1、InetAddress类
java.net包中的inetAddress类是与IP地址相关的类，利用该类可以获取IP地址、主机地址等信息。InetAddress类的常用方法如下：| 方法 | 返回值 | 说明 |
| getByName(String host) | InetAddress | 获取与Host相对应的InetAddress对象 |
| getHostAddress() | String | 获取InetAddress对象所包含的IP地址 |
| getHostName() | String | 获取此IP地址的主机名 |
| getLocalHost() | InetAddress | 返回本地主机的InetAddress对象 |
注意：InetAddress类的方法会抛出UnknownHostException异常，所以必须进行异常处理。这个异常在主机不存在或网络连接错误时发生。
2、ServerSocket类
java.net包中的ServerSocket类用于表示服务器套接字，其主要功能是等待来自网络上的“请求”，它可通过制定的端口来等待连接的套接字。服务器套接字依次可以与一个套接字连接。如果多台客户机同时提出连接请求，服务器套接字会将请求连接的客户机存入队列中，然后从中取出一个套接字，与服务器新建的套接字连接起来。若请求连接数大于最大容纳数，则多出的连接请求被拒绝。队列的默认大小是50.
ServerSocket类的构造方法都抛出IOException异常，分别有以下几种形式： ServerSocket():创建非绑定服务器套接字 ServerSocket(int port):创建绑定到特定端口的服务器套接字 ServerSocket(int port, int backlog):利用指定的backlog创建服务器套接字并将其绑定到指定的本地端口号 ServerSocket(int prot, int backlog, InetAddress bindAddress):使用指定的端口、侦听backlog和要绑定到的本地IP地址创建服务器。这种情况适用于极端及上有多块网卡和多个IP地址的情况，用于可以明确规定ServerSocket在哪块网卡或IP地址上等待客户的连接请求。ServerSocket类的常用方法如下：| 方法 | 返回值 | 说 明 |
| accept() | Socket | 等待客户机的连接。若连接，则创建一套接字 |
| isBound() | boolean | 判断ServerSocket的绑定状态 |
| getInetAddress() | InetAddress | 返回此服务器套接字的本地地址 |
| isClosed() | boolean | 返回服务器套接字的关闭状态 |
| close() | void | 关闭服务器套接字 |
| bind(SocketAddress endpoint) | void | 将ServerSocket绑定到特定地址（IP地址和端口号） |
| getInetAddress() | int | 返回服务器套接字等待的端口号 |
调用ServerSocket类的accept()方法会返回一个和客户端Socket对象向连接的Socket对象，服务器的Socket对象使用getOutputStream()方法获得的输出流将指向客户端Socket对象使用getInputStream()方法获得的那个输入流；同样，服务器端的Socket对象使用getInputStream()方法获得的输入流将指向客户端Socket对象使用getOutputStream()方法获得的那个输出流。也就是说，当服务器向输出流协议信息时，客户端通过相应的输入流就能读取，反之亦然。
注意：（1）、accept()方法会阻塞线程的继续执行，知道接收到客户的呼叫。如果没有客户呼叫服务器，那么System.out.print(“连接中”)语句将不会执行。语句如果没有客户请求，accept()方法没有发生阻塞，肯定是程序出现了问题。通常是使用了一个还在被其它程序占用的端口号，ServerSoket绑定没有成功。 （2）、当一台机器上安装了多个网络应用程序时，很可能指定的端口号已被占用。还可能遇到以前运行良好的网络程序突然运行不了的情况，这种情况很可能也是由于端口被别的程序韩勇了。此时可以运行netstat -an来查看该程序锁使用的端口号是否被占用。3、相关参考例子
1 package com.lzw; 2 3 import java.io.*; 4 import java.net.*; 5 6 public class MyTcp { // 创建类MyTcp 7 private BufferedReader reader; // 创建BufferedReader对象 8 private ServerSocket server; // 创建ServerSocket对象 9 private Socket socket; // 创建Socket对象socket10 11 void getserver() {12 try {13 server = new ServerSocket(8998); // 实例化Socket对象14 System.out.println("服务器套接字已经创建成功"); // 输出信息15 while (true) { // 如果套接字是连接状态16 System.out.println("等待客户机的连接"); // 输出信息17 socket = server.accept(); // 实例化Socket对象18 reader = new BufferedReader(new InputStreamReader(socket19 .getInputStream())); // 实例化BufferedReader对象20 getClientMessage(); // 调用getClientMessage()方法21 }22 } catch (Exception e) {23 e.printStackTrace(); // 输出异常信息24 }25 }26 27 private void getClientMessage() {28 try {29 while (true) { // 如果套接字是连接状态30 if (reader.ready()) {31 // 获得客户端信息32 System.out.println("客户机:" + reader.readLine());33 }34 }35 } catch (Exception e) {36 e.printStackTrace(); // 输出异常信息37 }38 try {39 if (reader != null) {40 reader.close(); // 关闭流41 }42 if (socket != null) {43 socket.close(); // 关闭套接字44 }45 } catch (IOException e) {46 e.printStackTrace();47 }48 }49 50 public static void main(String[] args) { // 主方法51 MyTcp tcp = new MyTcp(); // 创建本类对象52 tcp.getserver(); // 调用方法53 }54 } 
1 package com.lzw; 2 3 import java.awt.*; 4 import java.awt.event.*; 5 import java.io.*; 6 import java.net.*; 7 8 import javax.swing.*; 9 import javax.swing.border.*;10 11 public class MyClien extends JFrame { // 创建类继承JFrame类12 /**13 * 14 */15 private static final long serialVersionUID = 1L;16 private PrintWriter writer; // 声明PrintWriter类对象17 Socket socket; // 声明Socket对象18 private JTextArea ta = new JTextArea(); // 创建JtextArea对象19 private JTextField tf = new JTextField(); // 创建JtextField对象20 Container cc; // 声明Container对象21 22 public MyClien(String title) { // 构造方法23 super(title); // 调用父类的构造方法24 setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);25 cc = this.getContentPane(); // 实例化对象26 27 final JScrollPane scrollPane = new JScrollPane();28 scrollPane.setBorder(new BevelBorder(BevelBorder.RAISED));29 getContentPane().add(scrollPane, BorderLayout.CENTER);30 scrollPane.setViewportView(ta);31 cc.add(tf, "South"); // 将文本框放在窗体的下部32 tf.addActionListener(new ActionListener() {33 // 绑定事件34 public void actionPerformed(ActionEvent e) {35 // 将文本框中信息写入流36 writer.println(tf.getText());37 // 将文本框中信息显示在文本域中38 ta.append(tf.getText() + '\n');39 ta.setSelectionEnd(ta.getText().length());40 tf.setText(""); // 将文本框清空41 }42 });43 }44 45 private void connect() { // 连接套接字方法46 ta.append("尝试连接\n"); // 文本域中提示信息47 try { // 捕捉异常48 socket = new Socket("127.0.0.1", 8998); // 实例化Socket对象49 writer = new PrintWriter(socket.getOutputStream(), true);50 ta.append("完成连接\n"); // 文本域中提示信息51 } catch (Exception e) {52 e.printStackTrace(); // 输出异常信息53 }54 }55 56 public static void main(String[] args) { // 主方法57 MyClien clien = new MyClien("向服务器送数据"); // 创建本例对象58 clien.setSize(200, 200); // 设置窗体大小59 clien.setVisible(true); // 将窗体显示60 clien.connect(); // 调用连接方法61 }62 } 
1 package com.lzw; 2 3 import java.net.*; 4 5 public class MyHost { 6 public static void main(String args[]) { 7 InetAddress ip = null; 8 9 try {10 ip = InetAddress.getByName("localhost");// 修改为指定的主机名称11 System.out.println("主机名：" + ip.getHostName());12 System.out.println("主机IP地址：" + ip.getHostAddress());13 System.out.println("本机IP地址："14 + InetAddress.getLocalHost().getHostAddress());15 } catch (UnknownHostException e) {16 e.printStackTrace();17 }18 19 }20 } 
1 package com.lzw; 2 3 import java.io.*; 4 import java.net.*; 5 6 /** 7 * @author Administrator 8 */ 9 public class ComputerServer {10 public static void main(String[] args) {11 try {12 ServerSocket ss = new ServerSocket(8001);13 while (!ss.isClosed()) {14 Socket s = ss.accept();15 InputStream ips = s.getInputStream();16 OutputStream ops = s.getOutputStream();17 String str = "欢迎进入程序\n2．编写TCP服务器程序，"18 + "实现创建一个在8001端口上等待的ServerSocket"19 + "对象，当接收到一个客户机的连接请求后，"20 + "程序从与客户机建立了连接的Socket对象中获得输入输出"21 + "流。通过输出流向客户机发送信息。";22 ops.write(str.getBytes());23 byte[] buf = new byte[1024];24 int len = 0;25 if (ips.available() > 0)26 len = ips.read(buf);27 System.out.println(new String(buf, 0, len));28 ips.close();29 ops.close();30 s.close();31 }32 ss.close();33 } catch (IOException e) {34 e.printStackTrace();35 }36 }37 } 1 package com.lzw; 2 3 import java.awt.*; 4 import java.awt.event.*; 5 import java.io.*; 6 import java.net.*; 7 8 import javax.swing.*; 9 10 public class TestClient extends JFrame { 11 12 /** 13 * 14 */ 15 private static final long serialVersionUID = 1L; 16 private JTextArea textArea; 17 private JTextField portField; 18 private JTextField hostField; 19 20 /** 21 * Launch the application 22 * 23 * @param args 24 */ 25 public static void main(String args[]) { 26 EventQueue.invokeLater(new Runnable() { 27 public void run() { 28 try { 29 TestClient frame = new TestClient(); 30 frame.setVisible(true); 31 } catch (Exception e) { 32 e.printStackTrace(); 33 } 34 } 35 }); 36 } 37 38 /** 39 * Create the frame 40 */ 41 public TestClient() { 42 super(); 43 setBounds(100, 100, 500, 212); 44 setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 45 46 final JPanel panel = new JPanel(); 47 panel.setLayout(new BoxLayout(panel, BoxLayout.X_AXIS)); 48 getContentPane().add(panel, BorderLayout.NORTH); 49 50 final JLabel label = new JLabel(); 51 label.setText("连接主机："); 52 panel.add(label); 53 54 hostField = new JTextField(); 55 hostField.setText("localhost"); 56 panel.add(hostField); 57 58 final JLabel label_1 = new JLabel(); 59 label_1.setText("端口："); 60 panel.add(label_1); 61 62 portField = new JTextField(); 63 portField.setText("8001"); 64 panel.add(portField); 65 66 final JButton button = new JButton(); 67 button.addActionListener(new ActionListener() { 68 public void actionPerformed(final ActionEvent e) { 69 final String hostName = hostField.getText(); 70 String portNum = portField.getText(); 71 final int port = Integer.parseInt(portNum); 72 new Thread() { 73 public void run() { 74 try { 75 final InetAddress host = InetAddress.getByName(hostName); 76 Socket socket = new Socket(host, port); 77 final InputStream is = socket.getInputStream(); 78 InputStreamReader reader=new InputStreamReader(is); 79 int data = 0; 80 while ((data=reader.read()) != -1) { 81 textArea.append((char)data+""); 82 textArea.revalidate(); 83 Thread.sleep(100); 84 } 85 } catch (Exception e1) { 86 textArea.append(e1.toString()); 87 e1.printStackTrace(); 88 } 89 } 90 }.start(); 91 92 } 93 }); 94 button.setText("连接"); 95 panel.add(button); 96 97 final JScrollPane scrollPane = new JScrollPane(); 98 getContentPane().add(scrollPane, BorderLayout.CENTER); 99 100 textArea = new JTextArea();101 textArea.setLineWrap(true);102 scrollPane.setViewportView(textArea);103 }104 } 
1 package com.lzw; 2 3 //服务器端程序 4 import java.awt.*; 5 import java.io.*; 6 import java.net.*; 7 import java.util.*; 8 import java.util.List; 9 10 import javax.swing.*; 11 12 public class TCPServer extends JFrame { 13 /** 14 * 15 */ 16 private static final long serialVersionUID = 1L; 17 private ServerSocket ss = null; 18 private boolean bStart = false; 19 20 private JTextArea taContent = new JTextArea(); 21 22 private int index = 0; 23 24 List clients = new ArrayList (); 25 26 public void launchFrame() { 27 // Container con = this.getContentPane(); 28 taContent.setEditable(false); 29 30 taContent.setBackground(Color.DARK_GRAY); 31 taContent.setForeground(Color.YELLOW); 32 this.add(taContent); 33 this.setSize(300, 350); 34 this.setLocation(400, 200); 35 this.setTitle("TCP Server"); 36 this.setVisible(true); 37 this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 38 tcpMonitor(); 39 } 40 41 public void tcpMonitor() { 42 try { 43 ss = new ServerSocket(8888); 44 bStart = true; 45 } catch (IOException e) { 46 47 e.printStackTrace(); 48 } 49 50 try { 51 while (bStart) { 52 index++; 53 Socket s = ss.accept(); 54 Client c = new Client(s); 55 clients.add(c); 56 57 taContent.append(s.getInetAddress().getHostAddress() 58 + " connected " + index + " clients\n"); 59 new Thread(c).start(); 60 61 } 62 } catch (IOException e) { 63 e.printStackTrace(); 64 } finally { 65 try { 66 ss.close(); 67 } catch (IOException e) { 68 69 e.printStackTrace(); 70 } 71 } 72 73 } 74 75 public static void main(String args[]) { 76 TCPServer ts = new TCPServer(); 77 ts.launchFrame(); 78 } 79 80 private class Client implements Runnable { 81 DataInputStream dis = null; 82 DataOutputStream dos = null; 83 84 Socket s = null; 85 boolean bStart = false; 86 87 Client(Socket s) { 88 this.s = s; 89 try { 90 dis = new DataInputStream(s.getInputStream()); 91 dos = new DataOutputStream(s.getOutputStream()); 92 } catch (IOException e) { 93 e.printStackTrace(); 94 } 95 96 bStart = true; 97 } 98 99 public void sendToEveryClient(String str) {100 try {101 dos.writeUTF(str);102 dos.flush();103 104 } catch (IOException e) {105 index--;106 clients.remove(this);107 taContent.append(s.getInetAddress().getHostAddress()108 + " exited " + index + " clients\n");109 System.out.println("对方退出了！我从List里面去掉了！");110 }111 }112 113 public void run() {114 try {115 while (bStart) {116 String str = dis.readUTF();117 System.out.println(str);118 for (int i = 0; i < clients.size(); i++) {119 Client c = clients.get(i);120 c.sendToEveryClient(str);121 }122 }123 } catch (EOFException e) {124 clients.remove(this);125 taContent.append(s.getInetAddress().getHostAddress()126 + " exited " + clients.size() + " clients\n");127 System.out.println("client closed");128 } catch (SocketException e) {129 System.out.println("client closed");130 } catch (IOException e) {131 e.printStackTrace();132 } finally {133 try {134 if (s != null)135 s.close();136 if (dis != null)137 dis.close();138 if (dos != null)139 dos.close();140 } catch (IOException e) {141 e.printStackTrace();142 }143 }144 }145 146 }147 148 } 
1 package com.lzw; 2 3 import java.awt.*; 4 import java.awt.event.*; 5 import java.io.*; 6 import java.net.*; 7 8 import javax.swing.*; 9 10 public class TCPClient extends JFrame { 11 /** 12 * 13 */ 14 private static final long serialVersionUID = 1L; 15 TextArea taContent = new TextArea(); 16 JTextField tfTxt = new JTextField(20); 17 18 JButton send = new JButton("发送"); 19 JButton connect = new JButton("连接"); 20 JButton clear = new JButton("清空"); 21 22 boolean live = false; 23 JPanel p1 = new JPanel(); 24 JPanel p2 = new JPanel(); 25 26 Socket s = null; 27 DataOutputStream dos = null; 28 DataInputStream dis = null; 29 30 boolean bConnected = false; 31 32 Thread t = new Thread(new RecToServer()); 33 34 public void launchFrame() { 35 36 taContent.setEditable(false); 37 38 p2.setLayout(new FlowLayout(FlowLayout.CENTER, 10, 5)); 39 p2.add(send); 40 p2.add(connect); 41 p2.add(clear); 42 43 Container con = this.getContentPane(); 44 45 con.add(taContent, "North"); 46 con.add(tfTxt, "Center"); 47 con.add(p2, "South"); 48 49 this.setSize(300, 350); 50 this.setLocation(400, 200); 51 this.setTitle("Chat Client"); 52 53 this.setVisible(true); 54 this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); 55 56 connect.addActionListener(new Connect()); 57 send.addActionListener(new SendMsg()); 58 clear.addActionListener(new ActionListener() { 59 public void actionPerformed(ActionEvent e) { 60 taContent.setText(""); 61 } 62 }); 63 } 64 65 public void connectToServer() { 66 try { 67 68 s = new Socket("127.0.0.1", 8888); 69 dos = new DataOutputStream(s.getOutputStream()); 70 dis = new DataInputStream(s.getInputStream()); 71 72 bConnected = true; 73 74 } catch (BindException e) { 75 System.out.println("找不到指定的服务器"); 76 } catch (UnknownHostException e) { 77 // TODO Auto-generated catch block 78 e.printStackTrace(); 79 } catch (IOException e) { 80 // TODO Auto-generated catch block 81 e.printStackTrace(); 82 } 83 84 } 85 86 public void disConnect() { 87 try { 88 if (s != null) { 89 s.close(); 90 } 91 92 if (dos != null) { 93 dos.close(); 94 } 95 if (dis != null) { 96 dis.close(); 97 } 98 } catch (IOException e) { 99 e.printStackTrace();100 }101 }102 103 public static void main(String args[]) {104 TCPClient tc = new TCPClient();105 tc.launchFrame();106 }107 108 private class Connect implements ActionListener {109 public void actionPerformed(ActionEvent e) {110 if (e.getActionCommand() == "连接") {111 112 connectToServer();113 try {114 t.start();115 } catch (IllegalThreadStateException ex) {116 117 }118 119 connect.setText("断开连接");120 121 } else if (e.getActionCommand() == "断开连接") {122 disConnect();123 connect.setText("连接");124 }125 126 }127 }128 129 private class SendMsg implements ActionListener {130 public void actionPerformed(ActionEvent e) {131 if (connect.getActionCommand() == "连接") {132 JOptionPane.showMessageDialog(TCPClient.this,133 "没有找到指定的服务器", "错误提示", 1);134 } else {135 String str = tfTxt.getText();136 tfTxt.setText("");137 138 try {139 dos.writeUTF(str);140 dos.flush();141 } catch (SocketException ex) {142 System.out.println("没有找到指定的服务器");143 JOptionPane.showMessageDialog(TCPClient.this,144 "没有找到指定的服务器", "错误提示", 1);145 } catch (IOException ex) {146 ex.printStackTrace();147 }148 }149 150 }151 }152 153 private class RecToServer implements Runnable {154 public void run() {155 try {156 while (bConnected) {157 String str = dis.readUTF();158 // System.out.println(str);159 160 taContent.append(str + "\n");161 }162 } catch (SocketException e) {163 System.out.println("服务器已关闭");164 } catch (IOException e) {165 e.printStackTrace();166 }167 }168 }169 } 