Netty使用Protobuf编解码-蒲公英云

Protobuf是一个灵活、高效、结构化的数据序列化框架，相比于XML等传统的序列化工具，它更小、更快、更简单。Protobuf支持数据结构化一次可以到处使用，甚至跨语言使用，通过代码生成工具可以自动生成不同语言版本的源代码，甚至可以在使用不同版本的数据结构进程间进行数据传递，实现数据结构的前向兼容。

下面结合一个例子看看在Netty如何使用Protobuf对POJO对象进行编解码。

1.Protobuf环境搭建

从https://developers.google.com/protocol-buffers/docs/downloads下载Protobuf，本例中是3.0.0版本。

下载后对压缩包进行解压，在/bin目录可以看到protoc.exe。protoc.exe根据.proto文件生成代码。下面根据图书订购程序定义SubcribeReq.proto和SubcribeResp.proto文件。
SubcribeReq.proto文件内容：

syntax = "proto3";
package netty;
option java_package = "com.tommy.netty.protobuf";
option java_outer_classname = "SubcribeReqProto";
message SubcribeReq { int32 subReqID = 1; string userName = 2; string productName = 3; repeated string address = 4; }

SubcribeResp.proto文件内容：

syntax = "proto3";
package netty;
option java_package = "com.tommy.netty.protobuf";
option java_outer_classname = "SubcribeRespProto";
message SubcribeResp {
    int32 subReqID = 1;
    int32 respCode = 2;
    string desc = 3;
}

通过protoc.exe生成代码。
进入到protoc.exe目录，分别执行：
protoc.exe --java_out=.\src .\netty\SubcribeReq.proto和protoc.exe --java_out=.\src .\netty\SubcribeResp.proto
在/bin目录的src目录中可以看到生成的文件。（注意：要提前创建好src目录）

将生成的SubcribeReqProto.java和SubcribeRespProto.java复制到工程中。

在工程中导入protobuf3.0.0的包：

<!-- https://mvnrepository.com/artifact/com.google.protobuf/protobuf-java -->
<dependency>
  <groupId>com.google.protobuf</groupId>
  <artifactId>protobuf-java</artifactId>
  <version>3.0.0</version>
</dependency>

2.Protobuf编解码开发

/** * @author j.tommy * @version 1.0 * @date 2017/12/10 */
public class TestSubcribeReqProto { 
    private static byte[] encode(SubcribeReqProto.SubcribeReq subcribeReq) {
        return subcribeReq.toByteArray();
    }
    private static SubcribeReqProto.SubcribeReq decode(byte[] body) throws InvalidProtocolBufferException {
        return SubcribeReqProto.SubcribeReq.parseFrom(body);
    }
    private static SubcribeReqProto.SubcribeReq createSubcribeReq() {
        SubcribeReqProto.SubcribeReq.Builder builder = SubcribeReqProto.SubcribeReq.newBuilder();
        builder.setSubReqID(1);
        builder.setUserName("j.tommy");
        builder.setProductName("Netty权威指南");
        List<String> addressList = new ArrayList<String>();
        addressList.add("北京市");
        addressList.add("上海市");
        addressList.add("西安市");
        addressList.add("深圳市");
        builder.addAllAddress(addressList);
        return builder.build();
    }
    public static void main(String[] args) throws InvalidProtocolBufferException {
        SubcribeReqProto.SubcribeReq req = createSubcribeReq();
        System.out.println("Before encode:" + req);
        SubcribeReqProto.SubcribeReq req2 = decode(encode(req));
        System.out.println("After decode:" + req2);
        System.out.println("Assert equals:" + req.equals(req2));
    }
}

通过SubcribeReq的.newBuilder()创建Builder，通过Builder设置SubscribeReq的属性，最后通过builder.builder()方法生成对象。

编码时通过SubscribeReq的toByteArray()即可将SubcribeReq编码为直接数组。
解码时通过SubscribeReq的parseForm将二进制数组编码为SubscribeReq对象。

运行结果：

3.Netty的Protobuf订购程序开发

服务端代码：

/** * @author j.tommy * @version 1.0 * @date 2017/12/10 */
public class SubcribeServer { 
    public static void main(String[] args) {
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();
        ServerBootstrap s = new ServerBootstrap();
        s.group(bossGroup,workerGroup)
                .channel(NioServerSocketChannel.class)
                .handler(new LoggingHandler(LogLevel.INFO))
                .option(ChannelOption.SO_BACKLOG, 100)
                .childHandler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel sc) throws Exception {
                        sc.pipeline().addLast(new ProtobufVarint32FrameDecoder());
                        sc.pipeline().addLast(new ProtobufDecoder(SubcribeReqProto.SubcribeReq.getDefaultInstance()));
                        sc.pipeline().addLast(new ProtobufVarint32LengthFieldPrepender());
                        sc.pipeline().addLast(new ProtobufEncoder());
                        sc.pipeline().addLast(new SubcribeServerHandler());
                    }
                });
        try {
            ChannelFuture cf = s.bind(9989).sync();
            cf.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            bossGroup.shutdownGracefully();
            workerGroup.shutdownGracefully();
        }
    }
}
class SubcribeServerHandler extends ChannelHandlerAdapter {
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        ctx.close();
    }
    private SubcribeRespProto.SubcribeResp createSubcribeResp(int subReqID) {
        SubcribeRespProto.SubcribeResp.Builder builder = SubcribeRespProto.SubcribeResp.newBuilder();
        builder.setSubReqID(subReqID);
        builder.setRespCode(0);
        builder.setDesc("Order success.");
        return builder.build();
    }
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        SubcribeReqProto.SubcribeReq req = (SubcribeReqProto.SubcribeReq) msg;
        System.out.println("接收到客户端请求：" + req.getSubReqID() + ",userName:" + req.getUserName() + ",productName:" + req.getProductName());
        SubcribeRespProto.SubcribeResp resp = createSubcribeResp(req.getSubReqID());
        ctx.writeAndFlush(resp);
    }
}

客户端代码：

/** * @author j.tommy * @version 1.0 * @date 2017/12/10 */
public class SubcribleClient { 
    public static void main(String[] args) {
        EventLoopGroup group = new NioEventLoopGroup();
        Bootstrap b = new Bootstrap();
        b.group(group)
                .channel(NioSocketChannel.class)
                .option(ChannelOption.TCP_NODELAY, true)
                .handler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(SocketChannel sc) throws Exception {
                        sc.pipeline().addLast(new ProtobufVarint32FrameDecoder());
                        sc.pipeline().addLast(new ProtobufDecoder(SubcribeRespProto.SubcribeResp.getDefaultInstance()));
                        sc.pipeline().addLast(new ProtobufVarint32LengthFieldPrepender());
                        sc.pipeline().addLast(new ProtobufEncoder());
                        sc.pipeline().addLast(new SubcribleClientHandler());
                    }
                });
        try {
            ChannelFuture f = b.connect("127.0.0.1", 9989).sync();
            f.channel().closeFuture().sync();
        } catch (InterruptedException e) {
            e.printStackTrace();
        } finally {
            group.shutdownGracefully();
        }
    }
}
class SubcribleClientHandler extends ChannelHandlerAdapter {
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        cause.printStackTrace();
        ctx.close();
    }
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        SubcribeReqProto.SubcribeReq req = null;
        for (int i=0;i<10;i++) {
            req = createSubcribeReq(i);
            ctx.write(req);
        }
        ctx.flush();
    }
    private SubcribeReqProto.SubcribeReq createSubcribeReq(int subSeqID) {
        SubcribeReqProto.SubcribeReq.Builder builder = SubcribeReqProto.SubcribeReq.newBuilder();
        builder.setSubReqID(subSeqID);
        builder.setUserName("j.tommy");
        builder.setProductName("netty权威指南");
        List<String> addressList = new ArrayList<String>();
        addressList.add("北京市");
        addressList.add("西安市");
        addressList.add("深圳市");
        return builder.build();
    }
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        SubcribeRespProto.SubcribeResp resp = (SubcribeRespProto.SubcribeResp) msg;
        System.out.println("接收到服务端响应：" + resp.getSubReqID() + ",responseCode:" + resp.getRespCode() + ",desc:" + resp.getDesc());
    }
}

ProtobufVarint32FrameDecoder，它主要用来处理半包；

ProtobufDecoder解压器，它的参数是com.google.protobuf.MessageLite，实际上是告诉ProtobufDecoder需要解码的目标类是什么，否则仅仅从字节数组是无法知道要解码的目标类型信息的。

服务端中ProtobufEncoder用于对响应的SubcribeResp进行编码。

运行结果：
服务端：

客户端：

4.Protobuf的使用注意事项

ProtobufDecoder仅仅负责解码，它不支持读半包。因此在ProtobufDecoder的前面，一定要有能够处理半包消息的解码器。
有3种方式可以选择：
1.使用Netty提供的ProtobufVarint32FrameDecoder，它可以处理半包消息；
2.继承Netty提供的通用半包解码器LengthFieldBasedFrameDecoder;
3.继承ByteToMessageDecoder类，自己处理半包消息。

如果只使用ProtobufDecoder解码器，而忽略对半包消息的处理，程序没法正常工作。

参考《Netty权威指南》