今天突然間想用nio實現個Echo服務，程序實現起來實現不算困難，但跑起來后，在Server端的ServerSocket完成accept之后，我的CPU總是跳到100%。嗯，小郁悶，后來，才發現自己在Server端注冊了多余的監聽事件SelectionKey.OP_WRITE，改過來后好多了，希望記住這個教訓。

EchoServer.java

package edu.dlut.zxf.nio;  
 
import java.io.IOException;  
import java.net.InetAddress;  
import java.net.InetSocketAddress;  
import java.nio.ByteBuffer;  
import java.nio.channels.SelectionKey;  
import java.nio.channels.Selector;  
import java.nio.channels.ServerSocketChannel;  
import java.nio.channels.SocketChannel;  
import java.util.Set;  
 
/**  
 * Echo服務器  
 * @author finux  
 */ 
public class EchoServer {  
    public final static int BUFFER_SIZE = 1024; //默認端口  
    public final static String HOST = "210.30.107.17";  
    public final static int PORT = 8888;  
      
    public static void main(String[] args) {  
        ServerSocketChannel ssc = null;  
        //緩沖區  
        ByteBuffer buffer = ByteBuffer.allocate(BUFFER_SIZE);  
        Selector selector = null;  
        try {  
            selector = Selector.open();  
            ssc = ServerSocketChannel.open();  
            ssc.socket().bind(new InetSocketAddress(InetAddress.getByName(HOST), PORT));  
            ssc.configureBlocking(false);  
            ssc.register(selector, SelectionKey.OP_ACCEPT);       
            print("服務器啟動，準備好連接...");  
            while (selector.select() > 0) {       
                Set<SelectionKey> selectionKeys = selector.selectedKeys();  
                for (SelectionKey key: selectionKeys) {  
                    if (key.isAcceptable()) {  
                        SocketChannel sc = ssc.accept();  
                        print("有新的連接！地址：" + sc.socket().getRemoteSocketAddress());  
                        sc.configureBlocking(false);  
                        sc.register(selector, SelectionKey.OP_READ);  
                        // 不要寫成:  
                        // sc.register(selector, SelectionKey.OP_READ | SelectionKey.OP_WRITE);  
                        // 畢竟這樣多注冊的無用的事件SelectionKey.OP_WRTE  
                        // 如果是這樣，在完成accept后，CPU也許會跑到100%  
                          
                    }  
                    //same to if ((ops & SelectionKey.OP_READ) == SelectionKey.OP_READ) {  
                    if (key.isReadable()) {   
                        SocketChannel sc = (SocketChannel)key.channel();  
                        print("有新的讀??！地址：" + sc.socket().getRemoteSocketAddress());                        
                        buffer.clear();                       
                        sc.read(buffer);  
                        buffer.flip();  
                        byte[] b = new byte[buffer.limit()];  
                        buffer.get(b);  
                        String s = new String(b);  
                        if (s.equals("bye")) {  
                            print("斷開連接：" + sc.socket().getRemoteSocketAddress());    
                            //斷開連接后，取消此鍵的通道到其選擇器的注冊  
                            key.cancel();  
                            sc.close();  
                            continue;  
                        }  
                        print("讀取的內容為：" + s);     
                        buffer.clear();  
                        s = "echo: " + s;  
                        buffer.put(s.getBytes());  
                        buffer.flip();  
                        sc.write(buffer);  
                    }   
                }  
                selectionKeys.clear();  
            }  
        } catch(IOException e) {  
            e.printStackTrace();  
        }   
    }  
      
    private static void print(String s) {  
        System.out.println(s);  
    }  
} 

EchoClient.java

package edu.dlut.zxf.nio;  
 
import java.util.Set;  
import java.io.BufferedReader;  
import java.io.IOException;  
import java.io.InputStreamReader;  
import java.net.InetSocketAddress;  
import java.net.InetAddress;  
import java.nio.ByteBuffer;  
import java.nio.channels.SelectionKey;  
import java.nio.channels.Selector;  
import java.nio.channels.SocketChannel;  
 
/**  
 * Echo客戶端  
 * @author finux  
 */ 
public class EchoClient {  
    public static void main(String[] args) {  
        ByteBuffer buffer = ByteBuffer.allocate(EchoServer.BUFFER_SIZE);  
        Selector selector = null;  
        SocketChannel sc = null;  
        try {  
            selector = Selector.open();  
            sc = SocketChannel.open();  
            sc.configureBlocking(false);  
            sc.connect(new InetSocketAddress(InetAddress.getByName(EchoServer.HOST), EchoServer.PORT));  
            print("客戶端啟動，準備連接...");  
            if (sc.isConnectionPending()) {  
                sc.finishConnect();  
            }  
            print("完成連接");  
            sc.register(selector, SelectionKey.OP_READ | SelectionKey.OP_WRITE);  
              
            boolean writed = false;  
            boolean down = false;  
            while (!down && selector.select() > 0) {                  
                Set<SelectionKey> selectionKeys = selector.selectedKeys();  
                for (SelectionKey key: selectionKeys) {                   
                    //int ops = key.readyOps();  
                    //if ((ops & SelectionKey.OP_WRITE) == SelectionKey.OP_WRITE && !writed) {  
                    if (key.isWritable() && !writed) {  
                        System.out.print("Input(bye to end): ");  
                        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));   
                        String s = br.readLine();  
                        if (s != null && !s.trim().equals("")) {  
                            buffer.clear();  
                            buffer.put(s.getBytes());  
                            buffer.flip();  
                            sc.write(buffer);  
                            writed = true;  
                            if (s.equals("bye")) {  
                                down = true;  
                                break;  
                            }  
                        }  
                    }  
                    //if ((ops & SelectionKey.OP_READ) == SelectionKey.OP_READ && writed) {  
                    if (key.isReadable() && writed) {  
                        buffer.clear();  
                        sc.read(buffer);  
                        buffer.flip();  
                        byte[] b = new byte[buffer.limit()];  
                        buffer.get(b);  
                        print(new String(b));  
                        writed = false;  
                    }  
                }  
                selectionKeys.clear();  
            }  
        } catch(IOException e) {  
            e.printStackTrace();  
        }  
    }  
      
    private static void print(String s) {  
        System.out.println(s);  
    }  
} 

當然EchoClient也可以像下面這樣來實現：

EchoClient2.java

package edu.dlut.zxf.nio;  
 
import java.util.Set;  
import java.io.BufferedReader;  
import java.io.IOException;  
import java.io.InputStreamReader;  
import java.net.InetSocketAddress;  
import java.net.InetAddress;  
import java.nio.ByteBuffer;  
import java.nio.channels.SelectionKey;  
import java.nio.channels.Selector;  
import java.nio.channels.SocketChannel;  
 
/**  
 * Echo客戶端2  
 * @author finux  
 */ 
public class EchoClient2 {  
    public static void main(String[] args) {  
        ByteBuffer buffer = ByteBuffer.allocate(EchoServer.BUFFER_SIZE);  
        Selector selector = null;  
        SocketChannel sc = null;  
        try {  
            selector = Selector.open();  
            sc = SocketChannel.open();  
            sc.configureBlocking(false);  
            sc.register(selector, SelectionKey.OP_CONNECT);  
            sc.connect(new InetSocketAddress(InetAddress.getByName(EchoServer.HOST), EchoServer.PORT));  
            print("客戶端啟動，準備連接...");  
              
            boolean writed = false;  
            boolean down = false;  
            while (!down && selector.select() > 0) {                  
                Set<SelectionKey> selectionKeys = selector.selectedKeys();  
                for (SelectionKey key: selectionKeys) {                   
                    //int ops = key.readyOps();  
                    //if ((ops & SelectionKey.OP_CONNECT) == SelectionKey.OP_CONNECT) {  
                    if (key.isConnectable()) {  
                        print("完成連接！");  
                        if (sc.isConnectionPending()) {  
                            sc.finishConnect();  
                        }  
                        sc.register(selector, SelectionKey.OP_READ | SelectionKey.OP_WRITE);                  
                    }  
                    //if ((ops & SelectionKey.OP_WRITE) == SelectionKey.OP_WRITE && !writed) {  
                    if (key.isWritable() && !writed) {  
                        //從準備IO中讀取內容  
                        System.out.print("Input(bye to end): ");  
                        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));   
                        String s = br.readLine();  
                        if (s != null && !s.trim().equals("")) {  
                            buffer.clear();  
                            buffer.put(s.getBytes());  
                            buffer.flip();  
                            sc.write(buffer);  
                            writed = true;  
                            if (s.equals("bye")) {  
                                down = true;  
                                break;  
                            }  
                        }  
                    }  
                    //if ((ops & SelectionKey.OP_READ) == SelectionKey.OP_READ && writed) {  
                    if (key.isReadable() && writed) {  
                        buffer.clear();  
                        sc.read(buffer);  
                        buffer.flip();  
                        byte[] b = new byte[buffer.limit()];  
                        buffer.get(b);  
                        print(new String(b));  
                        writed = false;  
                    }  
                }  
                selectionKeys.clear();  
            }  
        } catch(IOException e) {  
            e.printStackTrace();  
        }  
    }  
      
    private static void print(String s) {  
        System.out.println(s);  
    }  
} 

但是這樣的話，顯然EchoClient2中的while循環中的for循環（若有n次），在每次循環中都會多出n-1次if判斷，就是下面這個：

if (key.isConnectable()) { 

所以，我個人更喜歡***個EchoClient，呵呵，不用注冊SelectionKey.OP_CONNECT監聽事件。呵呵...

原文鏈接：http://finux.iteye.com/blog/368955

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