Debugger

The Camel Debugger is intended for 3rd party tooling to make it possible to debug routes, trace messages and to use breakpoints with the EIP patterns in the Camel routes.

The Debugger allows tooling or the likes to attach breakpoints which is being invoked when Exchanges is being routed.

Debugging Camel routes from camel-test

If you are developing unit tests using the camel-test component, then the Debugger is available if you turn it on via overriding the isUseDebugger() method and return true.

In this unit test

public class DebugTest extends CamelTestSupport

We want to debug the following route

@Override
protected RouteBuilder createRouteBuilder() throws Exception {
    return new RouteBuilder() {
        @Override
        public void configure() throws Exception {
            // this is the route we want to debug
            from("direct:start")
                .to("mock:a")
                .transform(body().prepend("Hello "))
                .to("mock:b");
        }
    };
}

Which can easily done by overriding the debugBefore method as shown

@Override
public boolean isUseDebugger() {
    // must enable debugger
    return true;
}

@Override
protected void debugBefore(Exchange exchange, Processor processor,
                           ProcessorDefinition<?> definition, String id, String shortName) {
    // this method is invoked before we are about to enter the given processor
    // from your Java editor you can just add a breakpoint in the code line below
    log.info("Before " + definition + " with body " + exchange.getIn().getBody());
}

Then from your Java editor just add a breakpoint inside the debugBefore method. Then fire up the unit test and wait for the Java editor to hit the breakpoint. Then you can inspect the Exchange during debugging while it advances during routing. The ProcessorDefinition and the id and shortName parameters is all information which tells you where in the route the breakpoint was hit.

There is also a debugAfter method which is invoked after the processor has been invoked. This allows you to see what happens to the Exchange right after it has invoked a processor in the route.

The screenshot below shows the Debugger in action. The IDE (IDEA) has hit the breakpoint and we can inspect the parameters. Notice how we can see that the message is to be send to the "mock:a" endpoint.

image

Implementing a custom debugger

The debugger API is defined in org.apache.camel.spi.Debugger. This API has methods to attach and remove breakpoints. And to suspend/resume all breakpoints etc. You can also attach a condition to the breakpoint so it only reacts if the condition matches.

Camel provides a base implementation org.apache.camel.impl.DefaultDebugger, which can be used to extend for custom implementations.

JMX debugger

There is also a BacklogDebugger which allows to debug from JMX, and some 3rd party tooling such as hawtio uses this for its web based debugging functionality.

Camel requires to have camel-management JAR on the classpath for having JMX enabled.

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