How to decorate the json response with Resteasy

Question

I am implementing a restfull service with Resteasy that will be consumed by a Extjs client, and i want to decorate the json object retrieved in the http response with some more attributes without using a wrapper class with additional attributes in the service method or overriding JacksonJsonProvider
Example:

raw object:

{
   "id":"1",
   "name":"Diego"
}

decorated object:

{
   "success":"true",
   "root":{
             "id":"1",
             "name":"Diego"
          }
}

I found JAXB Decorators but i could not implement a decorator for json type.

I tried to replace the entity that will be serialized with a wrapper using Interceptors but it doesn't work if a replace the entity which is a Collection.

Any suggestions?

Answer 1

You could write an Interceptor that wraps your JSON response before it is passed to the client. Here is an example code:

1. Define custom HTTPServletResponseWrapper

   public class MyResponseWrapper extends HttpServletResponseWrapper {
       private ByteArrayOutputStream byteStream;
   
       public MyResponseWrapper(HttpServletResponse response, ByteArrayOutputStream byteStream) {
           super(response);
           this.byteStream = byteStream;
       }
   
       @Override
       public ServletOutputStream getOutputStream() throws IOException {
           return new ServletOutputStream() {
               @Override
               public void write(int b) throws IOException {
                   byteStream.write(b);
               }
           };
       }
       @Override
       public PrintWriter getWriter() throws IOException {
           return new PrintWriter(byteStream);
       }
   }
   

2. Define filter class:

   @WebFilter("/rest/*")
   public class JSONResponseFilter implements Filter {
   
       private final String JSON_RESPONSE = " { \"success\":\"true\", \"root\": ";
       private final String JSON_RESPONSE_CLOSE = "}";
   
       /* .. */
   
       @Override
       public void doFilter(ServletRequest request, ServletResponse response,
               FilterChain chain) throws IOException, ServletException {
   
           // capture result in byteStream by using custom responseWrapper
           final HttpServletResponse httpResponse = (HttpServletResponse) response;
           final ByteArrayOutputStream byteStream = new ByteArrayOutputStream();
           HttpServletResponseWrapper responseWrapper = new MyResponseWrapper(httpResponse, byteStream);
   
           // do normal processing but capture results in "byteStream"
           chain.doFilter(request, responseWrapper);
   
           // finally, wrap response with custom JSON
         // you can do fancier stuff here, but you get the idea
           out.write(JSON_RESPONSE.getBytes());
           out.write(byteStream.toByteArray());
           out.write(JSON_RESPONSE_CLOSE.getBytes());
       }
   }