本案例来源于《netty权威指南》
一、三大组件
- Selector：多路复用器。轮询注册在其上的Channel，当发现某个或者多个Channel处于“就绪状态”后（accept接收连接事件、connect连接完成事件、read读事件、write写事件），从阻塞状态返回就绪的Channel的SelectionKey集合，之后进行IO操作。
- Channel：封装了socket。
- ServerSocketChannel：封装了ServerSocket，用于accept客户端连接请求；
- SocketChannel：一对SocketChannel组成一条虚电路，进行读写通信
- Buffer：用于存取数据，最主要的是ByteBuffer
- position：下一个将被操作的字节位置
- limit：在写模式下表示可以进行写的字节数，在读模式下表示可以进行读的字节数
- capacity：Buffer的大小
二、服务端代码
1、服务端启动类
public class Server {
public static void main(String[] args) throws IOException {
new Thread(new ServerHandler(), "server-1").start();
}
}
创建一个任务ServerHandler，然后创建一条线程，启动执行该任务。
2、逻辑处理类
public class ServerHandler implements Runnable {
private Selector selector;
private ServerSocketChannel ssChannel;
public ServerHandler(int port) {
try {
//等价于 Selector selector = SelectorProvider.provider().openSelector();
selector = Selector.open();
//等价于 SelectorProvider.provider().openServerSocketChannel()
ssChannel = ServerSocketChannel.open();
ssChannel.configureBlocking(false);
ssChannel.bind(new InetSocketAddress(port), 1024);
ssChannel.register(selector, SelectionKey.OP_ACCEPT);
} catch (IOException e) {
e.printStackTrace();
System.exit(1);
}
}
public void run() {
for (; ; ) {
try {
selector.select();
Iterator<SelectionKey> it = selector.selectedKeys().iterator();
while (it.hasNext()) {
SelectionKey key = it.next();
it.remove();
handleInput(key);
}
} catch (Throwable t) {
t.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(1024);
int readBytes = sc.read(readBuffer);
if (readBytes > 0) {
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 < 0) {
// 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() > 0) {
byte[] bytes = response.getBytes();
ByteBuffer writeBuffer = ByteBuffer.allocate(bytes.length);
writeBuffer.put(bytes);
writeBuffer.flip();
channel.write(writeBuffer);
}
}
}
步骤：
1、创建一个Selector和ServerSocketChannel实例
2、配置ServerSocketChannel实例为非阻塞
3、ServerSocketChannel实例bind端口
4、将ServerSocketChannel实例注册到selector上，监听OP_ACCEPT事件
下面的任务在Server创建的新的线程中执行，不影响主线程执行其他逻辑
5、之后进入死循环
5.1、使用select.select()阻塞等待就绪事件（这里是等待OP_ACCEPT事件），一旦有有就绪事件到达，立即向下执行
5.2、使用selector.selectedKeys()获取已经就绪的SelectionKey（即OP_ACCEPT/OP_CONECT/OP_READ/OP_WRITE）集合，之后循环遍历
5.3、从迭代器删除该SelectionKey，防止下一次再被遍历到
5.4、如果SelectionKey==OP_ACCEPT，则通过ServerSocketChannel.accept()创建SocketChannel，该SocketChannel是后续真正的与客户端的SocketChannel进行通信的实体
5.5、配置新创建的SocketChannel实例为非阻塞，然后将该SocketChannel实例注册到selector实例上，监听OP_READ事件
5.6、等客户端发出请求数据时，此处监听到SelectionKey==OP_READ，则创建ByteBuffer实例，将SocketChannel中的数据读取到ByteBuffer中，然后再创建ByteBuffer将信息写回到SocketChannel（也就是说数据的读写一定要通过Buffer）
三、客户端代码
1、客户端启动类
public class Client {
public static void main(String[] args) {
new Thread(new ClientHandler("127.0.0.1", 8080), "client-1").start();
}
}
创建一个任务ClientHandler，然后创建一条线程，启动执行该任务。
2、逻辑处理类
public class ClientHandler implements Runnable {
private String host;
private int port;
private Selector selector;
private SocketChannel socketChannel;
public ClientHandler(String host, int port) {
this.host = host;
this.port = port;
try {
selector = Selector.open();
socketChannel = SocketChannel.open();
socketChannel.configureBlocking(false);
} catch (IOException e) {
e.printStackTrace();
System.exit(1);
}
}
public void run() {
try {
doConnect();
} catch (IOException e) {
e.printStackTrace();
System.exit(1);
}
while (true) {
try {
selector.select();
Iterator<SelectionKey> it = selector.selectedKeys().iterator();
while (it.hasNext()) {
SelectionKey key = it.next();
it.remove();
handleInput(key);
}
} catch (Exception e) {
e.printStackTrace();
System.exit(1);
}
}
}
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(1);// 连接失败，进程退出
} else if (key.isReadable()) {
ByteBuffer readBuffer = ByteBuffer.allocate(1024);
int readBytes = sc.read(readBuffer);
if (readBytes > 0) {
readBuffer.flip();
byte[] bytes = new byte[readBuffer.remaining()];
readBuffer.get(bytes);
String body = new String(bytes, "UTF-8");
System.out.println("Now is : " + body);
} else if (readBytes < 0) {
// 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.");
}
}
步骤：
1、创建一个Selector和SocketChannel实例
2、配置SocketChannel实例为非阻塞
下面的任务在Cilent创建的新的线程中执行，不影响主线程执行其他逻辑
3、SocketChannel.connect连接到server端，如果连接没有马上成功，将该SocketChannel实例注册到selector上，监听OP_CONNECT事件；如果连接成功，将该SocketChannel实例注册到selector上，监听OP_READ事件，之后写数据给server端
4、之后进入死循环
4.1、使用select.select()阻塞等待就绪事件，一旦有有就绪事件到达，立即向下执行
4.2、使用selector.selectedKeys()获取已经就绪的SelectionKey（即OP_ACCEPT/OP_CONECT/OP_READ/OP_WRITE）集合，之后循环遍历
4.3、从迭代器删除该SelectionKey，防止下一次再被遍历到
4.4、如果SelectionKey==OP_CONNECT，将该SocketChannel实例注册到selector上，监听OP_READ事件，之后写数据给server端；如果监听到SelectionKey==OP_READ，则创建ByteBuffer实例，将SocketChannel中的数据读取到ByteBuffer中