方法介绍
protobuf的介绍在这里就不详细介绍了，主要是俺也是刚接触，感兴趣的同学可以去搜索相关博客或者直接去看源码以及google的官方文档(官方文档表示很吃力)或者去这个网站：https://developers.google.com/protocol-buffers/docs/overview查看相应内容，这里面内容很全面，可以很方面的查询各个函数的使用方法以及功能。本篇文章主要介绍一下本人最近做的一个protobuf转json的小工具，下面进行拆分讲解，完整的代码在：git@github.com:chengfeiGitHub/P-bToJson.git。
protobuf自带一个MessageToJson()的函数可以将对应的消息转换成json，一般情况下该函数可以满足转换需求。但是，最近项目的要求使用MessageToJson()无法实现，主要要求是：
- 选择特定的messge进行转换（主要是提供包含需求字段号的set或者vector，根据提供的字段号进行转换）；
- 对于Enum类型的消息，可以选择显示枚举名或者枚举值；
- 对于字段值为0的字段，可以选择显示或者不显示.
主要有这三个要求，对于功能2、3现在最新的protobuf应该是支持的，但是没有功能1的实现方式，所以只好自己写一个小工具。
说明：本工具由C++编写完成
首先是函数的声明：
#pragma once
#include <iostream>
#include <google/protobuf/message.h>
#include <google/protobuf/descriptor.h> void ChooseSomeFieldsToJson(std::string& pb2jsonstring, const ::google::protobuf::Message& msg, std::vector<uint>& needs, bool Enum_2_Str, bool Showzero);
//Enum_2_Str: ture显示枚举名，false:显示枚举值； Showzero: ture显示值为０的fields，false,不显示值为０的fields。
void GetRepeatedJson(std::string& pb2jsonstring, const ::google::protobuf::Message& msg, const google::protobuf::FieldDescriptor *field, const ::google::protobuf::Reflection *reflection, bool Enum_2_Str,bool Showzero);
void NeedEmptyToJson(std::string& pb2jsonstring, const ::google::protobuf::Message& msg, bool Enum_2_Str, bool Showzero);
void NeedNotEmptyToJson(std::string& pb2jsonstring, const ::google::protobuf::Message& msg, std::vector<uint>& needs, bool Enum_2_Str, bool Showzero);
int AppendTmpString1(std::string& pb2jsonstring,std::string& tmp_string, int judge);
int AppendTmpString2(std::string& pb2jsonstring,std::string& tmp_string, int judge);
pb2jsonstring是存储转换结果的字符串，msg是需要转换的消息，needs是需要转换的字段号；函数GetRepeatedJson()是对重复的字段进行操作；NeedEmptyToJson()是当needs为空时对应的操作(needs为空表示需要转换所有的字段)；NeedNotEmptyToJson()是当needs不为空时对应的操作；AppendTmpStrign1()以及AppendTmpStrign2()是将临时字符串添加到pb2jsonstring后的操作。
上面的代码保存到一个头文件当中,就叫pbjsontest3.h吧，然后是pbjsontest3.cpp
#include <iostream>
#include <google/protobuf/descriptor.h>
#include <google/protobuf/message.h>
#include <set>
#include <string>
#include "pbjsontest3.h" using namespace ::google::protobuf; void ChooseSomeFieldsToJson(std::string& pb2jsonstring, const ::google::protobuf::Message& msg, std::vector<uint>& need, bool Enum_2_Str, bool Showzero)
{ const Descriptor* descriptor = msg.GetDescriptor();
const Reflection* reflection = msg.GetReflection();
if (need.empty()) //如果needs为空，表示需要将所有的字段转换为json
{
NeedEmptyToJson(pb2jsonstring, msg, Enum_2_Str, Showzero);
}
else
{
NeedNotEmptyToJson(pb2jsonstring, msg, need, Enum_2_Str, Showzero);
}
}
这一部分主要就是判断need是否为空，然后选择相应的函数进行操作，不在做详细的叙述，下面是NeedEmptyToJson()的介绍。由于这一部分代码太长，所以相应的介绍在代码中进行注释说明。
void NeedEmptyToJson(std::string& pb2jsonstring, const ::google::protobuf::Message& msg, bool Enum_2_Str, bool Showzero)
{
const Descriptor* descriptor = msg.GetDescriptor();
const Reflection* reflection = msg.GetReflection();
const uint count = descriptor->field_count(); //count为当前消息中所有的字段总数
uint judge = ;//ｊｕｄｇｅ用来判断是否在当前ｊｓｏｎ元素前加“，”用来分隔前后元素，如果ｊｕｄｇｅ＝＝０，则不加，如果ｊｕｇｄｇｅ＝＝１，则加“，”
std::string tmp_string; //临时变量
std::int32_t v32=;
std::uint32_t vu32=;
std::int64_t v64=;
std::uint64_t vu64=;
double vd=;
std::string str;
pb2jsonstring.append("{"); //添加第一个"{"
for (int it = ; it <count; ++it)
{
const FieldDescriptor* goal_field=descriptor->field(it);
/*这里要用field()来取字段，因为field()是按字段的实际标号来取字段，而不是根据字段号来进行取字段，这样就避免的字段号不连续造成的某些字段取不到的问题。 */
if(nullptr==goal_field) //不存在字段
{
continue;
} if (goal_field->is_repeated()) //判断字段是否为repeated
{
if (reflection->FieldSize(msg, goal_field) > )
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string .append("["); //重复的字段用[]包围
GetRepeatedJson(tmp_string, msg, goal_field, reflection, Enum_2_Str,Showzero);
tmp_string.append("]");
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
continue;
}
switch (goal_field->type())
{
case FieldDescriptor::TYPE_MESSAGE:
{
const Message& tmp_msg = reflection->GetMessage(msg, goal_field);
if ( != tmp_msg.ByteSize())
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
NeedEmptyToJson(tmp_string,tmp_msg, Enum_2_Str, Showzero);
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
break; case FieldDescriptor::TYPE_INT32:
{
v32=reflection->GetInt32(msg, goal_field);
if(v32==)
{
if(Showzero) //字段值为０，也需要进行打印
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(v32)); //需要抓换成字符型
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(v32));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
break; case FieldDescriptor::TYPE_UINT32:
{
vu32=reflection->GetUInt32(msg, goal_field);
if(vu32==)
{
if(Showzero)
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(vu32));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(vu32));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
break; case FieldDescriptor::TYPE_INT64:
{
v64=reflection->GetInt64(msg, goal_field);
if(v64==)
{
if(Showzero)
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(v64));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(v64));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
break;
case FieldDescriptor::TYPE_UINT64:
{
vu64=reflection->GetUInt64(msg, goal_field);
if(vu64==)
{
if(Showzero)
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(vu64));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(vu64));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
break;
case FieldDescriptor::TYPE_STRING:
case FieldDescriptor::TYPE_BYTES:
{ str=reflection->GetString(msg, goal_field);
if(str.empty())
{
if(Showzero)
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append("\"").append(str).append("\"");
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append("\"").append(str).append("\"");
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge); }
}
break;
case FieldDescriptor::TYPE_DOUBLE:
{
vd=reflection->GetDouble(msg, goal_field);
if(vd==)
{
if(Showzero)
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(vd));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(vd));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
break;
case FieldDescriptor::TYPE_BOOL:
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
if (reflection->GetBool(msg, goal_field))
tmp_string.append("true");
else
tmp_string.append("false");
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge); }
break;
case FieldDescriptor::TYPE_ENUM:
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
if (Enum_2_Str) //判断显示枚举名还是枚举值
{
tmp_string.append("\"").append(reflection->GetEnum(msg,goal_field)->name()).append("\"");
}
else
{
static char enumstr[];
memset(enumstr, , sizeof(enumstr));
snprintf(enumstr, sizeof(enumstr), "%d", reflection->GetEnum(msg,goal_field)->number());
tmp_string.append(enumstr);
}
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
break;
default:
break;
}
}
pb2jsonstring.append("}");
} int AppendTmpString1(std::string &pb2jsonstring,std::string &tmp_string, int judge)
{
if ( judge!= && tmp_string.length()!=)
{
pb2jsonstring.append(",").append(tmp_string);
return judge;
}
else if(judge== && tmp_string.length()!=)
{
pb2jsonstring.append(tmp_string);
return ;
}
return judge;
}
下面need不为空时候的转换：
void NeedNotEmptyToJson(std::string& pb2jsonstring, const ::google::protobuf::Message& msg, std::vector<uint>& needs, bool Enum_2_Str, bool Showzero)
{
const Descriptor* descriptor = msg.GetDescriptor();
const Reflection* reflection = msg.GetReflection(); uint judge = ;
std::string tmp_string;
std::int32_t v32=;
std::uint32_t vu32=;
std::int64_t v64=;
std::uint64_t vu64=;
double vd=;
std::string str; pb2jsonstring.append("{"); for (auto it=needs.begin(); it != needs.end(); ++it)
{
const FieldDescriptor* goal_field=descriptor->FindFieldByNumber(*it);
//need为空的转换和不为空的几乎一样，主要差别是对字段的提取，不为空时需要使用FindFieldByNumber()来进行操作，这样可以取任意字段号对应的字段。将need为空和不为空分开写主要是测试中这样可以节省时间，其实是可以写到一块的，有兴趣的同学可以进行修改。 if(nullptr==goal_field) //不存在字段
{
continue;
} if (goal_field->is_repeated())
{
if (reflection->FieldSize(msg, goal_field) > )
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string .append("[");
GetRepeatedJson(tmp_string, msg, goal_field, reflection, Enum_2_Str,Showzero);
tmp_string.append("]");
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
continue;
}
switch (goal_field->type())
{
case FieldDescriptor::TYPE_MESSAGE:
{
const Message& tmp_msg = reflection->GetMessage(msg, goal_field);
if ( != tmp_msg.ByteSize())
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
NeedEmptyToJson(tmp_string,tmp_msg, Enum_2_Str, Showzero);
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
break; case FieldDescriptor::TYPE_INT32:
{
v32=reflection->GetInt32(msg, goal_field);
if(v32==)
{
if(Showzero) //字段值为０，也需要进行打印
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(v32));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(v32));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
break; case FieldDescriptor::TYPE_UINT32:
{
vu32=reflection->GetUInt32(msg, goal_field);
if(vu32==)
{
if(Showzero)
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(vu32));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(vu32));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
break; case FieldDescriptor::TYPE_INT64:
{
v64=reflection->GetInt64(msg, goal_field);
if(v64==)
{
if(Showzero)
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(v64));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(v64));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
break;
case FieldDescriptor::TYPE_UINT64:
{
vu64=reflection->GetUInt64(msg, goal_field);
if(vu64==)
{
if(Showzero)
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(vu64));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(vu64));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
break;
case FieldDescriptor::TYPE_STRING:
case FieldDescriptor::TYPE_BYTES:
{ str=reflection->GetString(msg, goal_field);
if(str.empty())
{
if(Showzero)
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append("\"").append(str).append("\"");
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append("\"").append(str).append("\"");
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge); }
}
break;
case FieldDescriptor::TYPE_DOUBLE:
{
vd=reflection->GetDouble(msg, goal_field);
if(vd==)
{
if(Showzero)
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(vd));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
tmp_string.append(std::to_string(vd));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
break;
case FieldDescriptor::TYPE_BOOL:
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
if (reflection->GetBool(msg, goal_field))
tmp_string.append("true");
else
tmp_string.append("false");
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge); }
break;
case FieldDescriptor::TYPE_ENUM:
{
tmp_string="";
tmp_string.append("\"").append(goal_field->name()).append("\":");
if (Enum_2_Str)
{
tmp_string.append("\"").append(reflection->GetEnum(msg,goal_field)->name()).append("\"");
}
else
{
static char enumstr[];
memset(enumstr, , sizeof(enumstr));
snprintf(enumstr, sizeof(enumstr), "%d", reflection->GetEnum(msg,goal_field)->number());
tmp_string.append(enumstr);
}
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
break;
default:
break;
}
}
pb2jsonstring.append("}");
}
然后就是需要对repeated的字段进行相应的转换，
void GetRepeatedJson(std::string& pb2jsonstring, const ::google::protobuf::Message& msg, const google::protobuf::FieldDescriptor *goal_field, const ::google::protobuf::Reflection *reflection, bool Enum_2_Str,bool Showzero)
{
std::string tmp_string;
int judge=;
std::int32_t v32=;
std::uint32_t vu32=;
std::int64_t v64=;
std::uint64_t vu64=;
double vd=;
std::string str;
for (int i = ; i < reflection->FieldSize(msg, goal_field); ++i)
{
switch (goal_field->type())
{
case FieldDescriptor::TYPE_MESSAGE:
{
const Message& tmp_msg = reflection->GetRepeatedMessage(msg, goal_field, i);
if ( != tmp_msg.ByteSize())
{
tmp_string="";
//当重复的是message时，需要全部进行转换，不需要选择特定的字段进行转换，当然有这个需求的也可以进行相应的改进，不过会麻烦一些。重复字段的提取主要就是Get方式的不同，这个可以查阅文章开头中提到的文档，里面有详细说明
NeedEmptyToJson(tmp_string, tmp_msg, Enum_2_Str,Showzero);
judge = AppendTmpString2(pb2jsonstring,tmp_string,judge);
}
}
break;
case FieldDescriptor::TYPE_INT32:
{
v32=reflection->GetRepeatedInt32(msg, goal_field,i);
if(v32==)
{
if(Showzero)
{
tmp_string="";
tmp_string.append(std::to_string(v32));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append(std::to_string(v32));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
} break;
case FieldDescriptor::TYPE_UINT32:
{
vu32=reflection->GetRepeatedUInt32(msg, goal_field,i);
if(vu32==)
{
if(Showzero)
{
tmp_string="";
tmp_string.append(std::to_string(vu32));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append(std::to_string(vu32));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
break;
case FieldDescriptor::TYPE_INT64:
{
v64=reflection->GetRepeatedInt64(msg, goal_field,i);
if(v64==)
{
if(Showzero)
{
tmp_string="";
tmp_string.append(std::to_string(v64));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append(std::to_string(v64));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
break;
case FieldDescriptor::TYPE_UINT64:
{
vu64=reflection->GetRepeatedUInt64(msg, goal_field,i);
if(vu64==)
{
if(Showzero)
{
tmp_string="";
tmp_string.append(std::to_string(vu64));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append(std::to_string(vu64));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
} }
break;
case FieldDescriptor::TYPE_STRING:
case FieldDescriptor::TYPE_BYTES:
{
str="";
str=reflection->GetRepeatedString(msg, goal_field,i);
if(str.empty())
{
if(Showzero)
{
tmp_string="";
tmp_string.append("\"").append(str).append("\"");
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append("\"").append(str).append("\"");
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge); }
}
break;
case FieldDescriptor::TYPE_DOUBLE:
{
vd=reflection->GetRepeatedDouble(msg, goal_field,i);
if(vd==)
{
if(Showzero)
{
tmp_string="";
tmp_string.append(std::to_string(vd));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
}
}
else
{
tmp_string="";
tmp_string.append(std::to_string(vd));
judge = AppendTmpString1(pb2jsonstring,tmp_string,judge);
} }
break;
case FieldDescriptor::TYPE_BOOL:
{
tmp_string="";
if(reflection->GetRepeatedBool(msg, goal_field,i))
tmp_string.append("true");
else
tmp_string.append("false");
judge = AppendTmpString2(pb2jsonstring,tmp_string,judge); }
break;
case FieldDescriptor::TYPE_ENUM:
{
tmp_string="";
if (Enum_2_Str)
{
tmp_string.append("\"").append(reflection->GetRepeatedEnum(msg,goal_field,i)->name()).append("\"");
}
else
{
static char enumstr[];
memset(enumstr, , sizeof(enumstr));
snprintf(enumstr, sizeof(enumstr), "%d", reflection->GetRepeatedEnum(msg,goal_field,i)->number());
tmp_string.append(enumstr);
}
judge = AppendTmpString2(pb2jsonstring,tmp_string,judge);
}
break;
default:
break;
}
}
}
int AppendTmpString2(std::string &pb2jsonstring,std::string &tmp_string, int judge)
{
if( judge!= && tmp_string.length()!=)
{
pb2jsonstring.append(",").append(tmp_string);
return judge;
}
else if( judge== && tmp_string.length()!=)
{
pb2jsonstring.append(tmp_string);
return ;
}
return judge;
}
总结说明
本文中介绍的方法从逻辑上来说没有什么特别的地方，就是读取字段名，字段值然后添加到对应的字符串当中，代码比较繁琐，还有很大的改进空间，后来使用宏定义的##操作减少了很多代码量，比如GetInt()与GetRepeatedInt()可以通过使用“##”操作合并到一个函数中进行操作。
文中有不合理的地方希望各位批评指正。