Google Protobuf結合Netty實踐

1.Win版Protobuf代碼生成工具下載：

https://github.com/protocolbuffers/protobuf/releases

注意下載protoc-3.6.1-win32.zip

2.編寫.proto文件注意：

指定包爲外層目錄名稱，指定java包名爲你想使用的java工程該序列化類包名，還須要指定生成Java類的名稱。字段賦予的數值或表明次序，而不是字段默認值。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.使用工具時須要注意

a.須要指定一個--proto_path路徑，根據錯誤提示：

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).

這個路徑須要是.proto文件所在目錄

b.須要在.proto文件中指定它的proto語法版本，這樣生成時不會出現警告，根據提示，這個版本默認是proto2，能夠設置爲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.)

參照：

https://www.jianshu.com/p/42a480a45cd6

https://www.cnblogs.com/gifisan/p/5976208.html?utm_source=itdadao&utm_medium=referral

生成效果以下：

Win版本安裝參考與示例：

https://www.cnblogs.com/tyw66/p/7352033.html

Linux版本安裝參考與示例：

https://www.cnblogs.com/learn21cn/p/6206206.html

http://www.javashuo.com/article/p-hevhtyia-bb.html

4.實踐時採用了3.6.1版本代碼生成，因此Java工程引入依賴也選擇了3.6.1版本，且從新用proto3生成了代碼，該語法不支持required字段，因此去掉：

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裏面沒有list,須要指定爲repeated + 元素類型！！

未寫元素類型致使的報錯：

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.

參照（定義複雜對象）：

https://blog.csdn.net/hry2015/article/details/70766603

https://blog.csdn.net/qq_33951440/article/details/80599712

5.源碼中的報錯：@Override問題和支持1.6+的Java版本問題

參考https://blog.csdn.net/jdjdndhj/article/details/70256789

是由於IDEA源碼版本設置的緣由：

6.編譯報錯

Error:java: Compilation failed: internal java compiler error

這是IDEA編譯版本設置的緣由，注意本項目（nettydemo）的編譯版本也要設置成1.8,這裏是坑：

參考：https://www.cnblogs.com/comeluder/p/8215317.html

7.序列化測試

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));
    }
}

輸出結果：

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.結合netty（netty版本須要5.0.0.Alpha1）

ChannelHandlerAdapter版本問題：

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.例子中客戶端和服務端可一直保持鏈接，和雙向互傳數據。若是一方斷開，另外一方報異常：

java.io.IOException: 遠程主機強迫關閉了一個現有的鏈接。
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)

須要進行處理。

客戶端從新鏈接，仍可與服務端繼續通訊。

b.例子中序列化類int類型字段值爲0沒法傳輸該字段，其餘值則能夠，待查。