Sending data from a servlet to an applet: how to implement this?

Question

I want to send the send HashMap object to the applet that requested it. The servlet has this HashMap object. Is there a way I can do this?

 Applet ------requests HashMap object---->Servlet listens to this request | | Servlet searches that HashMap Object | | \ / <--Finally Send this to applet------------ Servlet gets the HashMap object 

I made a connection to the servlet, and my servlet also has a HashMap object, but I don’t know how to send it to the applet, and I wonder if it can be sent!

Answer 1

I am going to use some external libraries to answer your question: Google Gson and Apache IO Utils .

So, you already have a HashMap in your servlet and you want to send it to the applet:

 Map<String, String> myMap = new HashMap<String, String>();// or whatever Gson gson = new GsonBuilder().create(); String jsonString = gson.toJson(myMap); IOUtils.write(jsonString, resp.getOutputStream());// where 'resp' is your HttpServletResponse IOUtils.closeQuietly(resp.getOutputStream()); 

And get it in your applet:

 String jsonString = IOUtils.toString(conn.getInputStream()); // where 'conn' is an HttpURLConnection IOUtils.closeQuietly(connection.getInputStream()); Gson gson = new GsonBuilder().create(); // The TypeToken is needed when Generics are involved Type typeOfHashMap = new TypeToken<Map<String, String>>() {}.getType(); Map<String, String> myMap = gson.fromJson(jsonString, typeOfHashMap); 

What is it. This is just a simple example, but I hope you get some of this.

Of course, you can do it manually instead of using external libraries, but this method is much simpler.

Answer 2

How about serializing it and sending it back? Consider converting it to JSON or XML.

Answer 3

You can open the URL connection to the servlet if the servlet is located on the same server from which the applet was loaded. You can read

 URL site = new URL("your site") URLConnection urlCon = site.openConnection(); BufferedReader in = new BufferedReader(new InputStreamReader( urlCon.getInputStream())); String inputLine; while ((inputLine = in.readLine()) != null) System.out.println(inputLine); in.close(); 

Meanwhile, in the servlet, you are returning data back to the client using the HttpServletResponse.

If you need something more “sophisticated,” you can use the axis as the webservice stack in your applet, or include a lightweight REST library such as Jersey. But these solutions force you to use a different server component instead of Servlet.

This post will help you:

• To write a servlet: How to send json to a client in response .
• To write your client: How to read JSON with http response .

They use json-lib to parse / serialize objects from JSON format.

I hope for this help.

Answer 4

You can simply serialize the object and write it directly to the HttpServletResponse, writing a stream of bytes.

On the applet side, you have to read the byte stream and deserialize it with the stream. Keep in mind that the Applet sends a POST request, otherwise you may have a limit of 1024 bytes if you use a GET request.

Hope this helps you.