RESTEasy Interceptors

RESTEasy can intercept JAX-RS invocations and route them through listener-like objects called interceptors. There are four interception points on the server side:

• wrapping around MessageBodyWriter invocations
• wrapping around MessageBodyReader invocations
• through pre-processors, which intercept the incoming request before unmarshalling occurs
• through post-processors, which are invoked immediately after the JAX-RS method finishes 

An interceptor can be very useful to implement crosscutting concerns such as logging and security. Although interceptors are not as powerful as Aspect Oriented Programming (AOP) - (e.g. no type-safety or debugging) , they still offer a quick way to create more compact and maintainable code.

In this article I will describe how to use RESTEasy interceptors to log incoming requests into a REST API.

I am currently using RESTEasy to expose HealthCare web services for consumption by mobiles applications, and there is a need to log transactions for auditing purpose, including for HIPAA compliance.

The first step is to specify in your web.xml file, that you are going to use a new interceptor  - (e.g. named LogInterceptor):

<web-app>
   ...  
   <context-param>
      <param-name>resteasy.providers</param-name>
      <param-value>com.acme.api.rest.service.LogInterceptor</param-value>
   </context-param>
   ...
</web-app>

Then you create the corresponding java class for LogInterceptor:

package com.acme.api.rest.service;
  
import javax.servlet.http.HttpServletRequest;
import javax.ws.rs.core.Context;
import javax.ws.rs.core.HttpHeaders;
import javax.ws.rs.ext.Provider;
import javax.ws.rs.WebApplicationException;

 
import org.jboss.resteasy.annotations.interception.ServerInterceptor;
import org.jboss.resteasy.core.ResourceMethod;
import org.jboss.resteasy.core.ServerResponse;
import org.jboss.resteasy.spi.HttpRequest;
import org.jboss.resteasy.spi.interception.PreProcessInterceptor;
import org.jboss.resteasy.spi.Failure;

...
 
@Provider
@ServerInterceptor
public class LogInterceptor implements PreProcessInterceptor {
 
 // An handler to the Transaction log
 private static final Logger translog = Logger.getLogger(JNDIMessageLoggingHandler.class);

 // Getting the request as a context
 @Context HttpServletRequest request;

 @Override
 public ServerResponse preProcess(HttpRequest arg0, ResourceMethod method) throws Failure, WebApplicationException {
  final TransactionLogEntry transactionLogEntry = new TransactionLogEntry(Long.toString(Thread.currentThread().getId()),
                         System.currentTimeMillis(), 
                         getClientIP(request), 
                         request.getRequestURL().toString());
      translog.info(transactionLogEntry);
 }  
 
}

In this example, the TransactionLogEntry constructor takes :

• a transaction ID
• a timestamp
• the client that initiated the request  (e.g. request.getRemoteAddr()+":"+request.getRemotePort())
• the request URL

but you can also log additional information such as the body content of POST requests (storing XML or JSON content).