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2.11. OnCompletion
Overview
The OnCompletion DSL name is used to define an action that is to take place when a
Unit of Work is completed. A Unit of Work is a Camel concept that encompasses an entire exchange. See Section 43.1, “Exchanges”. The onCompletion command has the following features:
- The scope of the
OnCompletioncommand can be global or per route. A route scope overrides global scope. OnCompletioncan be configured to be triggered on success for failure.- The
onWhenpredicate can be used to only trigger theonCompletionin certain situations. - You can define whether or not to use a thread pool, though the default is no thread pool.
Route Only Scope for onCompletion
When an
onCompletion DSL is specified on an exchange, Camel spins off a new thread. This allows the original thread to continue without interference from the onCompletion task. A route will only support one onCompletion. In the following example, the onCompletion is triggered whether the exchange completes with success or failure. This is the default action.
from("direct:start")
.onCompletion()
// this route is only invoked when the original route is complete as a kind
// of completion callback
.to("log:sync")
.to("mock:sync")
// must use end to denote the end of the onCompletion route
.end()
// here the original route contiues
.process(new MyProcessor())
.to("mock:result");
For XML the format is as follows:
<route>
<from uri="direct:start"/>
<!-- this onCompletion block will only be executed when the exchange is done being routed -->
<!-- this callback is always triggered even if the exchange failed -->
<onCompletion>
<!-- so this is a kinda like an after completion callback -->
<to uri="log:sync"/>
<to uri="mock:sync"/>
</onCompletion>
<process ref="myProcessor"/>
<to uri="mock:result"/>
</route>
To trigger the
onCompletion on failure, the onFailureOnly parameter can be used. Similarly, to trigger the onCompletion on success, use the onCompleteOnly parameter.
from("direct:start")
// here we qualify onCompletion to only invoke when the exchange failed (exception or FAULT body)
.onCompletion().onFailureOnly()
.to("log:sync")
.to("mock:sync")
// must use end to denote the end of the onCompletion route
.end()
// here the original route continues
.process(new MyProcessor())
.to("mock:result");
For XML,
onFailureOnly and onCompleteOnly are expressed as booleans on the onCompletion tag:
<route>
<from uri="direct:start"/>
<!-- this onCompletion block will only be executed when the exchange is done being routed -->
<!-- this callback is only triggered when the exchange failed, as we have onFailure=true -->
<onCompletion onFailureOnly="true">
<to uri="log:sync"/>
<to uri="mock:sync"/>
</onCompletion>
<process ref="myProcessor"/>
<to uri="mock:result"/>
</route>
Global Scope for onCompletion
To define
onCompletion for more than just one route:
// define a global on completion that is invoked when the exchange is complete
onCompletion().to("log:global").to("mock:sync");
from("direct:start")
.process(new MyProcessor())
.to("mock:result");
Using onWhen
To trigger the
onCompletion under certain circumstances, use the onWhen predicate. The following example will trigger the onCompletion when the body of the message contains the word Hello:
/from("direct:start")
.onCompletion().onWhen(body().contains("Hello"))
// this route is only invoked when the original route is complete as a kind
// of completion callback. And also only if the onWhen predicate is true
.to("log:sync")
.to("mock:sync")
// must use end to denote the end of the onCompletion route
.end()
// here the original route contiues
.to("log:original")
.to("mock:result");
Using onCompletion with or without a thread pool
As of Camel 2.14,
onCompletion will not use a thread pool by default. To force the use of a thread pool, either set an executorService or set parallelProcessing to true. For example, in Java DSL, use the following format:
onCompletion().parallelProcessing()
.to("mock:before")
.delay(1000)
.setBody(simple("OnComplete:${body}"));
For XML the format is:
<onCompletion parallelProcessing="true">
<to uri="before"/>
<delay><constant>1000</constant></delay>
<setBody><simple>OnComplete:${body}<simple></setBody>
</onCompletion>
Use the
executorServiceRef option to refer to a specific thread pool:
<onCompletion executorServiceRef="myThreadPool"
<to uri="before"/>
<delay><constant>1000</constant></delay>
<setBody><simple>OnComplete:${body}</simple></setBody>
</onCompletion>>
Run onCompletion before Consumer Sends Response
onCompletion can be run in two modes:
- AfterConsumer - The default mode which runs after the consumer is finished
- BeforeConsumer - Runs before the consumer writes a response back to the callee. This allows
onCompletionto modify the Exchange, such as adding special headers, or to log the Exchange as a response logger.
For example, to add a
created by header to the response, use modeBeforeConsumer() as shown below:
.onCompletion().modeBeforeConsumer()
.setHeader("createdBy", constant("Someone"))
.end()
For XML, set the mode attribute to
BeforeConsumer:
<onCompletion mode="BeforeConsumer">
<setHeader headerName="createdBy">
<constant>Someone</constant>
</setHeader>
</onCompletion>
