docs/user-manual/en/exception-clause.adoc

[[ExceptionClause-ExceptionClause]]
=== Exception Clause

You can use the _Exception Clause_ in the Java link:dsl.adoc[DSL] to
specify the error handling you require on a per exception type basis
using the *`onException()`* method. To get started we give quick sample
before digging into how it works.

For example if you want to perform a specific piece of processing if a
certain exception is raised you can do this simply via:

[source,java]
----
onException(ValidationException.class)
    .to("activemq:validationFailed");

from("seda:inputA")
    .to("validation:foo/bar.xsd", "activemq:someQueue");

from("seda:inputB")
    .to("direct:foo")
    .to("rnc:mySchema.rnc", "activemq:anotherQueue");
----

Here if the processing of *`seda:inputA`* or *`seda:inputB`* cause
a *`ValidationException`* to be thrown (such as due to the XSD
validation of the <<validator-components,Validation>> component or the
Relax NG Compact syntax validation of the <<jing-component,Jing>>
component), then the message will be sent to the
*`activemq:validationFailed`* queue.

You can define multiple *`onException`* clauses for different behavior:

[source,java]
----
onException(ValidationException.class)
    .to("activemq:validationFailed");

onException(ShipOrderException.class)
    .to("activemq:shipFailed");

from("seda:order")
    .to("bean:processOrder");
----

[[ExceptionClause-Scopes]]
==== Scopes

Exception clauses is scoped as either:

* global (for Java DSL that is per *`RouteBuilder`* instances, to reuse,
see note below)
* or route specific

Where the *global* are the simplest and most easy to understand. In the
advanced section we dig into the route specific and even combining them.
However

Global scope for Java DSL is per *`RouteBuilder`* instance, so if you
want to share among multiple *`RouteBuilder`* classes, then create a
base abstract *`RouteBuilder`* class and put the error handling logic in
its *`configure`* method. And then extend this class, and make sure to
class *`super.configure()`*. We are just using the Java inheritance
technique.

[[ExceptionClause-HowDoesCamelSelectWhichClauseShouldHandleaGivenThrownException]]
==== How Does Camel Select Which Clause Should Handle a Given Thrown Exception?

Camel uses *`DefaultExceptionPolicyStrategy`* to determine a strategy
how an exception being thrown should be handled by which *`onException`*
clause. The strategy is:

* the order in which the *`onException`* is configured takes precedence.
Camel will test from first...last defined.
* Camel will start from the bottom (nested caused by) and recursive up
in the exception hierarchy to find the first matching *`onException`*
clause.
* *`instanceof`* test is used for testing the given exception with the
*`onException`* clause defined exception list. An exact *`instanceof`*
match will always be used, otherwise the *`onException`* clause that has
an exception that is the closets super of the thrown exception is
selected (recurring up the exception hierarchy).

This is best illustrated with an exception:

[source,java]
----
onException(IOException.class)
    .maximumRedeliveries(3);

onException(OrderFailedException.class)
    .maximumRedeliveries(2);
----

In the sample above we have defined two exceptions in
which *`IOException`* is first, so Camel will pickup this exception if
there is a match. *`IOException`* that is more general is selected then.

So if an exception is thrown with this hierarchy:

....
+ RuntimeCamelException (wrapper exception by Camel)
    + OrderFailedException
        + IOException
            + FileNotFoundException
....

Then Camel will try testing the exception in this order:
*`FileNotFoundException`*, *`IOException`*, *`OrderFailedException`* and
*`RuntimeCamelException`*.
As we have defined a *`onException(IOException.class)`* Camel will
select this as it's the *closest* match.

If we add a third *`onException`* clause with the
*`FileNotFoundException`*

[source,java]
----
onException(IOException.class)
    .maximumRedeliveries(3);

onException(OrderFailedException.class)
    .maximumRedeliveries(2);

onException(FileNotFoundException.class)
    .handled(true)
    .to("log:nofile");
----

Then with the previous example Camel will now use the last
*`onException(FileNotFoundException.class)`* as its an *exact* match.
Since this is an exact match it will override the
general *`IOException`* that was used before to handle the same
exception thrown.

Now a new situation if this exception was thrown instead:

....
+ RuntimeCamelException (wrapper exception by Camel)
    + OrderFailedException
        + OrderNotFoundException
....

Then the *`onException(OrderFailedException.class)`* will be selected -
no surprise here.

And this last sample demonstrates the *`instanceof`* test aspect in
which Camel will select an exception if it's an instance of the defined
exception in the *`onException`* clause. Illustrated as:

....
+ RuntimeCamelException (wrapper exception by Camel)
    + SocketException
....

Since *`SocketException`* is an *`instanceof IOException`*, Camel will
select the *`onException(IOException.class)`* clause.

[[ExceptionClause-ConfiguringRedeliveryPolicyredeliveroptions]]
==== Configuring RedeliveryPolicy (redeliver options)

http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/processor/RedeliveryPolicy.html[RedeliveryPolicy]
requires to use the <<deadLetterChannel-eip,Dead Letter Channel>>
as the link:error-handler.adoc[Error Handler]. Dead Letter Channel
supports attempting to redeliver the message exchange a number of times
before sending it to a dead letter endpoint. See
<<deadLetterChannel-eip,Dead Letter Channel>> for further
information about redeliver and which redeliver options exists.

===== No redelivery is default for onException

By default any link:exception-clause.adoc[Exception Clause] will *not*
redeliver! (as it sets the `maximumRedeliveries` option to 0).

Sometimes you want to configure the redelivery policy on a per exception
type basis. By default in the top examples, if an
*`org.apache.camel.ValidationException`* occurs then the message will
not be redelivered; however if some other exception occurs, e.g.,
*`IOException`* or whatever, the route will be retried according to the
settings from the <<deadLetterChannel-eip,Dead Letter Channel>>.

However if you want to customize any methods on the
http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/processor/RedeliveryPolicy.html[RedeliveryPolicy]
object, you can do this via the fluent API. So lets retry in case
of *`org.apache.camel.ValidationException`* up till two times.

*Java DSL*:

[source,java]
----
onException(ValidationException.class)
    .maximumRedeliveries(2);
----

*Spring XML DSL*:

[source,xml]
----
<onException>
    <exception>com.mycompany.ValidationException</exception>
    <redeliveryPolicy maximumRedeliveries="2"/>
</onException>
----

You can customize any of the
http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/processor/RedeliveryPolicy.html[RedeliveryPolicy]
so we can for instance set a different delay of *`5000`* millis:

[source,xml]
----
<onException>
    <exception>com.mycompany.ValidationException</exception>
    <redeliveryPolicy maximumRedeliveries="2" delay="5000"/>
</onException>
----

[[ExceptionClause-PointofEntryforRedeliveryAttempts]]
==== Point of Entry for Redelivery Attempts

All redelivery attempts start at the point of the failure. So the route:

[source,java]
----
onException(ConnectException.class)
    .from("direct:start")
    .process("processor1")
    .process("processor2") // <--- throws a ConnectException
    .to("mock:theEnd")
----

Will retry from *`processor2`* - not the complete route.

[[ExceptionClause-ReusingRedeliveryPolicy]]
==== Reusing RedeliveryPolicy

*Available as of Camel 1.5.1 or later*

You can reference a *`RedeliveryPolicy`* so you can reuse existing
configurations and use standard spring bean style configuration that
supports property placeholders.

[source,xml]
----
<bean id="myRedeliveryPolicy" class="org.apache.camel.processor.RedeliveryPolicy">
    <property name="maximumRedeliveries" value="${myprop.max}"/>
</bean>

<!-- here we reference our redelivery policy defined above -->
<onException redeliveryPolicyRef="myRedeliveryPolicy">
    <!-- you can define multiple exceptions just adding more exception elements as show below -->
    <exception>com.mycompany.MyFirstException</exception>
    <exception>com.mycompany.MySecondException</exception>
</onException>
----

[[ExceptionClause-AsynchronousDelayedRedelivery]]
==== Asynchronous Delayed Redelivery

*Available as of Camel 2.4*

From *Camel 2.4*: Camel has a feature to *not block* while waiting for a
delayed redelivery to occur. However if you use transacted routes then
Camel will block as its mandated by the transaction manager to execute
all the work in the same thread context. You can enable the non blocking
asynchronous behavior by the *`asyncDelayedRedelivery`* option. This
option can be set on the *`errorHandler`*, *`onException`* or the
redelivery policies.

By default the error handler will create and use a scheduled thread pool
to trigger redelivery in the future. From *Camel 2.8*: you can configure
the *`executorServiceRef`* on the link:error-handler.adoc[Error Handler]
to indicate a reference to either a shared thread pool you can enlist in
the registry, or a thread pool profile in case you want to be able to
control pool settings.

[[ExceptionClause-CatchingMultipleExceptions]]
==== Catching Multiple Exceptions

*Available as of Camel 1.5*

In Camel 1.5 the *exception* clauses has been renamed to *`onException`*
and it also supports multiple exception classes:

[source,java]
----
onException(MyBusinessException.class, MyOtherBusinessException.class)
    .maximumRedeliveries(2)
    .to("activemq:businessFailed");
----

And in Spring DSL you just add another exception element:

[source,xml]
----
<onException>
    <exception>com.mycompany.MyBusinessException</exception>
    <exception>com.mycompany.MyOtherBusinessException</exception>
    <redeliveryPolicy maximumRedeliveries="2"/>
    <to uri="activemq:businessFailed"/>
</onException>
----

[[ExceptionClause-UsingaProcessorasaFailureHandler]]
==== Using a Processor as a Failure Handler

We want to handle certain exceptions specially so we add
a *`onException`* clause for that exception.

/camel-core/src/test/java/org/apache/camel/processor/onexception/OnExceptionProcessorInspectCausedExceptionTest.java

So what happens is that whenever a *`MyFunctionalException`* is thrown it
is being routed to our processor *`MyFunctionFailureHandler`*. So you
can say that the exchange is diverted when a *`MyFunctionalException`*
is thrown during processing. It's important to distinct this as perfect
valid. The default redelivery policy from the
<<deadLetterChannel-eip,Dead Letter Channel>> will not kick in, so
our processor receives the Exchange directly, without any redeliver
attempted. In our processor we need to determine what to do. Camel
regards the Exchange as *failure handled*. So our processor is the end
of the route. So lets look the code for our processor.

/camel-core/src/test/java/org/apache/camel/processor/onexception/OnExceptionProcessorInspectCausedExceptionTest.java

Notice how we get the *caused by* exception using a property on the Exchange.
This is where Camel stores any caught exception during processing. So
you can fetch this property and check what the exception message and do
what you want. In the code above we just route it to a mock endpoint
using a producer template from Exchange.

[[ExceptionClause-MarkingExceptionsasHandled]]
=== Marking Exceptions as Handled

*Available as of Camel 1.5*

===== Continued

See also the section <<ExceptionClause-HandleandContinueExceptions,Handle and continue exceptions>> below.

Using *`onException`* to handle known exceptions is a very powerful
feature in Camel. However prior to Camel 1.5 you could not mark the
exception as being handled, so the caller would still receive the caused
exception as a response. In Camel 1.5 you can now change this behavior
with the new *handle* DSL. The handle is a
link:predicate.adoc[Predicate] that is overloaded to accept three types
of parameters:

* Boolean
* link:predicate.adoc[Predicate]
* link:expression.adoc[Expression] that will be evaluates as a
link:predicate.adoc[Predicate] using this rule set: If the expressions
returns a Boolean its used directly. For any other response its regarded
as `true` if the response is `not null`.

For instance to mark all *`ValidationException`* as being handled we can
do this:

[source,java]
----
onException(ValidationException)
    .handled(true);
----

[[ExceptionClause-ExampleUsingHandled]]
==== Example Using Handled

In this route below we want to do special handling of
all *`OrderFailedException`* as we want to return a customized response
to the caller. First we setup our routing as:

/camel-core/src/test/java/org/apache/camel/processor/DeadLetterChannelHandledExampleTest.java

Then we have our service beans that is just plain POJO demonstrating how you
can use link:bean-integration.adoc[Bean Integration] in Camel to avoid
being tied to the Camel API:

/camel-core/src/test/java/org/apache/camel/processor/DeadLetterChannelHandledExampleTest.java

And finally the exception that is being thrown is just a regular exception:

/camel-core/src/test/java/org/apache/camel/processor/DeadLetterChannelHandledExampleTest.java

So what happens?

If we sent an order that is being processed OK then the caller will
receive an Exchange as reply containing *`Order OK`* as the payload and
*`orderid=123`* in a header.

If the order could *not* be processed and thus
an *`OrderFailedException`* was thrown the caller will *not* receive
this exception (as opposed to in Camel 1.4, where the caller received
the *`OrderFailedException`*) but our customized response that we have
fabricated in the *`orderFailed`* method in our *`OrderService`*. So the
caller receives an Exchange with the payload *`Order ERROR`* and a
*`orderid=failed`* in a header.

[[ExceptionClause-UsingHandledwithSpringDSL]]
==== Using Handled with Spring DSL

The same route as above in Spring DSL:

/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/onexception/deadLetterChannelHandledExampleTest.xml

[[ExceptionClause-HandlingandSendingaFixedResponseBacktotheClient]]
==== Handling and Sending a Fixed Response Back to the Client

In the route above we handled the exception but routed it to a different
endpoint. What if you need to alter the response and send a fixed
response back to the original caller (the client). No secret here just
do as you do in normal Camel routing, use
<<messageTranslator-eip,transform>> to set the response, as shown in
the sample below:

/camel-core/src/test/java/org/apache/camel/processor/onexception/OnExceptionHandleAndTransformTest.java

We modify the sample slightly to return the original caused exception
message instead of the fixed text `Sorry`:

/camel-core/src/test/java/org/apache/camel/processor/onexception/OnExceptionHandleAndTransformTest.java

And we can use the link:simple-language.adoc[Simple] language to set a readable error
message with the caused exception message:

/camel-core/src/test/java/org/apache/camel/processor/onexception/OnExceptionHandleAndTransformTest.java

[[ExceptionClause-HandleandContinueExceptions]]
=== Handle and Continue Exceptions

*Available as of Camel 2.3*

In Camel 2.3 we introduced a new option `continued` which allows you to
both *`handle`* and *`continue`* routing in the original route as if the
exception did not occur.

For example: to ignore and continue when the *`IDontCareException`* was
thrown we can do this:

[source,java]
----
onException(IDontCareException)
    .continued(true);
----

You can maybe compare continued with a having a *`try ... catch`* block
around each step and then just ignore the exception. Using continued
makes it easier in Camel as you otherwise had to use
link:try-catch-finally.adoc[Try Catch Finally] style for this kind of
use case.

[[ExceptionClause-ExampleUsingcontinued]]
==== Example Using continued

In this route below we want to do special handling of
all *`IllegalArgumentException`* as we just want to continue routing.

/camel-core/src/test/java/org/apache/camel/processor/onexception/OnExceptionContinueTest.java

And the same example in Spring XML:

/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/onexception/OnExceptionContinueTest.xml

[[ExceptionClause-WhatistheDifferenceBetweenHandledandContinued?]]
==== What is the Difference Between Handled and Continued?

If handled is true, then the thrown exception will be _handled_ and
Camel will *not* continue routing in the original route, but break out.
However you can configure a route in the *`onException`* which will be
used instead. You use this route if you need to create some custom
response message back to the caller, or do any other processing because
that exception was thrown.

If continued is true, then Camel will catch the exception and in fact
just ignore it and continue routing in the original route. However if
you have a route configured in the *`onException`* it will route that
route first, before it will continue routing in the original route.

[[ExceptionClause-UsinguseOriginalMessage]]
==== Using `useOriginalMessage`

*Available as of Camel 2.0*

The option *`useOriginalMessage`* is used for routing the original input
body instead of the current body that potential is modified during routing.

For example: if you have this route:

[source,java]
----
from("jms:queue:order:input")
    .to("bean:validateOrder");
    .to("bean:transformOrder")
    .to("bean:handleOrder");
----

The route listen for JMS messages and validates, transforms and handle
it. During this the link:exchange.adoc[Exchange] payload is
transformed/modified. So in case something goes wrong and we want to
move the message to another JMS destination, then we can add an
*`onException`*. But when we move the link:exchange.adoc[Exchange] to
this destination we do not know in which state the message is in. Did
the error happen in before the *`transformOrder`* or after? So to be
sure we want to move the original input message we received from
`jms:queue:order:input`. So we can do this by enabling the
*`useOriginalMessage`* option as shown below:

[source,java]
----
// will use original input body
onException(MyOrderException.class)
    .useOriginalMessage()
    .handled(true)
    .to("jms:queue:order:failed");
----

Then the messages routed to the *`jms:queue:order:failed`* is the
original input. If we want to manually retry we can move the JMS message
from the failed to the input queue, with no problem as the message is
the same as the original we received.

[[ExceptionClause-useOriginalMessagewithSpringDSL]]
==== `useOriginalMessage` with Spring DSL

The *`useOriginalMessage`* option is defined as a boolean attribute on
the *`<onException>`* XML tag in Spring DSL. So the definition above
would be:

[source,xml]
----
<onException useOriginalMessage="true">
    <exception>com.mycompany.MyOrderException</exception>
    <handled><constant>true</constant></handled>
    <to uri="jms:queue:order:failed"/>
</onException>
----

[[ExceptionClause-AdvancedUsageofExceptionClause]]
=== Advanced Usage of link:exception-clause.adoc[Exception Clause]

[[ExceptionClause-UsingGlobalandPerRouteExceptionClauses]]
==== Using Global and Per Route Exception Clauses

Camel supports quite advanced configuration of exception clauses.

You can define exception clauses either as:

* global
* or route specific

We start off with the sample sample that we change over time. First off
we use only global exception clauses:

/camel-core/src/test/java/org/apache/camel/processor/onexception/OnExceptionRouteTest.java

In the next sample we change the global exception policies to be pure route
specific.

===== Must use `.end()` for route specific exception policies

[IMPORTANT] This requires to end the *`onException`* route with
*`.end()`* to indicate where it stops and when the regular route
continues.

/camel-core/src/test/java/org/apache/camel/processor/onexception/OnExceptionSubRouteTest.java

And now it gets complex as we combine global and route specific exception
policies as we introduce a second route in the sample:

/camel-core/src/test/java/org/apache/camel/processor/onexception/OnExceptionComplexRouteTest.java

Notice that we can define the same exception *`MyFunctionalException`* in both
routes, but they are configured differently and thus is handled
different depending on the route. You can of course also add a
new *`onException`* to one of the routes so it has an additional
exception policy.

And finally we top this by throwing in a nested error handler as well,
as we add the 3rd route shown below:

/camel-core/src/test/java/org/apache/camel/processor/onexception/OnExceptionComplexWithNestedErrorHandlerRouteTest.java

===== Global exception policies and nested error handlers

The sample above with both nested error handlers and both global and per
route exception clauses is a bit advanced. It's important to get the
fact straight that the *global* exception clauses is really global so
they also applies for nested error handlers. So if a
*`MyTechnicalException`* is thrown then it's the global exception policy
that is selected.

[[ExceptionClause-UsingFineGrainedSelectionUsingonWhenPredicate]]
==== Using Fine Grained Selection Using `onWhen` Predicate

*Available as of Camel 1.5.1 or later*

You can attach an link:expression.adoc[Expression] to the exception
clause to have fine grained control when a clause should be selected or
not. As it's an link:expression.adoc[Expression] you can use any kind of
code to perform the test. Here is a sample:

/camel-core/src/test/java/org/apache/camel/processor/exceptionpolicy/DefaultExceptionPolicyStrategyUsingWhenTest.java

In the sample above we have two *`onException`*'s defined. The first has
an *`onWhen`* expression attached to only trigger if the message has a
header with the key user that is not null. If so this clause is selected
and is handling the thrown exception. The second clause is a for coarse
gained selection to select the same exception being thrown but when the
expression is evaluated to false.

NOTE: this is not required, if the second clause is omitted, then the
default error handler will kick in.

[[ExceptionClause-UsingonRedeliveryProcessor]]
==== Using `onRedelivery` Processor

*Available as of Camel 2.0*

<<deadLetterChannel-eip,Dead Letter Channel>> has support
for *`onRedelivery`* to allow custom processing of a Message before its
being redelivered. It can be used to add some customer header or
whatnot. In Camel 2.0 we have added this feature to
link:exception-clause.adoc[Exception Clause] as well, so you can use per
exception scoped on redelivery. Camel will fallback to use the one
defined on <<deadLetterChannel-eip,Dead Letter Channel>> if any, if
none exists on the link:exception-clause.adoc[Exception Clause]. See
<<deadLetterChannel-eip,Dead Letter Channel>> for more details on
*`onRedelivery`*.

In the code below we want to do some custom code before redelivering any
*`IOException`*. So we configure an *`onException`* for
the *`IOException`* and set the *`onRedelivery`* to use our custom
processor:

/camel-core/src/test/java/org/apache/camel/processor/DeadLetterChannelOnExceptionOnRedeliveryTest.java

And in our custom processor we set a special timeout header to the message.
You can of course do anything what you like in your code.

/camel-core/src/test/java/org/apache/camel/processor/DeadLetterChannelOnExceptionOnRedeliveryTest.java

[[ExceptionClause-UsingonRedeliveryinSpringDSL]]
==== Using `onRedelivery` in Spring DSL

In Spring DSL you need to use the *`onRedeliveryRef`* attribute to refer
to a spring bean id that is your custom processor:

/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/onexception/DeadLetterChannelOnExceptionOnRedeliveryTest.xml

And our processor is just a regular spring bean (we use *`$`* for the inner
class as this code is based on unit testing):

/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/onexception/DeadLetterChannelOnExceptionOnRedeliveryTest.xml

[[ExceptionClause-UsingonExceptionOccurredProcessor]]
==== Using `onExceptionOccurred` Processor

*Available as of Camel 2.17*

<<deadLetterChannel-eip,Dead Letter Channel>> has support
for *`onExceptionOccurred`* to allow custom processing of a Message just
after the exception was thrown. It can be used to do some custom logging
or whatnot. The difference between *`onRedelivery`* processor
and *`onExceptionOccurred`* processor, is that the former is processed
just before a redelivery attempt is being performed, that means it will
not happen right after an exception was thrown. For example if the error
handler has been configured to perform 5 seconds delay between
redelivery attempts, then the redelivery processor is invoked 5 seconds
later sine the exception was thrown. On the other hand
the *`onExceptionOccurred`* processor is always invoked right after the
exception was thrown, and also if redelivery has been disabled.

NOTE: Any new exceptions thrown from the *`onExceptionOccurred`*
processor is logged as *`WARN`* and ignored, to not override the
existing exception. 

In the code below we want to do some custom logging when an exception
happened. Therefore we configure an *`onExceptionOccurred`* to use our
custom processor:

[source.java]
----
errorHandler(defaultErrorHandler()
    .maximumRedeliveries(3)
    .redeliveryDelay(5000)
    .onExceptionOccurred(myProcessor));
----

[[ExceptionClause-UsingonRedeliveryinSpringDSL.1]]
Using `onRedelivery` in Spring DSL
++++++++++++++++++++++++++++++++++

In Spring DSL you need to use the *`onExceptionOccurredRef`* attribute
to refer to a spring bean id that is your custom processor:

[source,xml]
----
<bean id="myProcessor" class="com.foo.MyExceptionLoggingProcessor"/>

<camelContext errorHandlerRef="eh" xmlns="http://camel.apache.org/schema/spring">
    <errorHandler id="eh" type="DefaultErrorHandler" onExceptionOccurredRef="myProcessor">
        <redeliveryPolicy maximumRedeliveries="3" redeliveryDelay="5000"/>
    </errorHandler>
    ...
</camelContext>
----

[[ExceptionClause-UsingFineGrainedRetryUsingretryWhilePredicate]]
==== Using Fine Grained Retry Using `retryWhile` Predicate

*Available as of Camel 2.0*

===== RetryUntil

In Camel 2.0 to 2.3 its called *`retryUntil`*. From *Camel 2.4*: its
named *`retryWhile`* because Camel will continue doing retries _while_
the predicate returns true.

When you need fine grained control for determining if an exchange should
be retried or not you can use the *`retryWhile`* predicate. Camel will
redeliver until the predicate returns false.

Example:

/camel-core/src/test/java/org/apache/camel/processor/onexception/OnExceptionRetryUntilTest.java

Where the bean *`myRetryHandler`* is computing if we should retry or not:

/camel-core/src/test/java/org/apache/camel/processor/onexception/OnExceptionRetryUntilTest.java

[[ExceptionClause-UsingCustomExceptionPolicyStrategy]]
==== Using Custom `ExceptionPolicyStrategy`

*Available in Camel 1.4*

The default
http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/processor/exceptionpolicy/ExceptionPolicyStrategy.html[ExceptionPolicyStrategy]
in Camel should be sufficient in nearly all use-cases (see section
<<ExceptionClause-HowDoesCamelSelectWhichClauseShouldHandleaGivenThrownException,How does Camel select which clause should handle a given thrown Exception>>).
However, if you need to use your own this can be configured as the
sample below illustrates:

/camel-core/src/test/java/org/apache/camel/processor/exceptionpolicy/CustomExceptionPolicyStrategyTest.java

Using our own strategy *`MyPolicy`* we can change the default behavior of
Camel with our own code to resolve which
http://camel.apache.org/maven/camel-core/apidocs/org/apache/camel/model/ExceptionType.html[ExceptionType]
from above should be handling the given thrown exception.

/camel-core/src/test/java/org/apache/camel/processor/exceptionpolicy/CustomExceptionPolicyStrategyTest.java

[[ExceptionClause-UsingtheExceptionClauseinSpringDSL]]
==== Using the Exception Clause in Spring DSL

You can use all of the above mentioned exception clause features in the
Spring DSL as well. Here are a few examples:

* Global scoped - *Available in Camel 2.0*
/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/onexception/deadLetterChannelHandledExampleTest.xml

* Route specific scoped
/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/onexception/onExceptionSubRouteTest.xml

[[ExceptionClause-Seealso]]
==== See also

* The link:error-handler.adoc[Error Handler] for the general error handling documentation
* The <<deadLetterChannel-eip,Dead Letter Channel>> for further details
* The <<transactionalClient-eip,Transactional Client>> for transactional behavior