Camel Components

Header

Since Camel 1.5

The Header Expression Language allows you to extract values of named headers.

Header Options

The Header language supports the following options which are listed below.

Name Default Java Type Description

trim (advanced)

true

Boolean

Whether to trim the source code to remove leading and trailing whitespaces and line breaks.

resolveResource (advanced)

false

Boolean

Whether a result of the expression that is a String starting with resource: is loaded as a resource and its content becomes the result, e.g. a script that returns resource:file:order.json or resource:classpath:templates/order.json (a name without a scheme is a classpath resource). Off by default; the resource: prefix on the expression text itself is always resolved. Applies to the expression used as a value, not as a predicate.

Message Body

The message body at each side of the Header language: Expression input is the body its expressions can read, and Expression result what they return.

Side Body Description

Expression result

unknown

The value of the header as it is, null when there is none. A missing header falls back to the exchange property of that name.

The bodies are the ones with the default options. A side that is not listed is not known, and tooling does not guess it. The carriers, the sides and the tools that use them are described in Message Body Types.

Example usage

The recipientList EIP can utilize a header:

  • Java

  • XML

  • YAML

from("direct:a").recipientList(header("myHeader"));
<route>
  <from uri="direct:a" />
  <recipientList>
    <header>myHeader</header>
  </recipientList>
</route>
- route:
    from:
      uri: direct:a
      steps:
        - recipientList:
            expression:
              header:
                expression: myHeader

In this case, the list of recipients are contained in the header 'myHeader'.

Dependencies

The Header language is part of camel-core.