Application to application connectivity with IBM MQ
Application-to-application connectivity is typically used when putting together a diverse set of application subsystems. To facilitate application integration, WebSphere® MQ provides the means to interconnect applications.
The Request-and-reply method is very common when interconnecting applications.
Request-and-reply communication method
The request-and-reply method enables one application to request the services of another application. One way to do this is for the requester to send a message to the service provider to request that some work be performed. When the work has been completed, the provider might decide to send results, or just a confirmation of completion, back to the requester. Unless the requester waits for a reply before continuing, IBM MQ must provide a way to associate the reply with its request.
IBM MQ provides a correlation identifier to correlate messages in an exchange between a requester and a provider. The requester marks a message with a known correlation identifier. The provider marks its reply with the same correlation identifier. To retrieve the associated reply, the requester provides that correlation identifier when receiving messages from the queue. The first message with a matching correlation identifier is returned to the requester.
The following examples use the DB2MQ schema for single-phase commit.
Examples of request-and-reply communication
- Example
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The following SQL SELECT statement sends a message consisting of the string "
Msg with corr id" to the service MYSERVICE, using the policy MYPOLICY with correlation identifier CORRID1:
The MQSEND function is invoked once because SYSIBM.SYSDUMMY1 has only one row. Because this MQSEND uses single-phase commit, IBM MQ adds the message to the queue, and you do not need to use a COMMIT statement.SELECT DB2MQ.MQSEND ('MYSERVICE', 'MYPOLICY', 'Msg with corr id', 'CORRID1') FROM SYSIBM.SYSDUMMY1; - Example
- The following SQL SELECT statement receives the first message that matches the identifier CORRID1 from the queue that is specified by the service MYSERVICE, using the policy MYPOLICY:
The SELECT statement returns a VARCHAR(4000) string. If no messages are available with this correlation identifier, a null value is returned, and the queue does not change.SELECT DB2MQ.MQRECEIVE ('MYSERVICE', 'MYPOLICY', 'CORRID1') FROM SYSIBM.SYSDUMMY1;