefixes assigned to those namespace URIs, use the
     * {@link #getPreferredPrefix(String, String, boolean)} method. 
     * 
     * @return
     *      A list of namespace URIs as an array of {@link String}s.
     *      This method can return a length-zero array but not null.
     *      None of the array component can be null. To represent
     *      the empty namespace, use the empty string <code>""</code>.
     * 
     * @since
     *      JAXB RI 1.0.2 
     */
    public String[] getPreDeclaredNamespaceUris() {
        return EMPTY_STRING;
    }

    /**
     * Similar to {@link #getPreDeclaredNamespaceUris()} but allows the
     * (prefix,nsUri) pairs to be returned.
     *
     * <p>
     * With {@link #getPreDeclaredNamespaceUris()}, applications who wish to control
     * the prefixes as well as the namespaces needed to implement both
     * {@link #getPreDeclaredNamespaceUris()} and {@link #getPreferredPrefix(String, String, boolean)}.
     *
     * <p>
     * This version eliminates the needs by returning an array of pairs.
     *
     * @return
     *      always return a non-null (but possibly empty) array. The array stores
     *      data like (prefix1,nsUri1,prefix2,nsUri2,...) Use an empty string to represent
     *      the empty namespace URI and the default prefix. Null is not allowed as a value
     *      in the array.
     *
     * @since
     *      JAXB RI 2.0 beta
     */
    public String[] getPreDeclaredNamespaceUris2() {
        return EMPTY_STRING;
    }

    /**
     * Returns a list of (prefix,namespace URI) pairs that represents
     * namespace bindings available on ancestor elements (that need not be repeated
     * by the JAXB RI.)
     *
     * <p>
     * Sometimes JAXB is used to marshal an XML document, which will be
     * used as a subtree of a bigger document. When this happens, it's nice
     * for a JAXB marshaller to be able to use in-scope namespace bindings
     * of the larger document and avoid declaring redundant namespace URIs.
     *
     * <p>
     * This is automatically done when you are marshalling to {@link XMLStreamWriter},
     * {@link XMLEventWriter}, {@link DOMResult}, or {@link Node}, because
     * those output format allows us to inspect what's currently available
     * as in-scope namespace binding. However, with other output format,
     * such as {@link OutputStream}, the JAXB RI cannot do this automatically.
     * That's when this method comes into play.
     *
     * <p>
     * Namespace bindings returned by this method will be used by the JAXB RI,
     * but will not be re-declared. They are assumed to be available when you insert
     * this subtree into a bigger document.
     *
     * <p>
     * It is <b>NOT</b> OK to return  the same binding, or give
     * the receiver a conflicting binding information.
     * It's a responsibility of the caller to make sure that this doesn't happen
     * even if the ancestor elements look like:
     * <pre><xmp>
     *   <foo:abc xmlns:foo="abc">
     *     <foo:abc xmlns:foo="def">
     *       <foo:abc xmlns:foo="abc">
     *         ... JAXB marshalling into here.
     *       </foo:abc>
     *     </foo:abc>
     *   </foo:abc>
     * </xmp></pre>
     *
     * @return
     *      always return a non-null (but possibly empty) array. The array stores
     *      data like (prefix1,nsUri1,prefix2,nsUri2,...) Use an empty string to represent
     *      the empty namespace URI and the default prefix. Null is not allowed as a value
     *      in the array.
     *
     * @since JAXB RI 2.0 beta
     */
    public String[] getContextualNamespaceDecls() {
        return EMPTY_STRING;
    }
}

See the Sample Apps sample application for a detailed example.

This property controls the string used for the indentation of XML. An element of depth k will be indented by printing this string k times. Note that the "jaxb.formatted.output" property needs to be set to "true" for the formatting/indentation of the output to occur. See the API documentation for javax.xml.bind.Marshaller interface for details of this property.

By default, the marshaller implementation of the JAXB RI tries to escape characters so they can be safely represented in the output encoding (by using Unicode numeric character references of the form &#dddd;)

Unfortunately, due to various technical reasons, the default behavior may not meet your expectations. If you need to handle escaping more adroitly than the default manner, you can do so by doing the following:

See the Sample Apps sample application for more details.

This experimental JAXB RI 1.0.x property has been adopted as a standard in JAXB 2.0. The 2.0 RI will continue to support this property, but client code should be using the Marshaller.JAXB_FRAGMENT property instead. Please refer to the Marshaller javadoc for a complete description of the behavior.

In JAXB 2.0, calling:

marshaller.setProperty("com.sun.xml.bind.xmlDeclaration", true);

is equivalent to calling:

marshaller.setProperty(Marshaller.JAXB_FRAGMENT, true);

JAXB 1.0 generated code and clients will continue to work exactly the same on the JAXB 2.0 runtime as they did on the JAXB 1.0 runtime.

Enabling fragment marshalling could be useful if you are inserting the output of the XML into another XML.

This property allows you to specify an XML preamble (<?xml ...> declaration) and any additional PIs, comments, DOCTYPE declaration that follows it. This property takes effect only when you are marshalling to OutputStream, Writer, or StreamResult. Note that this property interacts with the Marshaller.JAXB_FRAGMENT property. If that property is untouched or set to false, then JAXB would always write its XML preamble, so this property can be only used to write PIs, comments, DOCTYPE, etc. On the other hand, if it is set to true, then JAXB will not write its own XML preamble, so this property may contain custom XML preamble.

This property provides support for a custom com.sun.xml.bind.v2.runtime.reflect.Accessor implementation.  It allows the user to control the access to class fields and properties.

In JAXB 2.1, set the property to enable:

marshaller.setProperty("com.sun.xml.bind.XmlAccessorFactory", true);

The JAXB RI supports the use of schema component designator as a means of specifying the customization target (of all standard JAXB customizations as well as vendor extensions explained below.) To use this feature, use the scd attribute on <bindings> element instead of the schemaLocation and node attributes.

<bindings xmlns:tns="http://example.com/myns"
          xmlns="http://java.sun.com/xml/ns/jaxb" version="2.1">
    <bindings
            ...
            scd="tns:foo">
        <!-- this customization applies to the global element declaration -->
        <!-- 'foo' in the http://example.com/myns namespace -->
        <class name="FooElement"/>
    </bindings>
    <bindings
            ...
            scd="~tns:bar">
        <!-- this customization applies to the global type declaration -->
        <!-- 'bar' in the http://example.com/myns namespace -->
        <class name="BarType"/>
    </bindings>
</bindings>  

Compared to the standard XPath based approach, SCD allows more robust and concise way of identifying a target of a customization. For more about SCD, refer to the scd example. Note that SCD is a W3C working draft, and may change in the future.

The <xjc:superClass> customization allows you to specify the fully qualified name of the Java class that is to be used as the super class of all the generated implementation classes. The <xjc:superClass> customization can only occur within your <jaxb:globalBindings> customization on the <xs:schema> element:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:jaxb="http://java.sun.com/xml/ns/jaxb"
           xmlns:xjc="http://java.sun.com/xml/ns/jaxb/xjc"
           jaxb:extensionBindingPrefixes="xjc"
           jaxb:version="2.0">

    <xs:annotation>
        <xs:appinfo>
            <jaxb:globalBindings>
                <xjc:superClass
                        name="org.acme.RocketBooster"/>
            </jaxb:globalBindings>
        </xs:appinfo>
    </xs:annotation>
    
    ...
    
</xs:schema>

In the sample above, the <xjc:superClass> customization will cause all of the generated implementation classes to extend the named class, org.acme.RocketBooster.

The <xjc:superInterface> customization allows you to specify the fully qualified name of the Java interface that is to be used as the root interface of all the generated interfaces. The <xjc:superInterface> customization can only occur within your <jaxb:globalBindings> customization on the <xs:schema> element:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:jaxb="http://java.sun.com/xml/ns/jaxb"
           xmlns:xjc="http://java.sun.com/xml/ns/jaxb/xjc"
           jaxb:extensionBindingPrefixes="xjc"
           jaxb:version="2.0">

    <xs:annotation>
        <xs:appinfo>
            <jaxb:globalBindings>
                <xjc:superInterface
                        name="org.acme.RocketBooster"/>
            </jaxb:globalBindings>
        </xs:appinfo>
    </xs:annotation>

    ...

</xs:schema>

In the sample above, the <xjc:superInterface> customization will cause all of the generated interfaces to extend the named interface, org.acme.RocketBooster.

The <xjc:javaType> customization can be used just like the standard <jaxb:javaType> customization, except that it allows you to specify an XmlAdapter-derived class, instead of parse&print method pair.

This customization can be used in all the places <jaxb:javaType> is used, but nowhere else:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:jaxb="http://java.sun.com/xml/ns/jaxb"
           xmlns:xjc="http://java.sun.com/xml/ns/jaxb/xjc"
           jaxb:extensionBindingPrefixes="xjc"
           jaxb:version="2.0">
    
    ...
    
    <xsd:simpleType name="LayerRate_T">
        <xsd:annotation>
            <xsd:appinfo>
                <xjc:javaType name="org.acme.foo.LayerRate"
                              adapter="org.acme.foo.LayerRateAdapter"/>
            </xsd:appinfo>
        </xsd:annotation>
        
        ... gory simple type definition here ...
        
    </xsd:simpleType>
</xsd:schema>

In the above example, LayerRate_T simple type is adapted by org.acme.foo.LayerRateAdapter, which extends from XmlAdapter.

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:jaxb="http://java.sun.com/xml/ns/jaxb"
           xmlns:xjc="http://java.sun.com/xml/ns/jaxb/xjc"
           jaxb:extensionBindingPrefixes="xjc"
           jaxb:version="2.0">
    
    <xsd:annotation>
        <xsd:appinfo>
            <jaxb:globalBindings>
                <xjc:javaType name="org.acme.foo.MyDateType"
                              xmlType="xsd:dateTime"
                              adapter="org.acme.foo.MyAdapterImpl"/>
            </jaxb:globalBindings>
        </xsd:appinfo>
    </xsd:annotation>

    ...
    
</xsd:schema>

In the above example, all the use of xsd:dateTime type is adapter by org.acme.foo.MyAdapterImpl to org.acme.foo.MyDateType

This experimental binding mode can be enabled as a part of the global binding. See below:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:jaxb="http://java.sun.com/xml/ns/jaxb"
           xmlns:xjc="http://java.sun.com/xml/ns/jaxb/xjc"
           jaxb:extensionBindingPrefixes="xjc"
           jaxb:version="2.0">

    <xs:annotation>
        <xs:appinfo>
            <jaxb:globalBindings generateValueClass="false">
                <xjc:simple/>
            </jaxb:globalBindings>
        </xs:appinfo>
    </xs:annotation>

    ...

</xs:schema>

When enabled, XJC produces Java source code that are more concise and easier to use. Improvements include:

Once again, readers are warned that this is an experimental binding mode, and therefore the binding is subject to change in future versions of the JAXB RI without notice. Please send feedbacks on this binding to https://javaee.groups.io/g/metro

Normally, the JAXB specification requires that a derivation-by-restriction be mapped to an inheritance betwee n two Java classes. This is necessary to preserve the type hierarchy, but one of the downsides is that the derived class does not really provide easy-to-use properties that reflect the restricted content model.

This experimental <xjc:treatRestrictionLikeNewType> changes this behavior by not preserving the type inheritance to Java. Instead, it generates two unrelated Java classes, both with proper properties. For example, given the following schema:

<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
           xmlns:xjc="http://java.sun.com/xml/ns/jaxb/xjc"
           jaxb:extensionBindingPrefixes="xjc"
           xmlns:jaxb="http://java.sun.com/xml/ns/jaxb"
           jaxb:version="2.0"
           elementFormDefault="qualified">

    <xs:annotation>
        <xs:appinfo>
            <jaxb:globalBindings>
                <xjc:treatRestrictionLikeNewType/>
            </jaxb:globalBindings>
        </xs:appinfo>
    </xs:annotation>

    <xs:complexType name="DerivedType">
        <xs:complexContent>
            <xs:restriction base="ResponseOptionType">
                <xs:sequence>
                    <xs:element name="foo" type="xs:string"/>
                </xs:sequence>
            </xs:restriction>
        </xs:complexContent>
    </xs:complexType>

    <xs:complexType name="ResponseOptionType">
        <xs:sequence>
            <xs:element name="foo" type="xs:string"
                        maxOccurs="unbounded"/>
        </xs:sequence>
    </xs:complexType>

</xs:schema>

The generated Derived class will look like this (comment and annotations removed for brevity):

public class DerivedType {
    protected String foo;

    public String getFoo() { return foo; }
    public void setFoo(String value) { this.foo = value; }
} 

In contrast, without this customization the Derived class would look like the following:

public class DerivedType extends ResponseOptionType {

    // it simply inherits List<String> ResponseOptionType.getFoo()

}

In an attempt to make the generated code easier to use, the JAXB specification sometimes choose bindings based on how certain feature is used. One of them is element substitution feature. If no actual element substitution happens in the schema, JAXB assumes that the element is not used for substitution, and generates code that assumes it.

Most of the time this is fine, but when you expect other "extension" schemas to be compiled later on top of your base schema, and if those extension schemas do element substitutions, this binding causes a problem ( see example.)

<xjc:substitutable> customization is a work around for this issue. It explicitly tells XJC that a certain element is used for element substitution head, even though no actual substitution might be present in the current compilation. This customization should be attached in the element declaration itself, like this:

<xs:element name="Model" type="Model">
    <xs:annotation>
        <xs:appinfo>
            <xjc:substitutable/>
        </xs:appinfo>
    </xs:annotation>
</xs:element>

The customization syntax for DTD is roughly based on the ver.0.21 working draft of the JAXB specification, which is available at xml.coverpages.org. The deviations from this document are:

To write a plugin, do the following simple steps.

Users can then use your plugins by declaring an XJC ant task with your jar files.

<taskdef name="xjc" classname="com.sun.tools.xjc.XJCTask">
    <classpath>
        <fileset dir="jaxb-ri/lib" includes="*.jar"/>
        <fileset dir="your-plugin" includes="*.jar"/>
    </classpath>
</taskdef>

Although we will do our best to maintain the compatibility of the interfaces, it is still subject to change at this point.