通过编写一个客户端和服务器端的例子来熟悉selector的使用
服务端逻辑：
1. 绑定一个端口号
2. channel注册到selector中
3. 用死循环来监听如果有时间发生，遍历selectionKey set
4. 判断发生的事件类型，前面会注册accept事件，如果发生accept事件，那么注册读事件，同时清除selectionKey set 中的当前元素。、
5. 接收事件时，将channel保存下来。
6. 发生读事件时，说明有信息，发过来了，那么将消息，转发给所有的客户端。然后清除自身的事件。
import java.io.IOException;
import java.net.InetSocketAddress;
import java.net.ServerSocket;
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.nio.charset.Charset;
import java.util.*; public class NioServer { private static HashMap<String, SocketChannel> clientMap = new HashMap<String, SocketChannel>(); public static void main(String[] args) throws IOException {
ServerSocketChannel serverSocketChannel = ServerSocketChannel.open();
serverSocketChannel.configureBlocking(false); ServerSocket serverSocket = serverSocketChannel.socket();
serverSocket.bind(new InetSocketAddress(8899)); Selector selector = Selector.open(); serverSocketChannel.register(selector, SelectionKey.OP_ACCEPT); while(true) {
int number = selector.select();
// System.out.println("number:" + number);
Set<SelectionKey> selectionKeySet = selector.selectedKeys(); Iterator<SelectionKey> iterable = selectionKeySet.iterator(); if(number > 0 ) {
while(iterable.hasNext()) {
SelectionKey selectionKey = iterable.next(); if(selectionKey.isAcceptable()) {//如果是可接收连接的
ServerSocketChannel ssc = (ServerSocketChannel) selectionKey.channel();
SocketChannel socketChannel = ssc.accept();
socketChannel.configureBlocking(false); socketChannel.register(selector, SelectionKey.OP_READ);//注册读事件 clientMap.put(UUID.randomUUID() + "", socketChannel);//保存下channel iterable.remove();
} else if(selectionKey.isReadable()){//可读的
SocketChannel socketChannel = (SocketChannel) selectionKey.channel();
ByteBuffer byteBuffer = ByteBuffer.allocate(1024); int readCount = socketChannel.read(byteBuffer); //这里本该用while
if(readCount > 0 ) {//读取到数据，就写回到其他客户端
byteBuffer.flip(); Charset charset = Charset.forName("UTF-8");
String receiveStr = new String(charset.decode(byteBuffer).array()); System.out.println(socketChannel + " receive msg :" + receiveStr); String sendKey = ""; for(Map.Entry<String, SocketChannel> entry : clientMap.entrySet()) {//第一遍遍历找到发送者
if(socketChannel == entry.getValue()) {
sendKey = entry.getKey();
break;
}
} for (Map.Entry<String, SocketChannel> entry: clientMap.entrySet() ) {//给每个保存的连接，都发送消息
ByteBuffer writeBuffer = ByteBuffer.allocate(1024);
writeBuffer.put((sendKey + ":" + receiveStr).getBytes()); writeBuffer.flip();
entry.getValue().write(writeBuffer);
}
}
iterable.remove();//这个 删除很关键 每次循环完selectionKeySet ，一定要清楚事件，不然肯定会影响下一次的事件触发，或者直接不触发下次的事件
}
}
} }
}
}
客户端逻辑
1. 建立socketChannel 连接到对应的端口
2. 新建selector对象，然后把socketChannel注册到selector上
3. 建立死循环 ，监听是否有事件发生，若有，则遍历seletionKey set ,
4. 判断发生的事件是什么，
5. 如果是连接事件 ，做对应的连接处理，注册读事件
判断是否在等待连接 ，在进程中
if (channel.isConnectionPending()) {
channel.finishConnect(); 完成连接，这里是阻塞的
6. 如果发生了读事件，读取数据
import java.io.BufferedReader;
import java.io.InputStream;
import java.io.InputStreamReader;
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.time.LocalDateTime;
import java.util.Iterator;
import java.util.Set;
import java.util.concurrent.Executor;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.ThreadFactory; public class NioClient { public static void main(String[] args) {
try{
SocketChannel socketChannel = SocketChannel.open();
socketChannel.configureBlocking(false);
socketChannel.connect(new InetSocketAddress(8899));//服务端就是bind 然后accept serverSocketChannel Selector selector = Selector.open(); socketChannel.register(selector, SelectionKey.OP_CONNECT);//注册连接事件 while(true) {
int number = selector.select(); if(number > 0) {
Set<SelectionKey> selectionKeySet = selector.selectedKeys(); Iterator<SelectionKey> iterable = selectionKeySet.iterator();
while(iterable.hasNext()) {//有事件发生
SelectionKey selectionKey = iterable.next(); SocketChannel client = (SocketChannel) selectionKey.channel();
if(selectionKey.isConnectable()) {//判断 selectionkey 状态 可连接的
if(client.isConnectionPending()) {//是否在准备连接的进程中
client.finishConnect();//这里会阻塞，如果连接未建立，抛异常 ， ByteBuffer byteBuffer = ByteBuffer.allocate(1024); byteBuffer.put((LocalDateTime.now() + "，连接成功").getBytes());
byteBuffer.flip();
client.write(byteBuffer); ExecutorService executorService = Executors.newSingleThreadExecutor(Executors.defaultThreadFactory()); executorService.submit(() -> {//起一个新的线程，去接收控制台的输入 ，不影响其他线程
while(true) {
try{
byteBuffer.clear();
InputStreamReader inputStreamReader = new InputStreamReader(System.in);
BufferedReader bufferedReader = new BufferedReader(inputStreamReader); byteBuffer.put(bufferedReader.readLine().getBytes());
byteBuffer.flip();
client.write(byteBuffer); }catch (Exception e) {
e.printStackTrace();
}
}
});
} iterable.remove();//这个事件清楚，很关键
client.register(selector, SelectionKey.OP_READ);//注册读事件
} else if(selectionKey.isReadable()){//可读取
SocketChannel socketChannel1 = (SocketChannel) selectionKey.channel();
ByteBuffer readBuffer = ByteBuffer.allocate(1024); int readCount = socketChannel.read(readBuffer);
if(readCount > 0) {
String receiveMsg = new String(readBuffer.array());
System.out.println("receiveMsg : " + receiveMsg);
} iterable.remove();
} }
}
} }catch (Exception e ) {
e.printStackTrace();
} }
}
