Java: Simple HTTP Server application that responds in JSON

Question

I want to create a very simple HTTP server application in Java.

For example, if I run the server on localhost in port 8080, and I make

Answer 1

If you are already familiar with servlet you do not need much to create a simple server to achieve what you want. But I would like to emphasize that your needs will likely to increase rapidly and therefore you may need to move to a RESTful framework (e.g.: Spring WS, Apache CXF) down the road.

You need to register URIs and get parameters using the standard servlet technology. Maybe you can start here: http://docs.oracle.com/cd/E13222_01/wls/docs92/webapp/configureservlet.html

Next, you need a JSON provider and serialize (aka marshall) it in JSON format. I recommend JACKSON. Take a look at this tutorial: http://www.sivalabs.in/2011/03/json-processing-using-jackson-java-json.html

Finally, your code will look similar to this:

public class Func1Servlet extends HttpServlet {
  public void doGet(HttpServletRequest req, HttpServletResponse resp)
    throws ServletException, IOException {

    String p1 = req.getParameter("param1");
    String p2 = req.getParameter("param2");

    // Do Something with the params

    ResponseJSON resultJSON = new ResponseJSON();
    resultJSON.setProperty1(yourPropert1);
    resultJSON.setProperty2(yourPropert2);

    // Convert your JSON object into JSON string
    Writer strWriter = new StringWriter();
    mapper.writeValue(strWriter, resultJSON);
    String resultString = strWriter.toString();

    resp.setContentType("application/json");
    out.println(resultString );
  }
}

Map URLs in your web.xml:

  func1Servlet
  myservlets.func1servlet


  func1Servlet
  /func1/*

Keep in mind this is a pseudo-code. There are lots you can do to enhance it, adding some utility classes, etc...

Nevertheless, as your project grows your need for a more comprehensive framework becomes more evident.