最近在一个需要高并发的项目中使用到json,最开始使用jsoncpp进行解析和序列化,但是在json数据比较大时jsoncpp会抛异常,在多线程的情况下抛异常的概率更加频繁!后来发现是因为jsoncpp版本比较老,老版本的jsoncpp不是多线程安全的(参考 https://github.com/open-source-parsers/jsoncpp/issues/823) 更新到最新的版本后,处理性能达不到预期,于是查找原因,经过hotspots分析,发现大部分时间消耗在jsoncpp的readValue函数,在一些存在大量float数值的json中解析数值的操作耗时较大。
于是找到了rapidjson,根据benchmark结果看起来不错,经过实际测试发现在40线程的压力测试下相比jsoncpp性能提升10倍左右,一些存在大量float数值的case性能提升更明显!
如下,整理一下rapidjson使用的方法:
1. 通用解析方法放在rapidjson_utils.hpp文件中
#ifndef rapidjson_utils_h__
#define rapidjson_utils_h__
#include "rapidjson/rapidjson.h"
#include "rapidjson/document.h"
#include "rapidjson/pointer.h"
#include "rapidjson/writer.h"
#include "rapidjson/prettywriter.h"
#include "rapidjson/error/en.h"
#include
namespace utils
{
using std::string;
static int get_rapidjson_string(const rapidjson::Value& js_in,
std::string key,
std::string& value) {
rapidjson::Pointer pointer(key.c_str());
if (!pointer.IsValid()) {
return -1;
}
const rapidjson::Value *pValue = rapidjson::GetValueByPointer(js_in, pointer);
if (NULL == pValue || !pValue->IsString()) {
return -1;
}
value = pValue->GetString();
return 0;
}
static int get_rapidjson_int(const rapidjson::Value& js_in,
std::string key,
int& value) {
rapidjson::Pointer pointer(key.c_str());
if (!pointer.IsValid()) {
return -1;
}
const rapidjson::Value *pValue = rapidjson::GetValueByPointer(js_in, pointer);
if (NULL == pValue || !pValue->IsNumber()) {
return -1;
}
value = pValue->GetInt();
return 0;
}
///< get float number
static int get_rapidjson_number(const rapidjson::Value& js_in,
std::string key,
float& value) {
rapidjson::Pointer pointer(key.c_str());
if (!pointer.IsValid()) {
return -1;
}
const rapidjson::Value *pValue = rapidjson::GetValueByPointer(js_in, pointer);
if (NULL == pValue || !pValue->IsNumber()) {
return -1;
}
rapidjson::Type valueType = pValue->GetType();
switch (valueType) {
case rapidjson::Type::kNumberType:
value = pValue->GetDouble();
break;
default:
return -1;
}
return 0;
}
static int get_rapidjson_bool(const rapidjson::Value& js_in,
std::string key,
bool& value) {
rapidjson::Pointer pointer(key.c_str());
if (!pointer.IsValid()) {
return -1;
}
const rapidjson::Value *pValue = rapidjson::GetValueByPointer(js_in, pointer);
if (NULL == pValue || !pValue->IsBool()) {
return -1;
}
value = pValue->GetBool();
return 0;
}
static void add_member_string(rapidjson::Value& node, string key, string value, rapidjson::Document::AllocatorType &alloc) {
node.AddMember(rapidjson::Value(key.c_str(), key.length(), alloc).Move(),
rapidjson::Value(value.c_str(), value.length(), alloc).Move(), alloc);
}
static void add_member_int(rapidjson::Value& node, string key, int value,
rapidjson::Document::AllocatorType &alloc) {
node.AddMember(rapidjson::Value(key.c_str(), key.length(), alloc).Move(),
rapidjson::Value(value).Move(), alloc);
}
static void add_member_float(rapidjson::Value& node, string key, double value,
rapidjson::Document::AllocatorType &alloc) {
node.AddMember(rapidjson::Value(key.c_str(), key.length(), alloc).Move(),
rapidjson::Value(value).Move(), alloc);
}
static void add_member_bool(rapidjson::Value& node, string key, bool value,
rapidjson::Document::AllocatorType &alloc) {
node.AddMember(rapidjson::Value(key.c_str(), key.length(), alloc).Move(),
rapidjson::Value(value).Move(), alloc);
}
static string to_string(const rapidjson::Value& v) {
rapidjson::StringBuffer sb;
rapidjson::Writer writer(sb);
v.Accept(writer);
std::string sResult = sb.GetString();
return sResult;
}
static string to_styled_string(const rapidjson::Value& v) {
rapidjson::StringBuffer sb;
rapidjson::PrettyWriter writer(sb);
v.Accept(writer);
std::string s = sb.GetString();
return s;
}
} //namespace utils
#endif // rapidjson_utils_h__
2. 测试代码放在rapidjson_example.cpp中
#include
#include
#include
#include
#include "rapidjson_utils.hpp"
using std::string;
int main(int argc, char** argv)
{
string data = "{\"user\":\"hello\",\"movies\":[{\"name\":\"TENET\",\"like\":10000}],\"song\":{\"暗里着迷\":\"已经播放了3遍\"},\"ratio\":0.98}";
rapidjson::Document doc;
rapidjson::ParseResult ok = doc.Parse(data.c_str());
if (!ok) {
printf("parse json failure id=%d offset=%d msg=%s\n", doc.GetParseError(), doc.GetErrorOffset(), rapidjson::GetParseError_En(doc.GetParseError()));
return -1;
}
string user;
utils::get_rapidjson_string(doc, "/user", user);
printf("user=%s\n", user.c_str());
///< 使用迭代器遍历数组
const rapidjson::Value* pMovies = rapidjson::GetValueByPointer(doc, "/movies");
if (nullptr != pMovies && pMovies->IsArray() && !pMovies->Empty()) {
for (rapidjson::Value::ConstValueIterator iter = pMovies->Begin(); iter != pMovies->End(); iter++) {
string name;
int like;
utils::get_rapidjson_string(*iter, "/name", name);
utils::get_rapidjson_int(*iter, "/like", like);
printf("movie=%s like=%d\n", name.c_str(), like);
}
}
const rapidjson::Value* pSong = rapidjson::GetValueByPointer(doc, "/song");
if (nullptr != pSong && pSong->IsObject() && !pSong->ObjectEmpty()) {
///< 使用迭代器遍历object
const rapidjson::Value& song = *pSong;
for (rapidjson::Value::ConstMemberIterator miter = song.MemberBegin(); miter != song.MemberEnd(); miter++) {
const rapidjson::Value& name = miter->name;
const rapidjson::Value& value = miter->value;
printf("song=%s message=%s\n", name.GetString(), value.GetString());
}
}
float ratio;
utils::get_rapidjson_number(doc, "/ratio", ratio);
printf("ratio=%f\n", ratio);
///< 生成一个新的json
rapidjson::Document out(rapidjson::kObjectType);
rapidjson::Document::AllocatorType &a = out.GetAllocator();
out.CopyFrom(doc, a);
rapidjson::Value* pNewMovies = rapidjson::GetValueByPointer(out, "/movies");
rapidjson::Value movie(rapidjson::kObjectType);
utils::add_member_string(movie, "name", "Memento", a);
utils::add_member_int(movie, "like", 12366, a);
utils::add_member_float(movie, "score", 0.95, a);
pNewMovies->PushBack(movie.Move(), a);
///< SetValueByPointer可以新增节点
rapidjson::SetValueByPointer(out, "/version", 2.0, a);
string s = utils::to_styled_string(out);
printf("after modify json=%s\n", s.c_str());
return 0;
}
参考:
rapidjson官网:http://rapidjson.org/zh-cn/
git仓库:https://github.com/Tencent/rapidjson.git
一些json解析器的性能对比:https://github.com/miloyip/nativejson-benchmark
jsoncpp和rapidjson哪个好用?:https://www.zhihu.com/question/23654513