| [[constant-language]] |
| = Constant Language |
| :page-source: core/camel-base/src/main/docs/constant-language.adoc |
| |
| *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. |
| |
| NOTE: 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 |
| |
| |
| // language options: START |
| The Constant language supports 1 options, which are listed below. |
| |
| |
| |
| [width="100%",cols="2,1m,1m,6",options="header"] |
| |=== |
| | Name | Default | Java Type | Description |
| | trim | true | Boolean | Whether to trim the value to remove leading and trailing whitespaces and line breaks |
| |=== |
| // language options: END |
| |
| |
| == Example usage |
| |
| The setHeader element of the Spring DSL can utilize a constant |
| expression like: |
| |
| [source,xml] |
| ---- |
| <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: |
| |
| [source,java] |
| ---- |
| 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: |
| |
| [source,java] |
| ---- |
| .setHeader("myHeader").constant("resource:classpath:constant.txt") |
| ---- |
| |
| == Dependencies |
| |
| The Constant language is part of *camel-core*. |