IOException while trying to save output from ObjectInputStream to a file

Question

I am new to the concept of working with streams and with files in Java.

I'm writing a piece of code, I have a very simple server that is listening for an incoming file.

Then I have a handler that deals with the incoming file.

Now, here is the code (stripped of try/catch blocks)

ObjectInputStream in;

in = new ObjectInputStream(new BufferedInputStream(
        clientSocket.getInputStream()));

File f = new File(fileName);
int byteCount = in.readInt();
byte[] fileArray = (byte[]) in.readObject();
Files.write(f.toPath(), fileArray);

There comes an IOException when the program hits the ``byte[] fileArray = (byte[]) in.readObject();line. And - to be sure, theint byteCount` shows the correct number of bytes, the filename is also correct...

Stacktrace looks like this:

java.io.OptionalDataException
    at java.io.ObjectInputStream.readObject0(ObjectInputStream.java:1304)
    at java.io.ObjectInputStream.readObject(ObjectInputStream.java:370)
    at com.fileservice.util.ClientHandlerRunnable.run(ClientHandlerRunnable.java:85)
    at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:471)
    at java.util.concurrent.FutureTask.run(FutureTask.java:262)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:744)

Code of the client sending the file:

    Socket socket = new Socket(data.getIp(), data.getTcpPort());
    FileInputStream fis = null;
    BufferedInputStream bis = null;
    // OutputStream os = null;

    // send file
    File myFile = new File(data.getFileName());
    String test = myFile.getAbsolutePath();
    byte[] mybytearray = new byte[(int) myFile.length()];
    fis = new FileInputStream(myFile);
    bis = new BufferedInputStream(fis);
    bis.read(mybytearray, 0, mybytearray.length);
    ObjectOutputStream os = new ObjectOutputStream(
            new BufferedOutputStream(socket.getOutputStream()));
    os.flush();
    System.out.println("Sending " + data.getFileName() + "("
            + mybytearray.length + " bytes)");
    if (os != null) {
        os.writeInt(mybytearray.length);
        os.write(mybytearray, 0, mybytearray.length);
        os.flush();
        System.out.println("Done.");
    }
    if (bis != null) {
        bis.close();
    }
    if (os != null) {
        os.close();
    }
    if (socket != null) {
        socket.close();

    }

What's the stack trace of the exception? What is the code of the client sending the "file"? What's the point of sending/reading the byteCount, since it isn't used at all? — JB Nizet
– JB Nizet, Commented Oct 19, 2015 at 18:25

JB Nizet · Accepted Answer · 2015-10-19 18:34:01Z

1

You're sending raw bytes, and you're reading an object. That can't work. If you read an object, then the sender must have written an object (with writeObject()). If the sender writes bytes, then you must read bytes (with read()).

Note that your file reading section is wrong as well. read() gives no guarantee that it will read the number of bytes you ask it to read. You MUST use a loop to read everything. Or you can simply use Files.readAllBytes(), which will correctly read all the bytes from the file for you.

answered Oct 19, 2015 at 18:34

JB Nizet

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