How do I retry processing a message from a certain point back or an entire route

By default Apache Camel will perform any redelivery (retry) attempts from the point of failure. So if you want to retry from a point before this, you would need to split up your route.

In the example below we have 2 routes (direct:start, direct:sub). In case of a failure anywhere in the direct:sub route, then the entire route is retried. This happens because we have instructed the direct:sub route to not use any error handler (eg the no error handler). Then we link the routes using the Direct component by calling the sub route from the 1st route.

// in case of io exception then try to redeliver up till 2 times
// (do not use any delay due faster unit testing)
onException(IOException.class)
    .maximumRedeliveries(2).redeliveryDelay(0);

from("direct:start")
    .to("mock:a")
    // call sub route (using direct)
    .to("direct:sub")
    .to("mock:c");

from("direct:sub")
    // disable error handler, so the entire route can be retried in case of redelivery
    .errorHandler(noErrorHandler())
    .to("mock:b")
    .process(new MyProcessor());

The code above is based on an unit test, and as you can see the processor below is configured to fail the first 2 attempts. So that means the entire direct:sub route is redelivered, meaning that the mock:b endpoint receives the incoming message again.

public static class MyProcessor implements Processor {

    private int counter;

    @Override
    public void process(Exchange exchange) throws Exception {
        // use a processor to simulate error in the first 2 calls
        if (counter++ < 2) {
            throw new IOException("Forced");
        }
        exchange.getIn().setBody("Bye World");
    }
}

The same example is shown below using the XML DSL:

<!-- this is the processor that will fail the first 2 attempts -->
<bean id="myProcessor" class="org.apache.camel.processor.RedeliverToSubRouteTest.MyProcessor"/>

<camelContext xmlns="http://camel.apache.org/schema/spring">

    <!-- setup no error handler with an id, we refer to from the 2nd route -->
    <errorHandler id="noErrorHandler" type="NoErrorHandler"/>

    <!-- configure on exception to redelivery at most 2 times when an IOException was thrown
         do not use redelivery delay to run unit test faster -->
    <onException>
        <exception>java.io.IOException</exception>
        <redeliveryPolicy maximumRedeliveries="2" redeliveryDelay="0"/>
    </onException>

    <!-- 1st route, no need to setup error handler, as it will use the default error handler -->
    <route>
        <from uri="direct:start"/>
        <to uri="mock:a"/>
        <to uri="direct:sub"/>
        <to uri="mock:c"/>
    </route>

    <!-- disable error handler on this route, so the entire route can be redelivered
         when called from the 1st route -->
    <route errorHandlerRef="noErrorHandler">
        <from uri="direct:sub"/>
        <to uri="mock:b"/>
        <process ref="myProcessor"/>
    </route>
</camelContext>
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