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+"\n");
}
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。