java socket连接c/s (转)

java socket连接c/s (转)
2010年07月08日
　　用java实现的简单Server/Client文件传输关键字: java server client
　　用一种编程语言实现一个简单的Server/Client程序； 该程序的主要功能是利用Client从Server端下载一个文件； 在下载之前，需要有一定的用户身份验证机制（说白了就是先输入以下用户名和密码）； Server应该是多线程机制的，即为每个Client请求Server都要有一个线程去处理，而不是所有的Client都是一个Server线程处理。 ok，这就是需求，单从编程角度来讲，题目不难，单老师说过一句话，我觉得非常有道理，“看一万个程序，不如自己亲自写一个程序，写一万个程序，不如努力写一个好程序”，所以我就利用十一假期的最后两天，完成了这样一个作业，当然大部分时间还是画在了学习不太熟悉的python上。在这里，还要感谢一下CSDN上“wumingabc的专栏”的一篇blog，参考了他的一些代码。
　　处理流程：
　　server启动，监听client请求； client启动； server监听到client，发送“Hi”； client收到“Hi” client要求用户输入用户名； 用户输入用户名（如yangsq），发送到服务器（形式为“username:yangsq”）； 服务器验证是否存在这样一个用户，如果有到step 8，否则转到5； client用求用户输入密码（如123456），发送到服务器（形式为“password:123456”）； 服务器验证密码是否正确，不正确转到step 8，正确开始传输文件（为了简单，文件预先指定好）； client收到文件，结束后发送“bye”；同时server端收到“bye”后结束线程。 服务器端：
　　java 代码
　　import java.io.BufferedOutputStream;    import java.io.BufferedReader;    import java.io.BufferedWriter;    import java.io.DataOutputStream;    import java.io.File;    import java.io.FileInputStream;    import java.io.IOException;    import java.io.InputStream;    import java.io.InputStreamReader;    import java.io.OutputStream;    import java.io.OutputStreamWriter;    import java.io.PrintWriter;    import java.net.ServerSocket;    import java.net.Socket;    import java.util.HashMap;    import java.util.Map;       public class SimpleServer extends Thread{        private static final int DEFAULT_PORT = 4444;        private static final String DEFAULT_FILE_NAME = "PyNet.pdf";        private Socket socket;                public SimpleServer(Socket socket){            this.socket = socket;            start();        }                @Override       public void run() {            System.out.println("Connected from " + socket.getRemoteSocketAddress());            try {                BufferedReader in = new BufferedReader(                        new InputStreamReader(socket.getInputStream()));                PrintWriter out = new PrintWriter(                        new BufferedWriter(new OutputStreamWriter(socket.getOutputStream())), true);                String inputLine, outputLine;                                HandleInput handleInput = new HandleInput();                outputLine = handleInput.handle(null);                out.println(outputLine);                                while((inputLine = in.readLine()) != null){                    outputLine = handleInput.handle(inputLine);                    out.println(outputLine);                    out.flush();                    if(outputLine.equals("bye"))                        break;                    if(outputLine.equals("password:valid")){                        //prepare for the transmission of the file                        Thread.sleep(2000);                        InputStream fileInput = new FileInputStream(new File(DEFAULT_FILE_NAME));                        OutputStream fileOutput = new DataOutputStream(                                new BufferedOutputStream(socket.getOutputStream()));                        byte[] buf = new byte[2048];                                                //transmit the file                        int num = fileInput.read(buf);                        while(num != -1){                            fileOutput.write(buf, 0, num);                            fileOutput.flush();                            num = fileInput.read(buf);                        }                                                fileInput.close();                        fileOutput.close();                    }                }                                in.close();                out.close();                System.out.println("Disconnected from " + socket.getRemoteSocketAddress());                socket.close();            } catch (IOException e) {                // TODO Auto-generated catch block                e.printStackTrace();            } catch (InterruptedException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        }                private class HandleInput{            private  Map userInfo = new HashMap();            private String username = "";            private String password = "";                        public HandleInput(){                userInfo.put("yangsq", "yangsq");                userInfo.put("abc", "abc");                userInfo.put("123", "123");            }                        public String handle(String input){                String output = "";                if(input == null)                    output = "Hi";                else if(input.startsWith("username")){                    username = input.split(":")[1];                    if(userInfo.containsKey(username))                        output = "username:valid";                    else                       output = "username:invalid";                }else if(input.startsWith("password")){                    password = input.split(":")[1];                    if(userInfo.get(username).equals(password))                        output = "password:valid";                    else                       output = "password:invalid";                }else if(input.equals("bye")){                    output = "bye";                }                return output;            }        }           public static void main(String[] args) {                        int port = DEFAULT_PORT;                        if(args.length > 0){                port = Integer.parseInt(args[0]);            }                        try {                ServerSocket serverSocket = new ServerSocket(port);                System.out.println("Server Started");                try {                    while(true){                        Socket theSocket = serverSocket.accept();                        try {                            new SimpleServer(theSocket);                        } catch (Exception e) {                            e.printStackTrace();                            theSocket.close();                        }                    }                } catch (Exception e) {                    // TODO: handle exception                    e.printStackTrace();                } finally {                    if(serverSocket != null)                        serverSocket.close();                }            } catch (IOException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        }    }  
　　说明：
　　main函数是Server的启动点，在这里我们建立了一个ServerSocket的实例，这个类是java中专门进行Server端编程的，它可以进行很多的复杂配置，这里知识把它建立在了一个端口之上（line-125），然后为请求返回socket（line-131）。 SimpleServer类继承了Thread，也就是说，我的想法是为每一个Client请求，都有一个SimpleServer去处理。这是怎样实现的呢？看line-128到line-136，这里ServerSocket的实例在端口4444进行监听，只要有一个请求，就new一个SimpleServer去处理（如果没有请求，程序就会阻塞在ServerSocket的accept方法上line-129） 既然SimpleServer继承了Thread，那么它的最重要的方法就是run（line-29），可以看到，在new SimpleServer的时候就启动了它的run方法。 SimpleServer的主要处理流程在line-42到line-67，为了更清晰，把其中的用户身份验证提出来组成一个内部类HandleInput。 负责文件传输的是line-48到line-66，也即clien的密码正确后开始。这里需要说明的是流的实现，与用户交互的时候我们用的是New IO，他们是面向字节（1字节=2byte）的，这很合适，因为我们的用户信息都是字节的（简单的说就是面向asc字符的），所以这里我们就用了readline和println方法（这两个都是Reader和Writer的方法）；但是我们要传输的是一个二进制文件（说白了就是面向byte的），所以用New IO就不合适了，所以转向了InputStream（读入文件）和OutputStream（把文件通过socket写出）。 客户端：
　　java 代码
　　import java.io.BufferedInputStream;    import java.io.BufferedReader;    import java.io.DataInputStream;    import java.io.File;    import java.io.IOException;    import java.io.InputStream;    import java.io.InputStreamReader;    import java.io.PrintWriter;    import java.io.RandomAccessFile;    import java.net.Socket;    import java.net.UnknownHostException;       public class SimpleClient {        private static final int DEFAULT_PORT = 4444;        private static final String DEFAULT_HOST = "localhost";                public static void main(String[] args) {            String host = DEFAULT_HOST;            int port = DEFAULT_PORT;                        if(args.length > 0){                host = args[0];            }                        if(args.length >1 ){                port = Integer.parseInt(args[1]);            }                        Socket theSocket = null;            PrintWriter out = null;            BufferedReader in = null, userIn = null;                        try {                theSocket = new Socket(host, port);                                in = new BufferedReader(                        new InputStreamReader(theSocket.getInputStream()));                out = new PrintWriter(theSocket.getOutputStream());                userIn = new BufferedReader(                        new InputStreamReader(System.in));                                System.out.println("Connected to the simple file server");                String fromUser, fromServer;                                while((fromServer = in.readLine()) != null){                    if(fromServer.equals("bye"))                        break;                    else if(fromServer.equals("Hi")){                        System.out.println("Do you want to get the 'PyNet.pdf' file?(y/n):");                        fromUser = userIn.readLine();                        if(fromUser.equals("y")){                            System.out.println("Please input your username:");                            fromUser = userIn.readLine();                            out.println("username:" + fromUser);                            out.flush();//notice: if this sentence is lost, the info will not arrive at server side                        }else                           break;                    }else if(fromServer.startsWith("username")){                        if(fromServer.split(":")[1].equals("valid")){                            System.out.println("Please input your password:");                            fromUser = userIn.readLine();                            out.println("password:" + fromUser);                            out.flush();                        }else{                            System.out.println("Please input your username:");                            fromUser = userIn.readLine();                            out.println("username:" + fromUser);                            out.flush();                        }                    }else if(fromServer.startsWith("password")){                        if(fromServer.split(":")[1].equals("valid")){                            System.out.println("Downloading...");                                                        //prepare for the receiving                            File newFile = new File("new.pdf");                            newFile.createNewFile();                            RandomAccessFile raf = new RandomAccessFile(newFile, "rw");                                                        InputStream fileInput = new DataInputStream(                                    new BufferedInputStream(theSocket.getInputStream()));                            byte[] buf = new byte[2048];                                                        //receiving                            int num = fileInput.read(buf);                            while(num != -1){                                raf.write(buf, 0, num);                                raf.skipBytes(num);                                num = fileInput.read(buf);                            }                                                        in.close();                            raf.close();                            System.out.println("File download is finished");                            break;                        }else{                            System.out.println("Please input your password:");                            fromUser = userIn.readLine();                            out.println("password:" + fromUser);                            out.flush();                        }                    }                }                                out.println("bye");                out.flush();                                out.close();                in.close();                userIn.close();                theSocket.close();            } catch (UnknownHostException e) {                // TODO Auto-generated catch block                e.printStackTrace();            } catch (IOException e) {                // TODO Auto-generated catch block                e.printStackTrace();            }        }    }   
　　这个比较简单，除了用户交互外，最核心的就是line-71到line-94这段处理文件下载的了，当SimpleClient收到服务器的“password:valid"就表示用户身份验证通过，可以执行文件下载了。这部分也是混合使用了New IO和Old IO，原因和上边解释的一样。
　　这里还要强调一点的是在网络编程的时候，println以后，一定要flush以下。为什么呢？学过网络的人都知道，当一个package太小是，网络并不会把它发出去，而是等到足够大时。我在实际测试时，就忘记了在println后写flush，结果这边明明已经out出了，但Server端就是在那塞着，这个问题困扰了我半天，呵呵。