怎么用nio实现Echo服务
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这篇文章主要介绍“怎么用nio实现Echo服务”，在日常操作中，相信很多人在怎么用nio实现Echo服务问题上存在疑惑，小编查阅了各式资料，整理出简单好用的操作方法，希望对大家解答”怎么用nio实现Echo服务”的疑惑有所帮助！接下来，请跟着小编一起来学习吧！
今天突然间想用nio实现个Echo服务，程序实现起来实现不算困难，但跑起来后，在Server端的ServerSocket完成accept之后，我的CPU总是跳到100%。嗯，小郁闷，后来，才发现自己在Server端注册了多余的监听事件SelectionKey.OP_WRITE，改过来后好多了，希望记住这个教训。
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; public class EchoServer { public final static int BUFFER_SIZE = 1024; //默认端口 public final static String HOST = "210.30.107.17"; public final static int PORT = 8888; public static void main(String[] args) { ServerSocketChannel ssc = null; //缓冲区 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("服务器启动，准备好连接..."); while (selector.select() > 0) { Set<SelectionKey> selectionKeys = selector.selectedKeys(); for (SelectionKey key: selectionKeys) { if (key.isAcceptable()) { SocketChannel sc = ssc.accept(); print("有新的连接！地址：" + sc.socket().getRemoteSocketAddress()); sc.configureBlocking(false); sc.register(selector, SelectionKey.OP_READ); // 不要写成: // sc.register(selector, SelectionKey.OP_READ | SelectionKey.OP_WRITE); // 毕竟这样多注册的无用的事件SelectionKey.OP_WRTE // 如果是这样，在完成accept后，CPU也许会跑到100% } //same to if ((ops & SelectionKey.OP_READ) == SelectionKey.OP_READ) { if (key.isReadable()) { SocketChannel sc = (SocketChannel)key.channel(); print("有新的读取！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("断开连接：" + sc.socket().getRemoteSocketAddress()); //断开连接后，取消此键的通道到其选择器的注册 key.cancel(); sc.close(); continue; } print("读取的内容为：" + 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; 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("客户端启动，准备连接..."); if (sc.isConnectionPending()) { sc.finishConnect(); } print("完成连接"); 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); } }当然EchoClient也可以像下面这样来实现：
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; 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("客户端启动，准备连接..."); 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("完成连接！"); 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) { //从准备IO中读取内容 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); } }但是这样的话，显然EchoClient2中的while循环中的for循环（若有n次），在每次循环中都会多出n-1次if判断，就是下面这个：
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