docs/user-manual/en/defaulterrorhandler.adoc

[[DefaultErrorHandler-DefaultErrorHandler]]
=== DefaultErrorHandler

This is the new default error handler in Camel 2.0 onwards.

It has the same power as the <<deadLetterChannel-eip,Dead Letter Channel>>,
however it does *not* support a _dead letter queue_, which is
the only difference between the two of them.

The DefaultErrorHandler is configured differently from
<<deadLetterChannel-eip,Dead Letter Channel>> as
it is configured to:

* not redeliver
* not handled
* no dead letter queue (not possible)

By default, any exception thrown during routing will be propagated back
to the caller and the link:exchange.adoc[Exchange] ends immediately.
However, you can use the link:exception-clause.adoc[Exception Clause] to
catch a given exception and lower the exception by marking it as
handled. If so, the exception will *not* be sent back to the caller, and
the link:exchange.adoc[Exchange] continues to be routed.

[[DefaultErrorHandler-Example]]
==== Example

In this route below, any exception thrown in, eg the `validateOrder`
bean, will be propagated back to the caller via the jetty endpoint. It
will return an HTTP error message back to the client.

[source,java]
----
from("jetty:http://localhost/myservice/order")
  .to("bean:validateOrder")
  .to("jms:queue:order");
----

We can add an *onException* in case we want to catch certain exceptions
and route them differently, for instance to catch a
*ValidationException* and return a fixed response to the caller.

[source,java]
----
onException(ValidationException.class)
  .handled(true)
  .transform(body(constant("INVALID ORDER")));

from("jetty:http://localhost/myservice/order")
  .to("bean:validateOrder")
  .to("jms:queue:order");
----

When the `ValidationException` is thrown from the `validateOrder` bean,
it is intercepted by the DefaultErrorHandler that lets the
`onException(ValidationException.class)` handle it, so the
link:exchange.adoc[Exchange] is routed to this onException route, and
since we use `handled(true)`, then the original exception is cleared,
and we transform the message into a fixed response that is returned to
jetty endpoint that returns it to the original caller.

[[DefaultErrorHandler-SeeAlso]]
==== See Also

* link:error-handler.adoc[Error Handler]
* <<deadLetterChannel-eip,Dead Letter Channel>>