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 |
|---|---|---|
|
|
Camel 2.8: Whether or not copy mode is used. If |
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 |
|---|---|
|
Camel 1.x: Total number of iterations to be run |
|
Camel 1.x: Index of the current iteration (0 based) |
|
Camel 2.0: Total number of loops |
|
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
Use expression to determine loop count
Use expression to determine loop count
Using the Spring XML Extensions
Pass loop count as an argument
Use expression to determine loop count
For further examples of this pattern in use you could look at one of the junit test case
Using copy mode
Available as of Camel 2.8
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.
However if we do not enable copy mode then "mock:loop" will receive "AB", "ABB", "ABBB" messages.
The equivalent example in XML DSL in copy mode is as follows:
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.