Creating a channel exit in IBM MQ classes for Java

We can provide your own channel exits by defining a Java class that implements an appropriate interface.

To implement an exit, you define a new Java class that implements the appropriate interface. Three exit interfaces are defined in the com.ibm.mq.exits package:

WMQSendExit
WMQReceiveExit
WMQSecurityExit

Note: Channel exits are supported for client connections only; they are not supported for bindings connections. We cannot use a Java channel exit outside IBM MQ classes for Java, for example if you are using a client application written in C.

Any TLS encryption defined for a connection is performed after send and security exits have been invoked. Similarly, decryption is performed before receive and security exits are invoked.

The following sample defines a class that implements all three interfaces:

public class MyMQExits implements
WMQSendExit, WMQReceiveExit, WMQSecurityExit {
    // Default constructor
  public MyMQExits(){ 
  }
    // This method comes from the send exit interface
  public ByteBuffer channelSendExit(
MQCXP channelExitParms,
                                    MQCD channelDefinition,
                                    ByteBuffer agentBuffer)
  {
    // Fill in the body of the send exit here
  }
    // This method comes from the receive exit interface
  public ByteBuffer channelReceiveExit(
MQCXP channelExitParms,
                                       MQCD channelDefinition,
                                       ByteBuffer agentBuffer)
  {      
    // Fill in the body of the receive exit here
  }
    // This method comes from the security exit interface
  public ByteBuffer channelSecurityExit(
MQCXP channelExitParms,
                                        MQCD channelDefinition,
                                        ByteBuffer agentBuffer)
  {
    // Fill in the body of the security exit here
  }
}

Each exit is passed an MQCXP object and an MQCD object. These objects represent the MQCXP and MQCD structures defined in the procedural interface.

Any exit class you write must have a constructor. This can be either the default constructor or one that takes a string argument. If it takes a string then the user data will be passed into the exit class when it is created. If the exit class contains both a default constructor and a single argument constructor, the single argument constructor has priority.

For the send and security exits, your exit code must return the data to send to the server. For a receive exit, your exit code must return the modified data that you want IBM MQ to interpret.

The simplest possible exit body is:

{ return agentBuffer; }

Do not close the queue manager from within a channel exit.

Use existing channel exit classes

In versions of IBM MQ earlier than 7.0, you would implement these exits using the interfaces MQSendExit, MQReceiveExit, and MQSecurityExit, as in the following example. This method remains valid, but the new method is preferred for improved functionality and performance.

public class MyMQExits implements MQSendExit, MQReceiveExit, MQSecurityExit {
    // Default constructor
  public MyMQExits(){ 
  }
    // This method comes from the send exit
  public byte[] sendExit(MQChannelExit channelExitParms,
                         MQChannelDefinition channelDefParms,
                         byte agentBuffer[])
  {
    // Fill in the body of the send exit here
  }
    // This method comes from the receive exit
  public byte[] receiveExit(MQChannelExit channelExitParms,
                            MQChannelDefinition channelDefParms,
                            byte agentBuffer[])
  {
    // Fill in the body of the receive exit here
  }
    // This method comes from the security exit
  public byte[] securityExit(MQChannelExit channelExitParms,
                             MQChannelDefinition channelDefParms,
                             byte agentBuffer[])
  {
    // Fill in the body of the security exit here
  }
}