Socket 中 Inputstream 客户端阻塞问题

清疚 2023-10-05 21:35 22阅读 0赞

##  Socket 中 Inputstream 客户端阻塞问题 ##

## 场景 ##

今天看小伙伴的问题，原本是`TCP`请求后数据只返回了一半，第二次请求返回另一半，本地写了`TCP` 服务端与客户端后发现模拟场景，通过后给了小伙伴代码，但是发现客户端会阻塞，几经查找终于解决。

### 返回一半数据，第二次请求返回另一半 ###

小伙伴代码

Socket client = new Socket(host, port);
                new Thread(() -> {
        
                    OutputStream os = null;
                    InputStream is = null;
                    try {
        
                        while (!stopFlag) {
        
                            os = client.getOutputStream();
                            is = client.getInputStream();
                            if (request == null) {
        
                                continue;
                            }
                            os.write(request);
                            int capacity = 1024*32; //TODO 优化
                            byte[] buf = new byte[capacity];
                            int len = is.read(buf);
                            byte[] bytes = new byte[len];
                            System.arraycopy(buf, 0, bytes, 0, len);
                            response = bytes;
                            request = null;
                        }
                    } catch (IOException e) {
        
                        log.error("与服务端数据交互异常", e);
                    } finally {
        
                    // 关闭流等
                    }
                }).start();

修改后

Socket client = new Socket(host, port);
                new Thread(() -> {
        
                    OutputStream os = null;
                    InputStream is = null;
                    try {
        
                        while (!stopFlag) {
        
                            os = client.getOutputStream();
                            is = client.getInputStream();
                            if (request == null) {
        
                                continue;
                            }
                            os.write(request);
                            byte[] buffer = new byte[1024];
                            int len = 0;
                            ByteArrayOutputStream bos = new ByteArrayOutputStream();
                            while((len = is.read(buffer)) != -1) {
        
                                bos.write(buffer, 0, len);
                            }
                            bos.close();
                            response = bytes;
                            request = null;
                        }
                    } catch (IOException e) {
        
                        log.error("与服务端数据交互异常", e);
                    } finally {
        
                    // 关闭流等
                    }
                }).start();

改完后还没有解决问题，发现代码第二次走到`is.read(buffer)`会阻塞。

### Socket 的 InputStream 阻塞问题 ###

首先自己写了测试

*  服务端代码

public class TCPService {
        
        public static final String SERVICE_IP = "127.0.0.1";
        public static final int SERVICE_PORT = 10101;
    //    public static final char END_CHAR = '#';
        public void start(){
        
            startService();
        }
        private void startService(){
        
            try {
        
                InetAddress address = InetAddress.getByName(SERVICE_IP);
                Socket connect = null;
                ExecutorService pool = Executors.newFixedThreadPool(5);
                try (ServerSocket service = new ServerSocket(SERVICE_PORT,5,address)){
        
                    while(true){
        
                        System.out.println("TCP 服务端启动成功,正在等待新的连接……");
                        connect = service.accept();
                        System.out.println("TCP 服务端接到新的请求，已安排处理……");
                        //创建一个任务
                        ServiceTask serviceTask = new ServiceTask(connect);
                        //放入线程池等待运行
                        pool.execute(serviceTask);
                    }
                }catch (Exception e){
        
                    e.printStackTrace();
                }finally {
        
                    if(connect!=null)
                        connect.close();
                }
            } catch (Exception e) {
        
                e.printStackTrace();
            }
        }
    
        class ServiceTask implements Runnable{
        
            private Socket socket;
            ServiceTask(Socket socket){
        
                this.socket = socket;
            }
            @Override
            public void run() {
        
                try {
        
                    InputStream in = socket.getInputStream();
                    byte[] buffer = new byte[1027];
                    int len = in.read(buffer);
                    ByteArrayOutputStream bos = new ByteArrayOutputStream();
                    while(len != -1) {
        
                        bos.write(buffer, 0, len);
                        len = in.read(buffer);
                    }
                    bos.close();
                    System.out.println("请求信息为：" + bos );
                    System.out.println("\r\n");
                    String response = "终于等到你了，有缘人…………，你的输入是：" + bos ;
                    OutputStream out = socket.getOutputStream();
                    out.write(response.getBytes());
                }catch (Exception e){
        
                    e.printStackTrace();
                }finally {
        
                    if(socket!=null)
                        try {
        
                            socket.close();
                        } catch (IOException e) {
        
                            e.printStackTrace();
                        }
                }
            }
        }
    }

*  客户端代码

public class TCPClient {
        
        public String sendAndReceive(String ip, int port, String msg){
        
            //开启一个链接，需要指定地址和端口
            ByteArrayOutputStream bos = new ByteArrayOutputStream();
            try (Socket client = new Socket(ip, port)){
        
                //向输出流中写入数据，传向服务端
                OutputStream out = client.getOutputStream();
                out.write(msg.getBytes());
                // 关闭 输出，防止服务端继续等待
                client.shutdownOutput();
    
                //从输入流中解析数据，输入流来自服务端的响应
                InputStream in = client.getInputStream();
                byte[] buffer = new byte[1024];
                int len = 0;
                while((len = in.read(buffer)) != -1) {
        
                    bos.write(buffer, 0, len);
                }
                bos.close();
            }catch (Exception e){
        
                e.printStackTrace();
            }
            return bos.toString();
        }
    }

*  服务端测试代码

public class TestTcpService {
        
        public static void main(String[] args) {
        
            TCPService service1 = new TCPService();
            service1.start();
        }
    }

*  客户端测试代码

public class TestTcpClient {
        
        public static void main(String[] args) {
        
            TCPClient client = new TCPClient();
            SimpleDateFormat format = new SimpleDateFormat("hh-MM-ss");
            Scanner scanner = new Scanner(System.in);
    
            while (true){
        
                String msg = scanner.nextLine();
                //打印响应的数据
                System.out.println("send time : " + format.format(new Date()));
                System.out.println(client.sendAndReceive(TCPService.SERVICE_IP, TCPService.SERVICE_PORT,msg));
                System.out.println("receive time : " + format.format(new Date()));
            }
        }
    }

### 解决方案 ###

在socket 服务端发送完数据后，使用 `client.shutdownOutput();` 关闭输出。使得客户端知道服务端发送数据完成了。如 客户端代码中就加了句代码，如不添加则会使服务端获取客户端请求的地方阻塞。

**shutdownOutput()** 记得使用！！！

### 参考文章 ###

*  [HTTP 和 Socket 的区别 - 大雷同学 - 博客园 (cnblogs.com)][HTTP _ Socket _ - _ - _ _cnblogs.com]
 *  [网络通信基础（一）——HTTP（TCP/IP）通信协议\_Lenjor 的博客-CSDN博客][HTTP_TCP_IP_Lenjor _-CSDN]
 *  [ByteBuffer 到底怎么用？网络编程中一点总结！ - Java小强技术博客 (javacui.com)][ByteBuffer _ - Java_ _javacui.com]
 *  [java InputStream读取数据问题 - Java小强技术博客 (javacui.com)][java InputStream_ - Java_ _javacui.com]
 *  [Java socket详解,看这一篇就够了 - 简书 (jianshu.com)][Java socket_ - _ _jianshu.com]

[HTTP _ Socket _ - _ - _ _cnblogs.com]: https://www.cnblogs.com/zhuleixiao/p/9218121.html
[HTTP_TCP_IP_Lenjor _-CSDN]: https://blog.csdn.net/weixin_29053561/article/details/103944787
[ByteBuffer _ - Java_ _javacui.com]: http://www.javacui.com/java/29.html
[java InputStream_ - Java_ _javacui.com]: http://www.javacui.com/netcode/30.html
[Java socket_ - _ _jianshu.com]: https://www.jianshu.com/p/cde27461c226