Netty4.0学习笔记系列之四：混合使用coder和handler

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：

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 启动netty服务，并注册handler、coder，注意注册的顺序：

package com.guowl.testmulticoderandhandler;

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 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.guowl.testmulticoderandhandler;

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.guowl.utils.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 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.guowl.testmulticoderandhandler;

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 把字符串转换成HttpResponse

package com.guowl.testmulticoderandhandler;

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 ClientInitHandler
1、Client 与Server端建立连接，并向Server端发送HttpRequest请求。

package com.guowl.testmulticoderandhandler;

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 从Server端读取响应信息

package com.guowl.testmulticoderandhandler;

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.guowl.utils.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 

package com.guowl.utils;

import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;

public class ByteBufToBytes {
    private ByteBuf temp;

    private boolean end = true;

    public ByteBufToBytes() {}

    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：

2014-03-19 23:50:48 StringDecoder : msg's type is class io.netty.handler.codec.http.DefaultHttpRequest
2014-03-19 23:50:48 StringDecoder : msg's type is class io.netty.handler.codec.http.DefaultLastHttpContent
2014-03-19 23:50:48 StringDecoder : change httpcontent to string 
2014-03-19 23:50:48 BusinessHandler read msg from client :client said : Are you ok?
2014-03-19 23:50:48 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。