NIO相關知識點

IO、NIO、AIO 內部原理分析
NIO 之 Selector實現原理
NIO 之 Channel實現原理
NIO 之 ByteBuffer實現原理

服務器使用NIO來實現一個echo協議的服務器。
echo協議簡單也很有用，可以測試網絡連接。

消息的格式為：消息長度（int）+消息內容

通過消息長度來進行socket分包，防止讀取出現半包、粘包等問題。

服務端

import java.io.IOException; 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.Iterator; import java.util.Set;public class NioEchoServer {public static void server() {ServerSocketChannel ssc = null;Selector selector = null;try {ssc = ServerSocketChannel.open();//設置為非阻塞ssc.configureBlocking(false);ssc.bind(new InetSocketAddress(9000), 10);selector = Selector.open();ssc.register(selector, SelectionKey.OP_ACCEPT);} catch (IOException e) {e.printStackTrace();}while (true) {try {selector.select();} catch (IOException e) {e.printStackTrace();}try {Set<SelectionKey> set = selector.selectedKeys();Iterator<SelectionKey> it = set.iterator();while (it.hasNext()) {SelectionKey key = it.next();set.remove(key);try {if (key.isAcceptable()) {ServerSocketChannel serverChannel = (ServerSocketChannel) key.channel();SocketChannel clientChannel = serverChannel.accept();clientChannel.configureBlocking(false);MessageInfo messageInfo = new MessageInfo();clientChannel.register(selector, SelectionKey.OP_READ, messageInfo);} else if (key.isReadable()) {SocketChannel clientChannel = (SocketChannel) key.channel();MessageInfo messageInfo = (MessageInfo)key.attachment();if(messageInfo.getLenBuf() == null){messageInfo.setLenBuf(ByteBuffer.allocate(4));}//消息長度int len = messageInfo.getLen();//判斷消息長度是否讀取完成if(len!=-1){if(messageInfo.contentBuf == null){//創建指定消息長度的bufmessageInfo.contentBuf = ByteBuffer.allocate(len);}//如果消息未讀取完成，繼續讀取if(messageInfo.contentBuf.position()<len){if(clientChannel.read(messageInfo.contentBuf)==-1){clientChannel.register(selector, SelectionKey.OP_WRITE, messageInfo);}}if(len==0){System.out.println("空消息");key.cancel();key.channel().close();}else if(messageInfo.contentBuf.position()==len){messageInfo.contentBuf.flip();System.out.println(new String(messageInfo.contentBuf.array())); // clientChannel.register(selector, SelectionKey.OP_WRITE, messageInfo);key.interestOps(SelectionKey.OP_WRITE);}}//消息長度未讀取完成else{int i = clientChannel.read(messageInfo.getLenBuf());if(i==-1){System.out.println("消息異常:"+messageInfo.getLenBuf());break;}if(messageInfo.getLenBuf().position()==4){messageInfo.getLenBuf().flip();messageInfo.setLen(messageInfo.getLenBuf().getInt());}}}else if(key.isWritable()){SocketChannel clientChannel = (SocketChannel) key.channel();MessageInfo messageInfo = (MessageInfo)key.attachment();messageInfo.lenBuf.rewind();messageInfo.contentBuf.rewind();ByteBuffer[] bufs = new ByteBuffer[]{messageInfo.lenBuf, messageInfo.contentBuf};System.out.println(messageInfo.contentBuf.limit()+":"+messageInfo.contentBuf.capacity());clientChannel.write(bufs);key.cancel();key.channel().close();}} catch (Exception e) {key.cancel();key.channel().close();}}} catch (Exception e) {e.printStackTrace();break;}}System.out.println("");}public static void main(String[] args) {server();}//消息對象static class MessageInfo {private int len=-1;private ByteBuffer lenBuf;private ByteBuffer contentBuf;public int getLen() {return len;}public void setLen(int len) {this.len = len;}public ByteBuffer getLenBuf() {return lenBuf;}public void setLenBuf(ByteBuffer lenBuf) {this.lenBuf = lenBuf;}public ByteBuffer getContentBuf() {return contentBuf;}public void setContentBuf(ByteBuffer contentBuf) {this.contentBuf = contentBuf;}}}

客戶端

import java.io.IOException; import java.net.InetSocketAddress; import java.net.SocketAddress; import java.nio.ByteBuffer; import java.nio.channels.SocketChannel;public class NioEchoClient {public static void main(String[] args) {SocketAddress sa = new InetSocketAddress("127.0.0.1", 9000);try {SocketChannel client = SocketChannel.open(sa);byte[] data = "大家好".getBytes();ByteBuffer lenBuf = ByteBuffer.wrap(int2byte(data.length));ByteBuffer textBuf = ByteBuffer.wrap(data);ByteBuffer[] bufArray = new ByteBuffer[]{lenBuf, textBuf};client.write(bufArray);lenBuf.clear();textBuf.clear();client.read(bufArray);System.out.println("echo:"+new String(textBuf.array()));client.close();} catch (IOException e) {e.printStackTrace();}}/*** int 轉 byte[] 數組* @param len* @return*/public static byte[] int2byte(int len) {byte[] b = new byte[4];b[0] = (byte) (len >> 24);b[1] = (byte) (len >> 16 & 0XFF);b[2] = (byte) (len >> 8 & 0XFF);b[3] = (byte) (len & 0XFF);return b;} }

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