Constant Language

Available as of Camel version 1.5

The Constant Expression Language is really just a way to specify constant strings as a type of expression.

This is a fixed constant value that is only set once during starting up the route, do not use this if you want dynamic values during routing.

Constant Options

The Constant language supports 1 options, which are listed below.

Name Default Java Type Description

trim

true

Boolean

Whether to trim the value to remove leading and trailing whitespaces and line breaks

Example usage

The setHeader element of the Spring DSL can utilize a constant expression like:

<route>
  <from uri="seda:a"/>
  <setHeader name="theHeader">
    <constant>the value</constant>
  </setHeader>
  <to uri="mock:b"/>
</route>

in this case, the Message coming from the seda:a Endpoint will have 'theHeader' header set to the constant value 'the value'.

And the same example using Java DSL:

from("seda:a")
  .setHeader("theHeader", constant("the value"))
  .to("mock:b");

Loading constant from external resource

You can externalize the constant and have Camel load it from a resource such as "classpath:", "file:", or "http:".
This is done using the following syntax: "resource:scheme:location", eg to refer to a file on the classpath you can do:

.setHeader("myHeader").constant("resource:classpath:constant.txt")

Dependencies

The Constant language is part of camel-core.