Header language

The header language returns the value of one message header, or null when the header is not set.

Name: header · Crate: cameleer-core · Cargo feature: none, always included (build features) · Apache Camel: Header

When to use it

• Copy a header into the body, a property or another header without writing a Simple template.
• Use a header as a predicate in filter or choice: a header is true when it is set and not false, 0 or empty.
• Use a header that holds a list as the expression of a split.

Syntax

The expression text is the header name, for example priority or CamelFileName. Leading and trailing spaces are trimmed. The value keeps its type: a number stays a number and a list stays a list. The same value is ${header.priority} in Simple.

Examples

Route on a header set by the caller (for example a model's classification of a ticket):

- route:
    id: header-demo
    from:
      uri: direct:header
      steps:
        - choice:
            when:
              - header: urgent
                steps:
                  - setBody:
                      header: assignee
            otherwise:
              steps:
                - setBody:
                    constant: backlog

Checkout is down

on-call

Without the urgent header the predicate is false:

How do I change my address?

backlog

Split a header that holds a list:

- route:
    id: header-split
    from:
      uri: direct:header-split
      steps:
        - setHeader:
            name: tags
            simple: "${body.split(',')}"
        - split:
            header: tags
            aggregationStrategy: GroupedBodyAggregationStrategy
            steps:
              - setBody:
                  simple: "tag:${body}"

red,green,blue

["tag:red","tag:green","tag:blue"]

Values against a fixture message:

{"body": "x", "headers": {"priority": "high", "retries": 3, "tags": ["a", "b"]}}

Options

The header language has no options.

Rust DSL

b.from("direct:header-rust")
    .filter(header("urgent"))
    .set_body(header("assignee"));

Common questions

How do I read a header in a route?

Use header: name wherever an expression is expected, or ${header.name} inside a Simple template when you need it in a larger text.

What happens when the header does not exist?

The result is null. As a predicate it is false, and setBody with a missing header sets an empty body.

Are header names case sensitive?

Yes, names are matched exactly.

Related

• Simple language (${header.name}, ${headers})
• exchangeProperty language, variable language, constant language
• Apache Camel Header language

Found a problem?

If something on this page doesn't match what Cameleer does, or you hit a bug while building with it, please help fix it, whether you are a person or a coding agent: open an issue that describes what you saw, then fork the repository, fix it, add or update a test, run cargo test --workspace, and open a pull request. CONTRIBUTING.md explains the ground rules.