protobuf新增message报错：类型已存在

　　问题现象：在一个已有的proto文件（RecommendResponse.proto）中新增一个message（BookList），用maven编译proto文件时报错：

E:workspacems-selection-servicems-selection-api>mvn clean install
[INFO] Scanning for projects...
[INFO] ------------------------------------------------------------------------
[INFO] Detecting the operating system and CPU architecture
[INFO] ------------------------------------------------------------------------
[INFO] os.detected.name: windows
[INFO] os.detected.arch: x86_64
[INFO] os.detected.version: 10.0
[INFO] os.detected.version.major: 10
[INFO] os.detected.version.minor: 0
[INFO] os.detected.classifier: windows-x86_64
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building ms-selection-api 1.0.18061
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ ms-selection-api ---
[INFO] Deleting E:workspacems-selection-servicems-selection-api	arget
[INFO]
[INFO] --- protobuf-maven-plugin:0.5.0:compile (default) @ ms-selection-api ---
[INFO] Compiling 84 proto file(s) to E:workspacems-selection-servicems-selection-api	argetgenerated-sourcesprotobufjava
[ERROR] PROTOC FAILED: recommend/RecommendResponse.proto:34:16: "BookList.bookName" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto:35:16: "BookList.authorName" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto:36:16: "BookList.bookCover" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto:37:16: "BookList.bookUrl" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto:38:16: "BookList.coPercent" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto:39:16: "BookList.contentType" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto:33:9: "BookList" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto:13:19: "BookList" seems to be defined in "contentrecommend/ContentRecommendResponse.proto", which is not imported by "recommend/RecommendResponse.proto".  To use it here, please add the necessary import.

　　先看下RecommendResponse.proto：

syntax = "proto3";

option java_package = "cn.wlf.selection.proto.base";

message RecommendResponse {
    
     string pluginCode=1;
     string status=2;
     string isvisable=3;
     string isShowLine=4; 
     Recommend data=5; 
     string messageDesc=6;
     repeated BookList bookList= 7;

}

message Recommend{

    repeated RecommendData   buttons=1;
    map<string, string> ctag = 2;
    string isMarginTop=3;
    string isMarginBottom=4;

}

message RecommendData{

    string name=1;
    
    string url=2;    
}

message BookList{
    string bookName=1;
    string authorName=2;
    string bookCover=3;
    string bookUrl=4;
    string coPercent=5;
    string contentType=6;

}

　　再看ContentRecommendResponse.proto:

syntax = "proto3";

option java_package = "cn.wlf.selection.proto.base";

message  ContentRecommendResponse {
    string pluginCode=1;
    
    string status=2;
    
    string isvisable=3;
    
    string messageDesc=4;

    ContentRecommendData data=5;

}
message ContentRecommendData{
    
    string isMarginTop = 1;
    
    string isMarginBottom = 2;
    
    string isPaddingTop = 3;
    
    string isShowLine = 4;
    
    string dataFrom = 5;
    
    string title = 6;
    
    string style = 7;

    repeated BookList bookList=8;
    
    BiData biData = 9;
    
}
message BookList{
    string bookName=1;
    string authorName=2;
    string bookCover=3;
    string bookUrl=4;
    string coPercent=5;
    string contentType=6;
}

message BiData{
    
    string msisdn = 1;
    string bid = 2;
    string pageNo = 3;
    string showNum = 4;
    string clientVersion = 5;
    string instanceId = 6;
}

　　问题定位：从报错信息中其实已经告诉我们，在ContentRecommendResponse.proto已经存在BookList这个message了，从上面也能看到两个proto存在同名message。

　　问题解决：

　　1、如果新增的BookList跟已有的数据结构一样，那么只需要引入即可，RecommendResponse.proto改为：

syntax = "proto3";

option java_package = "cn.wlf.selection.proto.base";
import "contentrecommend/ContentRecommendResponse.proto";

message RecommendResponse {
    
     string pluginCode=1;
     string status=2;
     string isvisable=3;
     string isShowLine=4; 
     Recommend data=5; 
     string messageDesc=6;
     repeated BookList bookList= 7;

}

message Recommend{

    repeated RecommendData   buttons=1;
    map<string, string> ctag = 2;
    string isMarginTop=3;
    string isMarginBottom=4;

}

message RecommendData{

    string name=1;
    
    string url=2;    
}

　　2、如果BookList数据结构改了，那么就没法复用了，只能改类名，RecommendResponse.proto改为：

syntax = "proto3";

option java_package = "cn.wlf.selection.proto.base";

message RecommendResponse {
    
     string pluginCode=1;
     string status=2;
     string isvisable=3;
     string isShowLine=4; 
     Recommend data=5; 
     string messageDesc=6;
     repeated BookListNew bookList= 7;

}

message Recommend{

    repeated RecommendData   buttons=1;
    map<string, string> ctag = 2;
    string isMarginTop=3;
    string isMarginBottom=4;

}

message RecommendData{

    string name=1;
    
    string url=2;    
}

message BookListNew{
    string bookCover=1;
}

　　虽然类名从BookList改为BookListNew，但实例名没改，还是bookList，最终输出的响应字段名还是叫bookList的。

　　以上两种情况修改后跑maven均可成功编译出java文件。