构造ObjectInputStream时出现EOFException

Question

i'm trying to serialize a HashMap on serverside(Tomcat 6.0.29) and to deserealize it on a client-side android application.

First time i've tried this i got an StreamCorruptedException, but after i created a completly new servlet with a clean doGet/doPost-Method i've managed to solve this issue, unfortunatly i get an EOFException instead.

So first i'm posting my code and then i'll explain my problem in detail:

Server-Side Code (this will be executed when doPost Or doGet is invoked):

    if ("object".equals(request.getParameter("format")))
        {

            trace.log("Before Serializing");
            ObjectOutputStream out = null;
            try
            {
                out = new ObjectOutputStream(response.getOutputStream());
                out.writeObject(outerTable);
                trace.log("after Serializing");
            }
            finally
            {
                if(out != null)
                {
                    try
                    {
                        out.flush();
                        out.close();
                    }
                    catch(Exception ex)
                    {
                        trace.log("Exception has been thrown "+ex.getMessage());
                    }
                }
            }
            trace.log("after closing stream");
        }
        else
        {
            PrintWriter out = response.getWriter();
            out.println(outerTable.toString());
        }

outerTable is a HashMap wich is created exactly before this code-block and it has always correct values.

There are no errors thrown on server-side. When i try to access the servlet in my webbrowser with parameter "?format=object" i get the whole serialization string.

Script of Android-Application (this Method executes the http request after a specific button is pressed):

    private synchronized void performNetworkAccess()
    {
  Runnable run = new Runnable()
  {
    @Override
    public void run()
    {
    System.out.println("in run()-Method");
    ObjectInputStream objInput = null;
    try
    {
        URL url = new URL(myWebsite);
        URLConnection con = url.openConnection();
        InputStream in = con.getInputStream(); 
        objInput = new ObjectInputStream(in);

        outerTable = (HashMap<String, HashMap<String, Object>>)              objInput.readObject();
        synchronized (monitor)
        {
        monitor.notifyAll();
        }
    }
    catch (Exception ex)
    {
        ex.printStackTrace();
    }
    finally
    {
        if (objInput != null)
        {
        try
        {
            objInput.close();
        }
        catch (IOException e)
        {
            e.printStackTrace();
        }
        }
    }

    }

};
Thread t1 = new Thread(run);
t1.start();
}

The Exception occurs immediatly after the constructor of ObjectInputStream class is invoked.

Stacktrace:

• W/System.err(1797): java.io.EOFException
• W/System.err(1797): at libcore.io.Streams.readFully(Streams.java:83)
• W/System.err(1797): at java.io.DataInputStream.readShort(DataInputStream.java:169)
• W/System.err(1797): at java.io.ObjectInputStream.readStreamHeader(ObjectInputStream.java:2102)
• W/System.err(1797): at java.io.ObjectInputStream.(ObjectInputStream.java:372)
• W/System.err(1797): at de.tesla.jtheseuscontactsync.ContactSync$4.run(ContactSync.java:602)
• W/System.err(1797): at java.lang.Thread.run(Thread.java:856)

I've already found many occurences of this problem, but i didn't see one of them where this error occures before readObject() is invoked.

Things i've already tried:

• add out.flush() shortly after constructing ObjectOutputStream
• remove out.flush() and/or out.close() method(s)
• wrap Input-/OutputStream with BufferedInput-/-OutputStream
• retrieve stream as a file and try to deserealize the file

The odd thing is when i first write the Object to a file via FileOutputStream and access this file (on the server) from the client via Url.openStream() then ObjectOutputStream can read this object perfectly, unfortunatly this would mean a lot of trouble when multiple users trying to retrieve this object at the same time...

i hope you can help me out with this one :)

Answer 1

The servlet has got an exception of some kind and hasn't even constructed the ObjectOutputStream. You need to check the response code for 200 before you try to construct the ObjectInputStream at the client.

Answer 2

Some crazy idea... try to add a Content-Length header to your response. Could imply writing your bytes to a ByteArrayOutputStream, measuring the size, setting the header and only then writing to response... but could be the reason that URLConnection is prematurely cutting the connection...

ByteArrayOutputStream baos = new ByteArrayOutputStream();
ObejctOutputStream oos = new ObejctOutputStream(baos);
oos.write(...);

byte[] data = baos.toByteArray();

response.setHeader("Content-Length", "" + data.length);
response.getOutputStream().write(data);

Java Serialization

@Robert comment is right. Java serialization is not intented for communication between different environments. More if you're working between JVM and Dalvik. So another framework would be more suitable (something with XML or JSON could be nice, even wrapping it with a GZip[]Stream).