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## Chapter 19. Resources metadata configuration

When processing JAX-RS deployments, RESTEasy relies on ResourceBuilder to create metadata for each JAX-RS resource. Such metadata is defined using the metadata SPI in package org.jboss.resteasy.spi.metadata, in particular the ResourceClass interface:

    package org.jboss.resteasy.spi.metadata;

    public interface ResourceClass
    {
      String getPath();

      Class<?> getClazz();

      ResourceConstructor getConstructor();

      FieldParameter[] getFields();

      SetterParameter[] getSetters();

      ResourceMethod[] getResourceMethods();

      ResourceLocator[] getResourceLocators();
    }

Among the other classes and interfaces defining metadata SPI, the following interfaces are worth a mention here:

    public interface ResourceConstructor
    {
      ResourceClass getResourceClass();

      Constructor getConstructor();

      ConstructorParameter[] getParams();
    }

    public interface ResourceMethod extends ResourceLocator
    {
      Set<String> getHttpMethods();

      MediaType[] getProduces();

      MediaType[] getConsumes();

      boolean isAsynchronous();

      void markAsynchronous();
    }

    public interface ResourceLocator
    {
      ResourceClass getResourceClass();

      Class<?> getReturnType();

      Type getGenericReturnType();

      Method getMethod();

      Method getAnnotatedMethod();

      MethodParameter[] getParams();

      String getFullpath();

      String getPath();

    }

Now, the interesting point is that RESTEasy allows tuning the metadata generation by providing implementations of the ResourceClassProcessor interface:

    package org.jboss.resteasy.spi.metadata;

    public interface ResourceClassProcessor
    {

      /**
       * Allows the implementation of this method to modify the resource metadata represented by
       * the supplied {@link ResourceClass} instance. Implementation will typically create
       * wrappers which modify only certain aspects of the metadata.
       *
       * @param clazz The original metadata
       * @return the (potentially modified) metadata (never null)
       */
      ResourceClass process(ResourceClass clazz);

    }

The processors are meant to be, and are resolved as, regular JAX-RS annotated providers. They allow for wrapping resource metadata classes with custom versions that can be used for various advanced scenarios like

- adding additional resource method/locators to the resource
- altering the http methods
- altering the @Produces / @Consumes media types
- ...

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