<chapter id="Interceptors">
   <title>Filters and Interceptors</title>
   
   <para>
   Interceptors are another facility from Resteasy 2 that now appear in JAX-RS 2.0 but in a rather different
   form. There were four kinds of interceptors in Resteasy 2:
   </para>
   
   <orderedlist>
      <listitem>reader/writer interceptors</listitem>
      <listitem>server side <classname>PreProcessInterceptor</classname></listitem>
      <listitem>server side <classname>PostProcessInterceptor</classname></listitem>
      <listitem><classname>ClientExecutionInterceptor</classname></listitem>
   </orderedlist>
   
   <para>
   Of these, reader/writer interceptors, which wrap around the reading or writing of entities, carry over 
   essentially unchanged, except for class and method names.
   <classname>javax.ws.rs.ext.ReaderInterceptor</classname> and <classname>javax.ws.rs.ext.WriterInterceptor</classname>
   replace the old <classname>MessageBodyReaderInterceptor</classname> and
   <classname>MessageBodyWriterInterceptor</classname>.
   </para>
   
   <para>
   The two kinds of server side interceptors are replaced by <emphasis>filters</emphasis>, which behave similarly.
   There are four kinds of filters:
   </para>
   
   <orderedlist>
      <listitem><classname>ContainerRequestFilter</classname></listitem>
      <listitem><classname>ContainerResponseFilter</classname></listitem>
      <listitem><classname>ClientRequestFilter</classname></listitem>
      <listitem><classname>ClientResponseFilter</classname></listitem>
   </orderedlist>
   
   <para>
   Like the old <classname>PreProcessInterceptor</classname>s, <classname>ContainerRequestFilter</classname>s
   can access requests. A 
   </para>
   
   <programlisting>
public interface PreProcessInterceptor
{
   ServerResponse preProcess(HttpRequest request, ResourceMethod method) throws Failure, WebApplicationException;
}
   </programlisting>
   
   <para>
   can modify the <classname>HttpRequest</classname> and then return a response or null.
   If it returns a response, then the execution process is interrupted and
   that response is returned. Similarly, a new
   </para>
   
   <programlisting>
public interface ContainerRequestFilter
{
    public void filter(ContainerRequestContext requestContext) throws IOException;
}
   </programlisting>

   <para>
   can access and modify a JAX-RS <classname>Request</classname> by calling
   <methodname>ContainerRequestContext.getRequest()</methodname>, and it can supply a response    
   by calling <methodname>ContainerRequestContext.abortWith(Response)</methodname>.
   </para>
   
   <para>
   An old
   </para>
   
   <programlisting>
public interface PostProcessInterceptor
{
   void postProcess(ServerResponse response);
}
   </programlisting>
   
   <para>
   can modify the response, as can a new
   </para>
   
   <programlisting>
public interface ContainerResponseFilter
{
   public void filter(ContainerRequestContext requestContext, ContainerResponseContext responseContext) throws IOException;
}
   </programlisting>
   
   <para>
   by calling, for example, <methodname>ContainerResponseContext.setStatus()</methodname> or
   <methodname>ContainerResponseContext.setEntity()</methodname>.
   </para>
   
   <para>
   The situation is somewhat different with the old <classname>ClientExecutionInterceptor</classname>.
   Unlike <classname>PreProcessInterceptor</classname> and <classname>PreProcessInterceptor</classname>,
   this one really wraps the invocation process on the client side. That is, it can examine and/or modify
   the request and return by calling <methodname>ClientRequestContext.abortWith(Response)</methodname>, or
   proceed with the invocation and examine and/or modify the response.
   Two client side filters, <classname>ClientRequestFilter</classname> and <classname>ClientResponseFilter</classname>,
   are required to replace the functionality of <classname>ClientExecutionInterceptor</classname>. The former
   can access the request, and the latter can access both the request and response. 
   </para>
   
</chapter>