Passing objects between a servlet and an applet

[Chris Patton]

I know it is possible to pass objects between a servlet and an applet, but thus far I have been only partially successful. I can get the object in question to the applet from the servlet (by way of the doGet method), but I can't seem to be able to pass the object back to the servlet from the applet.
I have alread read numerous tutorials/articles on the subject, and I feel that I'm doing everything correctly. Still, it doesn't work.
For the sake of clarity, I'll post both my applet-side and servlet-side code (just the networking part, not all of it).
here is my applet-side code:
public void writeDB()
{
ObjectOutputStream outputToServlet = null;
try
{
URL skillsDBservlet = new URL("http://cpatton:8100/servlet/ServTest");
URLConnection servletConnection = skillsDBservlet.openConnection();
servletConnection.setDoInput(true);
servletConnection.setDoOutput(true);
servletConnection.setUseCaches (false);
servletConnection.setDefaultUseCaches (false);
servletConnection.setRequestProperty("Content-Type", "application/octet-stream");
outputToServlet = new ObjectOutputStream(servletConnection.getOutputStream());
outputToServlet.writeObject(theObject);
outputToServlet.flush();
outputToServlet.close();
}

catch(Exception e)
{
//if there's an exception, send it to the main text window.
subPanel1.removeAll();
subPanel1.repaint();
textBox.setText(e.toString());
subPanel1.add(textBox);
subPanel1.setVisible(false);
subPanel1.setVisible(true);
System.out.println(e);
}

}
here is my servlet-side code:
public void doPost(HttpServletRequest req,
HttpServletResponse res)
throws ServletException, IOException
{
if(DEBUG)System.out.println("in doPost(..)");
ObjectInputStream inputFromApplet = null;
Object tempObj = null;

try {
// get an input stream from the applet
inputFromApplet = new ObjectInputStream(req.getInputStream());

// read the serialized object from applet
tempObj = inputFromApplet.readObject();

inputFromApplet.close();

}catch (Exception e){
System.out.println(e);
}
setObject(tempObj);

}

Thanks
- Chris
PS love the site

[Todd M Bush]

The only thing I see is that theObject must be serialized to be passed. Sun has a good paper on this called Java Servlets and Serialization with RMI, just search on it. Here is snippets of code that I know work....
server side....
public void doPost(HttpServletRequest req, HttpServletResponse resp) throws
ServletException, IOException {

ObjectInputStream in = new ObjectInputStream(req.getInputStream());
ObjectOutputStream out = new ObjectOutputStream(resp.getOutputStream());
String sourceName = (String)in.readObject();
String sourceType = (String)in.readObject();
out.writeObject(add_Source(sourceName, sourceType));
// Where add_Source does something and returns a Boolean
}
the client
public Boolean addSource(String SourceName, String SourceType) throws Exception {
URL servlet = new URL(webBase,"servlet/AZUniversalServlet");
Integer code = new Integer(5);
Serializable objs[] = { code, SourceName, SourceType };
in = postObjects(servlet, objs);
Boolean result = (Boolean)in.readObject();
return result;
}
private ObjectInputStream postObjects(URL myServlet, Serializable myObjs[])
throws Exception {
URLConnection con = servlet.openConnection();
con.setDoInput(true);
con.setDoOutput(true);
con.setRequestProperty("Content-Type", "application/x-www-form-urlencoded");

ObjectOutputStream out = new ObjectOutputStream(con.getOutputStream());
int numObjects = myObjs.length;
for(int x= 0; x<numObjects; x++) {
out.writeObject(myObjs[x]);
}

out.flush();
out.close();

return new ObjectInputStream(con.getInputStream());
}
good luck
[This message has been edited by Todd M Bush (edited June 13, 2000).]

[paul wheaton]

See www.javaranch.com/common.html.
Use the HTTP class to send objects to your servlets. Inherit the ObjectServlet class for the servlet to catch the objects and send an object back.

[Tero Ahonen]

Hi Chris!
I have a same kind of problem, but I can pass Objects from applet to servlet but not from servlet to applet. How does your object transferring from servlet to applet works?
My applet to servlet code:
Applet
String location = "http://localhost:8080/servlet/TestServlet";
Hashtable h = new Hashtable();
URL url = new URL(location);
URLConnection con = url.openConnection();
con.setDoOutput(true);
con.setUseCaches(false);
con.setRequestProperty(
"Content-Type",
"application/x-www-form-urlencoded");
ObjectOutputStream out = new ObjectOutputStream
(con.getOutputStream());
out.writeObject(h);
out.flush();
Servlet
ObjectInputStream in = new ObjectInputStream
(request.getInputStream());
Hashtable h = (Hashtable)in.readObject();
in.close();

------------------

[Tero Ahonen]

Hi!
I have the ObjectServlet and all other javaranch.common classes. Is there any example how to use ObjectServlet for passing objects from applet to servlet and back.