java socket编程问题

Question

what's wrong with my code? sorry about my bad English

package sockettest;

import java.io.*;
import java.net.*;

class sevr implements Runnable{
    public void run() {
        ServerSocket sSkt = null;
        Socket skt = null;
        BufferedReader br = null;
        BufferedWriter bw = null;

        try{
            System.out.println("Server: is about to create socket");
            sSkt = new ServerSocket(6666);
            System.out.println("Server: socket created");
        }
        catch(IOException e){
            System.out.println("Server: socket creation failure");
        }
        try{
            System.out.println("Server: is listening");
            skt = sSkt.accept();
            System.out.println("Server: Connection Established");
        }
        catch(IOException e){
            System.out.println("Server: listening failed");
        }
        try{
            System.out.println("Server: creating streams");
            br = new BufferedReader(new InputStreamReader(skt.getInputStream()));
            bw = new BufferedWriter(new OutputStreamWriter(skt.getOutputStream()));
            System.out.println("Server: stream done");
        }
        catch(IOException e){
            System.out.println("Server: stream failed");
        }
        System.out.println("Server: reading the request");
        try{
            String line = null;
            while((line =br.readLine()) != null){
            System.out.println("Server: client said-> "+ line);
            }
        }
        catch(IOException e){
            System.out.println("Server: reading failed");
        }
        System.out.println("Server: reading fished");

        System.out.println("Server: responding");
        try{
            bw.write("Hi! I am server!");
        }
        catch(IOException e){
            System.out.println("Server: responding failed");
        }
        System.out.println("Server: responding finished");

        System.out.println("Server: is finishing");
        try {
            br.close();
            bw.close();
            skt.close();
            sSkt.close();
        } catch (IOException e) {
            System.out.println("Server: finishing failed");
        }
        System.out.println("Server: done");
    }
}

class clnt implements Runnable{
    public void run() {
        Socket skt = null;
        BufferedReader br = null;
        BufferedWriter bw = null;

        try{
            System.out.println("Client: about to create socket");
            skt = new Socket(InetAddress.getLocalHost(),6666);
            System.out.println("Client: socket created");
        }
        catch(IOException e){
            System.out.println("Client: socket creation failure");
        }

        try{
            System.out.println("Client: creating streams");
            br = new BufferedReader(new InputStreamReader(skt.getInputStream()));
            bw = new BufferedWriter(new OutputStreamWriter(skt.getOutputStream()));
            System.out.println("Client: stream done");
        }
        catch(IOException e){
            System.out.println("Client: stream failed");
        }
        System.out.println("Client: requesting");
        try{
            bw.write("Hi! I am Client!");
        }
        catch(IOException e){
            System.out.println("Client: requesting failed");
        }
        System.out.println("Client: requesting finished");
        System.out.println("Client: reading the respond");
        try{
            String line = null;
            while((line =br.readLine()) != null){
            System.out.println("Client: server said-> "+ line);
            }
        }
        catch(IOException e){
            System.out.println("Client: reading failed");
        }
        System.out.println("Client: reading fished");



        System.out.println("Clientrver: is finishing");
        try {
            br.close();
            bw.close();
            skt.close();
        } catch (IOException e) {
            System.out.println("Client: finishing failed");
        }
        System.out.println("Client: done");
    }
}


public class Main {


    public static void main(String[] args) {
        System.out.println("Main started");
        Thread sThread = new Thread(new sevr());
        Thread cThread = new Thread(new clnt());
        sThread.start();
        cThread.start();
        try {
            sThread.join();
            cThread.join();
        } catch (InterruptedException ex) {
            System.out.println("joining failed");
        }
        System.out.println("Main done");

    }

}

output:

Main started
Server: is about to create socket
Client: about to create socket
Client: socket created
Client: creating streams
Server: socket created
Server: is listening
Server: Connection Established
Server: creating streams
Server: stream done
Server: reading the request
Client: stream done
Client: requesting
Client: requesting finished
Client: reading the respond

and it waits here forever!

Answer 1

The program is using a BufferedWriter but this is not flushed (it will sit in the buffer until it is flushed, the buffer fills or closed) and there is no newline sent (the readLine will wait until you send a newline)

try

bw.write("I am the Client!!\n");
bw.flush();

Answer 2

两个线程都挂起while((line =br.readLine()) != null)

Answer 3

now it works

package sockettest;

import java.io.*;
import java.net.*;

class sevr implements Runnable{
    public void run() {
        ServerSocket sSkt = null;
        Socket skt = null;
        BufferedReader br = null;
        BufferedWriter bw = null;

        try{
            System.out.println("Server: is about to create socket");
            sSkt = new ServerSocket(6666);
            System.out.println("Server: socket created");
        }
        catch(IOException e){
            System.out.println("Server: socket creation failure");
        }
        try{
            System.out.println("Server: is listening");
            skt = sSkt.accept();
            System.out.println("Server: Connection Established");
        }
        catch(IOException e){
            System.out.println("Server: listening failed");
        }
        try{
            System.out.println("Server: creating streams");
            br = new BufferedReader(new InputStreamReader(skt.getInputStream()));
            bw = new BufferedWriter(new OutputStreamWriter(skt.getOutputStream()));
            System.out.println("Server: stream done");
        }
        catch(IOException e){
            System.out.println("Server: stream failed");
        }
        System.out.println("Server: reading the request");
        try{
            String line = null;
            line = br.readLine();
            System.out.println("Server: client said-> "+ line);
        }
        catch(IOException e){
            System.out.println("Server: reading failed");
        }
        System.out.println("Server: reading fished");

        System.out.println("Server: responding");
        try{
            bw.write("Hi! I am server!\n");
            bw.flush();
        }
        catch(IOException e){
            System.out.println("Server: responding failed");
        }
        System.out.println("Server: responding finished");

        System.out.println("Server: is finishing");
        try {
            br.close();
            bw.close();
            skt.close();
            sSkt.close();
        } catch (IOException e) {
            System.out.println("Server: finishing failed");
        }
        System.out.println("Server: done");
    }
}

class clnt implements Runnable{
    public void run() {
        Socket skt = null;
        BufferedReader br = null;
        BufferedWriter bw = null;

        try{
            System.out.println("Client: about to create socket");
            skt = new Socket(InetAddress.getLocalHost(),6666);
            System.out.println("Client: socket created");
        }
        catch(IOException e){
            System.out.println("Client: socket creation failure");
        }

        try{
            System.out.println("Client: creating streams");
            br = new BufferedReader(new InputStreamReader(skt.getInputStream()));
            bw = new BufferedWriter(new OutputStreamWriter(skt.getOutputStream()));
            System.out.println("Client: stream done");
        }
        catch(IOException e){
            System.out.println("Client: stream failed");
        }
        System.out.println("Client: requesting");
        try{
            bw.write("Hi! I am Client!\n");
            bw.flush();
        }
        catch(IOException e){
            System.out.println("Client: requesting failed");
        }
        System.out.println("Client: requesting finished");
        System.out.println("Client: reading the respond");
        try{
            String line = null;
            line =br.readLine();
            System.out.println("Client: server said-> "+ line);
        }
        catch(IOException e){
            System.out.println("Client: reading failed");
        }
        System.out.println("Client: reading fished");



        System.out.println("Client: is finishing");
        try {
            br.close();
            bw.close();
            skt.close();
        } catch (IOException e) {
            System.out.println("Client: finishing failed");
        }
        System.out.println("Client: done");
    }
}


public class Main {


    public static void main(String[] args) {
        System.out.println("Main started");
        Thread sThread = new Thread(new sevr());
        Thread cThread = new Thread(new clnt());
        sThread.start();
        cThread.start();
        try {
            sThread.join();
            cThread.join();
        } catch (InterruptedException ex) {
            System.out.println("joining failed");
        }
        System.out.println("Main done");

    }

}

output:

Main started
Server: is about to create socket
Client: about to create socket
Client: socket created
Client: creating streams
Server: socket created
Server: is listening
Server: Connection Established
Server: creating streams
Client: stream done
Server: stream done
Server: reading the request
Client: requesting
Client: requesting finished
Client: reading the respond
Server: client said-> Hi! I am Client!
Server: reading fished
Server: responding
Server: responding finished
Server: is finishing
Client: server said-> Hi! I am server!
Client: reading fished
Client: is finishing
Client: done
Server: done
Main done