IBM BPM, V8.0.1, All platforms > Authoring services in Integration Designer > Services and service-related functions > Access external services with messaging systems > WebSphere MQ (WMQ) > WebSphere MQ data bindings

Overview of the MQ function selectors

The function selector is run when an export is driven by a message read from a destination. The function selector determines which operation corresponds to the message.

There has to be some mechanism that can be used to determine which SCA operation the message corresponds with. An MQ message contains only data and carries no indication about the target operation for which it is intended. Therefore, we need to map an MQ message to an operation of the targeted service interface. The MQ export listens to a particular destination. When a message arrives to that destination, the function selector determines the target operation.

For the MQ function selector, you need to understand the set of function selectors that come with the MQ bindings and how you could create your own function selector, which are discussed in the following sections:

• Set of MQ function selectors
• Implementing your own function selector

Set of MQ function selectors

Several function selectors are provided for your selection at binding generation time. The function selector choices you will see on the user interface are as follows:

• Use handleMessage as the native function (default) returns handleMessage as a value. The value is mapped using the export's method bindings to the name of an operation on the interface. The native method is assumed to be handleMessage from the SCA application's perspective. The SCA application does not need to understand the internal representation of the MQ message, but only how it drives the current operation on the interface. It is the recommended selection for most applications. It may be necessary to edit one of the method bindings to bind an operation to the handleMessage native function.

• Use messagebody's format as the native function finds the Format field of the last header and returns that field as a String.

• Use Type information as the native function creates a method in your export binding by retrieving a URL containing the Msd, Set, Type and Format properties found in the MQRFH2 header. The name of the method will be the interface operation name. This selector can by used to interoperate with messages coming from MQ JMS clients and WebSphere Business Integration Message Broker flows.

• Use JMS default function selector means that the JMS function selector is used to create a method in your export binding (see Overview of JMS function selectors). The name of the method will be the interface operation name. This function selector reads the native operation from the TargetFunctionName property of the folder of an MQRFH2 header.
• Service Gateway function selector should be used in conjunction with an HTTP binding using the Service Gateway interface. It determines if the request is a one-way or two-way operation based on the message type field within the message.

• User supplied means you create your own function selector by implementing the com.ibm.websphere.sca.mq.selector.MQFunctionSelector class. Implementing your own function selector is discussed in the following section.

Implementing your own function selector

The easiest, and recommended, way to build an MQ function selector is to extend the MQFunctionSelector class implementing an abstract method. The function selector's generateEISFunctionName() method has a single argument with an array of type Object. The MQFunctionSelector class unmarshalls these parameters and calls an overloaded generateEISFunctionName() method with a more intuitive argument list, as shown in the following code. The array of four parameters represents different parts of the MQ message.

public abstract class MQFunctionSelector implements
		commonj.connector.runtime.FunctionSelector {
	public final String generateEISFunctionName(Object[] args)
			throws SelectorException;

	public abstract String generateEISFunctionName(MQMD md, String bodyFormat, 			List headers, MQDataInputStream input) throws IOException, 			SelectorException;}

You may alternately provide an implementation of the commonj.connector.runtime.FunctionSelector interface to create your own function selector. If you are implementing your own function selector, you will need to understand the header data binding and body data binding framework as the function selector is given a list of parsed header objects and an unparsed body in an MQDataInputStream input.

MQ data bindings

Related concepts:
Prepackaged MQ data format transformations
Prepackaged MQ function selectors

Related reference:
Overview of MQ data format transformations
Data handlers
Prepackaged JMS and MQ fault selectors