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Servlet to Applet Communcation

Mark Hatfield

Joined: Feb 15, 2012
Posts: 1
I am developing an application that uses an applet for the user interface and a servlet for data retrieval. I am having an issue getting the data from the Servlet back to the applet. My control flow is below:

1. The applet creates an serialized object that is sent to the servlet using the ObjectOutputStream. - This works fine.
2. The servlet receives the object via the ObjectInputStream and pulls date from the object to create a database query. - Also works fine.
3. Using the data from the query, the servlet builds a serialized object that it sends back to the Servlet via the ObjectOutputStream. - Seems to work.
4. The applet then reads the object sent via the ObjectInputStream, but the object is empty.

Just before sending the object from the servlet back to the applet, I print out the objects get methods and the data is in the object.
I do the same when the applet recieves the object from the servlet, but there is no data.

This is the code I am using to return the object (myPlayer) from the Communicator servlet to the applet:

System.out.println("Communicator ==>> getArmorClass = " + myPlayer.getArmorClass()); - The data displayed is correct.
System.out.println("Communicator ==>> getCharName = " + myPlayer.getCharName()); - The data displayed is correct.

res.setContentType("java-internal/" + Player.class.getName());
OutputStream out = res.getOutputStream();

ObjectOutputStream dataOutput = new ObjectOutputStream(out);

In the applet I read the object and display the same information:

ObjectInputStream objIn = new ObjectInputStream(urlConnection.getInputStream());
Player myPlayer = (Player)objIn.readObject(); // read object from Servlet

System.out.println("Applet Main getArmorClass = " + myPlayer.getArmorClass());
System.out.println("Applet Main getCharName = " + myPlayer.getCharName());

Not sure what I am doing wrong here, it seems strange that I can send a serialized object from the applet to the servlet, do my database work and build a new serialized object, but when I pass it back to the applet there is no data in it. Any suggestions would be greatly appreciated.

Ulf Dittmer

Joined: Mar 22, 2005
Posts: 42965
Not sure what the problem is, but be aware that object serialization between different JVMs can easily break if the two JVMs are not the exact same version. Unless you can guarantee that, you may be better off using the java.beans.XMLEncoder/XMLDecoder classes.
Paul Clapham

Joined: Oct 14, 2005
Posts: 19973

That all looks reasonable enough. But objects can't be "empty"... so what are the actual symptoms of your problem? Error messages? Stack traces? Unexpected actions?
I agree. Here's the link:
subject: Servlet to Applet Communcation
It's not a secret anymore!