Two exception handling methods are provided for catching exceptions in Java DSL routes, as follows:

This section provides a brief introduction to exception handling in FUSE Mediation Router. For full details, see Dead Letter Channel in Implementing Enterprise Integration Patterns.

The errorHandler() clause is defined in a RouteBuilder class and applies to all of the routes in that RouteBuilder class. It is triggered whenever an exception of any kind occurs in one of the applicable routes. For example, to define an error handler that routes all failed exchanges to the ActiveMQ deadLetter queue, you can define a RouteBuilder as follows:

public class MyRouteBuilder extends RouteBuilder {

    public void configure() {
        errorHandler(deadLetterChannel("activemq:deadLetter"));

        // The preceding error handler applies to all of the following routes:
        from("activemq:orderQueue").to("pop3://[email protected]");
        from("file:src/data?noop=true").to("file:target/messages");
        // ...
    }
}

Redirection to the dead letter channel does not occur, however, until all attempts at redelivery have been exhausted (see Redelivery policy).

The onException(Class exceptionType) clause is defined in a RouteBuilder class and applies to all of the routes in that RouteBuilder class. It is triggered whenever an exception of the specified type, exceptionType, occurs in one of the applicable routes. For example, you can define onException clauses for catching NullPointerException, IOException, and Exception exceptions as follows:

public class MyRouteBuilder extends RouteBuilder {

    public void configure() {
        onException(NullPointerException.class).to("activemq:ex.npex");
        onException(IOException.class).to("activemq:ex.ioex");
        onException(Exception.class).to("activemq:ex");

        // The preceding onException() clauses apply to all of the following routes:
        from("activemq:orderQueue").to("pop3://[email protected]");
        from("file:src/data?noop=true").to("file:target/messages");
        // ...
    }
}

When an exception occurs, FUSE Mediation Router selects the onException clause that matches the given exception type most closely. If no other clause matches the raised exception, the onException(Exception.class) clause (if present) matches by default, because java.lang.Exception is the base class of all Java exceptions. The applicable onException clause does not initiate processing, however, until all attempts at redelivery have been exhausted (see Redelivery policy).

Both the errorHandler clause and the onException clause support a redelivery policy that specifies how often FUSE Mediation Router attempts to redeliver the failed exchange before giving up and triggering the actions defined by the relevant error handler. The most important redelivery policy setting is the maximum redeliveries value, which specifies how many times redelivery is attempted. The default value is 6.

For full details about the redelivery policy and its associated settings, see Dead Letter Channel in Implementing Enterprise Integration Patterns.