Protobuf快速入门实例

1. 编码和解码的基本介绍

　　编写网络应用程序时，因为数据在网络中传输的都是二进制字节码数据，在发送数据时就需要编码，接收数据时就需要解码。codec(编解码器) 的组成部分有两个：decoder(解码器)和 encoder(编码器)。encoder 负责把业务数据转换成字节码数据，decoder 负责把字节码数据转换成业务数据。

1. Netty 本身的编码解码的机制

Netty 自身提供了一些 codec(编解码器)

Netty 提供的编码器

StringEncoder，对字符串数据进行编码

ObjectEncoder，对 Java 对象进行编码
…

Netty 提供的解码器

StringDecoder, 对字符串数据进行解码

ObjectDecoder，对 Java 对象进行解码

…

Netty 本身自带的 ObjectDecoder 和 ObjectEncoder 可以用来实现 POJO 对象或各种业务对象的编码和解码，底层使用的仍是 Java 序列化技术 , 而Java 序列化技术本身效率就不高，存在如下问题:
（1）无法跨语言
（2）序列化后的体积太大，是二进制编码的 5 倍多。
（3）序列化性能比较低

2. Protobuf

Protobuf 是 Google 发布的开源项目，全称 Google Protocol Buffers，是一种轻便高效的结构化数据存储格式，可以用于结构化数据串行化，或者说序列化。它很适合做数据存储或 RPC[远程过程调用 remote procedure call ] 数据交换格式 。

git地址： https://github.com/protocolbuffers/protobuf

2. Protobuf 简单实用

1. 到git 上下载Protobuf 客户端工具，用于将proto 文件反向生成java类文件

 2. 编写.proto 文件： protobuf 以Message 进行管理

syntax = "proto3"; //版本
option java_outer_classname = "StudentPOJO";//生成的外部类名，同时也是文件名
//protobuf 使用message 管理数据
message Student { //会在 StudentPOJO 外部类生成一个内部类 Student， 他是真正发送的POJO对象
    int32 id = 1; // Student 类中有 一个属性 名字为 id 类型为int32(protobuf类型) 1表示属性序号，不是值
    string name = 2;
}

3. 用上面第一步下载的客户端反向生成java 类， cmd 命令行执行如下命令

protoc.exe --java_out=. StudentPOJO.proto

4. 生成的类信息如下：

package netty.codec;// Generated by the protocol buffer compiler.  DO NOT EDIT!
// source: StudentPOJO.proto

public final class StudentPOJO {
  private StudentPOJO() {}
  public static void registerAllExtensions(
      com.google.protobuf.ExtensionRegistryLite registry) {
  }

  public static void registerAllExtensions(
      com.google.protobuf.ExtensionRegistry registry) {
    registerAllExtensions(
        (com.google.protobuf.ExtensionRegistryLite) registry);
  }
  public interface StudentOrBuilder extends
      // @@protoc_insertion_point(interface_extends:Student)
      com.google.protobuf.MessageOrBuilder {

    /**
     * <pre>
     * Student 类中有 一个属性 名字为 id 类型为int32(protobuf类型) 1表示属性序号，不是值
     * </pre>
     *
     * <code>int32 id = 1;</code>
     * @return The id.
     */
    int getId();

    /**
     * <code>string name = 2;</code>
     * @return The name.
     */
    String getName();
    /**
     * <code>string name = 2;</code>
     * @return The bytes for name.
     */
    com.google.protobuf.ByteString
        getNameBytes();
  }
  /**
   * <pre>
   *protobuf 使用message 管理数据
   * </pre>
   *
   * Protobuf type {@code Student}
   */
  public static final class Student extends
      com.google.protobuf.GeneratedMessageV3 implements
      // @@protoc_insertion_point(message_implements:Student)
      StudentOrBuilder {
  private static final long serialVersionUID = 0L;
    // Use Student.newBuilder() to construct.
    private Student(com.google.protobuf.GeneratedMessageV3.Builder<?> builder) {
      super(builder);
    }
    private Student() {
      name_ = "";
    }

    @Override
    @SuppressWarnings({"unused"})
    protected Object newInstance(
        UnusedPrivateParameter unused) {
      return new Student();
    }

    @Override
    public final com.google.protobuf.UnknownFieldSet
    getUnknownFields() {
      return this.unknownFields;
    }
    private Student(
        com.google.protobuf.CodedInputStream input,
        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
        throws com.google.protobuf.InvalidProtocolBufferException {
      this();
      if (extensionRegistry == null) {
        throw new NullPointerException();
      }
      com.google.protobuf.UnknownFieldSet.Builder unknownFields =
          com.google.protobuf.UnknownFieldSet.newBuilder();
      try {
        boolean done = false;
        while (!done) {
          int tag = input.readTag();
          switch (tag) {
            case 0:
              done = true;
              break;
            case 8: {

              id_ = input.readInt32();
              break;
            }
            case 18: {
              String s = input.readStringRequireUtf8();

              name_ = s;
              break;
            }
            default: {
              if (!parseUnknownField(
                  input, unknownFields, extensionRegistry, tag)) {
                done = true;
              }
              break;
            }
          }
        }
      } catch (com.google.protobuf.InvalidProtocolBufferException e) {
        throw e.setUnfinishedMessage(this);
      } catch (java.io.IOException e) {
        throw new com.google.protobuf.InvalidProtocolBufferException(
            e).setUnfinishedMessage(this);
      } finally {
        this.unknownFields = unknownFields.build();
        makeExtensionsImmutable();
      }
    }
    public static final com.google.protobuf.Descriptors.Descriptor
        getDescriptor() {
      return StudentPOJO.internal_static_Student_descriptor;
    }

    @Override
    protected FieldAccessorTable
        internalGetFieldAccessorTable() {
      return StudentPOJO.internal_static_Student_fieldAccessorTable
          .ensureFieldAccessorsInitialized(
              Student.class, Builder.class);
    }

    public static final int ID_FIELD_NUMBER = 1;
    private int id_;
    /**
     * <pre>
     * Student 类中有 一个属性 名字为 id 类型为int32(protobuf类型) 1表示属性序号，不是值
     * </pre>
     *
     * <code>int32 id = 1;</code>
     * @return The id.
     */
    @Override
    public int getId() {
      return id_;
    }

    public static final int NAME_FIELD_NUMBER = 2;
    private volatile Object name_;
    /**
     * <code>string name = 2;</code>
     * @return The name.
     */
    @Override
    public String getName() {
      Object ref = name_;
      if (ref instanceof String) {
        return (String) ref;
      } else {
        com.google.protobuf.ByteString bs = 
            (com.google.protobuf.ByteString) ref;
        String s = bs.toStringUtf8();
        name_ = s;
        return s;
      }
    }
    /**
     * <code>string name = 2;</code>
     * @return The bytes for name.
     */
    @Override
    public com.google.protobuf.ByteString
        getNameBytes() {
      Object ref = name_;
      if (ref instanceof String) {
        com.google.protobuf.ByteString b = 
            com.google.protobuf.ByteString.copyFromUtf8(
                (String) ref);
        name_ = b;
        return b;
      } else {
        return (com.google.protobuf.ByteString) ref;
      }
    }

    private byte memoizedIsInitialized = -1;
    @Override
    public final boolean isInitialized() {
      byte isInitialized = memoizedIsInitialized;
      if (isInitialized == 1) return true;
      if (isInitialized == 0) return false;

      memoizedIsInitialized = 1;
      return true;
    }

    @Override
    public void writeTo(com.google.protobuf.CodedOutputStream output)
                        throws java.io.IOException {
      if (id_ != 0) {
        output.writeInt32(1, id_);
      }
      if (!getNameBytes().isEmpty()) {
        com.google.protobuf.GeneratedMessageV3.writeString(output, 2, name_);
      }
      unknownFields.writeTo(output);
    }

    @Override
    public int getSerializedSize() {
      int size = memoizedSize;
      if (size != -1) return size;

      size = 0;
      if (id_ != 0) {
        size += com.google.protobuf.CodedOutputStream
          .computeInt32Size(1, id_);
      }
      if (!getNameBytes().isEmpty()) {
        size += com.google.protobuf.GeneratedMessageV3.computeStringSize(2, name_);
      }
      size += unknownFields.getSerializedSize();
      memoizedSize = size;
      return size;
    }

    @Override
    public boolean equals(final Object obj) {
      if (obj == this) {
       return true;
      }
      if (!(obj instanceof Student)) {
        return super.equals(obj);
      }
      Student other = (Student) obj;

      if (getId()
          != other.getId()) return false;
      if (!getName()
          .equals(other.getName())) return false;
      if (!unknownFields.equals(other.unknownFields)) return false;
      return true;
    }

    @Override
    public int hashCode() {
      if (memoizedHashCode != 0) {
        return memoizedHashCode;
      }
      int hash = 41;
      hash = (19 * hash) + getDescriptor().hashCode();
      hash = (37 * hash) + ID_FIELD_NUMBER;
      hash = (53 * hash) + getId();
      hash = (37 * hash) + NAME_FIELD_NUMBER;
      hash = (53 * hash) + getName().hashCode();
      hash = (29 * hash) + unknownFields.hashCode();
      memoizedHashCode = hash;
      return hash;
    }

    public static Student parseFrom(
        java.nio.ByteBuffer data)
        throws com.google.protobuf.InvalidProtocolBufferException {
      return PARSER.parseFrom(data);
    }
    public static Student parseFrom(
        java.nio.ByteBuffer data,
        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
        throws com.google.protobuf.InvalidProtocolBufferException {
      return PARSER.parseFrom(data, extensionRegistry);
    }
    public static Student parseFrom(
        com.google.protobuf.ByteString data)
        throws com.google.protobuf.InvalidProtocolBufferException {
      return PARSER.parseFrom(data);
    }
    public static Student parseFrom(
        com.google.protobuf.ByteString data,
        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
        throws com.google.protobuf.InvalidProtocolBufferException {
      return PARSER.parseFrom(data, extensionRegistry);
    }
    public static Student parseFrom(byte[] data)
        throws com.google.protobuf.InvalidProtocolBufferException {
      return PARSER.parseFrom(data);
    }
    public static Student parseFrom(
        byte[] data,
        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
        throws com.google.protobuf.InvalidProtocolBufferException {
      return PARSER.parseFrom(data, extensionRegistry);
    }
    public static Student parseFrom(java.io.InputStream input)
        throws java.io.IOException {
      return com.google.protobuf.GeneratedMessageV3
          .parseWithIOException(PARSER, input);
    }
    public static Student parseFrom(
        java.io.InputStream input,
        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
        throws java.io.IOException {
      return com.google.protobuf.GeneratedMessageV3
          .parseWithIOException(PARSER, input, extensionRegistry);
    }
    public static Student parseDelimitedFrom(java.io.InputStream input)
        throws java.io.IOException {
      return com.google.protobuf.GeneratedMessageV3
          .parseDelimitedWithIOException(PARSER, input);
    }
    public static Student parseDelimitedFrom(
        java.io.InputStream input,
        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
        throws java.io.IOException {
      return com.google.protobuf.GeneratedMessageV3
          .parseDelimitedWithIOException(PARSER, input, extensionRegistry);
    }
    public static Student parseFrom(
        com.google.protobuf.CodedInputStream input)
        throws java.io.IOException {
      return com.google.protobuf.GeneratedMessageV3
          .parseWithIOException(PARSER, input);
    }
    public static Student parseFrom(
        com.google.protobuf.CodedInputStream input,
        com.google.protobuf.ExtensionRegistryLite extensionRegistry)
        throws java.io.IOException {
      return com.google.protobuf.GeneratedMessageV3
          .parseWithIOException(PARSER, input, extensionRegistry);
    }

    @Override
    public Builder newBuilderForType() { return newBuilder(); }
    public static Builder newBuilder() {
      return DEFAULT_INSTANCE.toBuilder();
    }
    public static Builder newBuilder(Student prototype) {
      return DEFAULT_INSTANCE.toBuilder().mergeFrom(prototype);
    }
    @Override
    public Builder toBuilder() {
      return this == DEFAULT_INSTANCE
          ? new Builder() : new Builder().mergeFrom(this);
    }

    @Override
    protected Builder newBuilderForType(
        BuilderParent parent) {
      Builder builder = new Builder(parent);
      return builder;
    }
    /**
     * <pre>
     *protobuf 使用message 管理数据
     * </pre>
     *
     * Protobuf type {@code Student}
     */
    public static final class Builder extends
        com.google.protobuf.GeneratedMessageV3.Builder<Builder> implements
        // @@protoc_insertion_point(builder_implements:Student)
        StudentOrBuilder {
      public static final com.google.protobuf.Descriptors.Descriptor
          getDescriptor() {
        return StudentPOJO.internal_static_Student_descriptor;
      }

      @Override
      protected FieldAccessorTable
          internalGetFieldAccessorTable() {
        return StudentPOJO.internal_static_Student_fieldAccessorTable
            .ensureFieldAccessorsInitialized(
                Student.class, Builder.class);
      }

      // Construct using StudentPOJO.Student.newBuilder()
      private Builder() {
        maybeForceBuilderInitialization();
      }

      private Builder(
          BuilderParent parent) {
        super(parent);
        maybeForceBuilderInitialization();
      }
      private void maybeForceBuilderInitialization() {
        if (com.google.protobuf.GeneratedMessageV3
                .alwaysUseFieldBuilders) {
        }
      }
      @Override
      public Builder clear() {
        super.clear();
        id_ = 0;

        name_ = "";

        return this;
      }

      @Override
      public com.google.protobuf.Descriptors.Descriptor
          getDescriptorForType() {
        return StudentPOJO.internal_static_Student_descriptor;
      }

      @Override
      public Student getDefaultInstanceForType() {
        return Student.getDefaultInstance();
      }

      @Override
      public Student build() {
        Student result = buildPartial();
        if (!result.isInitialized()) {
          throw newUninitializedMessageException(result);
        }
        return result;
      }

      @Override
      public Student buildPartial() {
        Student result = new Student(this);
        result.id_ = id_;
        result.name_ = name_;
        onBuilt();
        return result;
      }

      @Override
      public Builder clone() {
        return super.clone();
      }
      @Override
      public Builder setField(
          com.google.protobuf.Descriptors.FieldDescriptor field,
          Object value) {
        return super.setField(field, value);
      }
      @Override
      public Builder clearField(
          com.google.protobuf.Descriptors.FieldDescriptor field) {
        return super.clearField(field);
      }
      @Override
      public Builder clearOneof(
          com.google.protobuf.Descriptors.OneofDescriptor oneof) {
        return super.clearOneof(oneof);
      }
      @Override
      public Builder setRepeatedField(
          com.google.protobuf.Descriptors.FieldDescriptor field,
          int index, Object value) {
        return super.setRepeatedField(field, index, value);
      }
      @Override
      public Builder addRepeatedField(
          com.google.protobuf.Descriptors.FieldDescriptor field,
          Object value) {
        return super.addRepeatedField(field, value);
      }
      @Override
      public Builder mergeFrom(com.google.protobuf.Message other) {
        if (other instanceof Student) {
          return mergeFrom((Student)other);
        } else {
          super.mergeFrom(other);
          return this;
        }
      }

      public Builder mergeFrom(Student other) {
        if (other == Student.getDefaultInstance()) return this;
        if (other.getId() != 0) {
          setId(other.getId());
        }
        if (!other.getName().isEmpty()) {
          name_ = other.name_;
          onChanged();
        }
        this.mergeUnknownFields(other.unknownFields);
        onChanged();
        return this;
      }

      @Override
      public final boolean isInitialized() {
        return true;
      }

      @Override
      public Builder mergeFrom(
          com.google.protobuf.CodedInputStream input,
          com.google.protobuf.ExtensionRegistryLite extensionRegistry)
          throws java.io.IOException {
        Student parsedMessage = null;
        try {
          parsedMessage = PARSER.parsePartialFrom(input, extensionRegistry);
        } catch (com.google.protobuf.InvalidProtocolBufferException e) {
          parsedMessage = (Student) e.getUnfinishedMessage();
          throw e.unwrapIOException();
        } finally {
          if (parsedMessage != null) {
            mergeFrom(parsedMessage);
          }
        }
        return this;
      }

      private int id_ ;
      /**
       * <pre>
       * Student 类中有 一个属性 名字为 id 类型为int32(protobuf类型) 1表示属性序号，不是值
       * </pre>
       *
       * <code>int32 id = 1;</code>
       * @return The id.
       */
      @Override
      public int getId() {
        return id_;
      }
      /**
       * <pre>
       * Student 类中有 一个属性 名字为 id 类型为int32(protobuf类型) 1表示属性序号，不是值
       * </pre>
       *
       * <code>int32 id = 1;</code>
       * @param value The id to set.
       * @return This builder for chaining.
       */
      public Builder setId(int value) {
        
        id_ = value;
        onChanged();
        return this;
      }
      /**
       * <pre>
       * Student 类中有 一个属性 名字为 id 类型为int32(protobuf类型) 1表示属性序号，不是值
       * </pre>
       *
       * <code>int32 id = 1;</code>
       * @return This builder for chaining.
       */
      public Builder clearId() {
        
        id_ = 0;
        onChanged();
        return this;
      }

      private Object name_ = "";
      /**
       * <code>string name = 2;</code>
       * @return The name.
       */
      public String getName() {
        Object ref = name_;
        if (!(ref instanceof String)) {
          com.google.protobuf.ByteString bs =
              (com.google.protobuf.ByteString) ref;
          String s = bs.toStringUtf8();
          name_ = s;
          return s;
        } else {
          return (String) ref;
        }
      }
      /**
       * <code>string name = 2;</code>
       * @return The bytes for name.
       */
      public com.google.protobuf.ByteString
          getNameBytes() {
        Object ref = name_;
        if (ref instanceof String) {
          com.google.protobuf.ByteString b = 
              com.google.protobuf.ByteString.copyFromUtf8(
                  (String) ref);
          name_ = b;
          return b;
        } else {
          return (com.google.protobuf.ByteString) ref;
        }
      }
      /**
       * <code>string name = 2;</code>
       * @param value The name to set.
       * @return This builder for chaining.
       */
      public Builder setName(
          String value) {
        if (value == null) {
    throw new NullPointerException();
  }
  
        name_ = value;
        onChanged();
        return this;
      }
      /**
       * <code>string name = 2;</code>
       * @return This builder for chaining.
       */
      public Builder clearName() {
        
        name_ = getDefaultInstance().getName();
        onChanged();
        return this;
      }
      /**
       * <code>string name = 2;</code>
       * @param value The bytes for name to set.
       * @return This builder for chaining.
       */
      public Builder setNameBytes(
          com.google.protobuf.ByteString value) {
        if (value == null) {
    throw new NullPointerException();
  }
  checkByteStringIsUtf8(value);
        
        name_ = value;
        onChanged();
        return this;
      }
      @Override
      public final Builder setUnknownFields(
          final com.google.protobuf.UnknownFieldSet unknownFields) {
        return super.setUnknownFields(unknownFields);
      }

      @Override
      public final Builder mergeUnknownFields(
          final com.google.protobuf.UnknownFieldSet unknownFields) {
        return super.mergeUnknownFields(unknownFields);
      }


      // @@protoc_insertion_point(builder_scope:Student)
    }

    // @@protoc_insertion_point(class_scope:Student)
    private static final Student DEFAULT_INSTANCE;
    static {
      DEFAULT_INSTANCE = new Student();
    }

    public static Student getDefaultInstance() {
      return DEFAULT_INSTANCE;
    }

    private static final com.google.protobuf.Parser<Student>
        PARSER = new com.google.protobuf.AbstractParser<Student>() {
      @Override
      public Student parsePartialFrom(
          com.google.protobuf.CodedInputStream input,
          com.google.protobuf.ExtensionRegistryLite extensionRegistry)
          throws com.google.protobuf.InvalidProtocolBufferException {
        return new Student(input, extensionRegistry);
      }
    };

    public static com.google.protobuf.Parser<Student> parser() {
      return PARSER;
    }

    @Override
    public com.google.protobuf.Parser<Student> getParserForType() {
      return PARSER;
    }

    @Override
    public Student getDefaultInstanceForType() {
      return DEFAULT_INSTANCE;
    }

  }

  private static final com.google.protobuf.Descriptors.Descriptor
    internal_static_Student_descriptor;
  private static final 
    com.google.protobuf.GeneratedMessageV3.FieldAccessorTable
      internal_static_Student_fieldAccessorTable;

  public static com.google.protobuf.Descriptors.FileDescriptor
      getDescriptor() {
    return descriptor;
  }
  private static  com.google.protobuf.Descriptors.FileDescriptor
      descriptor;
  static {
    String[] descriptorData = {
      "
21StudentPOJO.proto"#
07Student22

02id3001 01" +
      "(052214
04name3002 01(	B
B13StudentPOJOb06proto3"
    };
    descriptor = com.google.protobuf.Descriptors.FileDescriptor
      .internalBuildGeneratedFileFrom(descriptorData,
        new com.google.protobuf.Descriptors.FileDescriptor[] {
        });
    internal_static_Student_descriptor =
      getDescriptor().getMessageTypes().get(0);
    internal_static_Student_fieldAccessorTable = new
      com.google.protobuf.GeneratedMessageV3.FieldAccessorTable(
        internal_static_Student_descriptor,
        new String[] { "Id", "Name", });
  }

  // @@protoc_insertion_point(outer_class_scope)
}

　　可以看到生成一堆信息。

5. 修改之前的类信息，客户端用Prodobuf 编码，服务器端用Protobuf 解码

Serverl

package netty.codec;

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.protobuf.ProtobufDecoder;

public class NettyServer {

    public static void main(String[] args) throws InterruptedException {
        // 1. 创建bossGrou好eworkerGroup
        // bossGroup只负责连接请求，其他交给workerGroup, 两个都是无线循环
        EventLoopGroup bossGroup = new NioEventLoopGroup();
        EventLoopGroup workerGroup = new NioEventLoopGroup();

        // 创建服务器端启动对象用于设置参数
        ServerBootstrap bootstrap = new ServerBootstrap();
        // 使用链式编程设置参数
        bootstrap.group(bossGroup, workerGroup)// 设置两个组
                .channel(NioServerSocketChannel.class) // 设置服务器的通道
                .option(ChannelOption.SO_BACKLOG, 128) // 设置线程队列得到连接个数
                .childOption(ChannelOption.SO_KEEPALIVE, true) // 设置保持活动连接状态
                .childHandler(new ChannelInitializer<SocketChannel>() { // 设置通道测试对象(匿名对象)
                    @Override
                    protected void initChannel(SocketChannel socketChannel) throws Exception {
                        // 加入ProtobufEncoder
                        socketChannel.pipeline().addLast(new ProtobufDecoder(StudentPOJO.Student.getDefaultInstance()));
                        socketChannel.pipeline().addLast(new ServerHandler());
                    }
                });

        System.out.println("服务端is ok。。。");

        // 启动服务器并绑定端口。绑定一个端口并且同步，生成一个ChannelFuture对象
        ChannelFuture channelFuture = bootstrap.bind(6666).sync();
        // 对关闭通道进行监控
        channelFuture.channel().closeFuture().sync();
    }
}

ServerHandler

package netty.codec;


import io.netty.buffer.Unpooled;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.SimpleChannelInboundHandler;
import io.netty.util.CharsetUtil;

/**
 * 自定义服务器端处理handler，需要继承netty定义的ChannelInboundHandlerAdapter 类
 */
public class ServerHandler extends SimpleChannelInboundHandler<StudentPOJO.Student> {

    /**
     * 读取事件
     *
     * @param ctx
     * @param msg
     * @throws Exception
     */
    @Override
    protected void channelRead0(ChannelHandlerContext ctx, StudentPOJO.Student msg) throws Exception {
        System.out.println("客户端发送的数据 id=" + msg.getId() + " 名字=" + msg.getName());
    }

    /**
     * 数据读取完毕事件
     *
     * @param ctx
     * @throws Exception
     */
    @Override
    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
        // 将数据写到客户端(write + flush)
        ctx.writeAndFlush(Unpooled.copiedBuffer("hello, 客户端！", CharsetUtil.UTF_8));
    }

    /**
     * 发生异常事件
     *
     * @param ctx
     * @param cause
     * @throws Exception
     */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        ctx.close();
    }
}

Client

package netty.codec;

import io.netty.bootstrap.Bootstrap;
import io.netty.channel.ChannelFuture;
import io.netty.channel.ChannelInitializer;
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.protobuf.ProtobufEncoder;

public class NettyClient {

    public static void main(String[] args) throws InterruptedException {
        // 创建一个事件循环组
        EventLoopGroup eventExecutors = new NioEventLoopGroup();
        try {
            // 创建一个启动Bootstrap(注意是Netty包下的)
            Bootstrap bootstrap = new Bootstrap();
            // 链式设置参数
            bootstrap.group(eventExecutors) // 设置线程组
                    .channel(NioSocketChannel.class) // 设置通道class
                    .handler(new ChannelInitializer<SocketChannel>() {
                        @Override
                        protected void initChannel(SocketChannel socketChannel) throws Exception {
                            // 加入ProtobufEncoder
                            socketChannel.pipeline().addLast(new ProtobufEncoder());
                            socketChannel.pipeline().addLast(new ClientHandler());
                        }
                    });
            System.out.println("客户端is ok...");

            // 启动客户端连接服务器(ChannelFuture 是netty的异步模型)
            ChannelFuture channelFuture = bootstrap.connect("127.0.0.1", 6666).sync();
            // 监听关闭通道
            channelFuture.channel().closeFuture().sync();
        } finally {
            // 关闭
            eventExecutors.shutdownGracefully();
        }
    }
}

ClientHandler

package netty.codec;

import io.netty.buffer.ByteBuf;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInboundHandlerAdapter;
import io.netty.util.CharsetUtil;

/**
 * 自定义服务器端处理handler，需要继承netty定义的ChannelInboundHandlerAdapter 类
 */
public class ClientHandler extends ChannelInboundHandlerAdapter {

    /**
     * 通道就绪事件
     *
     * @param ctx
     * @throws Exception
     */
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("ClientHandler ctx: " + ctx);
        ctx.writeAndFlush(StudentPOJO.Student.newBuilder().setId(1).setName("张三").build());
    }

    /**
     * 读取事件
     *
     * @param ctx 上下文对象，含有pipeline管道；通道channel；地址address等信息
     * @param msg 客户端发送的数据(实际类型是ByteBuf - netty 封装的ByteBuffer)
     * @throws Exception
     */
    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
        // 强转为netty的ByteBuffer(实际就是包装的ByteBuffer)
        ByteBuf byteBuf = (ByteBuf) msg;
        System.out.println("服务器会送的消息是：" + byteBuf.toString(CharsetUtil.UTF_8));
        System.out.println("服务器地址：" + ctx.channel().remoteAddress());
    }

    /**
     * 发生异常事件
     *
     * @param ctx
     * @param cause
     * @throws Exception
     */
    @Override
    public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
        ctx.close();
    }
}

3. 案例二

　　实现一个对象包含两个对象。 根据类型传递不同的对象，服务器端根据对应的对象解开。

(1) proto 文件如下

MyData.proto

syntax = "proto3";
option optimize_for = SPEED; // 加快解析
option java_package="netty.codec";   //指定生成到哪个包下
option java_outer_classname="MyDataInfo"; // 外部类名, 文件名

//protobuf 可以使用message 管理其他的message
message MyMessage {

  //定义一个枚举类型
  enum DataType {
    StudentType = 0; //在proto3 要求enum的编号从0开始
    WorkerType = 1;
  }

  //用data_type 来标识传的是哪一个枚举类型
  DataType data_type = 1;

  //表示每次枚举类型最多只能出现其中的一个, 节省空间
  oneof dataBody {
    Student student = 2;
    Worker worker = 3;
  }

}

message Student {
  int32 id = 1;//Student类的属性
  string name = 2; //
}
message Worker {
  string name=1;
  int32 age=2;
}

(2) cmd 用如下命令生成java 类

protoc.exe --java_out=. MyData.proto

(3) ClientHandler 改造：

    /**
     * 通道就绪事件
     *
     * @param ctx
     * @throws Exception
     */
    @Override
    public void channelActive(ChannelHandlerContext ctx) throws Exception {
        System.out.println("ClientHandler ctx: " + ctx);
        MyDataInfo.MyMessage myMessage = MyDataInfo.MyMessage.newBuilder().setDataType(MyDataInfo.MyMessage.DataType.StudentType).setStudent(MyDataInfo.Student.newBuilder().setId(1).setName("李四").build()).build();
        ctx.writeAndFlush(myMessage);
    }

(4) ServerHandler 改造

    @Override
    protected void channelRead0(ChannelHandlerContext ctx, MyDataInfo.MyMessage msg) throws Exception {
        if (msg.getDataType().equals(MyDataInfo.MyMessage.DataType.StudentType)) {
            System.out.println("student name: " + msg.getStudent().getName());
        }
    }