输入流后输出流不起作用

Question

I'm quite new to sockets and to J2ME and I want to create an app, that would send some text to a server (via socket) and then receive answer. So when I try to write the output, I get an exception:

java.net.SocketException: Socket is closed
    at java.net.Socket.getOutputStream(Socket.java:943)
    at server.run(server.java:55)
    at java.lang.Thread.run(Thread.java:748)

Here is my server code (the run() method):

public void run() {
        try {
            serverSocket = new ServerSocket(7997);
            while (true) {
                try {
                    Socket socket = serverSocket.accept();
                    System.out.println("connected");
                    InputStream in = socket.getInputStream();
                    String str = readAll(in);
                    in.close();
                    System.out.println(str);
                    JSONParser parser = new JSONParser();
                    JSONObject json = null;
                    json = (JSONObject) parser.parse(str);
                    text = (String) json.get("text");
                    presalt = (String) json.get("salt");
                    keytoCipher = (String) json.get("key2");
                    String presdvig = (String) json.get("key1");
                    sdvig = Long.parseLong(presdvig);
                    //some methods that work with input
                    caesarEncode();
                    ConKey();
                    precipher();
                    base64code();
                    OutputStream outputStream = socket.getOutputStream();
                    outputStream.write(ciphered.getBytes());
                    outputStream.flush();
                    outputStream.close();
                } catch (ParseException | IOException e) {
                    e.printStackTrace();
                }
            }
            //serverSocket.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

And this is the J2ME client code:

try {
                    System.out.println("connected");
                    JSONObject json = new JSONObject();
                   json.put("text", textField.getString());
                   json.put("salt", "defaultsalt");
                   json.put("key1", "228");
                   json.put("key2", "1488");
                    OutputStream out = sc.openOutputStream();
                    out.write(json.toString().getBytes());
                    out.flush();
                    out.close();
                    InputStream in = sc.openInputStream();
                  String str = readAll(in);
                  System.out.println(str);
                    fieldzwei.setString(str);
                } catch (IOException ex) {
                    ex.printStackTrace();
                } catch (JSONException ex) {
                    ex.printStackTrace();
                }

Also, if I do not send anything to a server and simply send a message from it when it's connected, it works fine. Any ideas where I could be wrong?

Answer 1

The problem here is that you close the InputStream returned by Socket.getInputStream() :

InputStream in = socket.getInputStream();
String str = readAll(in);
in.close();

From the Javadoc of Socket.getInputStream() :

Closing the returned InputStream will close the associated socket.

So after executing the code above, your socket will be closed.

tl;dr : Don't close the InputStream if you still need the OutputStream.