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！

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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;   /**   * Echo服务器   * @author finux   */ 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 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;   /**   * Echo客户端   * @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 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;   /**   * Echo客户端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("客户端启动，准备连接...");                            boolean writed = false;              boolean down = false;              while (!down && selector.select() > 0) {                                  Set 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：

if (key.isConnectable()) {

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