Validation Component

The Validation component provides a simple means to validate the internal state of newly created objects, to ensure that the object is in a valid [internal] state. The validation component can be used without requiring the presence of any particular execution environment, such as a JEE or Spring container. (Of course, the validation component works just as well inside a container as outside of it.)

Validating object state

The process to receive automatic validation is trivial if your artifact project uses the nazgul-parent pom as a parent within its inheritance chain:

  1. Ensure that your pom.xml has the nazgul-parent pom as direct or indirect parent.
  2. Let your relevant class implement the Validatable interface. (This is illustrated in row 1 in the listing below).
  3. Define the expression for validating the internal state of the instance within the validateInternalState method. (This is illustrated in rows 32 - 34 in the listing below.)

If your artifact project does not use the nazgul-parent pom as a parent within its inheritance chain, please refer to the nazgul-parent pom to see how to configure the AspectJ plugin to automatically weave all your classes with the validationAspect. The validation aspect is what ultimately drives the invocation of the validateInternalState method.

For API details regarding which methods/validations are available for writing the validateInternalState method, please refer to the ExpressionBuilder class. Several concrete examples can be found within the test cases within the validation-aspect project and within the nazgul-core project/reactor.

public class DummyEntity implements Validatable {

    // Internal state
    public int value = 0;

    /**
     * JAXB/JPA-friendly constructor.
     */
    public DummyEntity() {
        // Validation not performed after calling the default constructor.
    }

    /**
     * Compound constructor, so the validateInternalState method
     * will be invoked after the constructor is run.
     */
    public DummyEntity(int value) {
        this.value = value;

        // Validation performed after calling this [non-default] constructor.
    }

    /**
     * Performs validation of the internal state of this Validatable.
     *
     * @throws InternalStateValidationException
     *          if the state of this Validatable was in an incorrect
     *          state (i.e. invalid).
     */
    @Override
    public void validateInternalState() throws InternalStateValidationException {

        InternalStateValidationException.create()
                .notTrue(value < 5, "Value cannot be < 5!")
                .endExpressionAndValidate();
    }
}