Solving "socket is closed" exception while copying file from server to client and vice versa

Question

I'm doing simple Client-Server applications which copying file from client to server and vice versa. I'm using Sockets of course. Apps shows Client menu with some options to choose: 1. Make Copy on sever 2. Get fileCopy from Server etc.

The issue is when I'm choosing first option, I can't do second one. I read about this exception, but i have no idea how to solve this problem. I'm looking forward for your ideas.

There is part of clientside code:

public Client(String host, int port) {
        try {
            s = new Socket(host, port);
            System.out.println("Witaj w programie");
            boolean finished = false;
            Scanner sc = new Scanner(System.in);
            while(!finished){
                System.out.println("\n\n1.Zrob kopie zapasowa pliku");
                System.out.println("2. Przywroc kopie");
                System.out.println("0.Zakoncz");
                char c = sc.nextLine().charAt(0);
                switch(c){
                case '1':
                    this.sendMessage(1);
                    makeCopy(s);
                    //s.close();
                    break; ...

sendMessage method code:

public void sendMessage(int message_id) throws IOException{
        oos = new ObjectOutputStream(s.getOutputStream());
        ois = new ObjectInputStream(s.getInputStream());
        oos.writeInt(message_id);
        oos.flush();
    }

and makeCopy method code:

private void makeCopy(Socket clientSock) throws IOException {
        File file = new File("D:\\klient\\doKopii.bmp");
        DataOutputStream dos = new DataOutputStream(clientSock.getOutputStream());
        FileInputStream fis = new FileInputStream(file);
        byte[] buffer = new byte[4096];

        while (fis.read(buffer) > 0) {
            dos.write(buffer);
        }

        fis.close();
        dos.close();
    }

Download copy from Server code:

private void saveFile(Socket clientSock) throws IOException {
        //DataInputStream dis = new DataInputStream(clientSock.getInputStream());
        FileOutputStream fos = new FileOutputStream("D:\\klient\\przywroconaKopia.bmp");
        File zSerwera = new File("D:\\serwer\\kopiaPliku.bmp");
        byte[] buffer = new byte[4096];

        int filesize = (int)zSerwera.length();
        int read = 0;
        int totalRead = 0;
        int remaining = filesize;
        while((read = ois.read(buffer, 0, Math.min(buffer.length, remaining))) > 0) {
            totalRead += read;
            remaining -= read;
            System.out.println("read " + totalRead + " bytes.");
            fos.write(buffer, 0, read);
        }

        //fos.close();
        //ois.close();
    }

I am aware of that this does not work because of DataOutputStream closing which means socket is also closed. I deleted this line, but after choosing one option then second (when first one has done), application just freezes.

i wanted to know u get the still exception even after that ? — Priyamal, Apr 23 '16 at 19:30
No. I don't. I'm not sure but the problem is with FileInputStream or DataOutputStream — Infexo, Apr 23 '16 at 19:33

score 0 · Answer 1 · edited May 23 '17 at 11:45

0

There are several problems here.

You need to send the file length ahead of the file, and read exactly that many bytes at the receiver, as shown in this answer.
Don't mix stream types, and don't keep creating new streams. Use the same ObjectInputStream/ObjectOutputStream pair for the life of the socket, at both ends.

edited May 23 '17 at 11:45

Community

1
1

answered Apr 23 '16 at 19:00

user207421

305,947
44
307
483

I don't understand your advice completely. Now im using ObjectInputStream and ObjectOutputStream only. But where do i have to create those streams ? When i moved "oos" and "ois" streams creations outside sendMessage method, app gives more exceptions than before. – Infexo Apr 23 '16 at 19:10
You 'don't understand the advice completely' even though you've accepted an answer that says exactly the same thing? and which is only a partial answer? – user207421 Apr 25 '16 at 10:24
Consider that you've answered earlier and after your pust i didnt get your advice. After Priyamal's answer i understood what I was doing wrong. Sorry that I can't delete comments... Anyway thanks. – Infexo Apr 25 '16 at 12:01

score 0 · Accepted Answer · answered Apr 23 '16 at 19:51

0

    oos = new ObjectOutputStream(s.getOutputStream());
    ois = new ObjectInputStream(s.getInputStream());

public void sendMessage(int message_id) throws IOException{
        oos.writeInt(message_id);
}

make oos and ois as instance variables and make sure that they are instantiated only for one single time. why you have to get a dataoutput stream seperately you can send byte array in same objectoutputstream

private void makeCopy(Socket clientSock) throws IOException {
        File file = new File("D:\\klient\\doKopii.bmp");
        FileInputStream fis = new FileInputStream(file);
        byte[] buffer = new byte[4096];

        while (fis.read(buffer) > 0) {
            oos.write(buffer);
        }
}

this is not very good coding practise bt maybe u should try this approach

answered Apr 23 '16 at 19:51

Priyamal

2,919
2
25
52

It helped me to some extent, but now i have problem with saveFile method. It creates new File but it doesnt write content/bytes to it (let's see edited post please) – Infexo Apr 23 '16 at 20:10
seriously you have to ask another question in the same post ?. what will you do if you get another error after this one , – Priyamal Apr 23 '16 at 20:11
here is an article on how to write to a file reading an byte array http://www.java2s.com/Code/Java/File-Input-Output/Readfiletobytearrayandsavebytearraytofile.htm . may be you should consider marking this as the correct answer . since you got the answer. the second question was asked after you got the answer for the first edit – Priyamal Apr 23 '16 at 20:23

Solving "socket is closed" exception while copying file from server to client and vice versa

2 Answers2