Loop
The Loop allows to process the a message a number of times and possibly process them in a different way. Useful mostly for testing.
![]() | Default mode
Notice by default the loop uses the same exchange throughout the looping. So the result from the previous iteration is used for the next (eg Pipes and Filters). From Camel 2.8 onwards you can enable copy mode instead. See the options table for more details. |
Options
| Name |
Default Value |
Description |
| copy |
false |
Camel 2.8: Whether or not copy mode is used. If false then the same Exchange is being used throughout the looping. So the result from the previous iteration will be visible for the next iteration. Instead you can enable copy mode, and then each iteration is restarting with a fresh copy of the input Exchange. |
Exchange properties
For each iteration two properties are set on the Exchange that could be used by processors down the pipeline to process the Message in different ways.
| Property |
Description |
| CamelIterationCount |
Camel 1.x: Total number of iterations to be run |
| CamelIterationIndex |
Camel 1.x: Index of the current iteration (0 based) |
| CamelLoopSize |
Camel 2.0: Total number of loops |
| CamelLoopIndex |
Camel 2.0: Index of the current iteration (0 based) |
that could be used by processors down the pipeline to process the Message in different ways.
Examples
The following example shows how to take a request from the direct:x endpoint , then send the message repetitively to mock:result. The number of times the message is sent is either passed as an argument to loop(), or determined at runtime by evaluating an _expression_. The _expression_ must evaluate to an int, otherwise a RuntimeCamelException is thrown.
Using the Fluent Builders
Pass loop count as an argument
from("direct:a").loop(8).to("mock:result");
Use _expression_ to determine loop count
from("direct:b").loop(header("loop")).to("mock:result");
Use _expression_ to determine loop count
from("direct:c").loop().xpath("/hello/@times").to("mock:result");
Using the Spring XML Extensions
Pass loop count as an argument
<route>
<from uri="direct:a"/>
<loop>
<constant>8</constant>
<to uri="mock:result"/>
</loop>
</route>
Use _expression_ to determine loop count
<route>
<from uri="direct:b"/>
<loop>
<header>loop</header>
<to uri="mock:result"/>
</loop>
</route>
For further examples of this pattern in use you could look at one of the junit test case
Using This Pattern
If you would like to use this EIP Pattern then please read the Getting Started, you may also find the Architecture useful particularly the description of Endpoint and URIs. Then you could try out some of the Examples first before trying this pattern out.
