How to make jetty ErrorHandler display error in json format in java

Question

I have the jetty server started this way by the sample code below where I have written my own errorHandler class. Through some few research, I got some information here. But it seems not enough to get me what I want. The name of the class that I set to be called by the server is HandleClient.

So if error 404 occurs, it display {"message":"HTTP error 404"} . the program works fine anyway But the response is in text/plain format.

My Problem is: How can I configure the class to format and display the error in MIME MediaType: application/json.

I have had sleepless nights on this. Will be very grateful to all helps.

    public class MVCPattern{

    public MVCPattern(){
    }

    public static void main(String args[]) throws JSONException, IOException{
        MVCPattern mvcPattern = new MVCPattern();


        ServletContextHandler context = new ServletContextHandler(ServletContextHandler.SESSIONS);
        context.setContextPath("/");

        Server jettyServer = new Server(9000);
        jettyServer.setHandler(context);
        context.setErrorHandler(new ErrorHandler());
        // default error handler for resources out of "context" scope
        jettyServer.addBean(new ErrorHandler());

        ServletHolder jerseyServlet = context.addServlet(org.glassfish.jersey.servlet.ServletContainer.class, "/*");
        jerseyServlet.setInitOrder(0);

        // Tells the Jersey Servlet which REST service/class to load.
        jerseyServlet.setInitParameter("jersey.config.server.provider.classnames",
                HandleClient.class.getCanonicalName() );

        try {
            jettyServer.start();            
            jettyServer.join();

        } catch (Exception ex) {
            Logger.getLogger(HandleClient.class.getName()).log(Level.SEVERE, null, ex);
        } finally {
            jettyServer.destroy();
        }
    }
    /**
     * Dummy error handler that disables any error pages or jetty related messages and returns our
     * ERROR status JSON with plain HTTP status instead. All original error messages (from our code) are preserved
     * as they are not handled by this code.
     */
    static class ErrorHandler extends ErrorPageErrorHandler {
        @Override
        public void handle(String target, org.eclipse.jetty.server.Request baseRequest, HttpServletRequest request, HttpServletResponse response) throws IOException {
            response.getWriter()
            .append("{\"message\":\"HTTP error ")
            .append(String.valueOf(response.getStatus()))
            .append("\"}");
        }
    }

}

Answer 1

You should check the Accept header in the HttpServletRequest.getHeader("Accept") to first see if the client can accept that type.

Then use HttpServletResponse.setContentType("text/json") to set the content type for the response.

Or, if you are using Jetty 9.3.11.v20160721 (or newer) you can override the ErrorHandler.generateAcceptableResponse(Request baseRequest, HttpServletRequest request, HttpServletResponse response, int code, String message, String mimeType) method and handle it accordingly.

See: https://github.com/eclipse/jetty.project/blob/jetty-9.3.11.v20160721/jetty-server/src/main/java/org/eclipse/jetty/server/handler/ErrorHandler.java#L196-L226 for example on its use.