HeadFirstJava学习心得——网络编程

编写简单的服务器应用程序

编写服务器应用程序需要用到一对Socket。他们是一个会等待用户请求（当用户创建Socket是）的ServerSocket和与用户进行通信用的Socket。

工作方式：

1. 服务器应用程序对特定端口创建出ServerSocket。

ServerSocket serverSocket = new ServerSocket(8080);

2. 客户端对服务器应用程序建立Socket连接。

Socket socket = new Socket("127.0.0.1", 8080);

3. 服务器创建出与客户端通信的新的Socket。

Socket socket = serverSocket.accept();

下面是一个简单的聊天室应用程序（这个版本只完成了客户端向服务端发送数据）

服务端：

import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import java.io.PrintWriter;import java.net.ServerSocket;import java.net.Socket;import java.util.Random;public class DailyAdviceServer {String[] adviceList = { "愿得一人心，白首不相离。", "天长地久有时尽，此恨绵绵无绝期。","东边日出西边雨，道是无晴却有晴。", "曾经沧海难为水，除却巫山不是云。", "两情若是久长时，又岂在朝朝暮暮。","庄生晓梦迷蝴蝶，望帝春心托杜鹃。" };public static void main(String[] args) {new DailyAdviceServer().go();}private void go() {try {ServerSocket serverSocket = new ServerSocket(8888);// ServerSocket会监听客户端对这台机器在8888端口上的请求System.out.println("服务器启动。。。");/* 服务器进入无限循环监听客户端请求 */while (true) {Socket socket = serverSocket.accept();// 该方法会停下来，直到满足要求才会继续/* 向客户端发送数据 */PrintWriter printWriter = new PrintWriter(socket.getOutputStream());// 使用Socket连接来送出真言信息String advice = getAdvice();printWriter.println(advice);System.out.println("欢迎信息：" + advice);/* 接收客户端数据 */BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));String info = null;while ((info = bufferedReader.readLine()) != null) {System.out.println("客户端数据：" + info);}}} catch (IOException e) {System.out.println("服务器错误！");System.exit(-1);}}private String getAdvice() {return adviceList[new Random().nextInt(adviceList.length)]; // 随即返回字符串数组中的一首诗}}

客户端：

import java.awt.BorderLayout;import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import java.io.IOException;import java.io.PrintWriter;import java.net.InetAddress;import java.net.Socket;import java.net.UnknownHostException;import javax.swing.JButton;import javax.swing.JFrame;import javax.swing.JPanel;import javax.swing.JTextField;public class SimpleClient {private PrintWriter printWriter;private JTextField textField;public static void main(String[] args) {new SimpleClient().go();}private void go() {/* 图形用户界面的绘制 */JFrame frame = new JFrame("一个简单的客户端程序");JPanel panel = new JPanel();textField = new JTextField("请输入需要发送的信息");JButton button = new JButton("发送");button.addActionListener(new ActionListener() {@Overridepublic void actionPerformed(ActionEvent e) {printWriter.println(textField.getText());printWriter.flush();textField.setText(""); // 每次发送之后清空输入textField.requestFocus();//请求焦点}});panel.add(textField);panel.add(button);frame.getContentPane().add(panel, BorderLayout.CENTER);frame.setVisible(true);frame.pack();frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);setUpNetwork();}private void setUpNetwork() {try {Socket socket = new Socket(InetAddress.getLocalHost(), 8888);printWriter = new PrintWriter(socket.getOutputStream());System.out.println("连接已建立！");} catch (UnknownHostException e) {e.printStackTrace();} catch (IOException e) {e.printStackTrace();}}}

运行结果：

以上代码有一个很明显的bug，即服务端只能接收一个客户端的输入。可以引入线程来解决。

更好的版本：

服务器：

import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import java.io.PrintWriter;import java.net.ServerSocket;import java.net.Socket;import java.util.ArrayList;import java.util.Iterator;public class VerySimpleChatServer {    ArrayList clientOutputStreams;    public class ClientHandler implements Runnable {BufferedReader bufferedReader;Socket socket;public ClientHandler(Socket socket) {    this.socket = socket;    try {bufferedReader = new BufferedReader(new InputStreamReader(socket.getInputStream()));    } catch (IOException e) {e.printStackTrace();    }}@Overridepublic void run() {    String message;    try {while ((message = bufferedReader.readLine()) != null) {    System.out.println("客户端发送数据：" + message);    tellEveryone(message);}    } catch (IOException e) {e.printStackTrace();    }}    }    public static void main(String[] args) {new VerySimpleChatServer().go();    }    private void go() {clientOutputStreams = new ArrayList();try {    ServerSocket serverSocket = new ServerSocket(8888);    while (true) {Socket clientSocket = serverSocket.accept();PrintWriter printWriter = new PrintWriter(clientSocket.getOutputStream());clientOutputStreams.add(printWriter);Thread t = new Thread(new ClientHandler(clientSocket));t.start();System.out.println("已连接。。");    }} catch (IOException e) {    e.printStackTrace();}    }    private void tellEveryone(String message) {Iterator iterator = clientOutputStreams.iterator();while (iterator.hasNext()) {    PrintWriter printWriter = (PrintWriter) iterator.next();    printWriter.println(message);    printWriter.flush();}    }}

客户端：

import java.awt.event.ActionEvent;import java.awt.event.ActionListener;import java.io.BufferedReader;import java.io.IOException;import java.io.InputStreamReader;import java.io.PrintWriter;import java.net.InetAddress;import java.net.Socket;import java.net.UnknownHostException;import javax.swing.JButton;import javax.swing.JFrame;import javax.swing.JLabel;import javax.swing.JPanel;import javax.swing.JScrollPane;import javax.swing.JTextArea;import javax.swing.JTextField;import javax.swing.ScrollPaneConstants;public class SimpleChatClient {    JTextField out;    PrintWriter printWriter;    JTextArea in;    public BufferedReader bufferedReader;    public static void main(String[] args) {new SimpleChatClient().go();    }    private void go() {/* 界面和事件 */JFrame frame = new JFrame("聊天室-客户端");JPanel panel = new JPanel();in = new JTextArea(10, 50);in.setLineWrap(true);in.setWrapStyleWord(true); // 单词空白处换行in.setEditable(false);JScrollPane scrollPane = new JScrollPane(in);scrollPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);scrollPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);out = new JTextField("请输入你要发送的信息！", 50);JButton button = new JButton("发送");button.addActionListener(new ActionListener() {    @Override    public void actionPerformed(ActionEvent e) {printWriter.println(out.getText());printWriter.flush(); // 这个是必须要有的out.setText("");out.requestFocus();    }});panel.add(out);panel.add(button);panel.add(new JLabel("服务器端信息："));panel.add(scrollPane);setUpNetWork();/* 启动新的线程，以内部类作为任务，此任务是读取服务端的socket串流，显示在文本域 */Thread readerThread = new Thread(new IncomingReader());readerThread.start();frame.getContentPane().add(panel);frame.setVisible(true);frame.pack();frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);    }    private void setUpNetWork() {Socket socket;try {    socket = new Socket(InetAddress.getLocalHost(), 8888);    bufferedReader = new BufferedReader(new InputStreamReader(    socket.getInputStream()));    printWriter = new PrintWriter(socket.getOutputStream());    System.out.println("建立连接。。。");} catch (UnknownHostException e) {    e.printStackTrace();} catch (IOException e) {    e.printStackTrace();}    }    public class IncomingReader implements Runnable {@Overridepublic void run() {    String message;    try {while ((message = bufferedReader.readLine()) != null) {    System.out.println("服务器信息：" + message);    in.append(message + "\n");}    } catch (IOException e) {e.printStackTrace();    }}    }}

运行结果：

基于UDP的聊天室的实现。

对于UDP编程，java提供了2个类给予支持。他们分别是DatagramSocket和DatagramPacket。UDP是面向无连接的，发送端和接收端哪个先启动并没有区别。在发送端在构造DatagramPacket（数据包）的时候需要为其指定目的主机和目标端口。在接收方我们只需要在初始化DatagramSocket的时候指定监听端口（发送端需要发送的端口）即可。然后通过此DatagramSocket的receive方法取得数据包，用数据包中的getData方法取得内容。

发送端Send.java

public class Send implements Runnable {DatagramSocket ds;int descport;public Send(DatagramSocket ds, int descport) {System.out.println("发送端已经启动。。。。。。。。。。。。。。。");this.ds = ds;this.descport = descport;}@SuppressWarnings("resource")@Overridepublic void run() {while (true) {System.out.println("请输入要发送的数据：");Scanner scanner = new Scanner(System.in);try {while (scanner.hasNext()) {System.out.println("请输入要发送的数据：");String line = scanner.nextLine();byte[] buf = line.getBytes();DatagramPacket dp = new DatagramPacket(buf, buf.length,InetAddress.getLocalHost(), descport); // 数据报的终点是127.0.0.1:8888ds.send(dp);if ("quit".equals(line))return;scanner = new Scanner(System.in);}} catch (IOException e) {throw new RuntimeException("发送失败！");}}}public static void main(String[] args) throws SocketException {// 对于发送方来说，从哪个端口发出数据报并不重要，重要的是数据报要发送到哪里new Thread(new Send(new DatagramSocket(1111), 8888)).start(); // 发送端127.0.0.1:1111，目的127.0.0.1:8888}}

接收端Receive.java

public class Receive implements Runnable {DatagramSocket ds;public Receive(DatagramSocket ds) {System.out.println("接收端已经启动。。。。。。。。。。。。。");this.ds = ds;}@Overridepublic void run() {while (true) {byte[] buf = new byte[1024];DatagramPacket dp = new DatagramPacket(buf, buf.length);try {ds.receive(dp);String data = new String(dp.getData(), 0, dp.getLength());if ("quit".equals(data)) {return;}System.out.println("收到来自：" + dp.getSocketAddress() + "的数据："+ data);} catch (IOException e) {throw new RuntimeException("接收失败！");}}}public static void main(String[] args) throws SocketException {// 对于接收端来说，只需要绑定接收端口即可，不需要关系数据的来源new Thread(new Receive(new DatagramSocket(8888))).start(); // 接收端在127.0.0.1:8888端口监听}}