Java网络编程-Socket编程初涉一（简易客户端-服务器）

偏执的太偏执、 2023-07-03 06:03 140阅读 0赞

推荐：[Java网络编程汇总][Java]

## Java网络编程-Socket编程初涉一（简易客户端-服务器） ##

**服务器**

服务器的socket程序有以下几个任务：

*  创建ServerSocket。
 *  绑定端口。
 *  监听端口。
 *  阻塞，等待客户端连接。
 *  与客户端连接成功后，可以数据交互。

[Java网络编程-Socket简介][Java_-Socket]  
服务器socket程序：

package socket;
    
    import java.io.*;
    import java.net.ServerSocket;
    import java.net.Socket;
    
    public class Server { 
        public static void main(String[] args) { 
    
            final String QUIT = "QUIT";
            final int DEFAULT_PORT = 8888;
            ServerSocket serverSocket = null;
    
            try { 
                // 绑定监听端口
                serverSocket = new ServerSocket(DEFAULT_PORT);
                System.out.println("启动服务器，监听端口"+DEFAULT_PORT);
                while(true){ 
                    //等待客户端连接
                    Socket socket = serverSocket.accept();
                    System.out.println("客户端["+socket.getPort()+"]已连接");
                    BufferedReader reader = new BufferedReader(
                            new InputStreamReader(socket.getInputStream()));
    
                    BufferedWriter writer = new BufferedWriter(
                            new OutputStreamWriter(socket.getOutputStream()));
    
                    String msg = null;
                    //读取客户端发送的消息，并且进行回复
                    while ((msg = reader.readLine()) != null){ 
                        System.out.println("客户端["+socket.getPort()+"]:"+msg);
    
                        //回复客户端
                        writer.write("服务器：已收到-"+msg+"\n");
                        writer.flush();
    
                        // 查看客户端是否退出
                        if(QUIT.equalsIgnoreCase(msg)){ 
                            System.out.println("客户端["+socket.getPort()+"]已退出");
                            break;
                        }
                    }
                }
            } catch (IOException e) { 
                e.printStackTrace();
            } finally { 
                if(serverSocket != null){ 
                    try { 
                        serverSocket.close();
                        System.out.println("关闭serverSocket");
                    } catch (IOException e) { 
                        e.printStackTrace();
                    }
                }
            }
        }
    }

**创建socket、绑定端口、监听端口**

创建ServerSocket、绑定端口、监听端口其实在我们的程序中，一行语句就实现了。

serverSocket = new ServerSocket(DEFAULT_PORT);

按住CTRL，进入该构造器。  
源码如下：

public ServerSocket(int port) throws IOException { 
            this(port, 50, null);
        }

进入再次调用的构造器。  
源码如下：

public ServerSocket(int port, int backlog, InetAddress bindAddr) throws IOException { 
            setImpl();
            if (port < 0 || port > 0xFFFF)
                throw new IllegalArgumentException(
                           "Port value out of range: " + port);
            if (backlog < 1)
              backlog = 50;
            try { 
                bind(new InetSocketAddress(bindAddr, port), backlog);
            } catch(SecurityException e) { 
                close();
                throw e;
            } catch(IOException e) { 
                close();
                throw e;
            }
        }

进入`bind方法`。  
源码如下:

public void bind(SocketAddress endpoint, int backlog) throws IOException { 
            if (isClosed())
                throw new SocketException("Socket is closed");
            if (!oldImpl && isBound())
                throw new SocketException("Already bound");
            if (endpoint == null)
                endpoint = new InetSocketAddress(0);
            if (!(endpoint instanceof InetSocketAddress))
                throw new IllegalArgumentException("Unsupported address type");
            InetSocketAddress epoint = (InetSocketAddress) endpoint;
            if (epoint.isUnresolved())
                throw new SocketException("Unresolved address");
            if (backlog < 1)
              backlog = 50;
            try { 
                SecurityManager security = System.getSecurityManager();
                if (security != null)
                    security.checkListen(epoint.getPort());
                getImpl().bind(epoint.getAddress(), epoint.getPort());
                getImpl().listen(backlog);
                bound = true;
            } catch(SecurityException e) { 
                bound = false;
                throw e;
            } catch(IOException e) { 
                bound = false;
                throw e;
            }
        }

其中有两行语句如下：

getImpl().bind(epoint.getAddress(), epoint.getPort());
    getImpl().listen(backlog);

很清楚了吧，程序调用了ServerSocket的构造器，创建了ServerSocket。  
而该构造器间接实现了绑定端口、监听端口（上面两行语句）。

**阻塞，等待客户端连接**

Socket socket = serverSocket.accept();

可以自己去看看源码。  
有客户端连接成功后，会生成一个socket。

BufferedReader reader = new BufferedReader(
                            new InputStreamReader(socket.getInputStream()));
    
    BufferedWriter writer = new BufferedWriter(
                            new OutputStreamWriter(socket.getOutputStream()));

获取向客户端读、写的字符流。  
[Java IO体系的学习总结][Java IO]

String msg = null;
                    //读取客户端发送的消息，并且进行回复
                    while ((msg = reader.readLine()) != null){ 
                        System.out.println("客户端["+socket.getPort()+"]:"+msg);
    
                        //回复客户端
                        writer.write("服务器：已收到-"+msg+"\n");
                        writer.flush();
    
                        // 查看客户端是否退出
                        if(QUIT.equalsIgnoreCase(msg)){ 
                            System.out.println("客户端["+socket.getPort()+"]已退出");
                            break;
                        }
                    }

上面是服务器读取客户端发送的消息的代码，一行一行的读取消息，并且只有当客户端发送`“quit”`给服务器时，才表示此客户端要退出，并且在这个过程中其他客户端是不能与服务器进行连接的，因为服务器一直在`while`里面读取此客户端发送的数据，不过，这只是一个体验版，以后会一步一步进行升级的，毕竟学习也是一步一步学出来的。

**关闭资源**

先不用纠结关闭资源的正确姿势，这是课程中讲师关闭资源的方法，等基础比较好以后，我会自己去实践一下，再进行总结，之后也会去阅读源码，写相关博客，现在的任务就是把整个流程搞明白即可，不去纠结细节，一层一层来揭开Java网络编程的面纱。

serverSocket.close();

**客户端**

客户端的socket程序有以下几个任务：

*  创建Socket。
 *  连接服务器。
 *  与服务器连接成功后，可以数据交互。

客户端socket程序：

package socket;
    
    import java.io.*;
    import java.net.Socket;
    
    public class Client { 
        public static void main(String[] args){ 
    
            final String QUIT = "QUIT";
            final String DEFAULT_SERVER_HOST = "127.0.0.1";
            final int DEFAULT_PORT = 8888;
            Socket socket = null;
            BufferedWriter writer = null;
    
            try { 
                //创建socket
                socket = new Socket(DEFAULT_SERVER_HOST , DEFAULT_PORT);
    
                //创建IO流
                BufferedReader reader = new BufferedReader(
                        new InputStreamReader(socket.getInputStream()));
    
                writer = new BufferedWriter(
                        new OutputStreamWriter(socket.getOutputStream()));
    
                //等待用户输入信息
                BufferedReader consoleReader = new BufferedReader(
                        new InputStreamReader(System.in));
    
                while (true){ 
                    String input = consoleReader.readLine();
    
                    //发送消息给服务器
                    writer.write(input+"\n");
                    writer.flush();
    
                    //读取服务器返回的消息
                    String msg = reader.readLine();
                    System.out.println(msg);
    
                    // 查看用户是否退出
                    if (QUIT.equalsIgnoreCase(input)){ 
                        break;
                    }
                }
            } catch (IOException e) { 
                e.printStackTrace();
            } finally { 
                if(writer != null){ 
                    try { 
                        writer.close(); // 会自动flush()
                        System.out.println("关闭socket");
                    } catch (IOException e) { 
                        e.printStackTrace();
                    }
                }
            }
        }
    }

**创建Socket、连接服务器**

socket = new Socket(DEFAULT_SERVER_HOST , DEFAULT_PORT);

进入构造器。  
源码如下：

/** * Creates a stream socket and connects it to the specified port * number on the named host. * <p> * If the specified host is {@code null} it is the equivalent of * specifying the address as * {@link java.net.InetAddress#getByName InetAddress.getByName}{@code (null)}. * In other words, it is equivalent to specifying an address of the * loopback interface. </p> * <p> * If the application has specified a server socket factory, that * factory's {@code createSocketImpl} method is called to create * the actual socket implementation. Otherwise a "plain" socket is created. * <p> * If there is a security manager, its * {@code checkConnect} method is called * with the host address and {@code port} * as its arguments. This could result in a SecurityException. * * @param host the host name, or {@code null} for the loopback address. * @param port the port number. * * @exception UnknownHostException if the IP address of * the host could not be determined. * * @exception IOException if an I/O error occurs when creating the socket. * @exception SecurityException if a security manager exists and its * {@code checkConnect} method doesn't allow the operation. * @exception IllegalArgumentException if the port parameter is outside * the specified range of valid port values, which is between * 0 and 65535, inclusive. * @see java.net.Socket#setSocketImplFactory(java.net.SocketImplFactory) * @see java.net.SocketImpl * @see java.net.SocketImplFactory#createSocketImpl() * @see SecurityManager#checkConnect */
        public Socket(String host, int port)
            throws UnknownHostException, IOException
        { 
            this(host != null ? new InetSocketAddress(host, port) :
                 new InetSocketAddress(InetAddress.getByName(null), port),
                 (SocketAddress) null, true);
        }

先不去看细节，先看注释`Creates a stream socket and connects it to the specified port number on the named host.`。创建流套接字并将其连接到命名主机上的指定端口号。很显然，客户端调用Socket构造器，创建了Socket，并且连接了服务器（服务器已经运行的情况下）。

BufferedReader reader = new BufferedReader(
                        new InputStreamReader(socket.getInputStream()));
    
    writer = new BufferedWriter(
                        new OutputStreamWriter(socket.getOutputStream()));

获取向服务器读、写的字符流。

//等待用户输入信息
    BufferedReader consoleReader = new BufferedReader(
                        new InputStreamReader(System.in));

等待用户输入信息，并且是控制台的输入`System.in`。

while (true){ 
                    String input = consoleReader.readLine();
    
                    //发送消息给服务器
                    writer.write(input+"\n");
                    writer.flush();
    
                    //读取服务器返回的消息
                    String msg = reader.readLine();
                    System.out.println(msg);
    
                    // 查看用户是否退出
                    if (QUIT.equalsIgnoreCase(input)){ 
                        break;
                    }
                }

向服务器发送消息，并且接收服务器的回复，也是一行一行的读取。

**关闭资源**

writer.close();

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9rYXZlbi5ibG9nLmNzZG4ubmV0_size_16_color_FFFFFF_t_70]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9rYXZlbi5ibG9nLmNzZG4ubmV0_size_16_color_FFFFFF_t_70 1]  
到这里，我们便实现了一个简易客户端-服务器编写。  
大家也自己进行测试，应该是没问题的。

如果有说错的地方，请大家不吝赐教（记得留言哦~~~~）。

[Java]: https://kaven.blog.csdn.net/article/details/104140118
[Java_-Socket]: https://kaven.blog.csdn.net/article/details/104149028
[Java IO]: https://blog.csdn.net/qq_37960603/article/details/104139795
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