首先是使用java原生nio类库编写的例子，开发一套nio框架不简单，所以选择了netty,该例完成后，是netty举例。
package com.smkj.netty;
public class TimeServer {
public static void main(String[] args) {
int port = ;
if(args!=null&&args.length!=) {
try {
port = Integer.valueOf(args[]);
} catch (NumberFormatException e) {
//采用默认值
}
}
MultiplexerTimeServer timeServer = new MultiplexerTimeServer(port);
new Thread(timeServer,"NIO-MultiplexerTimeServer-001").start();
}
}
package com.smkj.netty; 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 MultiplexerTimeServer implements Runnable {
private Selector selector;
private ServerSocketChannel servChannel;
private volatile boolean stop; /**
* 初始化多路复用器，绑定监听端口
*
* @param port
*/
public MultiplexerTimeServer(int port) {
try {
selector = Selector.open();
servChannel = ServerSocketChannel.open();
servChannel.configureBlocking(false);
servChannel.socket().bind(new InetSocketAddress(port), );
servChannel.register(selector, SelectionKey.OP_ACCEPT);
System.out.println("The time server is start in port:" + port);
} catch (IOException e) {
e.printStackTrace();
System.exit();
}
} public void stop() {
this.stop = true;
} @Override
public void run() {
while (!stop) {
try {
selector.select();
Set<SelectionKey> selectedKeys = selector.selectedKeys();
Iterator<SelectionKey> it = selectedKeys.iterator();
SelectionKey key = null;
while (it.hasNext()) {
key = it.next();
it.remove();
try {
handleInput(key); // 处理key
} catch (Exception e) {
// TODO: handle exception
if (key != null) {
key.cancel();
if (key.channel() != null) {
key.channel().close();
}
}
}
}
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
}
}
// 多路复用器关闭后，所有注册在上面的Channel和Pipe等资源都会被自动去注册，所以不需要重复释放资源
if (selector != null) {
try {
selector.close();
} catch (Exception e) {
// TODO: handle exception
e.printStackTrace();
}
} } private void handleInput(SelectionKey key) throws IOException {
if (key.isValid()) {
// 处理新接入的请求消息
if (key.isAcceptable()) { // Accept the new connection
ServerSocketChannel ssc = (ServerSocketChannel) key.channel();
SocketChannel sc = ssc.accept();
sc.configureBlocking(false); // Add the new connection to the selector
sc.register(selector, SelectionKey.OP_READ);
}
if (key.isReadable()) {
// Read the Data
SocketChannel sc = (SocketChannel) key.channel();
ByteBuffer readBuffer = ByteBuffer.allocate();
int readBytes = sc.read(readBuffer);
if (readBytes > ) {
readBuffer.flip();
byte[] bytes = new byte[readBuffer.remaining()];
readBuffer.get(bytes);
String body = new String(bytes, "UTF-8");
System.out.println("the time server receive order:" + body); String currentTime = "QUERY TIME ORDER".equalsIgnoreCase(body)
? new java.util.Date(System.currentTimeMillis()).toString()
: "Bad Order";
doWrite(sc,currentTime);
}else if(readBytes<) {
//对端链路关闭
key.cancel();
sc.close();
}else {
//读到0字节 忽略
;
}
}
}
} private void doWrite(SocketChannel channel,String response) throws IOException { if(response!=null&&response.trim().length()>) {
byte[] bytes = response.getBytes();
ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length);
writeBuffer.put(bytes);
writeBuffer.flip();
channel.write(writeBuffer);
if (!writeBuffer.hasRemaining()) System.out.println("Send response to client succeed."); }
} }
package com.smkj.netty;
public class TimeClient {
public static void main(String[] args) {
int port = ;
if(args!=null&&args.length!=) {
try {
port = Integer.valueOf(args[]);
} catch (NumberFormatException e) {
//采用默认值
}
}
new Thread(new TimeClientHandle("127.0.0.1",port),"TimeClient-001").start();
}
}
package com.smkj.netty; 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.SocketChannel;
import java.util.Iterator;
import java.util.Set; public class TimeClientHandle implements Runnable { private String host; private int port; private Selector selector; private SocketChannel socketChannel; private volatile boolean stop; public TimeClientHandle(String host, int port) { this.host = host == null ? "127.0.0.1" : host; this.port = port; try { selector = Selector.open(); socketChannel = SocketChannel.open(); socketChannel.configureBlocking(false); } catch (IOException e) { e.printStackTrace(); System.exit(); }
}
/*
022
* (non-Javadoc)
023
*
024
* @see java.lang.Runnable#run()
025
*/
@Override
public void run() {
try {
doConnect();
} catch (IOException e) {
e.printStackTrace(); System.exit(); } while (!stop) { try { selector.select(); Set<SelectionKey> selectedKeys = selector.selectedKeys(); Iterator<SelectionKey> it = selectedKeys.iterator(); SelectionKey key = null; while (it.hasNext()) { key = it.next(); it.remove(); try { handleInput(key); } catch (Exception e) { if (key != null) { key.cancel(); if (key.channel() != null) key.channel().close(); } } } } catch (Exception e) { e.printStackTrace(); System.exit(); } } // 多路复用器关闭后，所有注册在上面的Channel和Pipe等资源都会被自动去注册并关闭，所以不需要重复释放资源 if (selector != null) try { selector.close(); } catch (IOException e) { e.printStackTrace(); } } private void handleInput(SelectionKey key) throws IOException { if (key.isValid()) { // 判断是否连接成功 SocketChannel sc = (SocketChannel) key.channel(); if (key.isConnectable()) { if (sc.finishConnect()) { sc.register(selector, SelectionKey.OP_READ); doWrite(sc); } else System.exit();// 连接失败，进程退出 } if (key.isReadable()) { ByteBuffer readBuffer = ByteBuffer.allocate(); int readBytes = sc.read(readBuffer); if (readBytes > ) { readBuffer.flip(); byte[] bytes = new byte[readBuffer.remaining()]; readBuffer.get(bytes); String body = new String(bytes, "UTF-8"); System.out.println("Now is : " + body); this.stop = true; } else if (readBytes < ) { // 对端链路关闭 key.cancel(); sc.close();
} else ; // 读到0字节，忽略 } } }
private void doConnect() throws IOException { // 如果直接连接成功，则注册到多路复用器上，发送请求消息，读应答 if (socketChannel.connect(new InetSocketAddress(host, port))) { socketChannel.register(selector, SelectionKey.OP_READ); doWrite(socketChannel); } else socketChannel.register(selector, SelectionKey.OP_CONNECT); } private void doWrite(SocketChannel sc) throws IOException { byte[] req = "QUERY TIME ORDER".getBytes(); ByteBuffer writeBuffer = ByteBuffer.allocate(req.length); writeBuffer.put(req); writeBuffer.flip(); sc.write(writeBuffer); if (!writeBuffer.hasRemaining()) System.out.println("Send order 2 server succeed."); } }
可以发现服务端的最后进行了remove()操作，将SelectionKey从迭代器中删除了，博主一开始总觉得很纳闷，SelectionKey中可是记录了相关的channel信息，如果将SelectionKey删除了，那不就代表着将通道信息也抹除了吗，那后续还怎么继续获取通道，说来惭愧，这问题问的确实缺乏水准。
后来博主理了理selector的思路，要知道，一码事归一码事，channel是注册在selector中的，在后面的轮询中，是先将已准备好的channel挑选出来，即selector.select()，再通过selectedKeys()生成的一个SelectionKey迭代器进行轮询的，一次轮询会将这个迭代器中的每个SelectionKey都遍历一遍，每次访问后都remove()相应的SelectionKey，但是移除了selectedKeys中的SelectionKey不代表移除了selector中的channel信息(这点很重要)，注册过的channel信息会以SelectionKey的形式存储在selector.keys()中，也就是说每次select()后的selectedKeys迭代器中是不能还有成员的，但keys()中的成员是不会被删除的(以此来记录channel信息)。
那么为什么要删除呢，要知道，迭代器如果只需要访问的话，直接访问就好了，完全没必要remove()其中的元素啊，查询了相关资料，一致的回答是为了防止重复处理（大雾），后来又有信息说明：每次循环调用remove()是因为selector不会自己从已选择集合中移除selectionKey实例，必须在处理完通道时自己移除，这样，在下次select时，会将这个就绪通道添加到已选择通道集合中，其实到这里就已经可以理解了，selector不会自己删除selectedKeys()集合中的selectionKey，那么如果不人工remove()，将导致下次select()的时候selectedKeys()中仍有上次轮询留下来的信息，这样必然会出现错误，假设这次轮询时该通道并没有准备好，却又由于上次轮询未被remove()的原因被认为已经准备好了，这样能不出错吗？
即selector.select()会将准备好的channel以SelectionKey的形式放置于selector的selectedKeys()*使用者迭代，使用的过程中需将selectedKeys清空，这样下次selector.select()时就不会出现错误了。