Question

I am implementing two programs; Client and Server, and client asks for a file from server to download in local file system.

After downloading one file, the client should be able to download another file if it wishes to..

However after it downloads the file, Server gives me an exception says

java.net.SocketException: Socket closed

Here’s my code..

Client:

        byte[] aByte = new byte[0];
        int bytesRead;
        String msg;
        FileOutputStream fos = null;
        BufferedOutputStream bos = null;
        while (!(msg = input.readLine()).equals("end")) {

            String myFolderName = "ServerFolder";
            File folder=new File(myFolderName);   
            if (!folder.exists()){ 
                folder.mkdir();
            }
            System.out.println("file downloading");
            try {

                System.out.println("1");
                fos = new FileOutputStream("ServerFolder/"+fileToDownload);
                bos = new BufferedOutputStream(fos);

                System.out.println("MSG: "+msg);

                bytesRead = in.read(aByte, 0, aByte.length);

                System.out.println("2");



                do {
                    baos.write(aByte);
                    bytesRead = in.read(aByte);
                } while (bytesRead != -1);

                System.out.println("3");
                bos.write(baos.toByteArray());
                bos.flush();
            } catch (IOException ex) {
                System.err.println(ex.getMessage());
            }


        }
        bos.close();

    } catch (IOException ex) {
        System.err.println(ex);
    }    

Server:

if (outToClient != null) {
                    System.out.println("2");
                    File myFile = new File(msg);
                    byte[] mybytearray = new byte[(int) myFile.length()];


                    try {
                        fis = new FileInputStream(myFile);
                    } catch (FileNotFoundException ex) {
                        // Do exception handling
                    }
                    System.out.println("3");
                    bis = new BufferedInputStream(fis);

                    try {
                        bis.read(mybytearray, 0, mybytearray.length);   

                        System.out.println("mybytearray.length: "+(int) myFile.length());
                        out.write((int) myFile.length()+"\r\n");    
                        out.write("end\r\n");
                        out.flush();


                        outToClient.write(mybytearray, 0, mybytearray.length);
                        outToClient.flush();

                        s.shutdownOutput();

                        outToClient.close();


                        System.out.println("4");

                    } catch (IOException ex) {
                        System.out.println("5");
                        System.err.println(ex);
                    }

(All connection stuff are done in the beginning of each method)

I had

s.close();

in the Server but I deleted it just in case it causes the error but its not..

I am presuming that

outToClient.close();

is not causing it either?…

Also I googled this problem and some people suggested to tell the client the size of the file before the server sends the file.. but it didn’t work as well.. so I deleted that part as well(or maybe I did it wrong..)

Thanks:)

Answer 1

java.net.SocketException: Socket closed

This has one meaning only. You closed the socket, then you continued you use it. Possibly you are unware that closing either the input or the output stream of a Socket closes the other stream and the socket.

There are numerous other errors in your code: you are ignoring the value returned by read(); you are using unnecessary BytearrayOutputStreams when you could be writing directly to the target; etc etc. Too numerous to mention really. The canonical way to copy a stream in Java is as follows:

while ((count = in.read(buffer)) > 0)
{
  out.write(buffer, 0, count);
}

If you want to use the same connection to transfer more than one file you will have to send the length of the file ahead of the file so the peer knows when it has read all the file, using an obvious modification of the above loop. DataOutputStream.writeLong() and DataInputStream.readLong() provide the most obvious ways of doing that.