Java实现网络聊天中使用的socket API与Linux socket API之间的关系

尝试着用Java编写一个网络聊天程序，发现总不如网上写的好，所以就直接引用了网上大神的优秀代码。代码如下：

 package project1;

 import java.awt.*;
 import java.awt.event.*;
 import java.io.*;
 import java.net.*;
 import java.util.ArrayList;
 import java.util.Iterator;
 import javax.swing.*;

 public class Server {
     private JFrame serverFrame;
     private JLabel portLabel;
     private JLabel sayLabel;
     private JLabel nicknameLabel;
     private JTextField portText;
     private JTextField sayText;
     private JTextField nicknameText;
     private JButton startButton;
     private JButton sayButton;
     private JButton nicknameButton;
     private JPanel jPanelNorth;
     private JPanel jPanelSouth0;
     private JPanel jPanelSouth1;
     private JPanel jPanelSouth2;
     private JScrollPane scroller;
     private JTextArea serverTextArea;
     private ArrayList<PrintWriter> clientOutputStreams;
     private String nickname;

     public static void main(String[] args) {
         Server aServer = new Server();
         aServer.startUp();
     }

     // 初始化组件
     public Server() {
         nickname = "服务器";

         serverFrame = new JFrame();
         jPanelNorth = new JPanel();
         portLabel = new JLabel("端口", JLabel.LEFT);
         portText = new JTextField(30);
         startButton = new JButton("开始");
         serverTextArea = new JTextArea();
         scroller = new JScrollPane(serverTextArea);
         nicknameLabel = new JLabel("昵称", JLabel.LEFT);
         nicknameText = new JTextField(nickname, 30);
         nicknameButton = new JButton("确认");
         jPanelSouth0 = new JPanel();
         jPanelSouth1 = new JPanel();
         jPanelSouth2 = new JPanel();
         sayLabel = new JLabel("消息", JLabel.LEFT);
         sayText = new JTextField(30);
         sayButton = new JButton("确认");
     }

     // 构建GUI
     private void buildGUI() {
         // 窗口的设置
         serverFrame.setTitle("服务器");
         serverFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         serverFrame.setSize(550, 550);

         // 北区的组件
         jPanelNorth.add(portLabel);
         jPanelNorth.add(portText);
         jPanelNorth.add(startButton);
         serverFrame.getContentPane().add(BorderLayout.NORTH, jPanelNorth);

         // 中间的组件
         serverTextArea.setFocusable(false);
         scroller.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
         scroller.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
         serverFrame.getContentPane().add(BorderLayout.CENTER, scroller);

         // 南区的组件
         jPanelSouth1.add(nicknameLabel);
         jPanelSouth1.add(nicknameText);
         jPanelSouth1.add(nicknameButton);
         jPanelSouth2.add(sayLabel);
         jPanelSouth2.add(sayText);
         jPanelSouth2.add(sayButton);
         jPanelSouth0.setLayout(new BoxLayout(jPanelSouth0, BoxLayout.Y_AXIS));
         jPanelSouth0.add(jPanelSouth1);
         jPanelSouth0.add(jPanelSouth2);
         serverFrame.getContentPane().add(BorderLayout.SOUTH, jPanelSouth0);

         // 设置窗口可见
         serverFrame.setVisible(true);
     }

     // 服务器运行
     public void startUp() {
         buildGUI();

         // 监听Start按钮，建立端口
         ActionListener startListener = new ActionListener() {
             @Override
             public void actionPerformed(ActionEvent e) {
                 clientOutputStreams = new ArrayList<PrintWriter>();
                 String aPort = portText.getText();

                 if (aPort.equals("")) {
                     JOptionPane.showMessageDialog(serverFrame, "请输入正确的端口号！");
                 } else {
                     try {
                         // 等待客户端连接的线程
                         Runnable serverRunnable = new Runnable() {
                             @Override
                             public void run() {
                                 ServerSocket serverSocket;
                                 try {
                                     serverSocket = new ServerSocket(Integer.parseInt(aPort));
                                     serverTextArea.append("正在等待客户端连接...\n");
                                     while (true) {
                                         Socket clientSocket = serverSocket.accept();
                                         serverTextArea.append("客户端已连接...\n");

                                         PrintWriter writer = new PrintWriter(clientSocket.getOutputStream());
                                         clientOutputStreams.add(writer);

                                         Thread t = new Thread(new ClientHandler(clientSocket));
                                         t.start();
                                     }
                                 } catch (NumberFormatException | IOException e) {
                                     e.printStackTrace();
                                 }
                             }
                         };
                         Thread serverThread = new Thread(serverRunnable);
                         serverThread.start();
                     } catch (Exception ex) {
                         ex.printStackTrace();
                     }
                 }
             }
         };
         startButton.addActionListener(startListener);
         portText.addActionListener(startListener);

         // 监听nickname，设置昵称
         ActionListener nicknameListener = new ActionListener() {
             @Override
             public void actionPerformed(ActionEvent e) {
                 String aText = nicknameText.getText();
                 if (!aText.equals("")) {
                     nickname = aText;
                 }
             }
         };
         nicknameButton.addActionListener(nicknameListener);
         nicknameText.addActionListener(nicknameListener);
         nicknameText.addFocusListener(new FocusListener() {
             @Override
             public void focusGained(FocusEvent e) {
             }

             @Override
             public void focusLost(FocusEvent e) {
                 String aText = nicknameText.getText();
                 if (!aText.equals("")) {
                     nickname = aText;
                 }
             }
         });

         // 监听Say按钮，发送消息
         ActionListener SayListener = new ActionListener() {
             @Override
             public void actionPerformed(ActionEvent e) {
                 String aText = sayText.getText();
                 if (!aText.equals("")) {
                     aText = nickname + "：" + aText;
                     sendToEveryClient(aText);
                     serverTextArea.append(aText + "\n");
                     sayText.setText("");
                 } else {
                     JOptionPane.showMessageDialog(serverFrame, "内容不能为空！");
                 }
             }
         };
         sayButton.addActionListener(SayListener);
         sayText.addActionListener(SayListener);
     }

     // 多客户端的线程
     public class ClientHandler implements Runnable {
         BufferedReader bReader;
         Socket aSocket;

         public ClientHandler(Socket clientSocket) {
             try {
                 aSocket = clientSocket;
                 InputStreamReader isReader = new InputStreamReader(aSocket.getInputStream());
                 bReader = new BufferedReader(isReader);
             } catch (Exception ex) {
                 ex.printStackTrace();
             }
         }

         @Override
         public void run() {
             String message;
             try {
                 while ((message = bReader.readLine()) != null) {
                     sendToEveryClient(message);
                     serverTextArea.append(message + "\n");
                 }
             } catch (Exception ex) {
                 ex.printStackTrace();
             }
         }
     }

     // 发送消息给所有客户端的方法
     private void sendToEveryClient(String message) {
         Iterator<PrintWriter> it = clientOutputStreams.iterator();
         while (it.hasNext()) {
             try {
                 PrintWriter writer = (PrintWriter) it.next();
                 writer.println(message);
                 writer.flush();
             } catch (Exception ex) {
                 ex.printStackTrace();
             }
         }
     }

 }

 package project1;

 import java.awt.*;
 import java.awt.event.*;
 import java.io.*;
 import java.net.*;

 import javax.swing.*;

 public class Client {
     private JFrame clientFrame;
     private JLabel IPLabel;
     private JLabel PortLabel;
     private JLabel sayLabel;
     private JLabel nicknameLabel;
     private JTextField IPText;
     private JTextField PortText;
     private JTextField nicknameText;
     private JTextField sayText;
     private JButton connectButton;
     private JButton nicknameButton;
     private JButton sayButton;
     private JPanel jPanelNorth;
     private JPanel jPanelSouth0;
     private JPanel jPanelSouth1;
     private JPanel jPanelSouth2;
     private JTextArea clientTextArea;
     private JScrollPane scroller;
     private BufferedReader reader;
     private PrintWriter writer;
     private String nickname;

     public static void main(String args[]) {
         Client aClient = new Client();
         aClient.startUp();
     }

     // 初始化组件
     public Client() {
         nickname = "客户端";

         clientFrame = new JFrame();
         jPanelNorth = new JPanel();
         IPLabel = new JLabel("服务器IP", JLabel.LEFT);
         IPText = new JTextField(10);
         PortLabel = new JLabel("服务器端口", JLabel.LEFT);
         PortText = new JTextField(10);
         connectButton = new JButton("连接");
         clientTextArea = new JTextArea();
         scroller = new JScrollPane(clientTextArea);
         jPanelSouth0 = new JPanel();
         jPanelSouth1 = new JPanel();
         jPanelSouth2 = new JPanel();
         nicknameLabel = new JLabel("昵称", JLabel.LEFT);
         nicknameText = new JTextField(nickname, 30);
         nicknameButton = new JButton("确认");
         sayLabel = new JLabel("消息", JLabel.LEFT);
         sayText = new JTextField(30);
         sayButton = new JButton("确认");
     }

     // 构建GUI
     private void buildGUI() {
         // 窗口的设置
         clientFrame.setTitle("客户端");
         clientFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
         clientFrame.setSize(550, 550);

         // 北区的组件
         jPanelNorth.add(IPLabel);
         jPanelNorth.add(IPText);
         jPanelNorth.add(PortLabel);
         jPanelNorth.add(PortText);
         jPanelNorth.add(connectButton);
         clientFrame.getContentPane().add(BorderLayout.NORTH, jPanelNorth);

         // 中间的组件
         clientTextArea.setFocusable(false);
         scroller.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
         scroller.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_NEVER);
         clientFrame.getContentPane().add(BorderLayout.CENTER, scroller);

         // 南区的组件
         jPanelSouth1.add(nicknameLabel);
         jPanelSouth1.add(nicknameText);
         jPanelSouth1.add(nicknameButton);
         jPanelSouth2.add(sayLabel);
         jPanelSouth2.add(sayText);
         jPanelSouth2.add(sayButton);
         jPanelSouth0.setLayout(new BoxLayout(jPanelSouth0, BoxLayout.Y_AXIS));
         jPanelSouth0.add(jPanelSouth1);
         jPanelSouth0.add(jPanelSouth2);
         clientFrame.getContentPane().add(BorderLayout.SOUTH, jPanelSouth0);

         // 设置窗口可见
         clientFrame.setVisible(true);
     }

     // 客户端运行
     public void startUp() {
         buildGUI();

         // 接收服务器消息的线程
         Runnable incomingReader = new Runnable() {
             @Override
             public void run() {
                 String message;
                 try {
                     while ((message = reader.readLine()) != null) {
                         clientTextArea.append(message + "\n");
                     }
                 } catch (Exception ex) {
                     ex.printStackTrace();
                 }
             }
         };

         // 监听Connect按钮，实现服务器的连接
         connectButton.addActionListener(new ActionListener() {
             @Override
             public void actionPerformed(ActionEvent e) {
                 String aServerIP = IPText.getText();
                 String aServerPort = PortText.getText();

                 if (aServerIP.equals("") || aServerPort.equals("")) {
                     JOptionPane.showMessageDialog(clientFrame, "请输入 完整的 IP和端口！");
                 } else {
                     try {
                         @SuppressWarnings("resource")
                         Socket clientSocket = new Socket(aServerIP, Integer.parseInt(aServerPort));
                         InputStreamReader streamReader = new InputStreamReader(clientSocket.getInputStream());
                         reader = new BufferedReader(streamReader);
                         writer = new PrintWriter(clientSocket.getOutputStream());

                         clientTextArea.append("服务器已连接...\n");

                         Thread readerThread = new Thread(incomingReader);
                         readerThread.start();
                     } catch (Exception ex) {
                         JOptionPane.showMessageDialog(clientFrame, "连接不上服务器!\n请确认 IP 和 端口 输入正确。");
                     }
                 }
             }
         });

         // 监听nickname，设置昵称
         ActionListener nicknameListener = new ActionListener() {
             @Override
             public void actionPerformed(ActionEvent e) {
                 String aText = nicknameText.getText();
                 if (!aText.equals("")) {
                     nickname = aText;
                 }
             }
         };
         nicknameButton.addActionListener(nicknameListener);
         nicknameText.addActionListener(nicknameListener);
         nicknameText.addFocusListener(new FocusListener() {
             @Override
             public void focusGained(FocusEvent e) {
             }

             @Override
             public void focusLost(FocusEvent e) {
                 String aText = nicknameText.getText();
                 if (!aText.equals("")) {
                     nickname = aText;
                 }
             }
         });

         // 发送消息到服务器
         ActionListener SayListener = new ActionListener() {
             @Override
             public void actionPerformed(ActionEvent e) {
                 String aText = sayText.getText();
                 if (aText.equals("")) {
                     JOptionPane.showMessageDialog(clientFrame, "内容不能为空！");
                 } else {
                     try {
                         writer.println(nickname + "：" + aText);
                         writer.flush();
                     } catch (Exception ex) {
                         ex.printStackTrace();
                     }
                     sayText.setText("");
                 }
             }
         };
         sayButton.addActionListener(SayListener);
         sayText.addActionListener(SayListener);

     }

 }

运行结果如下：

下面主要探讨一下Java中的socket与Linux中的socket API之间的联系。主要思路当然是查看一下Java中的serversocket和socket的源码，这样更清楚地明白底层Java调用栈。

首先要明白的一点是，Java实现的socket与Linux提供的socket是否一定是有关呢？答案是否定的！关键要看Java虚拟机是怎么实现的。

如果Java虚拟机是在Linux系统之上的，并且使用了系统调用，那显然两者之间有关系。并且JVM最后一定是调用了LinuxSocket。

但是如果是在一个裸机上实现的虚拟机或者其他非Linux系统上实现Java虚拟机，那显然二者之间没有一毛钱关系，最终只是有相同的接口名称而已。

所以最终还是要看JVM是怎么实现的。JVM屏蔽了底层不同的机器特性，向上提供了一个统一的虚拟机接口，所以还是JVM牛逼。