Modified: websites/production/camel/content/dead-letter-channel.html
==============================================================================
--- websites/production/camel/content/dead-letter-channel.html (original)
+++ websites/production/camel/content/dead-letter-channel.html Sat Feb 4
01:20:14 2017
@@ -86,13 +86,13 @@
<tbody>
<tr>
<td valign="top" width="100%">
-<div class="wiki-content maincontent"><h2
id="DeadLetterChannel-DeadLetterChannel">Dead Letter Channel</h2><p>Camel
supports the <a shape="rect" class="external-link"
href="http://www.enterpriseintegrationpatterns.com/DeadLetterChannel.html";
rel="nofollow">Dead Letter Channel</a> from the <a shape="rect"
href="enterprise-integration-patterns.html">EIP patterns</a> using the <a
shape="rect" class="external-link"
href="http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/processor/DeadLetterChannel.html";>DeadLetterChannel</a>
processor which is an <a shape="rect" href="error-handler.html">Error
Handler</a>.</p><p><span class="confluence-embedded-file-wrapper"><img
class="confluence-embedded-image confluence-external-resource"
src="http://www.enterpriseintegrationpatterns.com/img/DeadLetterChannelSolution.gif";
data-image-src="http://www.enterpriseintegrationpatterns.com/img/DeadLetterChannelSolution.gif";></span></p><div
class="confluence-information-macro confluenc
e-information-macro-tip"><p class="title">Difference between Dead Letter
Channel and Default Error Handler</p><span class="aui-icon aui-icon-small
aui-iconfont-approve confluence-information-macro-icon"></span><div
class="confluence-information-macro-body"><p>The Default Error Handler does
very little: it ends the Exchange immediately and propagates the thrown
Exception back to the caller.</p><p>The Dead Letter Channel lets you control
behaviors including redelivery, whether to propagate the thrown Exception to
the caller (the <strong>handled</strong> option), and where the (failed)
Exchange should now be routed to.</p><p>The Dead Letter Channel is also by
default configured to not be verbose in the logs, so when a message is handled
and moved to the dead letter endpoint, then there is nothing logged. If you
want some level of logging you can use the various options on the redelivery
policy / dead letter channel to configure this. For example if you want the
message history then set
logExhaustedMessageHistory=true (and logHandled=true for Camel 2.15.x or
older).</p><p>When the DeadLetterChannel moves a message to the dead letter
endpoint, any new Exception thrown is by default handled by the dead letter
channel as well. This ensures that the DeadLetterChannel will always succeed.
From <strong>Camel 2.15</strong> onwards this behavior can be changed by
setting the option deadLetterHandleNewException=false. Then if a new Exception
is thrown, then the dead letter channel will fail and propagate back that new
Exception (which is the behavior of the default error handler). When a new
Exception occurs then the dead letter channel logs this at WARN level. This can
be turned off by setting logNewException=false.</p></div></div><h3
id="DeadLetterChannel-Redelivery">Redelivery</h3><p>It is common for a
temporary outage or database deadlock to cause a message to fail to process;
but the chances are if its tried a few more times with some time delay then it
will complete
fine. So we typically wish to use some kind of redelivery policy to decide how
many times to try redeliver a message and how long to wait before redelivery
attempts.</p><p>The <a shape="rect" class="external-link"
href="http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/processor/RedeliveryPolicy.html";>RedeliveryPolicy</a>
defines how the message is to be redelivered. You can customize things
like</p><ul><li>how many times a message is attempted to be redelivered before
it is considered a failure and sent to the dead letter channel</li><li>the
initial redelivery timeout</li><li>whether or not exponential backoff is used
(i.e. the time between retries increases using a backoff
multiplier)</li><li>whether to use collision avoidance to add some randomness
to the timings</li><li>delay pattern (see below for
details)</li><li><strong>Camel 2.11:</strong> whether to allow redelivery
during stopping/shutdown</li></ul><p>Once all attempts at redelivering the
message fa
ils then the message is forwarded to the dead letter queue.</p><h3
id="DeadLetterChannel-AboutmovingExchangetodeadletterqueueandusinghandled">About
moving Exchange to dead letter queue and using
handled</h3><p><strong>Handled</strong> on <a shape="rect"
href="dead-letter-channel.html">Dead Letter Channel</a></p><p>When all attempts
of redelivery have failed the <a shape="rect" href="exchange.html">Exchange</a>
is moved to the dead letter queue (the dead letter endpoint). The exchange is
then complete and from the client point of view it was processed. As such the
<a shape="rect" href="dead-letter-channel.html">Dead Letter Channel</a> have
handled the <a shape="rect" href="exchange.html">Exchange</a>.</p><p>For
instance configuring the dead letter channel as:</p><p><strong>Using the <a
shape="rect" href="fluent-builders.html">Fluent Builders</a></strong></p><div
class="code panel pdl" style="border-width: 1px;"><div class="codeContent
panelContent pdl">
+<div class="wiki-content maincontent"><h2
id="DeadLetterChannel-DeadLetterChannel">Dead Letter Channel</h2><p>Camel
supports the <a shape="rect" class="external-link"
href="http://www.enterpriseintegrationpatterns.com/DeadLetterChannel.html";
rel="nofollow">Dead Letter Channel</a> from the <a shape="rect"
href="enterprise-integration-patterns.html">EIP patterns</a> using the <a
shape="rect" class="external-link"
href="http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/processor/DeadLetterChannel.html";>DeadLetterChannel</a>
processor which is an <a shape="rect" href="error-handler.html">Error
Handler</a>.</p><p><span class="confluence-embedded-file-wrapper"><img
class="confluence-embedded-image confluence-external-resource"
src="http://www.enterpriseintegrationpatterns.com/img/DeadLetterChannelSolution.gif";
data-image-src="http://www.enterpriseintegrationpatterns.com/img/DeadLetterChannelSolution.gif";></span></p><div
class="confluence-information-macro confluenc
e-information-macro-tip"><p class="title">Differences Between The
DeadLetterChannel And The DefaultErrorHandler</p><span class="aui-icon
aui-icon-small aui-iconfont-approve
confluence-information-macro-icon"></span><div
class="confluence-information-macro-body"><p>The <strong><code>DefaultErrorHandler</code></strong>
does very little: it ends the Exchange immediately and propagates the thrown
Exception back to the
caller.</p><p>The <strong><code>DeadLetterChannel</code></strong> lets you
control behaviors including redelivery, whether to propagate the thrown
Exception to the caller (the <strong><code>handled</code></strong>
option), and where the (failed) Exchange should now be routed
to.</p><p>The <strong><code>DeadLetterChannel</code></strong> is also by
default configured to not be verbose in the logs, so when a message is handled
and moved to the dead letter endpoint, then there is nothing logged. If you
want some level of logging you can use the various opti
ons on the redelivery policy / dead letter channel to configure this. For
example if you want the message history then
set <strong><code>logExhaustedMessageHistory=true</code></strong>
(and <strong><code>logHandled=true</code></strong> for <strong>Camel
2.15.x</strong> or older).</p><p>When
the <strong><code>DeadLetterChannel</code></strong> moves a message to the
dead letter endpoint, any new Exception thrown is by default handled by the
dead letter channel as well. This ensures that
the <strong><code>DeadLetterChannel</code></strong> will always succeed.
From <strong>Camel 2.15</strong>: this behavior can be changed by setting the
option <strong><code>deadLetterHandleNewException=false</code></strong>. Then
if a new Exception is thrown, then the dead letter channel will fail and
propagate back that new Exception (which is the behavior of the default error
handler). When a new Exception occurs then the dead letter channel logs this
at <strong><code>WARN</co
de></strong> level. This can be turned off by setting
<strong><code>logNewException=false</code></strong>.</p></div></div><h3
id="DeadLetterChannel-Redelivery">Redelivery</h3><p>It is common for a
temporary outage or database deadlock to cause a message to fail to process;
but the chances are if its tried a few more times with some time delay then it
will complete fine. So we typically wish to use some kind of redelivery policy
to decide how many times to try redeliver a message and how long to wait before
redelivery attempts.</p><p>The <a shape="rect" class="external-link"
href="http://camel.apache.org/maven/current/camel-core/apidocs/org/apache/camel/processor/RedeliveryPolicy.html";>RedeliveryPolicy</a>
defines how the message is to be redelivered. You can customize things
like</p><ul><li>The number of times a message is attempted to be redelivered
before it is considered a failure and sent to the dead letter
channel.</li><li>The initial redelivery timeout.</li><li>Whether or not
exponential backoff is used, i.e., the time between retries increases using a
backoff multiplier.</li><li>Whether to use collision avoidance to add some
randomness to the timings.</li><li>Delay pattern (see below for
details).</li><li><strong>Camel 2.11:</strong> Whether to allow redelivery
during stopping/shutdown.</li></ul><p>Once all attempts at redelivering the
message fails then the message is forwarded to the dead letter queue.</p><h3
id="DeadLetterChannel-AboutMovingExchangetoDeadLetterQueueandUsinghandled()">About
Moving Exchange to Dead Letter Queue and
Using <strong><code>handled()</code></strong></h3><p><strong><code>handled()</code></strong>
on <a shape="rect" href="dead-letter-channel.html">Dead Letter
Channel</a></p><p>When all attempts of redelivery have failed the <a
shape="rect" href="exchange.html">Exchange</a> is moved to the dead letter
queue (the dead letter endpoint). The exchange is then complete and from the
client point of view it was processed. As such
the <a shape="rect" href="dead-letter-channel.html">Dead Letter Channel</a>
have handled the <a shape="rect" href="exchange.html">Exchange</a>.</p><p>For
instance configuring the dead letter channel as:</p><p><strong>Using the <a
shape="rect" href="fluent-builders.html">Fluent Builders</a></strong></p><div
class="code panel pdl" style="border-width: 1px;"><div class="codeContent
panelContent pdl">
<script class="brush: java; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[errorHandler(deadLetterChannel("jms:queue:dead")
.maximumRedeliveries(3).redeliveryDelay(5000));
]]></script>
</div></div><p><strong>Using the <a shape="rect"
href="spring-xml-extensions.html">Spring XML Extensions</a></strong></p><div
class="code panel pdl" style="border-width: 1px;"><div class="codeContent
panelContent pdl">
<script class="brush: xml; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[<route
errorHandlerRef="myDeadLetterErrorHandler">
- ...
+ <!-- ... -->
</route>
<bean id="myDeadLetterErrorHandler"
class="org.apache.camel.builder.DeadLetterChannelBuilder">
@@ -104,31 +104,32 @@
<property name="maximumRedeliveries" value="3"/>
<property name="redeliveryDelay" value="5000"/>
</bean>
-
]]></script>
-</div></div><p>The <a shape="rect" href="dead-letter-channel.html">Dead Letter
Channel</a> above will clear the caused exception
(<code>setException(null)</code>), by moving the caused exception to a property
on the <a shape="rect" href="exchange.html">Exchange</a>, with the key
<code>Exchange.EXCEPTION_CAUGHT</code>. Then the <a shape="rect"
href="exchange.html">Exchange</a> is moved to the <code>"jms:queue:dead"</code>
destination and the client will not notice the failure.</p><h3
id="DeadLetterChannel-AboutmovingExchangetodeadletterqueueandusingtheoriginalmessage">About
moving Exchange to dead letter queue and using the original message</h3><p>The
option <strong>useOriginalMessage</strong> is used for routing the original
input message instead of the current message that potentially is modified
during routing.</p><p>For instance if you have this route:</p><div class="code
panel pdl" style="border-width: 1px;"><div class="codeContent panelContent pdl">
+</div></div><p>The <a shape="rect" href="dead-letter-channel.html">Dead Letter
Channel</a> above will clear the caused exception
<strong><code>setException(null)</code></strong>, by moving the caused
exception to a property on the <a shape="rect"
href="exchange.html">Exchange</a>, with the key
<strong><code>Exchange.EXCEPTION_CAUGHT</code></strong>. Then the <a
shape="rect" href="exchange.html">Exchange</a> is moved to the
<strong><code>jms:queue:dead</code></strong> destination and the client will
not notice the failure.</p><h3
id="DeadLetterChannel-AboutMovingExchangetoDeadLetterQueueandUsingtheOriginalMessage">About
Moving Exchange to Dead Letter Queue and Using the Original Message</h3><p>The
option <strong><code>useOriginalMessage</code></strong> is used for routing the
original input message instead of the current message that potentially is
modified during routing.</p><p>For instance if you have this route:</p><div
class="code panel pdl" style="border-width: 1px;"><div class=
"codeContent panelContent pdl">
<script class="brush: java; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[ from("jms:queue:order:input")
.to("bean:validateOrder")
.to("bean:transformOrder")
.to("bean:handleOrder");
]]></script>
-</div></div><p>The route listen for JMS messages and validates, transforms and
handle it. During this the <a shape="rect" href="exchange.html">Exchange</a>
payload is transformed/modified. So in case something goes wrong and we want to
move the message to another JMS destination, then we can configure our <a
shape="rect" href="dead-letter-channel.html">Dead Letter Channel</a> with the
<strong>useOriginalMessage</strong> option. But when we move the <a
shape="rect" href="exchange.html">Exchange</a> 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 <code>jms:queue:order:input</code>. So we can do this
by enabling the <strong>useOriginalMessage</strong> option as shown
below:</p><div class="code panel pdl" style="border-width: 1px;"><div
class="codeContent panelContent pdl">
-<script class="brush: java; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[ // will use original body
- errorHandler(deadLetterChannel("jms:queue:dead")
- .useOriginalMessage().maximumRedeliveries(5).redeliverDelay(5000);
+</div></div><p>The route listen for JMS messages and validates, transforms and
handle it. During this the <a shape="rect" href="exchange.html">Exchange</a>
payload is transformed/modified. So in case something goes wrong and we want to
move the message to another JMS destination, then we can configure our <a
shape="rect" href="dead-letter-channel.html">Dead Letter Channel</a> with
the <strong><code>useOriginalMessage</code></strong> option. But when we
move the <a shape="rect" href="exchange.html">Exchange</a> to this destination
we do not know in which state the message is in. Did the error happen in before
the <strong><code>transformOrder</code></strong> or after? So to be sure
we want to move the original input message we received from
<strong><code>jms:queue:order:input</code></strong>. So we can do this by
enabling the <strong><code>useOriginalMessage</code></strong> option as
shown below:</p><div class="code panel pdl" style="border-width: 1px;"><div
class="code
Content panelContent pdl">
+<script class="brush: java; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[// will use original body
+errorHandler(deadLetterChannel("jms:queue:dead")
+ .useOriginalMessage()
+ .maximumRedeliveries(5)
+ .redeliverDelay(5000);
]]></script>
-</div></div><p>Then the messages routed to the <code>jms:queue:dead</code> 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.</p><h3
id="DeadLetterChannel-OnRedelivery">OnRedelivery</h3><p>When <a shape="rect"
href="dead-letter-channel.html">Dead Letter Channel</a> is doing redeliver its
possible to configure a <a shape="rect" href="processor.html">Processor</a>
that is executed just <strong>before</strong> every redelivery attempt. This
can be used for the situations where you need to alter the message before its
redelivered. See below for sample.</p><div class="confluence-information-macro
confluence-information-macro-tip"><p class="title">onException and
onRedeliver</p><span class="aui-icon aui-icon-small aui-iconfont-approve
confluence-information-macro-icon"></span><div
class="confluence-information-macro-body"><p>We also support for per <a sh
ape="rect" href="exception-clause.html"><strong>onException</strong></a> to
set a <strong>onRedeliver</strong>. That means you can do special on redelivery
for different exceptions, as opposed to onRedelivery set on <a shape="rect"
href="dead-letter-channel.html">Dead Letter Channel</a> can be viewed as a
global scope.</p></div></div><h3
id="DeadLetterChannel-Redeliverydefaultvalues">Redelivery default
values</h3><p>Redelivery is disabled by default.</p><p>The default redeliver
policy will use the following
values:</p><ul><li>maximumRedeliveries=0</li><li>redeliverDelay=1000L (1
second)</li><li>maximumRedeliveryDelay = 60 * 1000L (60 seconds)</li><li>And
the exponential backoff and collision avoidance is turned off.</li><li>The
retriesExhaustedLogLevel are set to LoggingLevel.ERROR</li><li>The
retryAttemptedLogLevel are set to LoggingLevel.DEBUG</li><li>Stack traces is
logged for exhausted messages from Camel 2.2 onwards.</li><li>Handled
exceptions is not logged from Camel 2.3 onwar
ds</li><li>logExhaustedMessageHistory is true for default error handler, and
false for dead letter channel.</li><li>logExhaustedMessageBody <strong>Camel
2.17:</strong> is disabled by default to avoid logging sensitive message
body/header details. If this option is true,
then logExhaustedMessageHistory must also be true.</li></ul><p>The maximum
redeliver delay ensures that a delay is never longer than the value, default 1
minute. This can happen if you turn on the exponential backoff.</p><p>The
maximum redeliveries is the number of <strong>re</strong> delivery attempts. By
default Camel will try to process the exchange 1 + 5 times. 1 time for the
normal attempt and then 5 attempts as redeliveries.<br clear="none"> Setting
the maximumRedeliveries to a negative value such as -1 will then always
redelivery (unlimited).<br clear="none"> Setting the maximumRedeliveries to 0
will disable any re delivery attempt.</p><p>Camel will log delivery failures at
the DEBUG logging level b
y default. You can change this by specifying retriesExhaustedLogLevel and/or
retryAttemptedLogLevel. See <a shape="rect" class="external-link"
href="http://svn.apache.org/repos/asf/camel/trunk/camel-core/src/test/java/org/apache/camel/builder/ExceptionBuilderWithRetryLoggingLevelSetTest.java";>ExceptionBuilderWithRetryLoggingLevelSetTest</a>
for an example.</p><p>You can turn logging of stack traces on/off. If turned
off Camel will still log the redelivery attempt. Its just much less
verbose.</p><h4 id="DeadLetterChannel-RedeliverDelayPattern">Redeliver Delay
Pattern</h4><p>Delay pattern is used as a single option to set a range pattern
for delays. If used then the following options does not apply: (delay,
backOffMultiplier, useExponentialBackOff, useCollisionAvoidance,
maximumRedeliveryDelay).</p><p>The idea is to set groups of ranges using the
following syntax: <code>limit:delay;limit 2:delay 2;limit 3:delay 3;...;limit
N:delay N</code></p><p>Each group has two values separated wit
h colon</p><ul class="alternate"><li>limit = upper limit</li><li>delay = delay
in millis<br clear="none"> And the groups is again separated with semi
colon.<br clear="none"> The rule of thumb is that the next groups should have a
higher limit than the previous group.</li></ul><p>Lets clarify this with an
example:<br clear="none">
<code>delayPattern=5:1000;10:5000;20:20000</code></p><p>That gives us 3
groups:</p><ul
class="alternate"><li>5:1000</li><li>10:5000</li><li>20:20000</li></ul><p>Resulting
in these delays for redelivery attempt:</p><ul
class="alternate"><li>Redelivery attempt number 1..4 = 0 millis (as the first
group start with 5)</li><li>Redelivery attempt number 5..9 = 1000 millis (the
first group)</li><li>Redelivery attempt number 10..19 = 5000 millis (the second
group)</li><li>Redelivery attempt number 20.. = 20000 millis (the last
group)</li></ul><p>Note: The first redelivery attempt is 1, so the first group
should start with 1 or higher.</p><p>You can start a group wi
th limit 1 to eg have a starting delay:
<code>delayPattern=1:1000;5:5000</code></p><ul class="alternate"><li>Redelivery
attempt number 1..4 = 1000 millis (the first group)</li><li>Redelivery attempt
number 5.. = 5000 millis (the last group)</li></ul><p>There is no requirement
that the next delay should be higher than the previous. You can use any delay
value you like. For example with <code>delayPattern=1:5000;3:1000</code> we
start with 5 sec delay and then later reduce that to 1 second.</p><h3
id="DeadLetterChannel-Redeliveryheader">Redelivery header</h3><p>When a message
is redelivered the <a shape="rect" class="external-link"
href="http://camel.apache.org/maven/camel-core/apidocs/org/apache/camel/processor/DeadLetterChannel.html";>DeadLetterChannel</a>
will append a customizable header to the message to indicate how many times
its been redelivered. <br clear="none"> Before Camel 2.6: The header is
<strong>CamelRedeliveryCounter</strong>, which is also defined on the
<code>Exchang
e.REDELIVERY_COUNTER</code>.<br clear="none"> Starting with 2.6: The header
<strong>CamelRedeliveryMaxCounter</strong>, which is also defined on the
<code>Exchange.REDELIVERY_MAX_COUNTER</code>, contains the maximum redelivery
setting. This header is absent if you use <code>retryWhile</code> or have
unlimited maximum redelivery configured.</p><p>And a boolean flag whether it is
being redelivered or not (first attempt)<br clear="none"> The header
<strong>CamelRedelivered</strong> contains a boolean if the message is
redelivered or not, which is also defined on the
<code>Exchange.REDELIVERED</code>.</p><p>Dynamically calculated delay from the
exchange<br clear="none"> In Camel 2.9 and 2.8.2: The header is
<strong>CamelRedeliveryDelay</strong>, which is also defined on the
<code>Exchange.REDELIVERY_DELAY</code>.<br clear="none"> Is this header is
absent, normal redelivery rules apply.</p><h4
id="DeadLetterChannel-Whichendpointfailed">Which endpoint
failed</h4><p><strong>Available as of
Camel 2.1</strong></p><p>When Camel routes messages it will decorate the <a
shape="rect" href="exchange.html">Exchange</a> with a property that contains
the <strong>last</strong> endpoint Camel send the <a shape="rect"
href="exchange.html">Exchange</a> to:</p><div class="code panel pdl"
style="border-width: 1px;"><div class="codeContent panelContent pdl">
+</div></div><p>Then the messages routed to the
<strong><code>jms:queue:dead</code></strong> 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.</p><h3 id="DeadLetterChannel-OnRedelivery">OnRedelivery</h3><p>When
<a shape="rect" href="dead-letter-channel.html">Dead Letter Channel</a> is
doing redeliver its possible to configure a <a shape="rect"
href="processor.html">Processor</a> that is executed just
<strong>before</strong> every redelivery attempt. This can be used for the
situations where you need to alter the message before its redelivered. See
below for sample.</p><div class="confluence-information-macro
confluence-information-macro-tip"><p class="title">onException and
onRedeliver</p><span class="aui-icon aui-icon-small aui-iconfont-approve
confluence-information-macro-icon"></span><div
class="confluence-information-macro-body"><p>We also supp
ort for per <a shape="rect"
href="exception-clause.html"><strong>onException</strong></a> to set an
<strong><code>onRedeliver</code></strong>. That means you can do special on
redelivery for different exceptions, as opposed
to <strong><code>onRedelivery</code></strong> set on <a shape="rect"
href="dead-letter-channel.html">Dead Letter Channel</a> can be viewed as a
global scope.</p></div></div><h3
id="DeadLetterChannel-RedeliveryDefaultValues">Redelivery Default
Values</h3><p>Redelivery is disabled by default.</p><p>The default redeliver
policy will use the following
values:</p><ul><li><strong><code>maximumRedeliveries=0</code></strong></li><li><strong><code>redeliverDelay=1000L</code></strong>
(1 second)</li><li><strong><code>maximumRedeliveryDelay = 60 *
1000L</code></strong> (60
seconds)</li><li><strong><code>backOffMultiplier</code></strong> and
<strong><code>useExponentialBackOff</code></strong> are
ignored.</li><li><strong><code>retriesExhaustedLogLevel=LoggingLevel.ERROR
</code></strong></li><li><strong><code>retryAttemptedLogLevel=LoggingLevel.DEBUG</code></strong></li><li>Stack
traces are logged for exhausted messages, from <strong>Camel
2.2</strong>.</li><li>Handled exceptions are not logged, from <strong>Camel
2.3</strong>.</li><li><strong><code>logExhaustedMessageHistory</code></strong>
is true for default error handler, and false for dead letter
channel.</li><li><strong><code>logExhaustedMessageBody</code></strong>
<strong>Camel 2.17:</strong> is disabled by default to avoid logging
sensitive message body/header details. If this option is
<strong><code>true</code></strong>,
then <strong><code>logExhaustedMessageHistory</code></strong> must also be
<strong><code>true</code></strong>.</li></ul><p>The maximum redeliver delay
ensures that a delay is never longer than the value, default 1 minute. This can
happen when
<strong><code>useExponentialBackOff=true</code></strong>.</p><p>The <strong><code>maximumRedeliveries</code></strong>
is the number of <strong>re</strong>-delivery attempts. By default Camel will
try to process the exchange 1 + 5 times. 1 time for the normal attempt and then
5 attempts as redeliveries.<br clear="none"> Setting
the <strong><code>maximumRedeliveries=-1 </code></strong>(or
< <strong><code>-1</code></strong>) will then always redelivery
(unlimited).<br clear="none"> Setting
the <strong><code>maximumRedeliveries=0</code></strong> will disable
re-delivery.</p><p>Camel will log delivery failures at
the <strong><code>DEBUG</code></strong> logging level by default. You can
change this by
specifying <strong><code>retriesExhaustedLogLevel</code></strong> and/or
<strong><code>retryAttemptedLogLevel</code></strong>. See <a shape="rect"
class="external-link"
href="http://svn.apache.org/repos/asf/camel/trunk/camel-core/src/test/java/org/apache/camel/builder/ExceptionBuilderWithRetryLoggingLevelSetTest.java";>ExceptionBuilderWithRetryLoggingLevelSetTest</a>
for an exampl
e.</p><p>You can turn logging of stack traces on/off. If turned off Camel will
still log the redelivery attempt. It's just much less verbose.</p><h4
id="DeadLetterChannel-RedeliverDelayPattern">Redeliver Delay
Pattern</h4><p>Delay pattern is used as a single option to set a range pattern
for delays. When a delay pattern is in use the following options no longer
apply:</p><ul><li><strong><code>delay</code></strong></li><li><strong><code>backOffMultiplier</code></strong></li><li><strong><code>useExponentialBackOff</code></strong></li><li><strong><code>useCollisionAvoidance</code></strong></li><li><strong><code>maximumRedeliveryDelay</code></strong></li></ul><p>The
idea is to set groups of ranges using the following syntax:
<strong><code>limit:delay;limit 2:delay 2;limit 3:delay 3;...;limit N:delay
N</code></strong></p><p>Each group has two values separated with colon:</p><ul
class="alternate"><li><strong><code>limit</code></strong> = upper
limit</li><li><strong><code>delay</code></str
ong> = delay in milliseconds<br clear="none"> And the groups is again
separated with semi-colon. The rule of thumb is that the next groups should
have a higher limit than the previous group.</li></ul><p>Lets clarify this with
an example:<br clear="none">
<strong><code>delayPattern=5:1000;10:5000;20:20000</code></strong></p><p>That
gives us three groups:</p><ul
class="alternate"><li><strong><code>5:1000</code></strong></li><li><strong><code>10:5000</code></strong></li><li><strong><code>20:20000</code></strong></li></ul><p>Resulting
in these delays between redelivery attempts:</p><ul
class="alternate"><li>Redelivery attempt number <strong><code>1..4 =
0ms</code></strong> (as the first group start with 5)</li><li>Redelivery
attempt number <strong><code>5..9 = 1000ms</code></strong> (the first
group)</li><li>Redelivery attempt number <strong><code>10..19 =
5000ms</code></strong> (the second group)</li><li>Redelivery attempt
number <strong><code>20.. = 20000ms</c
ode></strong> (the last group)</li></ul><p>Note: The first redelivery attempt
is <strong><code>1</code></strong>, so the first group should start
with <strong><code>1</code></strong> or higher.</p><p>You can start a
group with limit <strong><code>1</code></strong> to e.g., have a starting
delay: <strong><code>delayPattern=1:1000;5:5000</code></strong></p><ul
class="alternate"><li>Redelivery attempt number <strong><code>1..4 =
1000ms</code></strong> (the first group)</li><li>Redelivery attempt
number <strong><code>5.. = 5000ms</code></strong> (the last
group)</li></ul><p>There is no requirement that the next delay should be higher
than the previous. You can use any delay value you like. For example with
<strong><code>delayPattern=1:5000;3:1000</code></strong> we start with 5 sec
delay and then later reduce that to <strong><code>1</code></strong>
second.</p><h3 id="DeadLetterChannel-Redeliveryheader">Redelivery
header</h3><p>When a message is redelivered the <
a shape="rect" class="external-link"
href="http://camel.apache.org/maven/camel-core/apidocs/org/apache/camel/processor/DeadLetterChannel.html";>DeadLetterChannel</a>
will append a customizable header to the message to indicate how many times
its been redelivered. <br clear="none"> Before <strong>Camel 2.6</strong>: The
header is <strong><code>CamelRedeliveryCounter</code></strong>, which is also
defined on the <strong><code>Exchange.REDELIVERY_COUNTER</code></strong>.<br
clear="none"> From <strong>Camel 2.6</strong>: The
header <strong><code>CamelRedeliveryMaxCounter</code></strong>, which is
also defined on the
<strong><code>Exchange.REDELIVERY_MAX_COUNTER</code></strong>, contains the
maximum redelivery setting. This header is absent if you use
<strong><code>retryWhile</code></strong> or have unlimited maximum redelivery
configured.</p><p>And a boolean flag whether it is being redelivered or not
(first attempt). The header <strong><code>CamelRedelivered</code></strong>
co
ntains a boolean if the message is redelivered or not, which is also defined
on the <strong><code>Exchange.REDELIVERED</code></strong>.</p><h3
id="DeadLetterChannel-DynamicallyCalculatedDelayFromtheExchange">Dynamically
Calculated Delay From the Exchange</h3><p>In <strong>Camel 2.9</strong> and
<strong>2.8.2</strong>: The header
is <strong><code>CamelRedeliveryDelay</code></strong>, which is also
defined on the <strong><code>Exchange.REDELIVERY_DELAY</code></strong>. If this
header is absent, normal redelivery rules apply.</p><h4
id="DeadLetterChannel-WhichEndpointFailed">Which Endpoint
Failed</h4><p><strong>Available as of Camel 2.1</strong></p><p>When Camel
routes messages it will decorate the <a shape="rect"
href="exchange.html">Exchange</a> with a property that contains the
<strong>last</strong> endpoint Camel send the <a shape="rect"
href="exchange.html">Exchange</a> to:</p><div class="code panel pdl"
style="border-width: 1px;"><div class="codeContent panelContent pdl">
<script class="brush: java; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[String lastEndpointUri =
exchange.getProperty(Exchange.TO_ENDPOINT, String.class);
]]></script>
-</div></div><p>The <code>Exchange.TO_ENDPOINT</code> have the constant value
<code>CamelToEndpoint</code>.</p><p>This information is updated when Camel
sends a message to any endpoint. So if it exists its the <strong>last</strong>
endpoint which Camel send the Exchange to.</p><p>When for example processing
the <a shape="rect" href="exchange.html">Exchange</a> at a given <a
shape="rect" href="endpoint.html">Endpoint</a> and the message is to be moved
into the dead letter queue, then Camel also decorates the Exchange with another
property that contains that <strong>last</strong> endpoint:</p><div class="code
panel pdl" style="border-width: 1px;"><div class="codeContent panelContent pdl">
+</div></div><p>The <strong><code>Exchange.TO_ENDPOINT</code></strong> have the
constant value <strong><code>CamelToEndpoint</code></strong>. This information
is updated when Camel sends a message to any endpoint. So if it exists its the
<strong>last</strong> endpoint which Camel send the Exchange to.</p><p>When for
example processing the <a shape="rect" href="exchange.html">Exchange</a> at a
given <a shape="rect" href="endpoint.html">Endpoint</a> and the message is to
be moved into the dead letter queue, then Camel also decorates the Exchange
with another property that contains that <strong>last</strong>
endpoint:</p><div class="code panel pdl" style="border-width: 1px;"><div
class="codeContent panelContent pdl">
<script class="brush: java; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[String failedEndpointUri =
exchange.getProperty(Exchange.FAILURE_ENDPOINT, String.class);
]]></script>
-</div></div><p>The <code>Exchange.FAILURE_ENDPOINT</code> have the constant
value <code>CamelFailureEndpoint</code>.</p><p>This allows for example you to
fetch this information in your dead letter queue and use that for error
reporting.<br clear="none"> This is useable if the Camel route is a bit dynamic
such as the dynamic <a shape="rect" href="recipient-list.html">Recipient
List</a> so you know which endpoints failed.</p><p><strong>Notice:</strong>
These information is kept on the Exchange even if the message was successfully
processed by a given endpoint, and then later fails for example in a local <a
shape="rect" href="bean.html">Bean</a> processing instead. So beware that this
is a hint that helps pinpoint errors.</p><div class="code panel pdl"
style="border-width: 1px;"><div class="codeContent panelContent pdl">
+</div></div><p>The <strong><code>Exchange.FAILURE_ENDPOINT</code></strong>
have the constant value
<strong><code>CamelFailureEndpoint</code></strong>.</p><p>This allows for
example you to fetch this information in your dead letter queue and use that
for error reporting. This is usable if the Camel route is a bit dynamic such as
the dynamic <a shape="rect" href="recipient-list.html">Recipient List</a> so
you know which endpoints failed.</p><p><strong>Note:</strong> this information
is retained on the Exchange even if the message is subsequently processed
successfully by a given endpoint only to fail, for example, in local <a
shape="rect" href="bean.html">Bean</a> processing instead. So, beware that this
is a hint that helps pinpoint errors.</p><div class="code panel pdl"
style="border-width: 1px;"><div class="codeContent panelContent pdl">
<script class="brush: java; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[from("activemq:queue:foo")
.to("http://someserver/somepath")
.beanRef("foo");
]]></script>
-</div></div><p>Now suppose the route above and a failure happens in the
<code>foo</code> bean. Then the <code>Exchange.TO_ENDPOINT</code> and
<code>Exchange.FAILURE_ENDPOINT</code> will still contain the value of <code><a
shape="rect" class="external-link" href="http://someserver/somepath";
rel="nofollow">http://someserver/somepath</a></code>.</p><h3
id="DeadLetterChannel-OnPrepareFailure">OnPrepareFailure</h3><p><strong>Available
as of Camel 2.16</strong></p><p>Before the exchange is sent to the dead letter
queue, you can use onPrepare to allow a custom <code>Processor</code> to
prepare the exchange, such as adding information why the Exchange failed. For
example the following processor adds a header with the exception
message</p><div class="code panel pdl" style="border-width: 1px;"><div
class="codeContent panelContent pdl">
+</div></div><p>Now suppose the route above and a failure happens in the
<code>foo</code> bean. Then the
<strong><code>Exchange.TO_ENDPOINT</code></strong> and
<strong><code>Exchange.FAILURE_ENDPOINT</code></strong> will still contain the
value of <code><a shape="rect" class="external-link"
href="http://someserver/somepath";
rel="nofollow">http://someserver/somepath</a></code>.</p><h3
id="DeadLetterChannel-OnPrepareFailure"><code>OnPrepareFailure</code></h3><p><strong>Available
as of Camel 2.16</strong></p><p>Before the exchange is sent to the dead letter
queue, you can use <strong><code>onPrepare</code></strong> to allow a
custom <strong><code>Processor</code></strong> to prepare the exchange,
such as adding information why the Exchange failed.</p><p>For example, the
following processor adds a header with the exception message:</p><div
class="code panel pdl" style="border-width: 1px;"><div class="codeContent
panelContent pdl">
<script class="brush: java; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[ public static class MyPrepareProcessor
implements Processor {
@Override
public void process(Exchange exchange) throws Exception {
@@ -138,16 +139,14 @@
}]]></script>
</div></div><p>Then configure the error handler to use the processor as
follows:</p><div class="code panel pdl" style="border-width: 1px;"><div
class="codeContent panelContent pdl">
<script class="brush: java; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[errorHandler(deadLetterChannel("jms:dead").onPrepareFailure(new
MyPrepareProcessor()));]]></script>
-</div></div><p> </p><p>Configuring this from XML DSL is as shown:</p><div
class="code panel pdl" style="border-width: 1px;"><div class="codeContent
panelContent pdl">
-<script class="brush: java; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[ <bean id="myPrepare"
-
class="org.apache.camel.processor.DeadLetterChannelOnPrepareTest.MyPrepareProcessor"/>
-
+</div></div><p> </p><p>Configuring this from XML DSL is as
follows:</p><div class="code panel pdl" style="border-width: 1px;"><div
class="codeContent panelContent pdl">
+<script class="brush: xml; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[<bean id="myPrepare"
class="org.apache.camel.processor.DeadLetterChannelOnPrepareTest.MyPrepareProcessor"/>
- <errorHandler id="dlc" type="DeadLetterChannel"
deadLetterUri="jms:dead"
onPrepareFailureRef="myPrepare"/>]]></script>
-</div></div><p> </p><p>The onPrepare is also available using the default
error handler.</p><h3 id="DeadLetterChannel-Whichroutefailed">Which route
failed</h3><p><strong>Available as of Camel 2.10.4/2.11</strong></p><p>When
Camel error handler handles an error such as <a shape="rect"
href="dead-letter-channel.html">Dead Letter Channel</a> or using <a
shape="rect" href="exception-clause.html">Exception Clause</a> with
handled=true, then Camel will decorate<br clear="none"> the <a shape="rect"
href="exchange.html">Exchange</a> with the route id where the error
occurred.</p><div class="code panel pdl" style="border-width: 1px;"><div
class="codeContent panelContent pdl">
+<errorHandler id="dlc" type="DeadLetterChannel"
deadLetterUri="jms:dead"
onPrepareFailureRef="myPrepare"/>]]></script>
+</div></div><p> </p><p>The <strong><code>onPrepare</code></strong>
is also available using the default error handler.</p><h3
id="DeadLetterChannel-WhichRouteFailed">Which Route
Failed</h3><p><strong>Available as of Camel 2.10.4/2.11</strong></p><p>When
Camel error handler handles an error such as <a shape="rect"
href="dead-letter-channel.html">Dead Letter Channel</a> or using <a
shape="rect" href="exception-clause.html">Exception Clause</a> with
<strong><code>handled=true</code></strong>, then Camel will decorate the <a
shape="rect" href="exchange.html">Exchange</a> with the route id where the
error occurred.</p><p>Example:</p><div class="code panel pdl"
style="border-width: 1px;"><div class="codeContent panelContent pdl">
<script class="brush: java; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[String failedRouteId =
exchange.getProperty(Exchange.FAILURE_ROUTE_ID, String.class);
]]></script>
-</div></div><p>The <code>Exchange.FAILURE_ROUTE_ID</code> have the constant
value <code>CamelFailureRouteId</code>.</p><p>This allows for example you to
fetch this information in your dead letter queue and use that for error
reporting.</p><h3
id="DeadLetterChannel-Controlifredeliveryisallowedduringstopping/shutdown">Control
if redelivery is allowed during stopping/shutdown</h3><p><strong>Available as
of Camel 2.11</strong></p><p>Prior to Camel 2.10, Camel will perform redelivery
while stopping a route, or shutting down Camel. This has improved a bit in
Camel 2.10 onwards, as Camel will not perform redelivery attempts when shutting
down aggressively (eg during <a shape="rect"
href="graceful-shutdown.html">Graceful Shutdown</a> and timeout hit). From
Camel 2.11 onwards there is a new option
<code>allowRedeliveryWhileStopping</code> which you can use to control if
redelivery is allowed or not; notice that any in progress redelivery will still
be executed. This option can only disallow
any redelivery to be executed <strong>after</strong> the stopping of a
route/shutdown of Camel has been triggered. If a redelivery is dissallowed then
a <code>RejectedExcutionException</code> is set on the <a shape="rect"
href="exchange.html">Exchange</a> and the processing of the <a shape="rect"
href="exchange.html">Exchange</a> stops. This means any consumer will see the
<a shape="rect" href="exchange.html">Exchange</a> as failed due the
<code>RejectedExecutionException</code>.</p><p>The default value is
<code>true</code> to be backwards compatible as before. For example the
following sample shows how to do this with Java DSL and XML DSL</p><div
class="code panel pdl" style="border-width: 1px;"><div class="codeContent
panelContent pdl">
+</div></div><p>The <strong><code>Exchange.FAILURE_ROUTE_ID</code></strong>
have the constant value <strong><code>CamelFailureRouteId</code></strong>. This
allows for example you to fetch this information in your dead letter queue and
use that for error reporting.</p><h3
id="DeadLetterChannel-ControlifRedeliveryisAllowedDuringStopping/Shutdown">Control
if Redelivery is Allowed During Stopping/Shutdown</h3><p><strong>Available as
of Camel 2.11</strong></p><p>Before <strong>Camel 2.10</strong>, Camel would
perform redelivery while stopping a route, or shutting down Camel. This has
improved a bit in <strong>Camel 2.10</strong>: Camel will no longer perform
redelivery attempts when shutting down aggressively, e.g., during <a
shape="rect" href="graceful-shutdown.html">Graceful Shutdown</a> and timeout
hit.</p><p>From <strong>Camel 2.11</strong>: there is a new option
<strong><code>allowRedeliveryWhileStopping</code></strong> which you can use to
control if redelivery is allowed or not; no
tice that any in progress redelivery will still be executed. This option can
only disallow any redelivery to be executed <em><strong>after</strong></em> the
stopping of a route/shutdown of Camel has been triggered. If a redelivery is
disallowed then a <strong><code>RejectedExcutionException</code></strong> is
set on the <a shape="rect" href="exchange.html">Exchange</a> and the processing
of the <a shape="rect" href="exchange.html">Exchange</a> stops. This means any
consumer will see the <a shape="rect" href="exchange.html">Exchange</a> as
failed due the <strong><code>RejectedExcutionException</code></strong>. The
default value is <strong><code>true</code></strong> for backward
compatibility.</p><p>For example, the following snippet shows how to do this
with Java DSL and XML DSL:</p><div class="code panel pdl" style="border-width:
1px;"><div class="codeContent panelContent pdl">
<script class="brush: java; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[
// this error handler will try up till 20 redelivery attempts with 1 second
between.
@@ -204,7 +203,7 @@ RouteBuilder builder = new RouteBuilder(
}
};
]]></script>
-</div></div><h3
id="DeadLetterChannel-HowcanImodifytheExchangebeforeredelivery?">How can I
modify the Exchange before redelivery?</h3><p>We support directly in <a
shape="rect" href="dead-letter-channel.html">Dead Letter Channel</a> to set a
<a shape="rect" href="processor.html">Processor</a> that is executed
<strong>before</strong> each redelivery attempt.</p><p>When <a shape="rect"
href="dead-letter-channel.html">Dead Letter Channel</a> is doing redeliver its
possible to configure a <a shape="rect" href="processor.html">Processor</a>
that is executed just <strong>before</strong> every redelivery attempt. This
can be used for the situations where you need to alter the message before its
redelivered.</p><p>Here we configure the <a shape="rect"
href="dead-letter-channel.html">Dead Letter Channel</a> to use our processor
<code>MyRedeliveryProcessor</code> to be executed before each
redelivery.</p><div class="code panel pdl" style="border-width: 1px;"><div
class="codeContent panelConten
t pdl">
+</div></div><h3
id="DeadLetterChannel-HowCanIModifytheExchangeBeforeRedelivery?">How Can I
Modify the Exchange Before Redelivery?</h3><p>We support directly in <a
shape="rect" href="dead-letter-channel.html">Dead Letter Channel</a> to set a
<a shape="rect" href="processor.html">Processor</a> that is executed
<strong>before</strong> each redelivery attempt. When <a shape="rect"
href="dead-letter-channel.html">Dead Letter Channel</a> is doing redeliver its
possible to configure a <a shape="rect" href="processor.html">Processor</a>
that is executed just <strong>before</strong> every redelivery attempt. This
can be used for the situations where you need to alter the message before its
redelivered. Here we configure the <a shape="rect"
href="dead-letter-channel.html">Dead Letter Channel</a> to use our processor
<strong><code>MyRedeliveryProcessor</code></strong> to be executed before each
redelivery.</p><div class="code panel pdl" style="border-width: 1px;"><div
class="codeContent panelC
ontent pdl">
<script class="brush: java; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[
// we configure our Dead Letter Channel to invoke
// MyRedeliveryProcessor before a redelivery is
@@ -214,7 +213,7 @@ errorHandler(deadLetterChannel("moc
// setting delay to zero is just to make unit testing faster
.redeliveryDelay(0L));
]]></script>
-</div></div>And this is the processor <code>MyRedeliveryProcessor</code> where
we alter the message.<div class="code panel pdl" style="border-width:
1px;"><div class="codeContent panelContent pdl">
+</div></div>And this is the processor
<strong><code>MyRedeliveryProcessor</code></strong> where we alter the
message.<div class="code panel pdl" style="border-width: 1px;"><div
class="codeContent panelContent pdl">
<script class="brush: java; gutter: false; theme: Default"
type="syntaxhighlighter"><![CDATA[
// This is our processor that is executed before every redelivery attempt
// here we can do what we want in the java code, such as altering the message
@@ -236,7 +235,7 @@ public class MyRedeliverProcessor implem
}
}
]]></script>
-</div></div><h3
id="DeadLetterChannel-HowcanIlogwhatcausedtheDeadLetterChanneltobeinvoked?">How
can I log what caused the Dead Letter Channel to be invoked?</h3><p>You often
need to know what went wrong that caused the Dead Letter Channel to be used and
it does not offer logging for this purpose. So the Dead Letter Channel's
endpoint can be set to a endpoint of our own (such
as <code>direct:deadLetterChannel</code>). We write a route to accept this
Exchange and log the Exception, then forward on to where we want the failed
Exchange moved to (which might be a DLQ queue for instance). See also <a
shape="rect" class="external-link"
href="http://stackoverflow.com/questions/13711462/logging-camel-exceptions-and-sending-to-the-dead-letter-channel";
rel="nofollow">http://stackoverflow.com/questions/13711462/logging-camel-exceptions-and-sending-to-the-dead-letter-channel</a></p><p></p><h4
id="DeadLetterChannel-UsingThisPattern">Using This Pattern</h4>
+</div></div><h3
id="DeadLetterChannel-HowCanILogWhatCausedtheDeadLetterChanneltobeInvoked?">How
Can I Log What Caused the Dead Letter Channel to be Invoked?</h3><p>You often
need to know what went wrong that caused the Dead Letter Channel to be used and
it does not offer logging for this purpose. So the Dead Letter Channel's
endpoint can be set to a endpoint of our own (such
as <strong><code>direct:deadLetterChannel</code></strong>). We write a
route to accept this Exchange and log the Exception, then forward on to where
we want the failed Exchange moved to (which might be a DLQ queue for instance).
See also <a shape="rect" class="external-link"
href="http://stackoverflow.com/questions/13711462/logging-camel-exceptions-and-sending-to-the-dead-letter-channel";
rel="nofollow">http://stackoverflow.com/questions/13711462/logging-camel-exceptions-and-sending-to-the-dead-letter-channel</a></p><p></p><h4
id="DeadLetterChannel-UsingThisPattern">Using This Pattern</h4>
<p>If you would like to use this EIP Pattern then please read the <a
shape="rect" href="getting-started.html">Getting Started</a>, you may also find
the <a shape="rect" href="architecture.html">Architecture</a> useful
particularly the description of <a shape="rect"
href="endpoint.html">Endpoint</a> and <a shape="rect"
href="uris.html">URIs</a>. Then you could try out some of the <a shape="rect"
href="examples.html">Examples</a> first before trying this pattern out.</p><ul
class="alternate"><li><a shape="rect" href="error-handler.html">Error
Handler</a></li><li><a shape="rect" href="exception-clause.html">Exception
Clause</a></li></ul></div>
</td>
![http://www.enterpriseintegrationpatterns.com/img/DeadLetterChannelSolution.gif"](http://www.enterpriseintegrationpatterns.com/img/DeadLetterChannelSolution.gif"){kind=link}
