WPS: Mediation Routing Primitive : Message Filter

Message Filter : Routes messages down different paths, based on the message content.

• The Message Filter mediation primitive uses XPath expressions to allow you to direct messages, which meet certain criteria, down different paths of a flow. 
• The Message Filter mediation primitive has one input terminal (in), one fail terminal (fail), and multiple output terminals, (one of which is the default terminal). The in terminal is wired to accept a message and the other terminals are wired to propagate a message. 
• Each of the output terminals, apart from the default terminal, is associated with a simple, conditional expression. The contents of the input messageare compared with each expression in turn and, if the condition is met, the messageis propagated to the associated output terminal. The primitive can be configured either to use the first matching output terminal, or all matching output terminals. The default terminal is used if the messagemeets none of the conditions. 
• If an exception occurs during the filtering, the fail terminal propagates the original message, together with any exception information.

Usage of Message Filter:

You can use the Message Filter mediation primitive to check that the inbound message meets some criterion. For example, that a required field is set. If the criterion is not met you can raise a fault using the Fail mediation primitive, or send an error response.

The Message Filter mediation primitive lets different messages take different paths. For example, a message might need forwarding to different service providers based on the request details.

You can use the Message Filter mediation primitive to bypass unnecessary steps. You can test if certain data is in a message, and only perform a Database Lookup operation if the data is missing.

When used in combination with a Database Lookup primitive, the Message Filter can direct messages based on the contents of an independently administered lookup table. For example, you could route a message based on customer status even if the inbound message contained only the customer identifier.

By configuring the primitive to propagate messages to all matching terminals, you can trigger multiple events each requiring different conditions. For example, you could log requests relating to a particular account identifier and send requests relating to a particular product to be audited.

Properties of Message Filter:

Enabled :
    Defines whether the message is mediated by the Message Filter mediation primitive. By default the mediate action of the Message Filter mediation primitive is enabled. You can suspend the mediate action by clearing the checkbox. If you suspend the mediation, the message goes to the default terminal.

Filters :
    A list of expressions, and associated terminal names, that define the filtering performed by the mediation primitive.
    Note: Order is significant in the list of expressions. Expressions are evaluated in the order they appear in the table.

Pattern :
        An XPath 1.0 expression against which the message is tested. The expression is evaluated starting from the XPath expression /, which refers to the complete SMO.

Terminal name :
        The name of an output terminal. There is one terminal name for each pattern XPath expression. The terminal name must be a valid connection endpoint, and it must not be fail or default. The default value is empty, which is invalid.

Distribution mode :
    Determines the behavior of the mediation primitive when an inbound message matches multiple expressions. If the Distribution mode is set to First, the message is propagated to the first matching output terminal. If the Distribution mode is set to All, the message is propagated to all matching output terminals. If there is no matching output terminal, the default terminal is invoked.