Netty4.0学习笔记系列之四：混合使用coder和handler

布满荆棘的人生 2022-04-11 09:11 120阅读 0赞

Handler如何使用在前面的例子中已经有了示范，那么同样是扩展自ChannelHandler的Encoder和Decoder，与Handler混合后又是如何使用的？本文将通过一个实际的小例子来展示它们的用法。

该例子模拟一个Server和Client，两者之间通过http协议进行通讯，在Server内部通过一个自定义的StringDecoder把httprequest转换成String。Server端处理完成后，通过StringEncoder把String转换成httpresponse，发送给客户端。具体的处理流程如图所示：

![201703cd-c9e6-30d8-a25e-1e53bc7981d4.jpg][]  
        其中红色框中的Decoder、Encoder及request都是Netty框架自带的，灰色框中的三个类是我自己实现的。

Server端的类有：Server StringDecoder BusinessHandler StringEncoder四个类。

1.Server.java启动netty服务，并注册handler、coder，注意注册的顺序：

package com.bijian.netty.server;
    
    import io.netty.bootstrap.ServerBootstrap;
    import io.netty.channel.ChannelFuture;
    import io.netty.channel.ChannelInitializer;
    import io.netty.channel.ChannelOption;
    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 io.netty.handler.codec.http.HttpRequestDecoder;
    import io.netty.handler.codec.http.HttpResponseEncoder;
    
    // 测试coder 和 handler 的混合使用
    public class Server {
        
        public void start(int port) throws Exception {
            
            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
                            public void initChannel(SocketChannel ch) throws Exception {
                                // 都属于ChannelOutboundHandler，逆序执行
                                ch.pipeline().addLast(new HttpResponseEncoder());
                                ch.pipeline().addLast(new StringEncoder());
    
                                // 都属于ChannelIntboundHandler，按照顺序执行
                                ch.pipeline().addLast(new HttpRequestDecoder());
                                ch.pipeline().addLast(new StringDecoder());
                                ch.pipeline().addLast(new BusinessHandler());
                            }
                        }).option(ChannelOption.SO_BACKLOG, 128).childOption(ChannelOption.SO_KEEPALIVE, true);
    
                ChannelFuture f = b.bind(port).sync();
    
                f.channel().closeFuture().sync();
            } finally {
                workerGroup.shutdownGracefully();
                bossGroup.shutdownGracefully();
            }
        }
    
        public static void main(String[] args) throws Exception {
            Server server = new Server();
            server.start(8000);
        }
    }

2.StringDecoder.java把httpRequest转换成String，其中ByteBufToBytes是一个工具类，负责对ByteBuf中的数据进行读取

package com.bijian.netty.server;
    
    import io.netty.channel.ChannelHandlerContext;
    import io.netty.channel.ChannelInboundHandlerAdapter;
    import io.netty.handler.codec.http.HttpContent;
    import io.netty.handler.codec.http.HttpHeaders;
    import io.netty.handler.codec.http.HttpRequest;
    
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    
    import com.bijian.netty.util.ByteBufToBytes;
    
    public class StringDecoder extends ChannelInboundHandlerAdapter {
        
        private static Logger logger = LoggerFactory.getLogger(StringDecoder.class);
        private ByteBufToBytes reader;
    
        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            
            logger.info("StringDecoder : msg's type is " + msg.getClass());
            if (msg instanceof HttpRequest) {
                HttpRequest request = (HttpRequest) msg;
                reader = new ByteBufToBytes((int) HttpHeaders.getContentLength(request));
            }
    
            if (msg instanceof HttpContent) {
                HttpContent content = (HttpContent) msg;
                reader.reading(content.content());
    
                if (reader.isEnd()) {
                    byte[] clientMsg = reader.readFull();
                    logger.info("StringDecoder : change httpcontent to string ");
                    ctx.fireChannelRead(new String(clientMsg));
                }
            }
        }
    }

3.BusinessHandler.java具体处理业务的类，把客户端的请求打印出来，并向客户端发送信息

package com.bijian.netty.server;
    
    import io.netty.channel.ChannelHandlerContext;
    import io.netty.channel.ChannelInboundHandlerAdapter;
    
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    
    public class BusinessHandler extends ChannelInboundHandlerAdapter {
        
        private Logger logger = LoggerFactory.getLogger(BusinessHandler.class);
    
        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            String clientMsg = "client said : " + (String) msg;
            logger.info("BusinessHandler read msg from client :" + clientMsg);
            ctx.write("I am very OK!");
        }
        
        @Override
        public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
            ctx.flush();
        }
    }

4.StringEncoder.java把字符串转换成HttpResponse

package com.bijian.netty.server;
    
    import static io.netty.handler.codec.http.HttpHeaders.Names.CONNECTION;
    import static io.netty.handler.codec.http.HttpHeaders.Names.CONTENT_LENGTH;
    import static io.netty.handler.codec.http.HttpHeaders.Names.CONTENT_TYPE;
    import static io.netty.handler.codec.http.HttpResponseStatus.OK;
    import static io.netty.handler.codec.http.HttpVersion.HTTP_1_1;
    
    import org.slf4j.Logger;
    import org.slf4j.LoggerFactory;
    
    import io.netty.buffer.Unpooled;
    import io.netty.channel.ChannelHandlerContext;
    import io.netty.channel.ChannelOutboundHandlerAdapter;
    import io.netty.channel.ChannelPromise;
    import io.netty.handler.codec.http.DefaultFullHttpResponse;
    import io.netty.handler.codec.http.FullHttpResponse;
    import io.netty.handler.codec.http.HttpHeaders.Values;
    
    // 把String转换成httpResponse
    public class StringEncoder extends ChannelOutboundHandlerAdapter {
        
        private Logger logger = LoggerFactory.getLogger(StringEncoder.class);
    
        @Override
        public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
            
            logger.info("StringEncoder response to client.");
            String serverMsg = (String) msg;
    
            FullHttpResponse response = new DefaultFullHttpResponse(HTTP_1_1, OK, Unpooled.wrappedBuffer(serverMsg
                    .getBytes()));
            response.headers().set(CONTENT_TYPE, "text/plain");
            response.headers().set(CONTENT_LENGTH, response.content().readableBytes());
            response.headers().set(CONNECTION, Values.KEEP_ALIVE);
            ctx.write(response);
            ctx.flush();
        }
    }

Client端有两个类：Client.java、ClientInitHandler.java

1.Client.java与Server端建立连接，并向Server端发送HttpRequest请求。

package com.bijian.netty.client;
    
    import io.netty.bootstrap.Bootstrap;
    import io.netty.buffer.Unpooled;
    import io.netty.channel.ChannelFuture;
    import io.netty.channel.ChannelInitializer;
    import io.netty.channel.ChannelOption;
    import io.netty.channel.EventLoopGroup;
    import io.netty.channel.nio.NioEventLoopGroup;
    import io.netty.channel.socket.SocketChannel;
    import io.netty.channel.socket.nio.NioSocketChannel;
    import io.netty.handler.codec.http.DefaultFullHttpRequest;
    import io.netty.handler.codec.http.HttpHeaders;
    import io.netty.handler.codec.http.HttpMethod;
    import io.netty.handler.codec.http.HttpRequestEncoder;
    import io.netty.handler.codec.http.HttpResponseDecoder;
    import io.netty.handler.codec.http.HttpVersion;
    
    import java.net.URI;
    
    public class Client {
        
        public void connect(String host, int port) throws Exception {
            
            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 HttpResponseDecoder());
                        ch.pipeline().addLast(new HttpRequestEncoder());
                        ch.pipeline().addLast(new ClientInitHandler());
                    }
                });
    
                // Start the client.
                ChannelFuture f = b.connect(host, port).sync();
    
                URI uri = new URI("http://127.0.0.1:8000");
                String msg = "Are you ok?";
                DefaultFullHttpRequest request = new DefaultFullHttpRequest(HttpVersion.HTTP_1_1, HttpMethod.POST,
                        uri.toASCIIString(), Unpooled.wrappedBuffer(msg.getBytes()));
    
                request.headers().set(HttpHeaders.Names.HOST, host);
                request.headers().set(HttpHeaders.Names.CONNECTION, HttpHeaders.Values.KEEP_ALIVE);
                request.headers().set(HttpHeaders.Names.CONTENT_LENGTH, request.content().readableBytes());
                f.channel().write(request);
                f.channel().flush();
                f.channel().closeFuture().sync();
            } finally {
                workerGroup.shutdownGracefully();
            }
        }
    
        public static void main(String[] args) throws Exception {
            Client client = new Client();
            client.connect("127.0.0.1", 8000);
        }
    }

2.ClientInitHandler.java从Server端读取响应信息

package com.bijian.netty.client;
    
    import io.netty.buffer.ByteBuf;
    import io.netty.channel.ChannelHandlerContext;
    import io.netty.channel.ChannelInboundHandlerAdapter;
    import io.netty.handler.codec.http.HttpContent;
    import io.netty.handler.codec.http.HttpHeaders;
    import io.netty.handler.codec.http.HttpResponse;
    
    import com.bijian.netty.util.ByteBufToBytes;
    
    public class ClientInitHandler extends ChannelInboundHandlerAdapter {
        
        private ByteBufToBytes reader;
    
        @Override
        public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
            
            if (msg instanceof HttpResponse) {
                HttpResponse response = (HttpResponse) msg;
                if (HttpHeaders.isContentLengthSet(response)) {
                    reader = new ByteBufToBytes((int) HttpHeaders.getContentLength(response));
                }
            }
            if (msg instanceof HttpContent) {
                HttpContent httpContent = (HttpContent) msg;
                ByteBuf content = httpContent.content();
                reader.reading(content);
                content.release();
    
                if (reader.isEnd()) {
                    String resultStr = new String(reader.readFull());
                    System.out.println("Server said:" + resultStr);
                }
            }
        }
    
        @Override
        public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
            ctx.close();
        }
    }

工具类：ByteBufToBytes 对ByteBuf的数据进行读取，支持流式读取（reading 和 readFull方法结合使用）

ByteBufToBytes.java

package com.bijian.netty.util;
    
    import io.netty.buffer.ByteBuf;
    import io.netty.buffer.Unpooled;
    
    public class ByteBufToBytes {
        
        private ByteBuf temp;
    
        private boolean end = true;
    
        public ByteBufToBytes(int length) {
            temp = Unpooled.buffer(length);
        }
    
        public void reading(ByteBuf datas) {
            datas.readBytes(temp, datas.readableBytes());
            if (this.temp.writableBytes() != 0) {
                end = false;
            } else {
                end = true;
            }
        }
    
        public boolean isEnd() {
            return end;
        }
    
        public byte[] readFull() {
            if (end) {
                byte[] contentByte = new byte[this.temp.readableBytes()];
                this.temp.readBytes(contentByte);
                this.temp.release();
                return contentByte;
            } else {
                return null;
            }
        }
    
        public byte[] read(ByteBuf datas) {
            byte[] bytes = new byte[datas.readableBytes()];
            datas.readBytes(bytes);
            return bytes;
        }
    }

运行结果：

23:22:40.846 INFO  com.bijian.netty.server.StringDecoder 22 channelRead - StringDecoder : msg's type is class io.netty.handler.codec.http.DefaultHttpRequest
    23:22:40.848 INFO  com.bijian.netty.server.StringDecoder 22 channelRead - StringDecoder : msg's type is class io.netty.handler.codec.http.DefaultLastHttpContent
    23:22:40.848 INFO  com.bijian.netty.server.StringDecoder 34 channelRead - StringDecoder : change httpcontent to string 
    23:22:40.849 INFO  com.bijian.netty.server.BusinessHandler 16 channelRead - BusinessHandler read msg from client :client said : Are you ok?
    23:22:40.849 INFO  com.bijian.netty.server.StringEncoder 28 write - StringEncoder response to client.

可以看到执行顺序为：StringDecoder、BusinessHandler、StringEncoder，其它的都是Netty自身的，没有打印。

通过该实例证明，Encoder、Decoder的本质也是Handler，它们的执行顺序、使用方法与Handler保持一致。

执行顺序是：Encoder 先注册的后执行，与OutboundHandler一致；Decoder是先注册的先执行，与InboundHandler一致。

文章来源：[http://blog.csdn.net/u013252773/article/details/21564301][http_blog.csdn.net_u013252773_article_details_21564301]

[201703cd-c9e6-30d8-a25e-1e53bc7981d4.jpg]: /images/20220411/179c339cbd4b4698a31a82326c7f08f8.png
[http_blog.csdn.net_u013252773_article_details_21564301]: http://blog.csdn.net/u013252773/article/details/21564301