netty学习笔记之搭建http服务框架

以前看过不少netty的文章，也照着网上代码试着敲过一些示例代码，但没咋系统深入的看过，买过netty权威指南也没咋看，现在又双叒叕打算重新开始学一下，从浅入深的开始。

第一篇搭建一个简单的http服务，熟悉一下netty使用的大致流程。
netty版本：

dependencies {
    compile (
            "io.netty:netty-all:4.1.10.Final"
    )
}

启动类，主要是通过ServerBootstrap启动类来设置启动的各类参数：

public class TestServer {
    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 TestServerInitializer());

            ChannelFuture channelFuture = serverBootstrap.bind(8899).sync();
            channelFuture.channel().closeFuture().sync();
        } catch (Exception e) {
            e.printStackTrace();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }

    }
}

ChannelInitializer实现类，主要作用是向pipeline中添加Handler：

public class TestServerInitializer extends ChannelInitializer<SocketChannel> {
    @Override
    protected void initChannel(SocketChannel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();

        pipeline.addLast("httpServerCodex", new HttpServerCodec());
        pipeline.addLast("testHttpServerHandler", new TestHttpServerHandler());
    }
}

Handler类，实现SimpleChannelInboundHandler方法，主要是处理收到的消息：
channelRead0这个名字取的有点莫名其妙，在源码中的注释中看到本来要在5.0的版本中改名为messageReceived，结果后来5.0版本被废弃了。。。

public class TestHttpServerHandler extends SimpleChannelInboundHandler<HttpObject> {
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, HttpObject msg) throws Exception {
        if (msg instanceof HttpRequest) {

            HttpRequest httpRequest = (HttpRequest)msg;
            String name = httpRequest.method().name();
            System.out.println("请求方法名："+name);

            String uri = httpRequest.uri();
            System.out.println("请求uri："+uri);

            ByteBuf content = Unpooled.copiedBuffer("Hello World", CharsetUtil.UTF_8);
            DefaultFullHttpResponse response = new DefaultFullHttpResponse(HttpVersion.HTTP_1_1, HttpResponseStatus.OK, content);

            response.headers().set(HttpHeaderNames.CONTENT_TYPE, "text/plain");
            response.headers().set(HttpHeaderNames.CONTENT_LENGTH, content.readableBytes());

            ctx.writeAndFlush(response);
        }
    }

    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("channel active");
        super.channelActive(ctx);
    }

    @Override
    public void channelRegistered(ChannelHandlerContext ctx) throws Exception {
        System.out.println("channel registered");
        super.channelRegistered(ctx);
    }

    @Override
    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
        System.out.println("handler added");
        super.handlerAdded(ctx);
    }

    @Override
    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("channel inactive");
        super.channelInactive(ctx);
    }

    @Override
    public void channelUnregistered(ChannelHandlerContext ctx) throws Exception {
        System.out.println("channel unregistered");
        super.channelUnregistered(ctx);
    }
}

启动main方法，通过curl或者浏览器访问，即可看到服务器的返回: