Netty 应用：Socket服务器 - HelloWorld开发者社区

Socket服务器

Netty作为Socket服务器，需要编写服务端和客户端，服务器端和客户端收发消息通过自定义的Handler.channelRead0方法来交互，客户端连接上服务器后，需要在active时向服务器发送一条消息来触发服务器的行为。

服务端实现

/**
 * Created by fubin on 2019/7/11.
 */
public class SocketServer {
    public static void main(String[] args) {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try{
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup,workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new SocketServerInitializer());

            ChannelFuture channelFuture = serverBootstrap.bind(8899).sync();
            channelFuture.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}
class  SocketServerInitializer extends ChannelInitializer<SocketChannel>{
    protected void initChannel(SocketChannel socketChannel) throws Exception {
        ChannelPipeline channelPipeline = socketChannel.pipeline();
        channelPipeline.addLast(new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE,0,4,0,4));
        channelPipeline.addLast(new LengthFieldPrepender(4));
        channelPipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
        channelPipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));
        channelPipeline.addLast(new SocketServerHandler());
    }
}
class SocketServerHandler extends SimpleChannelInboundHandler<String>{
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        //远程地址
        System.out.println(ctx.channel().remoteAddress()+","+msg);
        //处理完业务，把结果返回给客户端
        ctx.channel().writeAndFlush("from server:"+ UUID.randomUUID());
    }
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        super.exceptionCaught(ctx, cause);
        //出现异常，关闭连接
        ctx.close();
    }
}

客户端实现

/**
 * Created by fubin on 2019/7/11.
 */
public class SocketClient {
    public static void main(String[] args) {
        EventLoopGroup eventLoopGroup = new NioEventLoopGroup();

        try{
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(eventLoopGroup).channel(NioSocketChannel.class).handler(new SocketClientInitializer());

            ChannelFuture future = bootstrap.connect("localhost",8899).sync();
            future.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            eventLoopGroup.shutdownGracefully();
        }
    }
}
class SocketClientInitializer extends ChannelInitializer<SocketChannel>{
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline channelPipeline = ch.pipeline();

        channelPipeline.addLast(new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE,0,4,0,4));
        channelPipeline.addLast(new LengthFieldPrepender(4));
        channelPipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
        channelPipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));
        channelPipeline.addLast(new SocketClientHandler());
    }
}
class SocketClientHandler extends SimpleChannelInboundHandler<String>{
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        System.out.println(ctx.channel().remoteAddress());
        System.out.println("client output:"+msg);
        ctx.channel().writeAndFlush("from client:"+ LocalDateTime.now());
    }
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        super.exceptionCaught(ctx, cause);
        ctx.close();
    }
    //在连接激活时，客户端向服务器发送一条消息
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        ctx.channel().writeAndFlush("hello world socket");
    }
}

Socket实现的聊天程序消息群发

netty实现多客户端消息群发的关键： ChannelGroup

服务端实现

/**
 * Created by fubin on 2019/7/11.
 * 聊天程序，消息群发
 */
public class ChatServer {
    public static void main(String[] args) {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        try{
            ServerBootstrap serverBootstrap = new ServerBootstrap();
            serverBootstrap.group(bossGroup,workerGroup)
                    .channel(NioServerSocketChannel.class)
                    .childHandler(new ChatServerInitializer());

            ChannelFuture channelFuture = serverBootstrap.bind(8899).sync();
            channelFuture.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}
class  ChatServerInitializer extends ChannelInitializer<SocketChannel> {
    protected void initChannel(SocketChannel socketChannel) throws Exception {
        ChannelPipeline channelPipeline = socketChannel.pipeline();
        //分隔符编解码器
        channelPipeline.addLast(new DelimiterBasedFrameDecoder(4096, Delimiters.lineDelimiter()));
        channelPipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
        channelPipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));
        channelPipeline.addLast(new ChatServerHandler());
    }
}
class ChatServerHandler extends SimpleChannelInboundHandler<String> {

    //保存channel对象
    private static ChannelGroup channels = new DefaultChannelGroup(GlobalEventExecutor.INSTANCE);

    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        Channel channel = ctx.channel();
        //广播消息
        channels.forEach(ch ->{
            if(channel != ch){
                ch.writeAndFlush(channel.remoteAddress() + "发送的消息："+ msg + "\n");
            }else{
                ch.writeAndFlush(" 【自己】" + msg + "\n");
            }
        });
    }
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        super.exceptionCaught(ctx, cause);
        //出现异常，关闭连接
        ctx.close();
    }
    /**
     * 连接建立，告诉其他客户端，xxx已经上线
     * @param ctx
     * @throws Exception
     */
    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        //广播
        channels.writeAndFlush("【服务器】 - " + channel.remoteAddress() + "加入\n");

        channels.add(channel);
    }
    @Override
    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        //广播
        channels.writeAndFlush("【服务器】 - " + channel.remoteAddress() + "离开\n");
        //此代码可不要，netty自动移除
        //channels.remove(channel);
        //验证
        System.out.println("channelGroup size :"+channels.size());
    }
    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        System.out.println("【服务器】- "+ channel.remoteAddress() + "下线\n");
    }
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        Channel channel = ctx.channel();
        System.out.println("【服务器】- "+ channel.remoteAddress() + "上线\n");
    }
}

客户端实现

/**
 * Created by fubin on 2019/7/11.
 */
public class ChatClient {
    public static void main(String[] args) {
        EventLoopGroup eventLoopGroup = new NioEventLoopGroup();

        try{
            Bootstrap bootstrap = new Bootstrap();
            bootstrap.group(eventLoopGroup).channel(NioSocketChannel.class).handler(new ChatClientInitializer());
            Channel channel = bootstrap.connect("localhost",8899).sync().channel();
            BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
            //循环监听客户端输入
            for(;;){
                channel.writeAndFlush(br.readLine()+"\r\n");
            }
        } catch (InterruptedException | IOException e) {
            e.printStackTrace();
        } finally {
            eventLoopGroup.shutdownGracefully();
        }
    }
}
class ChatClientInitializer extends ChannelInitializer<SocketChannel>{
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline channelPipeline = ch.pipeline();

        channelPipeline.addLast(new DelimiterBasedFrameDecoder(4096, Delimiters.lineDelimiter()));
        channelPipeline.addLast(new StringDecoder(CharsetUtil.UTF_8));
        channelPipeline.addLast(new StringEncoder(CharsetUtil.UTF_8));
        channelPipeline.addLast(new ChatClientHandler());
    }
}
class ChatClientHandler extends SimpleChannelInboundHandler<String>{
    protected void channelRead0(ChannelHandlerContext ctx, String msg) throws Exception {
        System.out.println(msg);
    }
}

应用内的推送的思考：服务器端和客户端维持长连接推送给app，如果客户端断线，服务端需要把消息保存在数据库或者mongodb中，当客户端重连后，服务端再再重新发送。