Netty简单使用

• 丢弃服务器
  • DiscardServerHandler
  • DiscardServer
  • 测试
• 应答服务器
• 时间服务器
  • TimeServerHandler
  • TimeClient
  • TimeClientHandler
  • 漏洞
  • 使用对象传递日期
• 聊天应用
  • ChatServerHandler
  • ChatServerInitializer
  • ChatServer
  • ChatClientHandler
  • ChatClientInitializer
  • ChatClient

丢弃服务器

详细代码：test-netty4-discard

丢弃服务器，就是将收到的所有数据都丢掉，不做任何处理

DiscardServerHandler

package org.zln.test.netty4.discard;

@Slf4j
public class DiscardServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        //丢弃收到的数据
        ((ByteBuf) msg).release();
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
//        出现异常时关闭连接
        ctx.close();
    }
}

DiscardServerHandler继承自ChannelInboundHandlerAdapter，

ChannelInboundHandlerAdapter实现了ChannelInboundHandler接口。

ChannelInboundHandler提供了很多事件处理方法

• channelRead

当服务端收到新数据的时候，channelRead方法被调用

收到的消息的类型是 ByteBuf，它是一个引用计数对象，必须显示调用release方法来释放。

一般在channelRead中处理的代码形如

@Override
public void channelRead(ChannelHandlerContext ctx, Object msg) {
	try {
	// Do something with msg
	} finally {
       ReferenceCountUtil.release(msg);
	}
}

• exceptionCaught

当服务端产生Throwable对象后，就会调用exceptionCaught

在大部分情况下，捕获的异常应该被记录下来并且把关联的 channel 给关闭掉。

然而这个方法的处理方式会在遇到不同异常的情况下有不同的实现，

比如你可能想在关闭连接之前发送一个错误码的响应消息。

DiscardServer

package org.zln.test.netty4.discard;

public class DiscardServer {
    private int port;

    public DiscardServer(int port) {
        this.port = port;
    }

    public static void main(String[] args) {
        int port = 8080;
        if (args.length > 0) {
            port = Integer.parseInt(args[0]);
        }
        new DiscardServer(port).run();
    }

    private void run() {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel socketChannel)
                            throws Exception {
                            socketChannel.pipeline()
                                .addLast(new DiscardServerHandler());
                        }
                    })
                    .option(ChannelOption.SO_BACKLOG, 128)
                    .childOption(ChannelOption.SO_KEEPALIVE, true);
            ChannelFuture f = b.bind(port).sync();
            f.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            workerGroup.shutdownGracefully();
            bossGroup.shutdownGracefully();
        }
    }
}

NioEventLoopGroup：用于处理I/O操作的多线程事件循环器

bossGroup：接收客户端连接

workerGroup：处理已经接收到的连接

​ 一旦boss接收到连接，就会把连接信息注册到worker中

ServerBootstrap：用于启动NIO服务的辅助类

测试

telnet localhost 8080

目前在DiscardServerHandler上，是直接丢弃的，没有打印出来，所以我们现在加一个打印

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf in = (ByteBuf) msg;
        System.out.println(in.toString(CharsetUtil.UTF_8));
    }

在toString中已经做了release动作，所以不需要再次手工释放资源

详细代码：test-netty4-discard-demo2

应答服务器

详细代码：test-netty4-ask

将客户端的请求消息原样返回

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ctx.write(msg);//写入后，内部已经实现了消息资源的释放
        ctx.flush();
    }

或者

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ctx.writeAndFlush(msg);//写入后，内部已经实现了消息资源的释放
    }

时间服务器

时间服务器

在与客户端建立连接时，就发送时间消息

TimeServerHandler

public class TimeServerHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        final ByteBuf time = ctx.alloc().buffer(4);
        time.writeInt((int) (System.currentTimeMillis() / 1000L + 2208988800L));
        final ChannelFuture f = ctx.writeAndFlush(time);
        f.addListener(new ChannelFutureListener() {
            @Override
            public void operationComplete(ChannelFuture future) {
                assert f == future;
                ctx.close();
            }
        });
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause)
        throws Exception {
        cause.printStackTrace();
//        出现异常时关闭连接
        ctx.close();
    }
}

final ByteBuf time = ctx.alloc().buffer(4);

分配指定大小的缓冲

因为要写入32位蒸熟，所以分配4个字节大小的缓冲区

为什么不需要flip操作？

传统NIO缓冲区，因为只有一个位置索引，所以在写完后，如果想要读区，需要执行一次flip操作，将位置指针设置到头部。

Netty提供的ByteBuf缓冲区对象，有读写两个指针，执行写的时候只是写的指针索引增加，读指针位置索引不变，所以不需要flip操作。

ChannelFuture

表示一个还未发送的I/O事件

对ChannelFuture添加监听，可以得知当前I/O操作的具体执行情况

addListener

添加一个事件监听。

如果直接ctx.close();的话，由于writeAndFlush是异步的，会出现还没写完连接就被关闭的情况。

所以要在监听到写完成的事件后再执行close操作

ctx.close()

连接关闭也不是立马生效的，其也是返回一个ChannelFuture对象

另一种简单的监听写法为

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        final ByteBuf time = ctx.alloc().buffer(4);
        time.writeInt((int) (System.currentTimeMillis() / 1000L + 2208988800L));
        final ChannelFuture f = ctx.writeAndFlush(time);
        f.addListener(ChannelFutureListener.CLOSE);
    }

内置的ChannelFutureListener.CLOSE其实和我们自己对ChannelFutureListener内容是完全一样的

TimeClient

public class TimeClient {

    private static final String HOST = "localhost";
    private static final int PORT = 8080;

    public static void main(String[] args) {
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(workerGroup);
            b.channel(NioSocketChannel.class);
            b.option(ChannelOption.SO_KEEPALIVE, true);
            b.handler(new ChannelInitializer<SocketChannel>() {
                @Override
                public void initChannel(SocketChannel ch) throws Exception {
                    ch.pipeline().addLast(new TimeClientHandler());
                }
            });
            ChannelFuture f = b.connect(HOST, PORT).sync();
            f.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            workerGroup.shutdownGracefully();
        }
    }
}

• 比较客户端与服务的启动类的若干不同

1、只有worker没有boss

2、使用NioSocketChannel，不是NioServerSocketChannel

3、不需要childOption。因为客户端的SocketChannel没有父类

4、使用connect，不是bind

TimeClientHandler

public class TimeClientHandler extends ChannelInboundHandlerAdapter {
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        ByteBuf m = (ByteBuf) msg;
        try {
            long currentTimeMillis = (m.readUnsignedInt() - 2208988800L) * 1000L;
            System.out.println(new Date(currentTimeMillis));
            ctx.close();
        } finally {
            m.release();
        }
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
//        出现异常时关闭连接
        ctx.close();
    }
}

客户端的Handler就比较简单了，就不细说了

整个流程是这样子的

1、客户端发起连接

2、服务端channelActive监听到连接，发送时间数据

3、客户端channelRead接收到服务端请求，打印数据

漏洞

这里其实是有一个漏洞的，就是我们其实是希望一条完整的消息大小为4个字节，可实际情况是不一定的。

也就是会函数TCP/IP协议的粘包与拆包的问题

使用对象传递日期

完整代码

我们需要处理的数据，往往是有一个结构的，一般会封装到一个对象中，

而数据在网络中实际传输的时候，肯定是以字节的形式的。

如果我们在代码上想要直接处理对象，那么就需要编写解码器和编码器。

编码器：将发送的对象转化为字节

解码器：将收到的字节转化为对象

• UnixTime

public class UnixTime {
    private final long value;

    public UnixTime() {
        this(System.currentTimeMillis() / 1000L + 2208988800L);
    }

    public UnixTime(long value) {
        this.value = value;
    }

    public long value() {
        return value;
    }

    @Override
    public String toString() {
        return new Date((value() - 2208988800L) * 1000L).toString();
    }

}

我们把时间戳封装在UnixTime对象中

• TimeDecoder：解码器

public class TimeDecoder extends ByteToMessageDecoder {
    @Override
    protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
        if (in.readableBytes() < 4) {
            return;
        }
        out.add(new UnixTime(in.readUnsignedInt()));
    }
}

• TimeEncoder：编码器

public class TimeEncoder extends MessageToByteEncoder<UnixTime> {

    @Override
    protected void encode(ChannelHandlerContext ctx, UnixTime msg, ByteBuf out)
        throws Exception {
        out.writeInt((int) msg.value());
    }
}

• TimeServerHandler

使用了编码器后，我们可以直接发送对象

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ChannelFuture f = ctx.writeAndFlush(new UnixTime());
        f.addListener(ChannelFutureListener.CLOSE);
    }

• TimeClientHandler

使用了解码器后，直接转化成对象

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        UnixTime m = (UnixTime) msg;
        System.out.println("收到：" + m);
        ctx.close();
    }

• 配置

编码器和解码器编写完后，需要配置到启动类中

服务端配置编码器:socketChannel.pipeline().addLast(new TimeEncoder(),new TimeServerHandler());

客户端配置解码器:ch.pipeline().addLast(new TimeDecoder(),new TimeClientHandler());

聊天应用

详细代码

ChatServerHandler

@Slf4j
public class ChatServerHandler extends SimpleChannelInboundHandler<String> {

    public static ChannelGroup channels = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);

    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        Channel incoming = ctx.channel();
        for (Channel channel : channels) {
            channel.writeAndFlush("[SERVER] - " + incoming.remoteAddress() + " 加入\n");
        }
        channels.add(ctx.channel());
    }

    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
        Channel incoming = ctx.channel();
        for (Channel channel : channels) {
            channel.writeAndFlush("[SERVER] - " + incoming.remoteAddress() + " 离开\n");
        }
        channels.remove(ctx.channel());
    }

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        Channel incoming = ctx.channel();
        for (Channel channel : channels) {
            if (channel != incoming) {
                channel.writeAndFlush("[" + incoming.remoteAddress() + "]" + msg + "\n");
            } else {
                channel.writeAndFlush("[响应]" + msg + "\n");
            }
        }
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        Channel incoming = ctx.channel();
        System.out.println("ChatClient:" + incoming.remoteAddress() + "在线");
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        Channel incoming = ctx.channel();
        System.out.println("ChatClient:" + incoming.remoteAddress() + "掉线");
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        Channel incoming = ctx.channel();
        System.out.println("ChatClient:" + incoming.remoteAddress() + "异常"); // 当出现异常就关闭连接
        cause.printStackTrace();
        ctx.close();
    }

}

ChatServerInitializer

public class ChatServerInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        pipeline.addLast("framer", new DelimiterBasedFrameDecoder(8192, Delimiters.lineDelimiter()));
        pipeline.addLast("decoder", new StringDecoder());
        pipeline.addLast("encoder", new StringEncoder());
        pipeline.addLast("handler", new ChatServerHandler());
        System.out.println("ChatClient:" + ch.remoteAddress() + "连接上");
    }
}

ChatServer

public class ChatServer {
    private int port;

    public ChatServer(int port) {
        this.port = port;
    }

    public static void main(String[] args) {
        int port = 8080;
        if (args.length > 0) {
            port = Integer.parseInt(args[0]);
        }
        new ChatServer(port).run();
    }

    private void run() {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            ServerBootstrap b = new ServerBootstrap();
            b.group(bossGroup, workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new ChatServerInitializer())
                    .option(ChannelOption.SO_BACKLOG, 128)
                    .childOption(ChannelOption.SO_KEEPALIVE, true);

            System.out.println("服务端启动完成");

            ChannelFuture f = b.bind(port).sync();
            f.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            workerGroup.shutdownGracefully();
            bossGroup.shutdownGracefully();
        }
    }
}

ChatClientHandler

public class ChatClientHandler extends SimpleChannelInboundHandler<String> {

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        System.out.println(msg);
    }

    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
//        出现异常时关闭连接
        ctx.close();
    }
}

ChatClientInitializer

public class ChatClientInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        pipeline.addLast("framer", new DelimiterBasedFrameDecoder(8192, Delimiters.lineDelimiter()));
        pipeline.addLast("decoder", new StringDecoder());
        pipeline.addLast("encoder", new StringEncoder());
        pipeline.addLast("handler", new ChatClientHandler());
    }
}

ChatClient

public class ChatClient {

    private static final String HOST = "localhost";
    private static final int PORT = 8080;

    public static void main(String[] args) {
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try {
            Bootstrap b = new Bootstrap();
            b.group(workerGroup);
            b.channel(NioSocketChannel.class);
            b.option(ChannelOption.SO_KEEPALIVE, true);
            b.handler(new ChatClientInitializer());
            ChannelFuture f = b.connect(HOST, PORT).sync();
            Channel channel = f.channel();
            BufferedReader bufferedReader = new BufferedReader(new InputStreamReader(System.in));
            while (true) {
                System.out.println("请输入：");
                String line = bufferedReader.readLine();
                if (line.startsWith("exit")) {
                    System.out.println("结束聊天");
                    break;
                }
                channel.writeAndFlush(line + "\r\n");
            }
            f.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } catch (IOException e) {
            e.printStackTrace();
        } finally {
            workerGroup.shutdownGracefully();
        }
    }
}