docs/user-manual/modules/ROOT/pages/faq/how-do-i-retry-processing-a-message-from-a-certain-point-back-or-an-entire-route.adoc

[[HowdoIretryprocessingamessagefromacertainpointbackoranentireroute-HowdoIretryprocessingamessagefromacertainpointbackoranentireroute]]
= 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 above 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 xref:components::direct-component.adoc[Direct] component by calling
the sub route from the 1st route.

[source,java]
----
// 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 redeliveried, meaning that
the `mock:b` endpoint receives the incoming message again.

[source,java]
----
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:

[source,xml]
----
<!-- 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>
----