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when transferring files they get corrupted with java sockets
DataInputStream input;
DataOutputStream ouput;
//these two variable are initialized somewhere else in the code.
private void downloadFile() {
    try {
        String fileName= input.readUTF();
        File f = new File(path + fileName);
        size= f.length();
        file= new FileInputStream(path+ fileName);
        ouput.writeLong(size);
        byte[] buffer = new byte[1024];
        int len;
        while ((len = file.read(buffer)) > 0) {
            output.write(buffer, 0, len);
        }
    } catch (IOException e) {
        e.printStackTrace();
    }
}

public void downloadFile(String fileName) {
    try {
        this.client= new Socket(ip,port);
        DataInputStream input= new DataInputStream(this.client.getInputStream());
        DataOutputStream ouput= new DataOutputStream(this.client.getOutputStream());

        output.writeUTF("DOWNLOAD");
        output.writeUTF(fileName);

        File f = new File(path+ fileName);
        file = new FileOutputStream(f);
        byte[] buffer = new byte[1024];
        int len;
        while ((len = input.read(buffer)) > 0) {
            file.write(buffer, 0, len);
        }
        file.flush();
        file.close();
        this.client.close();
    } catch (Exception e) {
        System.out.println("something went wrong");
    }
}

ouput.writeLong(size);

ouput.writeLong(size);