cd tut-install/jms/simple/producer
Java Platform, Enterprise Edition (Java EE) 8 The Java EE Tutorial |
Previous | Next | Contents |
This section shows how to create, package, and run simple JMS clients that are packaged as application clients.
The following topics are addressed here:
The clients demonstrate the basic tasks a JMS application must perform:
Creating a JMSContext
Creating message producers and consumers
Sending and receiving messages
Each example uses two clients: one that sends messages and one that receives them. You can run the clients in two terminal windows.
When you write a JMS client to run in an enterprise bean application, you use many of the same methods in much the same sequence as for an application client. However, there are some significant differences. Using the JMS API in Java EE Applications describes these differences, and this chapter provides examples that illustrate them.
The examples for this section are in the
tut-install/examples/jms/simple/
directory, under the following
subdirectories:
producer/
synchconsumer/
asynchconsumer/
messagebrowser/
clientackconsumer/
Before running the examples, you need to start GlassFish Server and create administered objects.
When you use GlassFish Server, your JMS provider is GlassFish Server. Start the server as described in Starting and Stopping GlassFish Server.
This example uses the following JMS administered objects:
A connection factory
Two destination resources: a topic and a queue
Before you run the applications, you can use the asadmin add-resources
command to create needed JMS resources, specifying as the argument a
file named glassfish-resources.xml
. This file can be created in any
project using NetBeans IDE, although you can also create it by hand. A
file for the needed resources is present in the
jms/simple/producer/src/main/setup/
directory.
The JMS examples use a connection factory with the logical JNDI lookup
name java:comp/DefaultJMSConnectionFactory
, which is preconfigured in
GlassFish Server.
You can also use the asadmin create-jms-resource
command to create
resources, the asadmin list-jms-resources
command to display their
names, and the asadmin delete-jms-resource
command to remove them.
A glassfish-resources.xml
file in one of the Maven projects can create
all the resources needed for the simple examples.
Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server).
In a command window, go to the Producer
example.
cd tut-install/jms/simple/producer
Create the resources using the asadmin add-resources
command:
asadmin add-resources src/main/setup/glassfish-resources.xml
Verify the creation of the resources:
asadmin list-jms-resources
The command lists the two destinations and connection factory specified
in the glassfish-resources.xml
file in addition to the platform
default connection factory:
jms/MyQueue
jms/MyTopic
jms/__defaultConnectionFactory
Command list-jms-resources executed successfully.
In GlassFish Server, the Java EE java:comp/DefaultJMSConnectionFactory
resource is mapped to a connection factory named
jms/__defaultConnectionFactory
.
To run the simple examples using GlassFish Server, package each example
in an application client JAR file. The application client JAR file
requires a manifest file, located in the src/main/java/META-INF/
directory for each example, along with the .class
file.
The pom.xml
file for each example specifies a plugin that creates an
application client JAR file. You can build the examples using either
NetBeans IDE or Maven.
The following topics are addressed here:
From the File menu, choose Open Project.
In the Open Project dialog box, navigate to:
tut-install/examples/jms
Expand the jms
node and select the simple
folder.
Click Open Project to open all the simple examples.
In the Projects tab, right-click the simple
project and select
Build to build all the examples.
This command places the application client JAR files in the target
directories for the examples.
This section describes how to use a client to send messages. The
Producer.java
client will send messages in all of these examples.
The following topics are addressed here:
General steps this example performs are as follows.
Inject resources for the administered objects used by the example.
Accept and verify command-line arguments. You can use this example to send any number of messages to either a queue or a topic, so you specify the destination type and the number of messages on the command line when you run the program.
Create a JMSContext
, then send the specified number of text
messages in the form of strings, as described in
Message Bodies.
Send a final message of type Message
to indicate that the consumer
should expect no more messages.
Catch any exceptions.
The sending client, Producer.java
, performs the following steps.
Injects resources for a connection factory, queue, and topic:
@Resource(lookup = "java:comp/DefaultJMSConnectionFactory")
private static ConnectionFactory connectionFactory;
@Resource(lookup = "jms/MyQueue")
private static Queue queue;
@Resource(lookup = "jms/MyTopic")
private static Topic topic;
Retrieves and verifies command-line arguments that specify the destination type and the number of arguments:
final int NUM_MSGS;
String destType = args[0];
System.out.println("Destination type is " + destType);
if ( ! ( destType.equals("queue") || destType.equals("topic") ) ) {
System.err.println("Argument must be \"queue\" or " + "\"topic\"");
System.exit(1);
}
if (args.length == 2){
NUM_MSGS = (new Integer(args[1])).intValue();
} else {
NUM_MSGS = 1;
}
Assigns either the queue or the topic to a destination object, based on the specified destination type:
Destination dest = null;
try {
if (destType.equals("queue")) {
dest = (Destination) queue;
} else {
dest = (Destination) topic;
}
} catch (Exception e) {
System.err.println("Error setting destination: " + e.toString());
System.exit(1);
}
Within a try
-with-resources block, creates a JMSContext
:
try (JMSContext context = connectionFactory.createContext();) {
Sets the message count to zero, then creates a JMSProducer
and
sends one or more messages to the destination and increments the count.
Messages in the form of strings are of the TextMessage
message type:
int count = 0;
for (int i = 0; i < NUM_MSGS; i++) {
String message = "This is message " + (i + 1)
+ " from producer";
// Comment out the following line to send many messages
System.out.println("Sending message: " + message);
context.createProducer().send(dest, message);
count += 1;
}
System.out.println("Text messages sent: " + count);
Sends an empty control message to indicate the end of the message stream:
context.createProducer().send(dest, context.createMessage());
Sending an empty message of no specified type is a convenient way for an application to indicate to the consumer that the final message has arrived.
Catches and handles any exceptions. The end of the
try
-with-resources block automatically causes the JMSContext
to be
closed:
} catch (Exception e) {
System.err.println("Exception occurred: " + e.toString());
System.exit(1);
}
System.exit(0);
You can run the client using the appclient
command. The Producer
client takes one or two command-line arguments: a destination type and,
optionally, a number of messages. If you do not specify a number of
messages, the client sends one message.
You will use the client to send three messages to a queue.
Make sure that GlassFish Server has been started (see Starting and Stopping GlassFish Server) and that you have created resources and built the simple JMS examples (see Creating JMS Administered Objects and Building All the Simple Examples).
In a terminal window, go to the producer
directory:
cd producer
Run the Producer
program, sending three messages to the queue:
appclient -client target/producer.jar queue 3
The output of the program looks like this (along with some additional output):
Destination type is queue
Sending message: This is message 1 from producer
Sending message: This is message 2 from producer
Sending message: This is message 3 from producer
Text messages sent: 3
The messages are now in the queue, waiting to be received.
Note: When you run an application client, the command may take a long time to complete. |
This section describes the receiving client, which uses the receive
method to consume messages synchronously. This section then explains how
to run the clients using GlassFish Server.
The following topics are addressed here:
The receiving client, SynchConsumer.java
, performs the following
steps.
Injects resources for a connection factory, queue, and topic.
Assigns either the queue or the topic to a destination object, based on the specified destination type.
Within a try
-with-resources block, creates a JMSContext
.
Creates a JMSConsumer
, starting message delivery:
consumer = context.createConsumer(dest);
Receives the messages sent to the destination until the end-of-message-stream control message is received:
int count = 0;
while (true) {
Message m = consumer.receive(1000);
if (m != null) {
if (m instanceof TextMessage) {
System.out.println(
"Reading message: " + m.getBody(String.class));
count += 1;
} else {
break;
}
}
}
System.out.println("Messages received: " + count);
Because the control message is not a TextMessage
, the receiving client
terminates the while
loop and stops receiving messages after the
control message arrives.
Catches and handles any exceptions. The end of the
try
-with-resources block automatically causes the JMSContext
to be
closed.
The SynchConsumer
client uses an indefinite while
loop to receive
messages, calling receive
with a timeout argument.
You can run the client using the appclient
command. The
SynchConsumer
client takes one command-line argument, the destination
type.
These steps show how to receive and send messages synchronously using
both a queue and a topic. The steps assume you already ran the
Producer
client and have three messages waiting in the queue.
In the same terminal window where you ran Producer
, go to the
synchconsumer
directory:
cd ../synchconsumer
Run the SynchConsumer
client, specifying the queue:
appclient -client target/synchconsumer.jar queue
The output of the client looks like this (along with some additional output):
Destination type is queue
Reading message: This is message 1 from producer
Reading message: This is message 2 from producer
Reading message: This is message 3 from producer
Messages received: 3
Now try running the clients in the opposite order. Run the
SynchConsumer
client:
appclient -client target/synchconsumer.jar queue
The client displays the destination type and then waits for messages.
Open a new terminal window and run the Producer
client:
cd tut-install/jms/simple/producer
appclient -client target/producer.jar queue 3
When the messages have been sent, the SynchConsumer
client receives
them and exits.
Now run the Producer
client using a topic instead of a queue:
appclient -client target/producer.jar topic 3
The output of the client looks like this (along with some additional output):
Destination type is topic
Sending message: This is message 1 from producer
Sending message: This is message 2 from producer
Sending message: This is message 3 from producer
Text messages sent: 3
Now, in the other terminal window, run the SynchConsumer
client
using the topic:
appclient -client target/synchconsumer.jar topic
The result, however, is different. Because you are using a subscription on a topic, messages that were sent before you created the subscription on the topic will not be added to the subscription and delivered to the consumer. (See Publish/Subscribe Messaging Style and Consuming Messages from Topics for details.) Instead of receiving the messages, the client waits for messages to arrive.
Leave the SynchConsumer
client running and run the Producer
client again:
appclient -client target/producer.jar topic 3
Now the SynchConsumer
client receives the messages:
Destination type is topic
Reading message: This is message 1 from producer
Reading message: This is message 2 from producer
Reading message: This is message 3 from producer
Messages received: 3
Because these messages were sent after the consumer was started, the client receives them.
This section describes the receiving clients in an example that uses a message listener for asynchronous message delivery. This section then explains how to compile and run the clients using GlassFish Server.
Note: In the Java EE platform, message listeners can be used only in application clients, as in this example. To allow asynchronous message delivery in a web or enterprise bean application, you use a message-driven bean, shown in later examples in this chapter. |
The following topics are addressed here:
The sending client is Producer.java
, the same client used in
Sending Messages and Receiving Messages
Synchronously.
An asynchronous consumer normally runs indefinitely. This one runs until
the user types the character q
or Q
to stop the client.
The client, AsynchConsumer.java
, performs the following steps.
Injects resources for a connection factory, queue, and topic.
Assigns either the queue or the topic to a destination object, based on the specified destination type.
In a try
-with-resources block, creates a JMSContext
.
Creates a JMSConsumer
.
Creates an instance of the TextListener
class and registers it as
the message listener for the JMSConsumer
:
listener = new TextListener();
consumer.setMessageListener(listener);
Listens for the messages sent to the destination, stopping when the
user types the character q
or Q
(it uses a
java.io.InputStreamReader
to do this).
Catches and handles any exceptions. The end of the
try
-with-resources block automatically causes the JMSContext
to be
closed, thus stopping delivery of messages to the message listener.
The message listener, TextListener.java
, follows these steps:
When a message arrives, the onMessage
method is called
automatically.
If the message is a TextMessage
, the onMessage
method displays
its content as a string value. If the message is not a text message, it
reports this fact:
public void onMessage(Message m) {
try {
if (m instanceof TextMessage) {
System.out.println(
"Reading message: " + m.getBody(String.class));
} else {
System.out.println("Message is not a TextMessage");
}
} catch (JMSException | JMSRuntimeException e) {
System.err.println("JMSException in onMessage(): " + e.toString());
}
}
For this example, you will use the same connection factory and destinations you created in To Create Resources for the Simple Examples.
The steps assume that you have already built and packaged all the examples using NetBeans IDE or Maven.
You will need two terminal windows, as you did in Receiving Messages Synchronously.
In the terminal window where you ran the SynchConsumer
client, go
to the asynchconsumer
example directory:
cd tut-install/jms/simple/asynchconsumer
Run the AsynchConsumer
client, specifying the topic
destination
type:
appclient -client target/asynchconsumer.jar topic
The client displays the following lines (along with some additional output) and then waits for messages:
Destination type is topic
To end program, enter Q or q, then <return>
In the terminal window where you ran the Producer
client
previously, run the client again, sending three messages:
appclient -client target/producer.jar topic 3
The output of the client looks like this (along with some additional output):
Destination type is topic
Sending message: This is message 1 from producer
Sending message: This is message 2 from producer
Sending message: This is message 3 from producer
Text messages sent: 3
In the other window, the AsynchConsumer
client displays the following
(along with some additional output):
Destination type is topic
To end program, enter Q or q, then <return>
Reading message: This is message 1 from producer
Reading message: This is message 2 from producer
Reading message: This is message 3 from producer
Message is not a TextMessage
The last line appears because the client has received the non-text
control message sent by the Producer
client.
Enter Q
or q
and press Return to stop the AsynchConsumer
client.
Now run the clients using a queue.
In this case, as with the synchronous example, you can run the
Producer
client first, because there is no timing dependency between
the sender and receiver:
appclient -client target/producer.jar queue 3
The output of the client looks like this:
Destination type is queue
Sending message: This is message 1 from producer
Sending message: This is message 2 from producer
Sending message: This is message 3 from producer
Text messages sent: 3
In the other window, run the AsynchConsumer
client:
appclient -client target/asynchconsumer.jar queue
The output of the client looks like this (along with some additional output):
Destination type is queue
To end program, enter Q or q, then <return>
Reading message: This is message 1 from producer
Reading message: This is message 2 from producer
Reading message: This is message 3 from producer
Message is not a TextMessage
Enter Q
or q
and press Return to stop the client.
This section describes an example that creates a QueueBrowser
object
to examine messages on a queue, as described in
JMS Queue Browsers. This section then
explains how to compile, package, and run the example using GlassFish
Server.
The following topics are addressed here:
To create a QueueBrowser
for a queue, you call the
JMSContext.createBrowser
method with the queue as the argument. You
obtain the messages in the queue as an Enumeration
object. You can
then iterate through the Enumeration
object and display the contents
of each message.
The MessageBrowser.java
client performs the following steps.
Injects resources for a connection factory and a queue.
In a try
-with-resources block, creates a JMSContext
.
Creates a QueueBrowser
:
QueueBrowser browser = context.createBrowser(queue);
Retrieves the Enumeration
that contains the messages:
Enumeration msgs = browser.getEnumeration();
Verifies that the Enumeration
contains messages, then displays the
contents of the messages:
if ( !msgs.hasMoreElements() ) {
System.out.println("No messages in queue");
} else {
while (msgs.hasMoreElements()) {
Message tempMsg = (Message)msgs.nextElement();
System.out.println("Message: " + tempMsg);
}
}
Catches and handles any exceptions. The end of the
try
-with-resources block automatically causes the JMSContext
to be
closed.
Dumping the message contents to standard output retrieves the message
body and properties in a format that depends on the implementation of
the toString
method. In GlassFish Server, the message format looks
something like this:
Text: This is message 3 from producer
Class: com.sun.messaging.jmq.jmsclient.TextMessageImpl
getJMSMessageID(): ID:8-10.152.23.26(bf:27:4:e:e7:ec)-55645-1363100335526
getJMSTimestamp(): 1129061034355
getJMSCorrelationID(): null
JMSReplyTo: null
JMSDestination: PhysicalQueue
getJMSDeliveryMode(): PERSISTENT
getJMSRedelivered(): false
getJMSType(): null
getJMSExpiration(): 0
getJMSPriority(): 4
Properties: {JMSXDeliveryCount=0}
Instead of displaying the message contents this way, you can call some
of the Message
interface’s getter methods to retrieve the parts of the
message you want to see.
For this example, you will use the connection factory and queue you created for Receiving Messages Synchronously. It is assumed that you have already built and packaged all the examples.
To run the MessageBrowser
example using the appclient
command,
follow these steps.
You also need the Producer
example to send the message to the queue,
and one of the consumer clients to consume the messages after you
inspect them.
To run the clients, you need two terminal windows.
In a terminal window, go to the producer
directory:
cd tut-install/examples/jms/simple/producer/
Run the Producer
client, sending one message to the queue, along
with the non-text control message:
appclient -client target/producer.jar queue
The output of the client looks like this (along with some additional output):
Destination type is queue
Sending message: This is message 1 from producer
Text messages sent: 1
In another terminal window, go to the messagebrowser
directory:
cd tut-install/jms/simple/messagebrowser
Run the MessageBrowser
client using the following command:
appclient -client target/messagebrowser.jar
The output of the client looks something like this (along with some additional output):
Message:
Text: This is message 1 from producer
Class: com.sun.messaging.jmq.jmsclient.TextMessageImpl
getJMSMessageID(): ID:9-10.152.23.26(bf:27:4:e:e7:ec)-55645-1363100335526
getJMSTimestamp(): 1363100335526
getJMSCorrelationID(): null
JMSReplyTo: null
JMSDestination: PhysicalQueue
getJMSDeliveryMode(): PERSISTENT
getJMSRedelivered(): false
getJMSType(): null
getJMSExpiration(): 0
getJMSPriority(): 4
Properties: {JMSXDeliveryCount=0}
Message:
Class: com.sun.messaging.jmq.jmsclient.MessageImpl
getJMSMessageID(): ID:10-10.152.23.26(bf:27:4:e:e7:ec)-55645-1363100335526
getJMSTimestamp(): 1363100335526
getJMSCorrelationID(): null
JMSReplyTo: null
JMSDestination: PhysicalQueue
getJMSDeliveryMode(): PERSISTENT
getJMSRedelivered(): false
getJMSType(): null
getJMSExpiration(): 0
getJMSPriority(): 4
Properties: {JMSXDeliveryCount=0}
The first message is the TextMessage
, and the second is the non-text
control message.
Go to the synchconsumer
directory.
Run the SynchConsumer
client to consume the messages:
appclient -client target/synchconsumer.jar queue
The output of the client looks like this (along with some additional output):
Destination type is queue
Reading message: This is message 1 from producer
Messages received: 1
To illustrate further the way point-to-point and publish/subscribe
messaging works, you can use the Producer
and SynchConsumer
examples
to send messages that are then consumed by two clients running
simultaneously.
Open three command windows. In one, go to the producer
directory.
In the other two, go to the synchconsumer
directory.
In each of the synchconsumer
windows, start running the client,
receiving messages from a queue:
appclient -client target/synchconsumer.jar queue
Wait until you see the "Destination type is queue" message in both windows.
In the producer
window, run the client, sending 20 or so messages
to the queue:
appclient -client target/producer.jar queue 20
Look at the output in the synchconsumer
windows. In point-to-point
messaging, each message can have only one consumer. Therefore, each of
the clients receives some of the messages. One of the clients receives
the non-text control message, reports the number of messages received,
and exits.
In the window of the client that did not receive the non-text control message, enter Control-C to exit the program.
Next, run the synchconsumer
clients using a topic. In each window,
run the following command:
appclient -client target/synchconsumer.jar topic
Wait until you see the "Destination type is topic" message in both windows.
In the producer
window, run the client, sending 20 or so messages
to the topic:
appclient -client target/producer.jar topic 20
Again, look at the output in the synchconsumer
windows. In
publish/subscribe messaging, a copy of every message is sent to each
subscription on the topic. Therefore, each of the clients receives all
20 text messages as well as the non-text control message.
JMS provides two alternative ways for a consuming client to ensure that a message is not acknowledged until the application has finished processing the message:
Using a synchronous consumer in a JMSContext
that has been
configured to use the CLIENT_ACKNOWLEDGE
setting
Using a message listener for asynchronous message delivery in a
JMSContext
that has been configured to use the default
AUTO_ACKNOWLEDGE
setting
Note: In the Java EE platform, |
The clientackconsumer
example demonstrates the first alternative, in
which a synchronous consumer uses client acknowledgment. The
asynchconsumer
example described in Using a Message
Listener for Asynchronous Message Delivery demonstrates the second
alternative.
For information about message acknowledgment, see Controlling Message Acknowledgment.
The following table describes four possible interactions between types of consumers and types of acknowledgment.
Table 49-3 Message Acknowledgment with Synchronous and Asynchronous Consumers
Consumer Type |
Acknowledgment Type |
Behavior |
Synchronous |
Client |
Client acknowledges message after processing is complete |
Asynchronous |
Client |
Client acknowledges message after processing is complete |
Synchronous |
Auto |
Acknowledgment happens immediately after |
Asynchronous |
Auto |
Message is automatically acknowledged when
|
The example is under the tut-install`/examples/jms/simple/clientackconsumer/` directory.
The example client, ClientAckConsumer.java
, creates a JMSContext
that specifies client acknowledgment:
try (JMSContext context =
connectionFactory.createContext(JMSContext.CLIENT_ACKNOWLEDGE);) {
...
The client uses a while
loop almost identical to that used by
SynchConsumer.java
, with the exception that after processing each
message, it calls the acknowledge
method on the JMSContext
:
context.acknowledge();
The example uses the following objects:
The jms/MyQueue
resource that you created for Receiving
Messages Synchronously.
java:comp/DefaultJMSConnectionFactory
, the platform default
connection factory preconfigured with GlassFish Server
In a terminal window, go to the following directory:
tut-install/examples/jms/simple/producer/
Run the Producer
client, sending some messages to the queue:
appclient -client target/producer.jar queue 3
In another terminal window, go to the following directory:
tut-install/examples/jms/simple/clientackconsumer/
To run the client, use the following command:
appclient -client target/clientackconsumer.jar
The client output looks like this (along with some additional output):
Created client-acknowledge JMSContext
Reading message: This is message 1 from producer
Acknowledging TextMessage
Reading message: This is message 2 from producer
Acknowledging TextMessage
Reading message: This is message 3 from producer
Acknowledging TextMessage
Acknowledging non-text control message
The client acknowledges each message explicitly after processing it,
just as a JMSContext
configured to use AUTO_ACKNOWLEDGE
does
automatically after a MessageListener
returns successfully from
processing a message received asynchronously.
Previous | Next | Contents |