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Because Stomp frames consist of plain text, it is possible to improvise a Stomp client by
starting up a telnet session and entering Stomp frames
directly at the keyboard. This can be a useful diagnostic tool and is also a good way to learn
about the Stomp protocol.
While most characters in a Stomp frame are just plain text, there is one required character, null, that you might have difficulty typing at the keyboard. On some keyboards, you can type null as Ctrl-@. Other keyboards might require you to do a bit of research, however.
For example, to type a null character on the 101-key keyboard that is commonly used with a Windows PC, proceed as follows:
Enable NumLock on the numeric keypad (this is
essential).
While holding down the Alt key, type zero, 0, four times in succession on the numeric
keypad.
To send and receive messages over the Stomp protocol using telnet clients, perform the following steps:
Start the default broker by entering the following at a command prompt:
activemq
Normally, the default broker is configured to initialize a Stomp connector that listens on port, 61613. Look for a line like the following in the broker’s log:
INFO TransportServerThreadSupport - Listening for connections at: stomp://localhost:61613
If the Stomp connector is not present in the broker, you will have to configure it—see Configure the broker for details.
Open a new command prompt and start a new telnet session
for the producer client, by entering the following command:
telnet
This command starts telnet in interactive mode. Now
enter the following telnet commands (the telnet prompt that begins each line is implementation dependent):
telnet> set localecho Local echo on telnet> open localhost 61613
After entering the open command, telnet should connect to the Stomp socket on your local ActiveMQ
broker (where the Stomp port is presumed to be 61613 here). You should now see a blank screen,
where you can directly type the contents of the Stomp frames you want to send over TCP.
Start a Stomp session for the producer by entering the following Stomp frame in the
telnet window:
CONNECT login:foo passcode:bar ^@
The login and passcode headers are currently ignored by the ActiveMQ broker, so you can enter any
values you like for these headers. Don’t forget to insert a blank line after the
headers. Finally, you must terminate the frame by typing the null character,
^@ (for notes on how to type the null character at your
keyboard, see Typing the null character ).
If all goes well, you will see a response similar to the following:
CONNECTED session:ID:fboltond820-2290-1190810591249-3:0
Send a message to the FOO.BAR queue by entering the
following frame:
SEND destination:/queue/FOO.BAR receipt: Hello, queue FOO.BAR ^@
As soon as you have finished typing the null character, ^@, you should receive the following RECEIPT frame
from the server:
RECEIPT receipt-id:
It is a good idea to include a receipt header in the
frames you send from a telnet client. It enables you to confirm that the connection is working
normally.
The status of the ActiveMQ broker can be monitored through a JMX port. To monitor the broker, start a new command prompt and enter the following command:
jconsole
The jconsole utility is a standard JMX client that is
included with Sun’s Java Development Kit (JDK). When you start the jconsole utility, a dialog appears and prompts you to connect to a JMX process, as
shown in Figure 3.1 .
Select the ActiveMQ broker process and click Connect.
The main jconsole window opens. To view the current status of
the FOO.BAR message queue, click on the MBeans tab and use the tree on the left hand side to drill down to
org.apache.activemq/localhost/Queue/FOO.BAR. Click on the
FOO.BAR icon to view the current status, as shown in Figure 3.2 .
The status shows an EnqueueCount of 1, which tells you
that the producer has successfully enqueued one message in the FOO.BAR queue.
Open a new command prompt and start a new telnet session
for the consumer client, by entering the following command:
telnet
Enter the following telnet commands to connect to the
Stomp socket on the broker:
telnet> set localecho Local echo on telnet> open localhost 61613
Start a Stomp session for the consumer by entering the following Stomp frame in the
consumer’s telnet window:
CONNECT login:foo passcode:bar ^@
If all goes well, you will see a response similar to the following:
CONNECTED session:ID:fboltond820-2290-1190810591249-3:1
Subscribe to the FOO.BAR queue by entering the following
Stomp frame in the consumer’s telnet window:
SUBSCRIBE destination:/queue/FOO.BAR ack:client ^@
The ack header is set to the value client, which implies that the consumer client is expected to
acknowledge each message it receives from the broker. After typing the terminating null
character, ^@, the broker dispatches the sole message on the
FOO.BAR queue by sending a MESSAGE frame, as follows:
MESSAGE destination:/queue/FOO.BAR receipt: timestamp:1190811984837 priority:0 expires:0 message-id:ID:fboltond820-2290-1190810591249-3:0:-1:1:1 Hello, queue FOO.BAR
To see what effect this has on the queue status, go to the jconsole window and click Refresh on the MBeans
tab. The DispatchCount attribute is now equal to 1,
indicating that the broker has dispatched the message to the consumer. The DequeueCount is equal to 0, however; this is because the message is
not considered to be dequeued until the consumer client sends an acknowledgement.
Acknowledge the received message by entering the following Stomp frame in the consumer’s
telnet window:
ACK message-id:ID:fboltond820-2290-1190810591249-3:0:-1:1:1 ^@
Where the message ID must match the value from the message-id header in the received MESSAGE frame.
To check that the acknowledgement has been effective, go back to the jconsole window and click Refresh on the
MBeans tab. You should now find that the DequeueCount has increased to 1.
Unsubscribe from the FOO.BAR queue by entering the
following Stomp frame in the consumer’s telnet window:
UNSUBSCRIBE destination:/queue/FOO.BAR receipt: ^@
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