Do Try

Camel supports the Java equivalent of try, catch, and finally directly in the DSL. It aims to work like its Java sisters but with more power.

In Camel, we prefix the keywords with do to avoid having same keyword as Java. So we have:

  • doTry

  • doCatch

  • doFinally

  • end to end the block in Java DSL

When using doTry …​ doCatch …​ doFinally , the regular Camel Error Handler is not in use; meaning any onException or the likes does not trigger.

The reason is that doTry …​ doCatch …​ doFinally is in fact its own error handler and mimics how try/catch/finally works in Java.

EIP options

The Do Try eip supports the following options which are listed below.

Name Description Default Type

note

The note for this node.

String

description

The description for this node.

String

disabled

Whether to disable this EIP from the route during build time. Once an EIP has been disabled then it cannot be enabled later at runtime.

false

Boolean

outputs

Required

List

doCatch

Catches exceptions as part of a try, catch, finally block.

List

doFinally

Path traversed when a try, catch, finally block exits.

FinallyDefinition

Using doTry …​ doCatch …​ doFinally

In the route below we have all of them in action:

  • Java

  • XML

  • YAML 

from("direct:start")
    .doTry()
        .process(new ProcessorFail())
        .to("mock:result")
    .doCatch(IOException.class, IllegalStateException.class)
        .to("mock:catch")
    .doFinally()
        .to("mock:finally")
    .end();
<route>
  <from uri="direct:start"/>
  <doTry>
    <process ref="processorFail"/>
    <to uri="mock:result"/>
    <doCatch>
      <exception>java.io.IOException</exception>
      <exception>java.lang.IllegalStateException</exception>
      <to uri="mock:catch"/>
    </doCatch>
    <doFinally>
       <to uri="mock:finally"/>
    </doFinally>
  </doTry>
</route>
- route:
    from:
      uri: direct:start
      steps:
        - doTry:
            steps:
              - process:
                  ref: processorFail
              - to:
                  uri: mock:result
              - doCatch:
                  exception:
                    - java.io.IOException
                    - java.lang.IllegalStateException
                  steps:
                    - to:
                        uri: mock:catch
              - doFinally:
                  steps:
                    - to:
                        uri: mock:finally

Using onWhen with doCatch

You can use Predicates with doCatch to make it determine at runtime if the block should be triggered or not. In this example, we only want to trigger if the caused exception message contains the word Damn .

  • Java

  • XML

  • YAML 

from("direct:start")
    .doTry()
        .process(new ProcessorFail())
        .to("mock:result")
    .doCatch(IOException.class, IllegalStateException.class)
        .onWhen(exceptionMessage().contains("Damn"))
        .to("mock:catch")
    .doCatch(CamelExchangeException.class)
        .to("mock:catchCamel")
    .doFinally()
        .to("mock:finally")
    .end();
<route>
  <from uri="direct:start"/>
  <doTry>
    <process ref="processorFail"/>
    <to uri="mock:result"/>
    <doCatch>
      <exception>java.io.IOException</exception>
      <exception>java.lang.IllegalStateException</exception>
      <onWhen>
        <simple>${exception.message} contains 'Damn'</simple>
      </onWhen>
      <to uri="mock:catch"/>
    </doCatch>
    <doCatch>
      <exception>org.apache.camel.CamelExchangeException</exception>
      <to uri="mock:catchCamel"/>
    </doCatch>
    <doFinally>
       <to uri="mock:finally"/>
    </doFinally>
  </doTry>
</route>
- route:
    from:
      uri: direct:start
      steps:
        - doTry:
            steps:
              - process:
                  ref: processorFail
              - to:
                  uri: mock:result
              - doCatch:
                  exception:
                    - java.io.IOException
                    - java.lang.IllegalStateException
                  steps:
                    - onWhen:
                        expression:
                          simple:
                            expression: "${exception.message} contains 'Damn'"
                    - to:
                        uri: mock:catch
              - doCatch:
                  exception:
                    - org.apache.camel.CamelExchangeException
                  steps:
                    - to:
                        uri: mock:catchCamel
              - doFinally:
                  steps:
                    - to:
                        uri: mock:finally

Use end() to end the block

When using Java DSL you must use end() to indicate where the try …​ catch …​ finally block ends. If the route has a doFinally , then the end() should be at the end of the finally block. If there is no doFinally , then the end() should be at the end of the last doCatch .

Instead of end() you can use endDoTry() to end and return back to the try …​ catch scope.

Nested doTry …​ doCatch

When nesting doTry …​ doCatch from an outer doTry …​ doCatch EIP, pay extra attention when using Java DSL as the Java programming language is not indent aware so you may write code that is indented in a way where you think a catch block is associated with the other doTry, but it is not.

Given the following Java DSL: 

from("direct:test")
    .doTry().
        doTry().
            throwException(new IllegalArgumentException("Forced by me"))
        .doCatch(Exception.class)
            .log("docatch 1")
            .throwException(new IllegalArgumentException("Second forced by me"))
    .doCatch(Exception.class)
        .log("docatch 2")
    .end();

Both docatch 1 and docatch 2 are in the inner doTry , and the outer doTry has no catch blocks. Use endDoTry() to end the blocks correctly: 

from("direct:test")
    .doTry().
        doTry().
            throwException(new IllegalArgumentException("Forced by me"))
        .doCatch(Exception.class)
            .log("docatch 1")
            .throwException(new IllegalArgumentException("Second forced by me"))
         .endDoTry() // end this doCatch block
     .endDoTry() // end the inner doTry
    .doCatch(Exception.class)
        .log("docatch 2")
    .end();