Java Socket 连接无需 ServerSocket 监听

Question

这是我在没有任何ServerSocket的情况下连接两个Socket的代码:

package primary;

import java.awt.FlowLayout;
import java.io.EOFException;
import java.io.IOException;
import java.io.ObjectInputStream;
import java.io.ObjectOutputStream;
import java.net.InetAddress;
import java.net.ServerSocket;
import java.net.Socket;
import java.net.UnknownHostException;
import java.util.concurrent.*;
import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class Client extends JFrame implements Runnable {
    private final String myName;
    private ServerSocket listener;
    private Socket connection1;
    private Socket connection2;
    private ObjectOutputStream output1;
    private ObjectOutputStream output2;
    private ObjectInputStream input1;
    private ObjectInputStream input2;
    private Object receiveObject;
    private Object1 sendObject1;
    private Object2 sendObject2;
    private final int[] myLocalPort;
    private final int[] connectionPort;
    private ExecutorService service;
    private Future<Boolean> future1;
    private Future<Boolean> future2;

    public Client(final String myName, int[] myLocalPort, int[] connectionPort) {
        super(myName);
        this.myName = myName;
        this.myLocalPort = myLocalPort;
        this.connectionPort = connectionPort;
        sendObject1 = new Object1("string1", "string2", myName);
        sendObject2 = new Object2("string1", 2.5, 2, true, myName);
        initComponents();
    }
    public void exe() {
        ExecutorService eService = Executors.newCachedThreadPool();
        eService.execute(this);
    }

    @Override
    public void run() {
        try {
                displayMessage("Attempting connection\n");
                try {
                    connection1  = new Socket(InetAddress.getByName("localhost"), connectionPort[0],
                            InetAddress.getByName("localhost"), myLocalPort[0]);
                    displayMessage(myName + " connection1\n");
                } catch (Exception e) {
                    displayMessage("failed1\n");
                    System.err.println("1" + myName + e.getMessage() + "\n");
                }
                try {
                    connection2  = new Socket(InetAddress.getByName("localhost"), connectionPort[1],
                            InetAddress.getByName("localhost"), myLocalPort[1]);
                    displayMessage(myName + " connection2\n");
                } catch (Exception e) {
                    displayMessage("failed2\n");
                    System.err.println("2" + myName + e.getMessage() + "\n");
                }
            displayMessage("Connected to: " + connection1.getInetAddress().getHostName() + "\n\tport: "
                    + connection1.getPort() + "\n\tlocal port: " + connection1.getLocalPort() + "\n"
                    + connection2.getInetAddress().getHostName() + "\n\tport: " + connection2.getPort()
                    + "\n\tlocal port: " + connection2.getLocalPort() + "\n\n");
            output1 = new ObjectOutputStream(connection1.getOutputStream());
            output1.flush();
            output2 = new ObjectOutputStream(connection2.getOutputStream());
            output2.flush();
            input1 = new ObjectInputStream(connection1.getInputStream());
            input2 = new ObjectInputStream(connection2.getInputStream());
            displayMessage("Got I/O stream\n");
            setTextFieldEditable(true);
            service = Executors.newFixedThreadPool(2);
            future1 = service.submit(
                    new Callable<Boolean>() {

                @Override
                public Boolean call() throws Exception {
                    try {
                        processConnection(input1);
                        displayMessage("input1 finished");
                    } catch (IOException e) {
                        displayMessage("blah");
                    }
                    return true;
                }
            });
            future2 = service.submit(
                    new Callable<Boolean>() {

                @Override
                public Boolean call() throws Exception {
                    try {
                        processConnection(input2);
                        displayMessage("input2 finished");
                    } catch (IOException e) {
                        displayMessage("foo");
                    }
                    return true;
                }
            });
        } catch (UnknownHostException e) {
            displayMessage("UnknownHostException\n");
            e.printStackTrace();
        } catch (EOFException e) {
            displayMessage("EOFException\n");
            e.printStackTrace();
        } catch (IOException e) {
            displayMessage("IOException\n");
            e.printStackTrace();
        } catch(NullPointerException e) {
            System.err.println("asdf " + e.getMessage());
        } finally {
            try {
                displayMessage("i'm here\n");
                if((future1 != null && future1.get()) && (future2 != null && future2.get())) {
                    displayMessage(future1.get() + " " + future2.get() + "\n");
                    displayMessage("Closing Connection\n");
                    setTextFieldEditable(false);
                    if(!connection1.isClosed()) {
                        output1.close();
                        input1.close();
                        connection1.close();
                    }
                    if(!connection2.isClosed()) {
                        output2.close();
                        input2.close();
                        connection2.close();
                    }
                    displayMessage("connection closed\n");
                }
            } catch (IOException e) {
                displayMessage("IOException on closing");
            } catch (InterruptedException e) {
                displayMessage("InterruptedException on closing");
            } catch (ExecutionException e) {
                displayMessage("ExecutionException on closing");
            }
        }
    }//method run ends
    private void processConnection(ObjectInputStream input) throws IOException {
        String message = "";
        do {
            try {
                receiveObject = input.readObject();
                if(receiveObject instanceof String) {
                    message = (String) receiveObject;
                    displayMessage(message + "\n");
                } else if (receiveObject instanceof Object1) {
                    Object1 receiveObject1 = (Object1) receiveObject;
                    displayMessage(receiveObject1.getString1() + " " + receiveObject1.getString2()
                            + " " + receiveObject1.toString() + "\n");
                } else if (receiveObject instanceof Object2) {
                    Object2 receiveObject2 = (Object2) receiveObject;
                    displayMessage(receiveObject2.getString1() + " " + receiveObject2.getD()
                            + " " + receiveObject2.getI() + " " + receiveObject2.toString() + "\n");
                }
            } catch (ClassNotFoundException e) {
                displayMessage("Unknown object type received.\n");
            }
            displayMessage(Boolean.toString(message.equals("terminate\n")));
        } while(!message.equals("terminate"));
        displayMessage("finished\n");
        input = null;
    }

    private void initComponents() {

        dataField = new javax.swing.JTextField();
        sendButton1 = new javax.swing.JButton();
        sendButton2 = new javax.swing.JButton();
        jScrollPane1 = new javax.swing.JScrollPane();
        resultArea = new javax.swing.JTextArea();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);
        setLayout(new FlowLayout());
        dataField.setEditable(false);
        dataField.setColumns(20);
        dataField.addActionListener(new java.awt.event.ActionListener() {
            @Override
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                dataFieldActionPerformed(evt);
            }
        });

        sendButton1.setText("Send Object 1");
        sendButton1.addActionListener(new java.awt.event.ActionListener() {
            @Override
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                sendButton1ActionPerformed(evt);
            }
        });

        sendButton2.setText("Send Object 2");
        sendButton2.addActionListener(new java.awt.event.ActionListener() {
            @Override
            public void actionPerformed(java.awt.event.ActionEvent evt) {
                sendButton2ActionPerformed(evt);
            }
        });

        resultArea.setColumns(25);
        resultArea.setRows(15);
        resultArea.setEditable(false);
        resultArea.setRows(5);
        jScrollPane1.setViewportView(resultArea);

        add(dataField);
        add(sendButton1);
        add(sendButton2);
        add(jScrollPane1);
        pack();
    }
    private void dataFieldActionPerformed(java.awt.event.ActionEvent evt) {                                          
        // TODO add your handling code here:
        sendData(evt.getActionCommand());
        dataField.setText("");
    }                                         

    private void sendButton1ActionPerformed(java.awt.event.ActionEvent evt) {                                            
        // TODO add your handling code here:
        sendData(sendObject1);
    }                                           

    private void sendButton2ActionPerformed(java.awt.event.ActionEvent evt) {                                            
        // TODO add your handling code here:
        sendData(sendObject2);
    }                                  

    private void displayMessage(final String messageToDisplay) {
        SwingUtilities.invokeLater(
                new Runnable() {
            @Override
                    public void run() {
                        resultArea.append(messageToDisplay);
                    }
                });
    }
    private void setTextFieldEditable(final boolean editable) {
        SwingUtilities.invokeLater(
                new Runnable() {

            @Override
            public void run() {
                dataField.setEditable(editable);
            }
        });
    }
    private void sendData(final Object object) {
        try {
            output1.writeObject(object);
            output1.flush();
            output2.writeObject(object);
            output2.flush();
            displayMessage(myName + ": " + object.toString() + "\n");
        } catch (IOException e) {
            displayMessage("Error writing object\n");
        }
    }

    private javax.swing.JTextField dataField;
    private javax.swing.JScrollPane jScrollPane1;
    private javax.swing.JTextArea resultArea;
    private javax.swing.JButton sendButton1;
    private javax.swing.JButton sendButton2;
}

主要内容:

    package primary;

import javax.swing.SwingUtilities;


public class Main {
    private static Object locker;

    public static void main(String[] args) {
        locker = new Object();
        final int[][] a = new int[6][];
        final int[][] b = new int[6][];
        final int[][] c;
        a[0] = new int[] {12340, 12341};
        a[1] = new int[] {12342, 12344};
        a[2] = new int[] {12342, 12343};
        a[3] = new int[] {12340, 12345};
        a[4] = new int[] {12344, 12345};
        a[5] = new int[] {12341, 12343};

        b[0] = new int[] {22340, 22341};
        b[1] = new int[] {22342, 22344};
        b[2] = new int[] {22342, 22343};
        b[3] = new int[] {22340, 22345};
        b[4] = new int[] {22344, 22345};
        b[5] = new int[] {22341, 22343};

        c = a;
        SwingUtilities.invokeLater(
                new Runnable() {

            @Override
            public void run() {
                Client client1 = new Client("client1", c[0], c[1]);
                client1.exe();
                client1.setLocation(0, 0);
                client1.setVisible(true);
            }
        });
        SwingUtilities.invokeLater(
                new Runnable() {

            @Override
            public void run() {
                Client client2 = new Client("client2", c[2], c[3]);
                client2.exe();
                client2.setLocation(0, 200);
                client2.setVisible(true);
            }
        });
        SwingUtilities.invokeLater(
                new Runnable() {

            @Override
            public void run() {
                Client client3 = new Client("client3", c[4], c[5]);
                client3.exe();
                client3.setLocation(0, 400);
                client3.setVisible(true);

            }
        });
    }
}

这里Object1和Object2只是两个可序列化对象。看起来所有的 socket 都连接得很好。如果我退出系统而不调用套接字及其输入、输出流的 close() 方法并重新运行，它仍然可以正常工作。但是，如果我在确保调用 close() 方法后退出系统，然后再次重新运行，我会得到以下结果: 1cli​​ent2地址已在使用:连接

1client3Address already in use: connect

2client3Address already in use: connect

asdf null
1client1Connection refused: connect

2client2Connection refused: connect

asdf null
2client1Connection refused: connect

asdf null

我一次又一次地重新运行，我不断收到此消息，除非我等待一定时间并再次重新运行，否则它会像第一次一样正常工作。为什么会发生这样的事情呢？为什么如果我关闭套接字而不是不关闭它们会花费这么多时间？当我不关闭套接字时，它们是真的关闭还是只是连接现有连接？但是当使用 ServerSocket 时，在我关闭的情况下似乎不会发生这种情况。到底发生了什么？

另一个问题，ServerSocket 据称将其 Socket 连接末端分发到其正在监听的本地端口之外的本地端口。如果是这样，为什么当我调用 Socket.getLocalPort() 时，我会获取它接受的所有套接字的监听本地端口？

Answer 1

创建Socket时不要使用第三个和第四个参数。没有真正需要指定本地地址，除非有 VPN，也没有真正需要指定本地端口，除了作为网络管理员想象中的虚构内容之外。

ServerSocket supposedly hands out its end of Socket connection to a localport other than on which it is listening.

不，没有。所有接受的套接字都使用相同的本地端口作为监听端口。