傳統(tǒng)的Java 的IO，利用Socket建立服務(wù)器，接收客戶端連接，一般都是為每一個(gè)連接建立一個(gè)線程，如果連接數(shù)巨大，那么服務(wù)器開銷也將巨大。。NIO的原理，可以參照圖：

Socket的Channel在Selector上注冊某一種動(dòng)作，Selector通過select操作，監(jiān)視所有在該Selector注冊過的Channel的對應(yīng)的動(dòng)作，如果監(jiān)測到某一對應(yīng)的動(dòng)作，則返回selectedKeys，自己手動(dòng)取到各個(gè)SelectionKey進(jìn)行相應(yīng)的處理。當(dāng)然NIO不僅可以接受Socket的Channel，還有文件操作等其他IO操作。

作業(yè)的要求：

使用socket編程實(shí)現(xiàn)一個(gè)簡單的文件服務(wù)器?？蛻舳顺绦?qū)崿F(xiàn)put功能(將一個(gè)文件從本地傳到文件服務(wù)器)和get功能(從文件服務(wù)器取一遠(yuǎn)程文件存為本地文件)?？蛻舳撕臀募?wù)器不在同一臺機(jī)器上。

put [-h hostname] [-p portname] local_filename remote_filename
get [-h hostname] [-p portname] remote_filename local_filename

服務(wù)器端不使用nio，直接使用io的socket代碼如下：

import java.io.*; 
import java.net.ServerSocket; 
import java.net.Socket; 
 
public class ServerMain { 
     
    public static void main(String[] args) { 
 
        class SocketThread extends Thread{ 
             
            private Socket socket; 
            private byte[] buf; 
            private int len = 0; 
            public SocketThread(Socket socket) {  
                this.socket = socket; 
                buf = new byte[1024]; 
            } 
 
            @Override 
            public void run() { 
                try {    
                    DataInputStream dis = new DataInputStream(socket.getInputStream()); 
                    DataOutputStream dos = new DataOutputStream(socket.getOutputStream());  
                     
                    //String command = dis.readUTF();  
                    len = dis.read(buf); 
                    String command = new String(buf,0,len); 
                     
                    System.out.println("command=="+command); 
                     
                    String[] temp =command.split(" "); 
                    command = temp[0];  //命令  是put還是get 
                    String filename = temp[1];  //文件名 
                     
                    File file = new File("C:\\",filename);//假設(shè)放在C盤 
                    if(command.equals("get")){ 
                        if(!file.exists()){ 
                            //dos.writeUTF("notexists"); 
                            dos.write("notexists".getBytes()); 
                            dos.flush(); 
                            System.out.println("沒有這個(gè)文件，無法提供下載！"); 
                            dis.close(); 
                            dos.close(); 
                            socket.close(); 
                            return; 
                        } 
                        //dos.writeUTF("DownloadReady "+file.length());  
                        dos.write("準(zhǔn)備下載".getBytes()); 
                        dos.flush(); 
                         
                        System.out.println("正在接受文件下載..."); 
                        DataInputStream fis = new DataInputStream(new BufferedInputStream(new FileInputStream(file)));  
   
                        while ((len = fis.read(buf))!= -1) {  
                            dos.write(buf, 0, len); 
                        } 
                        dos.flush(); 
                         
                        fis.close();      
                        System.out.println("文件傳輸完成"); 
                    } 
                    else {  
                        //dos.writeUTF("UploadReady");  
                        dos.write("UploadReady".getBytes()); 
                        dos.flush(); 
                         
                        System.out.println("正在接受文件上傳..."); 
                        DataOutputStream fileOut =  
                            new DataOutputStream(new BufferedOutputStream(new FileOutputStream(file))); 
  
                        while ((len = dis.read(buf))!=-1) {    
                            fileOut.write(buf, 0, len); 
                        } 
                        System.out.println("上傳完畢！"); 
                        fileOut.close();  
                    } 
                    dis.close(); 
                    dos.close(); 
                    socket.close();  
                } catch (Exception e) { 
                    e.printStackTrace(); 
                } 
            } 
             
        } 
         
        System.out.println("等待客戶端連接...."); 
        int index = 0; 
        try { 
            ServerSocket server = new ServerSocket(9527,300); //端口號9527  允許***連接數(shù)300 
            while (true) { 
                Socket socket = server.accept(); 
                System.out.println("收到第"+(++index)+"個(gè)連接"); 
                new SocketThread(socket).start(); //對每個(gè)連接創(chuàng)建一個(gè)線程 
            } 
        } catch (Exception e) { 
            e.printStackTrace(); 
        } 
    } 
} 

使用NIO建立的Socket服務(wù)器，代碼如下：

import java.io.BufferedInputStream; 
import java.io.BufferedOutputStream; 
import java.io.DataInputStream; 
import java.io.DataOutputStream; 
import java.io.File; 
import java.io.FileInputStream; 
import java.io.FileOutputStream; 
import java.io.IOException; 
import java.net.InetSocketAddress; 
import java.nio.ByteBuffer;  
import java.nio.CharBuffer; 
import java.nio.channels.SelectionKey; 
import java.nio.channels.Selector; 
import java.nio.channels.ServerSocketChannel; 
import java.nio.channels.SocketChannel; 
import java.nio.charset.Charset; 
import java.nio.charset.CharsetDecoder; 
import java.nio.charset.CharsetEncoder; 
import java.util.Iterator; 
 
public class NewSocketServer { 
  
    private static final int port = 9527; 
    private Selector selector; 
    private ByteBuffer clientBuffer = ByteBuffer.allocate(1024);   
    private CharsetDecoder decoder = Charset.forName("GB2312").newDecoder(); 
    private CharsetEncoder encoder = Charset.forName("GB2312").newEncoder();  
    //編碼解碼格式設(shè)置成GBK也行.UTF-8不行，中文亂碼  （前提都是客戶端沒有設(shè)置任何編碼解碼格式） 
     
    public void setListener() throws Exception{ 
         
        selector = Selector.open(); //打開選擇器    
         
        ServerSocketChannel server = ServerSocketChannel.open();  //定義一個(gè) ServerSocketChannel通道 
        server.socket().bind(new InetSocketAddress(port));  //ServerSocketChannel綁定端口   
        server.configureBlocking(false);   //配置通道使用非阻塞模式 
        server.register(selector, SelectionKey.OP_ACCEPT); //該通道在selector上注冊  接受連接的動(dòng)作 
         
        while(true) 
        {     
            selector.select();   //select() 會阻塞，直到在該selector上注冊的channel有對應(yīng)的消息讀入 
            Iterator iter = selector.selectedKeys().iterator();    
            while (iter.hasNext()) {     
                SelectionKey key = (SelectionKey) iter.next();    
                iter.remove();  // 刪除此消息  
                process(key);   // 當(dāng)前線程內(nèi)處理。（為了高效，一般會在另一個(gè)線程中處理此消息） 
            }    
        }    
    } 
     
     private void process(SelectionKey key) throws IOException {    
            if (key.isAcceptable()) { // 接收請求    
                ServerSocketChannel server = (ServerSocketChannel) key.channel();    
                SocketChannel channel = server.accept();//類似于io的socket，ServerSocketChannel的accept函數(shù)返回 SocketChannel 
                channel.configureBlocking(false);   //設(shè)置非阻塞模式    
                SelectionKey sKey = channel.register(selector, SelectionKey.OP_READ);  
                sKey.attach("read_command"); //這兒接收到連接請求之后可以為每個(gè)連接設(shè)置一個(gè)ID 
            }  
            else if (key.isReadable()) { // 讀信息     
                SocketChannel channel = (SocketChannel) key.channel();    
                String name = (String) key.attachment();  
                if(name.equals("read_command")){ 
                    int count = channel.read(clientBuffer);  
                    if (count > 0) {    
                        clientBuffer.flip();    
                        CharBuffer charBuffer = decoder.decode(clientBuffer);    
                        String command = charBuffer.toString();    
                         
                        //command形如：get abc.png 或者  put aaa.png 
                        System.out.println("command===="+command);  //得到客戶端傳來的命令  
                         
                        String[] temp =command.split(" "); 
                        command = temp[0];  //命令  是put還是get 
                        String filename = temp[1];  //文件名 
                         
                        SelectionKey sKey = channel.register(selector,SelectionKey.OP_WRITE);    
                        if(command.equals("put"))sKey.attach("UploadReady#"+filename);  //要保護(hù)該通道的文件名 
                        else if(command.equals("get")){  
                            if(!new File("C:\\",filename).exists()){ //假設(shè)文件都是在C盤根目錄 
                                System.out.println("沒有這個(gè)文件，無法提供下載！"); 
                                sKey.attach("notexists");  
                            } 
                            else sKey.attach("DownloadReady#"+filename); //要保護(hù)該通道的文件名 
                        } 
                    } else {    
                        channel.close();    
                    }    
                } 
                else if(name.startsWith("read_file")){//這兒可以新開一個(gè)線程     文件操作也可以用NIO  
                    DataOutputStream fileOut =  
                        new DataOutputStream( 
                                new BufferedOutputStream( 
                                        new FileOutputStream( 
                                                new File("C:\\",name.split("#")[1])))); 
  
                    int passlen = channel.read(clientBuffer);   
                    while (passlen>=0) {    
                        clientBuffer.flip();   
                        fileOut.write(clientBuffer.array(), 0, passlen);  
                        passlen = channel.read(clientBuffer); 
                    } 
                    System.out.println("上傳完畢！"); 
                    fileOut.close();  
                    channel.close(); 
                } 
                clientBuffer.clear();    
            }  
            else if (key.isWritable()) { // 寫事件    
                SocketChannel channel = (SocketChannel) key.channel();    
                String flag = (String) key.attachment();     
                if(flag.startsWith("downloading")){//這兒可以新開一個(gè)線程   文件操作也可以用NIO 
                    DataInputStream fis = new DataInputStream( 
                            new BufferedInputStream( 
                                    new FileInputStream( 
                                            new File("C:\\",flag.split("#")[1]))));  
                      
                    byte[] buf = new byte[1024]; 
                    int len =0;  
                    while ((len = fis.read(buf))!= -1) {  
                        channel.write(ByteBuffer.wrap(buf, 0, len));   
                    }   
                    fis.close();      
                    System.out.println("文件傳輸完成"); 
                    channel.close(); 
                } 
                else if(flag.equals("notexists")){  
                    //channel.write(encoder.encode(CharBuffer.wrap(flag)));    
                    channel.write(ByteBuffer.wrap(flag.getBytes())); //不用編碼也行    客戶端直接接收    中文也不是亂碼 
                    channel.close(); 
                } 
                else if(flag.startsWith("UploadReady")){  
                    channel.write(encoder.encode(CharBuffer.wrap("UploadReady")));  
                     
                    //這兒如果不重新注冊該通道的讀操作    selector選擇到該通道的將繼續(xù)永遠(yuǎn)是寫操作，也就無法跳轉(zhuǎn)到上面的接受上傳的處理 
                    SelectionKey sKey =channel.register(selector, SelectionKey.OP_READ);//register是覆蓋的????!!! 
                    sKey.attach("read_file#"+flag.split("#")[1]); 
                    //key.attach("read_file#"+flag.split("#")[1]); //select不到讀操作 
                } 
                else if(flag.startsWith("DownloadReady")){  
                    channel.write(ByteBuffer.wrap("準(zhǔn)備下載".getBytes()));  
                    //channel.write(encoder.encode(CharBuffer.wrap("準(zhǔn)備下載")));    
                    key.attach("downloading#"+flag.split("#")[1]); 
                }  
            }   
        }    
     
    public static void main(String[] args) { 
         
        try { 
             System.out.println("等待來至" + port + "端口的客戶端連接.....");  
            new NewSocketServer().setListener(); 
        } catch (Exception e) { 
            e.printStackTrace(); 
        } 
 
    } 
} 

客戶端代碼如下：

import java.io.*; 
import java.net.InetAddress; 
import java.net.Socket; 
import java.util.Scanner; 
 
public class ClientMain { 
 
    private   int ServerPort = 9527; 
    private   String ServerAddress = "192.168.1.154"; 
    private   String GetOrPut = "get";    
    private   String local_filename = "";  
    private   String remote_filename  = "";  
    private   byte[] buf; 
    private   int len; 
    class SocketThread extends Thread{ 
         
        @Override 
        public void run() { 
             try { 
                 
                File file = new File("C:\\",local_filename); //假設(shè)文件放在C盤 
                if(!file.exists()&&GetOrPut.equals("put")){  
                    System.out.println("本地沒有這個(gè)文件，無法上傳！");  
                    return; 
                }  
                 
                InetAddress loalhost = InetAddress.getLocalHost(); 
                Socket socket = new Socket(ServerAddress,ServerPort,loalhost,44); 
                                            //服務(wù)器IP地址  端口號   本機(jī)IP 本機(jī)端口號 
                DataInputStream dis = new DataInputStream(socket.getInputStream()); 
                DataOutputStream dos = new DataOutputStream(socket.getOutputStream()); 
                  
                //dos.writeUTF(GetOrPut+" "+remote_filename);//服務(wù)器端如果是io的socket，writeUTF和writeUTF對接 
                dos.write((GetOrPut+" "+remote_filename).getBytes()); 
                dos.flush();  
               
                //String tempString = dis.writeUTF();  
                buf = new byte[1024]; 
                len = dis.read(buf); 
                String tempString = new String(buf,0,len);//服務(wù)器反饋的信息 
                 
                //System.out.println(tempString);  
                if(tempString.equals("notexists")){ 
                    System.out.println("服務(wù)器沒有這個(gè)文件，無法下載！");  
                    dos.close(); 
                    dis.close(); 
                    socket.close(); 
                    return; 
                } 
                 
                if(tempString.startsWith("準(zhǔn)備下載")){   
                    DataOutputStream fileOut =  
                        new DataOutputStream(new BufferedOutputStream(new FileOutputStream(file))); 
  
                    while ((len = dis.read(buf))!=-1) {    
                        fileOut.write(buf, 0, len); 
                    } 
                    System.out.println("下載完畢！"); 
                    fileOut.close(); 
                    dos.close(); 
                    dis.close(); 
                    socket.close(); 
                } 
                else if(tempString.equals("UploadReady")){   
                    System.out.println("正在上傳文件......."); 
                    DataInputStream fis = new DataInputStream(new BufferedInputStream(new FileInputStream(file)));  
                       
                    while ((len = fis.read(buf))!= -1) {   
                        dos.write(buf, 0, len); 
                    } 
                    dos.flush(); 
                    System.out.println("上傳完畢！"); 
                    fis.close(); 
                    dis.close(); 
                    dos.close(); 
                    socket.close(); 
                } 
                 
            } catch (Exception e) { 
                e.printStackTrace(); 
            } 
        } 
         
    } 
     
    public boolean checkCommand(String command) 
    {  
        if(!command.startsWith("put")&&!command.startsWith("get")){ 
            System.out.println("輸入命令錯(cuò)誤"); 
            return false; 
        } 
         
        int index = -1; 
        String temp = ""; 
        String[] tempStrings = null; 
         
        if((index=command.indexOf("-h"))>0){ 
            temp = command.substring(index+3); 
            temp = temp.substring(0, temp.indexOf(' ')); 
            ServerAddress = temp; 
        } 
        if((index=command.indexOf("-p"))>0){ 
            temp = command.substring(index+3); 
            temp = temp.substring(0, temp.indexOf(' ')); 
            ServerPort = Integer.valueOf(temp); 
        } 
         
        tempStrings = command.split(" "); 
        if(command.startsWith("put")){ 
            GetOrPut = "put"; 
            local_filename = tempStrings[tempStrings.length-2]; 
            remote_filename = tempStrings[tempStrings.length-1]; 
        } 
        else if(command.startsWith("get")){ 
            GetOrPut = "get"; 
            local_filename = tempStrings[tempStrings.length-1]; 
            remote_filename = tempStrings[tempStrings.length-2]; 
        } 
         
        return true; 
    } 
     
    public static void main(String[] args) { 
        ClientMain thisC= new ClientMain();  
        Scanner sc = new Scanner(System.in); 
        String commandString = ""; 
        do { 
            System.out.println("請輸入命令：");  
            commandString = sc.nextLine(); 
        } while (!thisC.checkCommand(commandString));  
         
        ClientMain.SocketThread a = thisC.new SocketThread(); 
        a.start(); 
    } 
} 

原文鏈接：http://tonl.iteye.com/blog/1202817

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