1.回调
类A的a()方法调用类B的b()方法
类B的b()方法执行完毕主动调用类A的callback()方法
package nia.chapter1;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
/**
* Created by kerr.
*
* 代码清单 1-2 被回调触发的 ChannelHandler
*/
public class ConnectHandler extends ChannelInboundHandlerAdapter {
@Override
//当一个新的连接已经被建立时,channelActive(ChannelHandlerContext)将会被调用
public void channelActive(ChannelHandlerContext ctx)
throws Exception {
System.out.println(
"Client " + ctx.channel().remoteAddress() + " connected");
}
}
2.Future
Future提供了一种在操作完成时通知应用程序的方式。这个对象可以看作是一个异步操作的结果的占位符;它将在未来某个时刻完成,并提供对其结果的访问。
package nia.chapter1;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.Channel;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.socket.nio.NioSocketChannel;
import java.net.InetSocketAddress;
import java.nio.charset.Charset;
/**
* Created by kerr.
*
* 代码清单 1-3 异步地建立连接
*
* 代码清单 1-4 回调实战
*/
public class ConnectExample {
private static final Channel CHANNEL_FROM_SOMEWHERE = new NioSocketChannel();
/**
* 代码清单 1-3 异步地建立连接
*
* 代码清单 1-4 回调实战
* */
public static void connect() {
Channel channel = CHANNEL_FROM_SOMEWHERE; //reference form somewhere
// Does not block
//异步地连接到远程节点
ChannelFuture future = channel.connect(
new InetSocketAddress("192.168.0.1", 25));//第一个参数是hostname,主机名,第二个参数是port,端口
//注册一个 ChannelFutureListener,以便在操作完成时获得通知
future.addListener(new ChannelFutureListener() {
@Override
public void operationComplete(ChannelFuture future) {
//检查操作的状态
if (future.isSuccess()) {
//如果操作是成功的,则创建一个 ByteBuf 以持有数据
ByteBuf buffer = Unpooled.copiedBuffer(
"Hello", Charset.defaultCharset());
//将数据异步地发送到远程节点。返回一个 ChannelFuture
ChannelFuture wf = future.channel()
.writeAndFlush(buffer);
// ...
} else {
//如果发生错误,则访问描述原因的 Throwable
Throwable cause = future.cause();
cause.printStackTrace();
}
}
});
}
}
3.EchoSeverHandler
一个ChannelHandler可以处理多个Channel安全地共享
过程:
1.接收消息 channelRead()对于每个传入消息都会调用
2.把未决消息(暂存于ChannelOutboundBuffer的消息)将未决消息冲刷到远程节点
3.关闭该Channel
package nia.chapter2.echoserver;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelFutureListener;
import io.netty.channel.ChannelHandler.Sharable;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.CharsetUtil;
/**
* 代码清单 2-1 EchoServerHandler
*
* @author <a href="mailto:[email protected]">Norman Maurer</a>
*/
//标示一个ChannelHandler可以被多个 Channel 安全地共享
@Sharable
public class EchoServerHandler extends ChannelInboundHandlerAdapter {
@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) {
ByteBuf in = (ByteBuf) msg;
//将消息记录到控制台
System.out.println(
"Server received: " + in.toString(CharsetUtil.UTF_8));
//将接收到的消息写给发送者,而不冲刷出站消息
ctx.write(in);
}
@Override
public void channelReadComplete(ChannelHandlerContext ctx)
throws Exception {
//将未决消息冲刷到远程节点,并且关闭该 Channel
ctx.writeAndFlush(Unpooled.EMPTY_BUFFER)
.addListener(ChannelFutureListener.CLOSE);
}
@Override
public void exceptionCaught(ChannelHandlerContext ctx,
Throwable cause) {
//打印异常栈跟踪
cause.printStackTrace();
//关闭该Channel
ctx.close();
}
}
4.引导服务器
package nia.chapter2.echoserver;
import io.netty.bootstrap.ServerBootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioServerSocketChannel;
import java.net.InetSocketAddress;
/**
* 代码清单 2-2 EchoServer 类
*
* @author <a href="mailto:[email protected]">Norman Maurer</a>
*/
public class EchoServer {
private final int port;
public EchoServer(int port) {
this.port = port;
}
public static void main(String[] args)
throws Exception {
if (args.length != 1) {
System.err.println("Usage: " + EchoServer.class.getSimpleName() +
" <port>"
);
return;
}
//设置端口值(如果端口参数的格式不正确,则抛出一个NumberFormatException)
int port = Integer.parseInt(args[0]);
//调用服务器的 start()方法
new EchoServer(port).start();
}
public void start() throws Exception {
final EchoServerHandler serverHandler = new EchoServerHandler();
//(1) 创建EventLoopGroup
EventLoopGroup group = new NioEventLoopGroup();
try {
//(2) 创建ServerBootstrap
ServerBootstrap b = new ServerBootstrap();
b.group(group)
//(3) 指定所使用的 NIO 传输 Channel
.channel(NioServerSocketChannel.class)
//(4) 使用指定的端口设置套接字地址
.localAddress(new InetSocketAddress(port))
//(5) 添加一个EchoServerHandler到于Channel的 ChannelPipeline
.childHandler(new ChannelInitializer<SocketChannel>() {
@Override
public void initChannel(SocketChannel ch) throws Exception {
//EchoServerHandler 被标注为@Shareable,所以我们可以总是使用同样的实例
//这里对于所有的客户端连接来说,都会使用同一个 EchoServerHandler,因为其被标注为@Sharable,
//这将在后面的章节中讲到。
ch.pipeline().addLast(serverHandler);
}
});
//(6) 异步地绑定服务器;调用 sync()方法阻塞等待直到绑定完成
ChannelFuture f = b.bind().sync();
System.out.println(EchoServer.class.getName() +
" started and listening for connections on " + f.channel().localAddress());
//(7) 获取 Channel 的CloseFuture,并且阻塞当前线程直到它完成
f.channel().closeFuture().sync();
} finally {
//(8) 关闭 EventLoopGroup,释放所有的资源
group.shutdownGracefully().sync();
}
}
}