public interface Coder {
public String codeString(String s, int tval);
}
Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial |
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The encoder
example shows how to use alternatives to choose between
two beans at deployment time, as described in
Using Alternatives in CDI Applications. The
example includes an interface and two implementations of it, a managed
bean, a Facelets page, and configuration files.
The source files are located in the
tut-install/examples/cdi/encoder/src/main/java/javaeetutorial/encoder/
directory.
The following topics are addressed here:
The Coder
interface contains just one method, codeString
, that takes
two arguments: a string, and an integer value that specifies how the
letters in the string should be transposed.
public interface Coder {
public String codeString(String s, int tval);
}
The interface has two implementation classes, CoderImpl
and
TestCoderImpl
. The implementation of codeString
in CoderImpl
shifts the string argument forward in the alphabet by the number of
letters specified in the second argument; any characters that are not
letters are left unchanged. (This simple shift code is known as a Caesar
cipher because Julius Caesar reportedly used it to communicate with his
generals.) The implementation in TestCoderImpl
merely displays the
values of the arguments. The TestCoderImpl
implementation is annotated
@Alternative
:
import javax.enterprise.inject.Alternative;
@Alternative
public class TestCoderImpl implements Coder {
@Override
public String codeString(String s, int tval) {
return ("input string is " + s + ", shift value is " + tval);
}
}
The beans.xml
file for the encoder
example contains an
alternatives
element for the TestCoderImpl
class, but by default the
element is commented out:
<beans ...>
<!--<alternatives>
<class>javaeetutorial.encoder.TestCoderImpl</class>
</alternatives>-->
</beans>
This means that by default, the TestCoderImpl
class, annotated
@Alternative
, will not be used. Instead, the CoderImpl
class will be
used.
The simple Facelets page for the encoder
example, index.xhtml
, asks
the user to enter the string and integer values and passes them to the
managed bean, CoderBean
, as coderBean.inputString
and
coderBean.transVal
:
<html lang="en"
xmlns="http://www.w3.org/1999/xhtml"
xmlns:h="http://java.sun.com/jsf/html">
<h:head>
<h:outputStylesheet library="css" name="default.css"/>
<title>String Encoder</title>
</h:head>
<h:body>
<h2>String Encoder</h2>
<p>Type a string and an integer, then click Encode.</p>
<p>Depending on which alternative is enabled, the coder bean
will either display the argument values or return a string that
shifts the letters in the original string by the value you
specify. The value must be between 0 and 26.</p>
<h:form id="encodeit">
<p><h:outputLabel value="Enter a string: " for="inputString"/>
<h:inputText id="inputString"
value="#{coderBean.inputString}"/>
<h:outputLabel value="Enter the number of letters to shift by: "
for="transVal"/>
<h:inputText id="transVal" value="#{coderBean.transVal}"/></p>
<p><h:commandButton value="Encode"
action="#{coderBean.encodeString()}"/></p>
<p><h:outputLabel value="Result: " for="outputString"/>
<h:outputText id="outputString"
value="#{coderBean.codedString}"
style="color:blue"/></p>
<p><h:commandButton value="Reset"
action="#{coderBean.reset}"/></p>
</h:form>
...
</h:body>
</html>
When the user clicks the Encode button, the page invokes the managed
bean’s encodeString
method and displays the result,
coderBean.codedString
, in blue. The page also has a Reset button that
clears the fields.
The managed bean, CoderBean
, is a @RequestScoped
bean that declares
its input and output properties. The transVal
property has three Bean
Validation constraints that enforce limits on the integer value, so that
if the user enters an invalid value, a default error message appears on
the Facelets page. The bean also injects an instance of the Coder
interface:
@Named
@RequestScoped
public class CoderBean {
private String inputString;
private String codedString;
@Max(26)
@Min(0)
@NotNull
private int transVal;
@Inject
Coder coder;
...
In addition to simple getter and setter methods for the three
properties, the bean defines the encodeString
action method called by
the Facelets page. This method sets the codedString
property to the
value returned by a call to the codeString
method of the Coder
implementation:
public void encodeString() {
setCodedString(coder.codeString(inputString, transVal));
}
Finally, the bean defines the reset
method to empty the fields of the
Facelets page:
public void reset() {
setInputString("");
setTransVal(0);
}
You can use either NetBeans IDE or Maven to build, package, deploy, and
run the encoder
application.
Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).
From the File menu, choose Open Project.
In the Open Project dialog box, navigate to:
tut-install/examples/cdi
Select the encoder
folder.
Click Open Project.
In the Projects tab, right-click the encoder
project and select
Build.
This command builds and packages the application into a WAR file,
encoder.war
, located in the target
directory, and then deploys it to
GlassFish Server.
In a web browser, enter the following URL:
http://localhost:8080/encoder
On the String Encoder page, enter a string and the number of letters to shift by, and then click Encode.
The encoded string appears in blue on the Result line. For example, if
you enter Java
and 4
, the result is Neze
.
Now, edit the beans.xml
file to enable the alternative
implementation of Coder
.
In the Projects tab, under the encoder
project, expand the Web
Pages node, then expand the WEB-INF node.
Double-click the beans.xml
file to open it.
Remove the comment characters that surround the alternatives
element, so that it looks like this:
<alternatives>
<class>javaeetutorial.encoder.TestCoderImpl</class>
</alternatives>
Save the file.
Right-click the encoder
project and select Clean and Build.
In the web browser, reenter the URL to show the String Encoder page for the redeployed project:
http://localhost:8080/encoder/
Enter a string and the number of letters to shift by, and then click Encode.
This time, the Result line displays your arguments. For example, if you
enter Java
and 4
, the result is:
Result: input string is Java, shift value is 4
Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).
In a terminal window, go to:
tut-install/examples/cdi/encoder/
Enter the following command to deploy the application:
mvn install
This command builds and packages the application into a WAR file,
encoder.war
, located in the target
directory, and then deploys it to
GlassFish Server.
In a web browser, enter the following URL:
http://localhost:8080/encoder/
The String Encoder page opens.
Enter a string and the number of letters to shift by, and then click Encode.
The encoded string appears in blue on the Result line. For example, if
you enter Java
and 4
, the result is Neze
.
Now, edit the beans.xml
file to enable the alternative
implementation of Coder
.
In a text editor, open the following file:
tut-install/examples/cdi/encoder/src/main/webapp/WEB-INF/beans.xml
Remove the comment characters that surround the alternatives
element, so that it looks like this:
<alternatives>
<class>javaeetutorial.encoder.TestCoderImpl</class>
</alternatives>
Save and close the file.
Enter the following command:
mvn clean install
In the web browser, reenter the URL to show the String Encoder page for the redeployed project:
http://localhost:8080/encoder
Enter a string and the number of letters to shift by, and then click Encode.
This time, the Result line displays your arguments. For example, if you
enter Java
and 4
, the result is:
Result: input string is Java, shift value is 4
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