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:\workspace\ms-selection-service\ms-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:
[INFO] os.detected.version.minor:
[INFO] os.detected.classifier: windows-x86_64
[INFO]
[INFO] ------------------------------------------------------------------------
[INFO] Building ms-selection-api 1.0.
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ ms-selection-api ---
[INFO] Deleting E:\workspace\ms-selection-service\ms-selection-api\target
[INFO]
[INFO] --- protobuf-maven-plugin:0.5.:compile (default) @ ms-selection-api ---
[INFO] Compiling  proto file(s) to E:\workspace\ms-selection-service\ms-selection-api\target\generated-sources\protobuf\java
[ERROR] PROTOC FAILED: recommend/RecommendResponse.proto::: "BookList.bookName" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto::: "BookList.authorName" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto::: "BookList.bookCover" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto::: "BookList.bookUrl" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto::: "BookList.coPercent" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto::: "BookList.contentType" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto::: "BookList" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto::: "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=;
     string status=;
     string isvisable=;
     string isShowLine=;
     Recommend data=;
     string messageDesc=;
     repeated BookList bookList= ;

}

message Recommend{

    repeated RecommendData   buttons=;
    map<string, string> ctag = ;
    string isMarginTop=;
    string isMarginBottom=;

}

message RecommendData{

    string name=;

    string url=;
}

message BookList{
    string bookName=;
    string authorName=;
    string bookCover=;
    string bookUrl=;
    string coPercent=;
    string contentType=;

}

　　再看ContentRecommendResponse.proto:

syntax = "proto3";

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

message  ContentRecommendResponse {
    string pluginCode=;

    string status=;

    string isvisable=;

    string messageDesc=;

    ContentRecommendData data=;

}
message ContentRecommendData{

    string isMarginTop = ;

    string isMarginBottom = ;

    string isPaddingTop = ;

    string isShowLine = ;

    string dataFrom = ;

    string title = ;

    string style = ;

    repeated BookList bookList=;

    BiData biData = ;

}
message BookList{
    string bookName=;
    string authorName=;
    string bookCover=;
    string bookUrl=;
    string coPercent=;
    string contentType=;
}

message BiData{

    string msisdn = ;
    string bid = ;
    string pageNo = ;
    string showNum = ;
    string clientVersion = ;
    string instanceId = ;
}

　　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=;
     string status=;
     string isvisable=;
     string isShowLine=;
     Recommend data=;
     string messageDesc=;
     repeated BookList bookList= ;

}

message Recommend{

    repeated RecommendData   buttons=;
    map<string, string> ctag = ;
    string isMarginTop=;
    string isMarginBottom=;

}

message RecommendData{

    string name=;

    string url=;
}

　　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=;
     string status=;
     string isvisable=;
     string isShowLine=;
     Recommend data=;
     string messageDesc=;
     repeated BookListNew bookList= ;

}

message Recommend{

    repeated RecommendData   buttons=;
    map<string, string> ctag = ;
    string isMarginTop=;
    string isMarginBottom=;

}

message RecommendData{

    string name=;

    string url=;
}

message BookListNew{
    string bookCover=;
}

　　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。