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title	Default mode

Notice by default the loop uses the same exchange throughout the looping. So the result from the previous iteration will be used for the next (eg Pipes And and Filters). From Camel 2.8 onwards you can enable copy mode instead. See the options table for more details.

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Name	Default Value	Description
`copy`	`false`	Camel 2.8: Whether or not copy mode is used. If `false` then the same Exchange will be used for each iteration. So the result from the previous iteration will be visible for the next iteration. Instead you can enable copy mode, and then each iteration restarts with a fresh copy of the input Exchange.
doWhile		Camel 2.17: Enables the while loop that loops until the predicate evaluates to false or null.

Exchange properties

For each iteration two properties are set on the Exchange. Processors can rely on these properties to process the Message in different ways.

Property	Description
`CamelLoopSize`	Total number of loops. This is not available if running the loop in while loop mode.
`CamelLoopIndex`	Index of the current iteration (0 based)

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Pass loop count as an argument

Wiki Markup
{snippet:id=ex1\|lang=java\|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/LoopTest.java}

Use expression to determine loop count

Wiki Markup
{snippet:id=ex2\|lang=java\|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/LoopTest.java}

Use expression to determine loop count

Wiki Markup
{snippet:id=ex3\|lang=java\|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/LoopTest.java}

Using the Spring XML Extensions

Pass loop count as an argument

Wiki Markup
{snippet:id=ex1\|lang=xml\|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/loop.xml}

Use expression to determine loop count

Wiki Markup
{snippet:id=ex2\|lang=xml\|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/loop.xml}

For further examples of this pattern in use you could look at one of the junit test case

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Now suppose we send a message to "direct:start" endpoint containing the letter A.
The output of processing this route will be that, each "mock:loop" endpoint will receive "AB" as message.

Wiki Markup
{snippet:id=e1\|lang=java\|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/LoopCopyTest.java}

However if we do not enable copy mode then "mock:loop" will receive "AB", "ABB", "ABBB", etc. messages.

Wiki Markup
{snippet:id=e1\|lang=java\|url=camel/trunk/camel-core/src/test/java/org/apache/camel/processor/LoopNoCopyTest.java}

The equivalent example in XML DSL in copy mode is as follows:

Wiki Markup
{snippet:id=e1\|lang=xml\|url=camel/trunk/components/camel-spring/src/test/resources/org/apache/camel/spring/processor/SpringLoopCopyTest.xml}

Using while mode

Available as of Camel 2.17

The loop can act like a while loop that loops until the expression evaluates to false or null.

For example the route below loops while the length of the message body is 5 or less characters. Notice that the DSL uses loopDoWhile.

Code Block
from("direct:start") .loopDoWhile(simple("${body.length} <= 5")) .to("mock:loop") .transform(body().append("A")) .end() .to("mock:result");

And the same example in XML:

Code Block

	xml
	xml

    <route>
      <from uri="direct:start"/>
      <loop doWhile="true">
        <simple>${body.length} &lt;= 5</simple>
        <to uri="mock:loop"/>
        <transform>
          <simple>A${body}</simple>
        </transform>
      </loop>
      <to uri="mock:result"/>
    </route>

Notice in XML that the while loop is turned on using the doWhile attribute.

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Exchange properties

Using while mode