Validator

The Validator is a Message Transformation pattern from Hohpe and Woolf. It checks an exchange body against a schema or predicate. It rejects the exchange when the check fails, so the rest of the route only sees valid input.

    let route_xsd = RouteBuilder::from("timer:xsd-valid?period=3000&repeatCount=2")
        .route_id("xsd-valid")
        .set_body("<order><id>A1</id><amount>5</amount></order>")
        .log("Route 1: Validating XML order against XSD", LogLevel::Info)
        .validate(&xsd)
        .log("Route 1: XML is valid!", LogLevel::Info)
        .to("log:info?showBody=true")
        .build()?;

- id: xsd-valid
  from: timer:xsd-valid?period=3000&repeatCount=2
  steps:
    - set_body:
        value: "<order><id>A1</id><amount>5</amount></order>"
    - validate: "${body.contains('<order>')}"
    - to: log:info?showBody=true

The included route fires a timer twice. The .set_body(...) step sets the body to an XML order. The .validate(&xsd) step loads the XSD schema from the configured path and checks the body against it. The log step after the validator runs only when the body is valid. A second route in the example sends an invalid order. It pairs the validator with an error_handler, so the validation error is logged instead of crashing the process.

On a mismatch the validator returns an error. The error flows back through the same RouteErrorHandler boundary as any other step error. A route-level error_handler or a do-try catch block can recover it. Wrap the validator in a do-try block to keep the exchange in the pipeline after a failure. Use the bare validator to fail fast on bad input. The YAML validate step also accepts a predicate expression like ${body.contains('<order>')} for inline checks without a schema file.

The Validator differs from the Filter. The Validator stops the route on a failed check and surfaces the error. The Filter silently drops the exchange. Use the Validator for input validation and contract enforcement at a trust boundary. Use the Filter when an exchange is well-formed but not relevant.

Per ADR-0001, the validator compiles into a Service<Exchange> step. The schema engine runs inside the step. The processor contract is documented in camel-processor/CONTEXT.md.

The example source is at examples/validator.