• Java 网络编程 字符流的发送与接收 自定义数据边界


    在网络编程中,客户端调用了flush方法,就会将缓存在字符流中的文本发送给服务器,服务器该怎样判断客户端发送的文本已经结束了呢?

    我们先看一个例子:

    客户端:

    import java.io.IOException;
    import java.io.PrintWriter;
    import java.net.InetSocketAddress;
    import java.net.Socket;
    import java.util.Scanner;
    
    /**
     * Created by 290248126 on 14-5-9.
     */
    public class Client {
        public static void main(String[] args) throws IOException, InterruptedException {
            Socket socket = new Socket();
            socket.connect(new InetSocketAddress("localhost", 8088), 1000);
            socket.setSoTimeout(5000);
    
            PrintWriter printWriter = new PrintWriter(socket.getOutputStream());
            //键盘输入流
            Scanner keyboardScanner = new Scanner(System.in);
    
            while (keyboardScanner.hasNextLine()) {
                String line = keyboardScanner.nextLine();
                System.out.println("你输入:" + line);
                if ("ok".equals(line)) {//当客户端输入ok,代表客户要发送的信息已经完毕
                    break;
                }
                //这里只是写到printWriter的缓存去,兵们有真实的发送到服务器端
                printWriter.println(line);
            }
            System.out.println("客户端发送...");
            printWriter.flush();
            System.out.println("刷新,发送到服务器。");
            Thread.sleep(200000);
            socket.close();
        }
    }


    服务器:

    import java.io.IOException;
    import java.net.ServerSocket;
    import java.net.Socket;
    import java.util.Scanner;
    
    /**
     * Created by 290248126 on 14-5-9.
     */
    public class Server {
        public static void main(String[] args) throws IOException, InterruptedException {
            ServerSocket serverSocket = new ServerSocket(8088);
            Socket socket = serverSocket.accept();
    
            Scanner scanner = new Scanner(socket.getInputStream());
    
            StringBuilder stringBuilder = new StringBuilder();
            //循环里面没有判断客户发送结束的边界,因此while循环一直在阻塞运行着
            //除非客户断开连接,或者客户端断开输出流,此时才返回false,才会跳出循环。
            //要想获得用户发送的所有文本信息,就要自定义一个边界来判断。
            while (scanner.hasNextLine()) {
                String line = scanner.nextLine();
                System.out.println("检测到客户端输入:"+line);
                stringBuilder.append(line);
            }
            System.out.println("循环外");
            System.out.println(stringBuilder.toString());
            Thread.sleep(200000);
        }
    }

    上面的服务器端,不会输出“循环外”,因为scanner.hasNextLine()返回false的条件是,客户端断开连接或者客户端断开输出流。

    我们下面定义一个数据边界来解决这个问题。

    服务器:

    import java.io.IOException;
    import java.net.ServerSocket;
    import java.net.Socket;
    import java.util.Scanner;
    
    /**
     * Created by 290248126 on 14-5-9.
     */
    public class Server2 {
        public static void main(String[] args) throws IOException, InterruptedException {
            ServerSocket serverSocket = new ServerSocket(8088);
            Socket socket = serverSocket.accept();
    
            Scanner scanner = new Scanner(socket.getInputStream());
    
            StringBuilder stringBuilder = new StringBuilder();
            //重点判断边界
            while (scanner.hasNextLine()) {
                String line = scanner.nextLine();
                System.out.println("检测到客户端输入:"+line);
                if("bianjie".equals(line)) {//判断是否是边界
                    System.out.println("检测到边界,客户端输入完毕");
                    break;
                }
                stringBuilder.append(line+"
    ");
            }
            System.out.println("循环外");
            System.out.println("客户端发过来:");
            System.out.println(stringBuilder.toString());
            System.out.println("——————————");
            Thread.sleep(200000);
        }
    }

    客户端:

    import java.io.IOException;
    import java.io.PrintWriter;
    import java.net.InetSocketAddress;
    import java.net.Socket;
    import java.util.Scanner;
    
    /**
     * Created by 290248126 on 14-5-9.
     */
    public class Client2 {
        public static void main(String[] args) throws IOException, InterruptedException {
            Socket socket = new Socket();
            socket.connect(new InetSocketAddress("localhost", 8088), 1000);
            socket.setSoTimeout(5000);
    
            PrintWriter printWriter = new PrintWriter(socket.getOutputStream());
            //键盘输入流
            Scanner keyboardScanner = new Scanner(System.in);
    
            while (keyboardScanner.hasNextLine()) {
                String line = keyboardScanner.nextLine();
                System.out.println("你输入:" + line);
                if ("ok".equals(line)) {//当客户端输入ok,代表客户要发送的信息已经完毕
                    printWriter.println("bianjie");//使用它作为数据边界,告知服务器我这边已经发送完毕
                    break;
                }
                //这里只是写到printWriter的缓存去,兵们有真实的发送到服务器端
                printWriter.println(line);
            }
            System.out.println("客户端发送...");
            printWriter.flush();
            System.out.println("刷新,发送到服务器。");
            Thread.sleep(200000);
            socket.close();
        }
    }

    这样,服务器就能获取客户端输入的所有内容了。

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  • 原文地址:https://www.cnblogs.com/wuyou/p/3719692.html
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