Google Protobuf结合Netty实践
1.Win版Protobuf代码生成工具下载：
https://github.com/protocolbuffers/protobuf/releases
2.编写.proto文件注意：
指定包为外层目录名称，指定java包名为你想使用的java工程该序列化类包名，还需要指定生成Java类的名称。字段赋予的数值或代表次序，而不是字段默认值。示例：
syntax = "proto2";
package Protobuf;
option java_package = "com.xiaobai.codec.protobuf";
option java_outer_classname = "SubscribeReqProto";
message SubscribeReq{
required int32 subReqID = 1;
required string userName = 2;
required string productName = 3;
repeated string address = 4;
}
syntax = "proto2";
package Protobuf;
option java_package = "com.xiaobai.codec.protobuf";
option java_outer_classname = "SubscribeRespProto";
message SubscribeResp{
required int32 subReqID = 1;
required int32 respCode = 2;
required string desc = 3;
}
3.使用工具时需要注意
a.需要指定一个--proto_path路径，根据错误提示：
D:\protoc-3.6.1-win32\bin>protoc.exe --java_out=F:\NewAge\nettydemo\src\main\jav
a F:\NewAge\nettydemo\Protobuf\SubscribeReq.proto
F:\NewAge\nettydemo\Protobuf\SubscribeReq.proto: File does not reside within any
path specified using --proto_path (or -I). You must specify a --proto_path whi
ch encompasses this file. Note that the proto_path must be an exact prefix of t
he .proto file names -- protoc is too dumb to figure out when two paths (e.g. ab
solute and relative) are equivalent (it's harder than you think).
这个路径需要是.proto文件所在目录
b.需要在.proto文件中指定它的proto语法版本，这样生成时不会出现警告，根据提示，这个版本默认是proto2，可以设置为proto3：
D:\protoc-3.6.1-win32\bin>protoc.exe --proto_path=F:\NewAge\nettydemo\Protobuf -
-java_out=F:\NewAge\nettydemo\src\main\java F:\NewAge\nettydemo\Protobuf\Subscri
beReq.proto
[libprotobuf WARNING T:\src\github\protobuf\src\google\protobuf\compiler\parser.
cc:562] No syntax specified for the proto file: SubscribeReq.proto. Please use '
syntax = "proto2";' or 'syntax = "proto3";' to specify a syntax version. (Defaul
ted to proto2 syntax.)
参照：
https://www.jianshu.com/p/42a480a45cd6
https://www.cnblogs.com/gifisan/p/5976208.html?utm_source=itdadao&utm_medium=referral
生成效果如下：
Win版本安装参考与示例：
https://www.cnblogs.com/tyw66/p/7352033.html
Linux版本安装参考与示例：
https://www.cnblogs.com/learn21cn/p/6206206.html
https://www.cnblogs.com/luoxn28/p/5303517.html
4.实践时采用了3.6.1版本代码生成，所以Java工程引入依赖也选择了3.6.1版本，且重新用proto3生成了代码，该语法不支持required字段，所以去掉：
D:\protoc-3.6.1-win32\bin>protoc.exe --proto_path=F:\NewAge\nettydemo\Protobuf -
-java_out=F:\NewAge\nettydemo\src\main\java F:\NewAge\nettydemo\Protobuf\Subscri
beResp.proto
SubscribeResp.proto: Required fields are not allowed in proto3.
SubscribeResp.proto: Required fields are not allowed in proto3.
SubscribeResp.proto: Required fields are not allowed in proto3.
syntax = "proto3";
package Protobuf;
option java_package = "com.xiaobai.codec.protobuf";
option java_outer_classname = "SubscribeReqProto";
message SubscribeReq{
int32 subReqID = 1;
string userName = 2;
string productName = 3;
repeated string address = 4;
}
syntax = "proto3";
package Protobuf;
option java_package = "com.xiaobai.codec.protobuf";
option java_outer_classname = "SubscribeRespProto";
message SubscribeResp{
int32 subReqID = 1;
int32 respCode = 2;
string desc = 3;
}
注意Protobuf里面没有list,需要指定为repeated + 元素类型！！
未写元素类型导致的报错：
D:\protoc-3.6.1-win32\bin>protoc.exe --proto_path=F:\NewAge\nettydemo\Protobuf -
-java_out=F:\NewAge\nettydemo\src\main\java F:\NewAge\nettydemo\Protobuf\Subscri
beReq.proto
SubscribeReq.proto:10:22: Expected field name.
参照（定义复杂对象）：
https://blog.csdn.net/hry2015/article/details/70766603
https://blog.csdn.net/qq_33951440/article/details/80599712
5.源码中的报错：@Override问题和支持1.6+的Java版本问题
参考https://blog.csdn.net/jdjdndhj/article/details/70256789
是因为IDEA源码版本设置的原因：
6.编译报错
Error:java: Compilation failed: internal java compiler error
这是IDEA编译版本设置的原因，注意本项目（nettydemo）的编译版本也要设置成1.8,这里是坑：
参考：https://www.cnblogs.com/comeluder/p/8215317.html
7.序列化测试
package com.xiaobai.codec.protobuf;
import com.google.protobuf.InvalidProtocolBufferException;
import java.util.ArrayList;
import java.util.List;
public class TestSubscribeReqProto {
private static byte[] encode(SubscribeReqProto.SubscribeReq req) {
return req.toByteArray();
}
private static SubscribeReqProto.SubscribeReq decode(byte[] body) throws InvalidProtocolBufferException {
return SubscribeReqProto.SubscribeReq.parseFrom(body);
}
private static SubscribeReqProto.SubscribeReq createSubScribeReq() {
SubscribeReqProto.SubscribeReq.Builder builder = SubscribeReqProto.SubscribeReq.newBuilder();
builder.setSubReqID(1);
builder.setUserName("xiaobai");
builder.setProductName("Java Supior");
List<String> address = new ArrayList<>();
address.add("Shenyang YUEXING");
address.add("Jinzhou HUAGUANG");
address.add("Beijing HAIDIAN");
builder.addAllAddress(address);
return builder.build();
}
public static void main(String[] args) throws InvalidProtocolBufferException {
SubscribeReqProto.SubscribeReq req = createSubScribeReq();
System.out.println("Before encoding: ");
System.out.println(req.toString());
SubscribeReqProto.SubscribeReq req2 = decode(encode(req));
System.out.println("After encoding and decoding: ");
System.out.println(req2.toString());
System.out.println("Assert enqual: --> " + req2.equals(req));
}
}
输出结果：
Before encoding:
subReqID: 1
userName: "xiaobai"
productName: "Java Supior"
address: "Shenyang YUEXING"
address: "Jinzhou HUAGUANG"
address: "Beijing HAIDIAN"
After encoding and decoding:
subReqID: 1
userName: "xiaobai"
productName: "Java Supior"
address: "Shenyang YUEXING"
address: "Jinzhou HUAGUANG"
address: "Beijing HAIDIAN"
Assert enqual: --> true
8.结合netty（netty版本需要5.0.0.Alpha1）
ChannelHandlerAdapter版本问题：
https://my.oschina.net/linwl/blog/1823315
ChannelHandlerAdapter分析：
https://www.cnblogs.com/wade-luffy/p/6222960.html
GitHub:https://github.com/Xiaobai0419/nettydemo
注意：
a.例子中客户端和服务端可一直保持连接，和双向互传数据。如果一方断开，另一方报异常：
java.io.IOException: 远程主机强迫关闭了一个现有的连接。
at sun.nio.ch.SocketDispatcher.read0(Native Method)
at sun.nio.ch.SocketDispatcher.read(SocketDispatcher.java:43)
at sun.nio.ch.IOUtil.readIntoNativeBuffer(IOUtil.java:223)
at sun.nio.ch.IOUtil.read(IOUtil.java:192)
at sun.nio.ch.SocketChannelImpl.read(SocketChannelImpl.java:380)
at io.netty.buffer.UnpooledUnsafeDirectByteBuf.setBytes(UnpooledUnsafeDirectByteBuf.java:446)
at io.netty.buffer.AbstractByteBuf.writeBytes(AbstractByteBuf.java:871)
at io.netty.channel.socket.nio.NioSocketChannel.doReadBytes(NioSocketChannel.java:208)
at io.netty.channel.nio.AbstractNioByteChannel$NioByteUnsafe.read(AbstractNioByteChannel.java:119)
at io.netty.channel.nio.NioEventLoop.processSelectedKey(NioEventLoop.java:485)
at io.netty.channel.nio.NioEventLoop.processSelectedKeysOptimized(NioEventLoop.java:452)
at io.netty.channel.nio.NioEventLoop.run(NioEventLoop.java:346)
at io.netty.util.concurrent.SingleThreadEventExecutor$5.run(SingleThreadEventExecutor.java:794)
at java.lang.Thread.run(Thread.java:748)
需要进行处理。
客户端重新连接，仍可与服务端继续通信。
b.例子中序列化类int类型字段值为0无法传输该字段，其他值则可以，待查。
