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（MsgList），用maven编译proto文件时报错：

E:\workspace\wlf\wlf-msg-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 wlf-msg-api 1.0.18061
[INFO] ------------------------------------------------------------------------
[INFO]
[INFO] --- maven-clean-plugin:2.5:clean (default-clean) @ wlf-msg-api ---
[INFO] Deleting E:\workspace\wlf\wlf-msg-api\target
[INFO]
[INFO] --- protobuf-maven-plugin:0.5.0:compile (default) @ wlf-msg-api ---
[INFO] Compiling 84 proto file(s) to E:\workspace\wlf\wlf-msg-api\target\generated-sources\protobuf\java
[ERROR] PROTOC FAILED: recommend/RecommendResponse.proto:34:16: "MsgList.msgName" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto:35:16: "MsgList.authorName" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto:36:16: "MsgList.msgCover" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto:37:16: "MsgList.msgUrl" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto:33:9: "MsgList" is already defined in file "contentrecommend/ContentRecommendResponse.proto".
recommend/RecommendResponse.proto:13:19: "MsgList" 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 = "wlf.msg.proto.base";

message RecommendResponse {
    
     Recommend data=1; 
     string messageDesc=2;
     repeated MsgList msgList= 3;

}

message Recommend{

    repeated RecommendData   buttons=1;

}

message RecommendData{

    string name=1;
    
    string url=2;    
}

message MsgList{
    string msgName=1;
    string authorName=2;
    string msgCover=3;
    string msgUrl=4;

}

　　再看ContentRecommendResponse.proto:

syntax = "proto3";

option java_package = "wlf.msg.proto.base";

message  ContentRecommendResponse {

    ContentRecommendData data=1;

}
message ContentRecommendData{    
    
    string title = 1;
    
    string style = 2;

    repeated MsgList msgList=3;
    
    BiData biData = 4;
    
}
message MsgList{
    string msgName=1;
    string authorName=2;
    string msgCover=3;
    string msgUrl=4;
}

message BiData{
    
    string msisdn = 1;
}

　　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MsgList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MsgList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 = "wlf.msg.proto.base";
import "contentrecommend/ContentRecommendResponse.proto";

message RecommendResponse {
    
     Recommend data=1; 
     string messageDesc=2;
     repeated MsgList msgList= 3;

}

message Recommend{

    repeated RecommendData   buttons=1;

}

message RecommendData{

    string name=1;
    
    string url=2;    
}

　　2、如果MsgList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 = "wlf.msg.proto.base";

message RecommendResponse {
       
     Recommend data=1; 
     string messageDesc=2;
     repeated MsgListNew msgList= 3;

}

message Recommend{

    repeated RecommendData   buttons=1;

}

message RecommendData{

    string name=1;
    
    string url=2;    
}

message MsgListNew{
    string msgCover=1;
}

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

　　以上两种情况修改后跑maven均可成功编译出java文件。