伺服器端

package sterning;

import java.io.BufferedInputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.File;
import java.io.FileInputStream;
import java.net.ServerSocket;
import java.net.Socket;

public class ServerTest {
    int port = 8821;

    void start() {
        Socket s = null;
        try {
            ServerSocket ss = new ServerSocket(port);
            while (true) {
                // 選擇進行傳輸的檔案
                String filePath = "D:\\lib.rar";
                File fi = new File(filePath);

                System.out.println("檔案長度:" + (int) fi.length());

                // public Socket accept() throws
                // IOException偵聽並接受到此套接字的連線。此方法在進行連線之前一直阻塞。

                s = ss.accept();
                System.out.println("建立socket連結");
                DataInputStream dis = new DataInputStream(new BufferedInputStream(s.getInputStream()));
                dis.readByte();

                DataInputStream fis = new DataInputStream(new BufferedInputStream(new FileInputStream(filePath)));
                DataOutputStream ps = new DataOutputStream(s.getOutputStream());
                //將檔名及長度傳給客戶端。這裡要真正適用所有平臺，例如中文名的處理，還需要加工，具體可以參見Think In Java 4th裡有現成的程式碼。
                ps.writeUTF(fi.getName());
                ps.flush();
                ps.writeLong((long) fi.length());
                ps.flush();

                int bufferSize = 8192;
                byte[] buf = new byte[bufferSize];

                while (true) {
                    int read = 0;
                    if (fis != null) {
                        read = fis.read(buf);
                    }

                    if (read == -1) {
                        break;
                    }
                    ps.write(buf, 0, read);
                }
                ps.flush();
                // 注意關閉socket連結哦，不然客戶端會等待server的資料過來，
                // 直到socket超時，導致資料不完整。               
                fis.close();
                s.close();               
                System.out.println("檔案傳輸完成");
            }

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String arg[]) {
        new ServerTest().start();
    }
}

2.socket的Util輔助類

package sterning;

import java.net.*;
import java.io.*;

public class ClientSocket {
    private String ip;

    private int port;

    private Socket socket = null;

    DataOutputStream out = null;

    DataInputStream getMessageStream = null;

    public ClientSocket(String ip, int port) {
        this.ip = ip;
        this.port = port;
    }

    /*
     * 建立socket連線
     *
     * @throws Exception
     *             exception
     */
    public void CreateConnection() throws Exception {
        try {
            socket = new Socket(ip, port);
        } catch (Exception e) {
            e.printStackTrace();
            if (socket != null)
                socket.close();
            throw e;
        } finally {
        }
    }

    public void sendMessage(String sendMessage) throws Exception {
        try {
            out = new DataOutputStream(socket.getOutputStream());
            if (sendMessage.equals("Windows")) {
                out.writeByte(0x1);
                out.flush();
                return;
            }
            if (sendMessage.equals("Unix")) {
                out.writeByte(0x2);
                out.flush();
                return;
            }
            if (sendMessage.equals("Linux")) {
                out.writeByte(0x3);
                out.flush();
            } else {
                out.writeUTF(sendMessage);
                out.flush();
            }
        } catch (Exception e) {
            e.printStackTrace();
            if (out != null)
                out.close();
            throw e;
        } finally {
        }
    }

    public DataInputStream getMessageStream() throws Exception {
        try {
            getMessageStream = new DataInputStream(new BufferedInputStream(socket.getInputStream()));
            return getMessageStream;
        } catch (Exception e) {
            e.printStackTrace();
            if (getMessageStream != null)
                getMessageStream.close();
            throw e;
        } finally {
        }
    }

    public void shutDownConnection() {
        try {
            if (out != null)
                out.close();
            if (getMessageStream != null)
                getMessageStream.close();
            if (socket != null)
                socket.close();
        } catch (Exception e) {

        }
    }
}

3.客戶端

package sterning;

import java.io.BufferedOutputStream;
import java.io.DataInputStream;
import java.io.DataOutputStream;
import java.io.FileOutputStream;

public class ClientTest {
    private ClientSocket cs = null;

    private String ip = "localhost";// 設定成伺服器IP

    private int port = 8821;

    private String sendMessage = "Windwos";

    public ClientTest() {
        try {
            if (createConnection()) {
                sendMessage();
                getMessage();
            }

        } catch (Exception ex) {
            ex.printStackTrace();
        }
    }

    private boolean createConnection() {
        cs = new ClientSocket(ip, port);
        try {
            cs.CreateConnection();
            System.out.print("連線伺服器成功!" + "\n");
            return true;
        } catch (Exception e) {
            System.out.print("連線伺服器失敗!" + "\n");
            return false;
        }

    }

    private void sendMessage() {
        if (cs == null)
            return;
        try {
            cs.sendMessage(sendMessage);
        } catch (Exception e) {
            System.out.print("傳送訊息失敗!" + "\n");
        }
    }

    private void getMessage() {
        if (cs == null)
            return;
        DataInputStream inputStream = null;
        try {
            inputStream = cs.getMessageStream();
        } catch (Exception e) {
            System.out.print("接收訊息快取錯誤\n");
            return;
        }

        try {
            //本地儲存路徑，檔名會自動從伺服器端繼承而來。
            String savePath = "E:\\";
            int bufferSize = 8192;
            byte[] buf = new byte[bufferSize];
            int passedlen = 0;
            long len=0;
           
            savePath += inputStream.readUTF();
            DataOutputStream fileOut = new DataOutputStream(new BufferedOutputStream(new BufferedOutputStream(new FileOutputStream(savePath))));
            len = inputStream.readLong();
           
            System.out.println("檔案的長度為:" + len + "\n");
            System.out.println("開始接收檔案!" + "\n");
                   
            while (true) {
                int read = 0;
                if (inputStream != null) {
                    read = inputStream.read(buf);
                }
                passedlen += read;
                if (read == -1) {
                    break;
                }
                //下面進度條本為圖形介面的prograssBar做的，這裡如果是打檔案，可能會重複打印出一些相同的百分比
                System.out.println("檔案接收了" + (passedlen * 100/ len) + "%\n");
                fileOut.write(buf, 0, read);
            }
            System.out.println("接收完成，檔案存為" + savePath + "\n");

            fileOut.close();
        } catch (Exception e) {
            System.out.println("接收訊息錯誤" + "\n");
            return;
        }
    }

    public static void main(String arg[]) {
        new ClientTest();
    }
}