Servet Problem: java.io.EOFException

Hello to all Experts.

I have a java swing Gui giving the servlet a parameter:
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String empId="rom01";
ObjectOutputStream output = new      ObjectOutputStream(servletConnection.getOutputStream());
output.writeObject(new String(empId));

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The servlet gets the input:

                 //open InputStream
            ObjectInputStream input=new ObjectInputStream(req.getInputStream());
              String empId=(String)input.readObject();
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//servlet doGet method opens OutputStream
    ObjectOutputStream output=new ObjectOutputStream(res.getOutputStream());


                  
// Set the contenty type to application/octet-stream
                  res.setContentType("application/octet-stream");
                       
            
Vector emp = new Vector();
emp.add(0,new String("he"));
emp.add(1,new String("she"));

output.writeObject(emp);

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When I call the method which in turns communicates with the servlet I get this error message:

exception

java.io.EOFException
      java.io.ObjectInputStream$PeekInputStream.readFully(ObjectInputStream.java:2232)
      java.io.ObjectInputStream$BlockDataInputStream.readShort(ObjectInputStream.java:2698)
      ...

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also the application servers gives this exception message:

java.lang.NullPointerException
        at java.lang.String.<init>(String.java:144)
        at TableTest.doGet(TableTest.java:37)
        at TableTest.doPost(TableTest.java:66)
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I have left out try and catch blocks in order not to clutter the message.

What do you think is the problem with this code ?

Thanks

Mimo