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2.11. OnCompletion

Overview
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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 OnCompletion command can be global or per route. A route scope overrides global scope.
  • OnCompletion can be configured to be triggered on success for failure.
  • The onWhen predicate can be used to only trigger the onCompletion in 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
リンクのコピー

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");
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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>
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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");
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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>
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Global Scope for onCompletion
リンクのコピー

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");
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Using onWhen
リンクのコピー

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");
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Using onCompletion with or without a thread pool
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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:${body}"));
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For XML the format is: 
<onCompletion parallelProcessing="true">
   <to uri="before"/>
   <delay><constant>1000</constant></delay>
   <setBody><simple>OnComplete:${body}<simple></setBody>
 </onCompletion>
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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>>
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Run onCompletion before Consumer Sends Response
リンクのコピー

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 onCompletion to 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()
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For XML, set the mode attribute to BeforeConsumer: 
<onCompletion mode="BeforeConsumer">
   <setHeader headerName="createdBy">
     <constant>Someone</constant>
   </setHeader>
 </onCompletion>
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