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() {

@Override
public 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();
}
}

@Override
public 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
4000
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 {

@Override
public 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")
@Override
public 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127.0.0.1:8888
ds.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;
}

@Override
public 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
}

}