Newtonsoft.Json.JsonConvert.DeserializeObject首次转换太慢问题

不论是.net还是xamarin工程里面转换json一直使用的都是Newtonsoft包，一直也没觉得有什么问题

直到最近安卓设备出现了很奇怪的事情，有个方法居然花费了1秒多，定位后发现是Newtonsoft.Json.JsonConvert.DeserializeObject花了1秒多，这我就傻眼了，这玩意怎么处理，要是都这样，之前的工程不可能没发现啊。

于是用.net弄了个单元测试，居然也要120多毫秒，这也太慢了吧。

定义类

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public class testjson
{
public string aa { get; set; }
public string bb { get; set; }
public string cc { get; set; }
}

测试：

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string output = "{ "aa":"1","bb":"哈哈哈哈","cc":"和hi黑欸"} ";
DateTime start = DateTime.Now;
testjson res = new testjson();
object a = Newtonsoft.Json.JsonConvert.DeserializeObject(output, typeof(testjson));
DateTime end = DateTime.Now;
TimeSpan bbbb = end - start;
Console.WriteLine("第一次转换一次花费时间：" + bbbb.TotalMilliseconds);

去网上找了找，看到一些json转换的插件对比测试，Newtonsoft没有这么差啊。做个循环测试，跑个10000次，结果只要26毫秒。

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DateTime start1 = DateTime.Now;
for (int i = 0; i < 10000; i++)
{
string output1 = "{ "aa":"1","bb":"哈哈哈哈","cc":"和hi黑欸"} ";
testjson res1 = new testjson();
res1 = (testjson)Newtonsoft.Json.JsonConvert.DeserializeObject(output1, typeof(testjson));
}
DateTime end1 = DateTime.Now;
TimeSpan bbbb1 = end1 - start1;
Console.WriteLine("第二次转换10000次花费时间：" + bbbb1.TotalMilliseconds);

进一步测试，换了个类来转换，同样10000次，只要23毫秒。

换到垃圾安卓板上去测试，第一次转换1.7秒，接着循环10000次620毫秒。

所以基本可以确定，首次调用 Newtonsoft.Json.JsonConvert.DeserializeObject的时候，会比较慢。

如果没有单独调用第一次，直接循环10000次，就算花费145毫秒，估计也不会发现其中第一次耗费了120秒。

我的想法是，工程启动的时候，随便写个转换先调用下，把第一次的事情做掉，使实际的业务转换受到影响（即使只有第一次）下降到最低。

更多测试，反序列化的和序列化的对比。

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using Microsoft.VisualStudio.TestTools.UnitTesting;
using System;
namespace UnitTestProject1
{
[TestClass]
public class UnitTest1
{
[TestMethod]
public void TestMethod1()
{
int counts = 10000;
DateTime t1 = DateTime.Now;
DateTime t2 = DateTime.Now;

string output = "{ "aa":"1","bb":"哈哈哈哈","cc":""} ";
t1 = DateTime.Now;

testjson res = (testjson)Newtonsoft.Json.JsonConvert.DeserializeObject(output, typeof(testjson));
t2 = DateTime.Now;

Console.WriteLine($"第1次反序列化花费时间：{(t2 - t1).TotalMilliseconds}");

//string output = "{ "flag":"1","cause":"","data":{ "aac004":"1","ake007":"20200226","aac003":"黄方金","fplist":[{"bkc011":"0","bkc010":"0","aae072":"YD027088915","aka063_mc":"诊察费","akc227":"17","aaa027":"350200","aka063":"06","bkc008":"17","bkc009":"0"},{"bkc011":".2","bkc010":"0","aae072":"YD027088915","aka063_mc":"检查费","akc227":"137.2","aaa027":"350200","aka063":"08","bkc008":"111","bkc009":"26"}],"mzlist":[{"bka542_mc":"其中公务员医疗补助","bka542":"bkc059_1","bkeb34":"0.0"}],"akc227":"154.2","bkc014":"20200226","bke174_mc":"省内异地","aac999":"350426198801111010","bkc171":"1002","aaz149":"000000000000","akc190":"YD024926537","bkc075":"0","amc028":"0","bkc059":"0","ake026":"0","aab004":"厦门翼号网络服务有限公司","amc020":"0","aka150":"4","bke174":"1","bkc052":"0","aac002":"350426198801111010","bae029":"1002","bmc041":"0","bkc591":"0","aaz500":"D74781764","bkc102":"0","aae072":"YD027088915","aae011":"lh_hsj","bkc041":"154.2","akc087":"0","bkc040":"0","bkc045":"0","bkc062":"0","ake173":"0","bkc060":"0"},"traceid":""}";
t1 = DateTime.Now;
testjson item = new testjson()
{
aa = "aljfdlsjflkjsdlf",
bb = "sdfsdfsdfds啊哈哈的撒发",
cc = "af;djaf;lkdsjf"
};

string mmm = Newtonsoft.Json.JsonConvert.SerializeObject(item);
t2 = DateTime.Now;
Console.WriteLine("第1次序列化花费时间：" + (t2 - t1).TotalMilliseconds);

t1 = DateTime.Now;
for (int i = 0; i < counts; i++)
{
string output1 = "{ "aa":"1","bb":"哈哈哈哈","cc":"和hi黑欸"} ";
testjson res1 = new testjson();
res1 = (testjson)Newtonsoft.Json.JsonConvert.DeserializeObject(output1, typeof(testjson));
}
t2 = DateTime.Now;

Console.WriteLine($"第2次反序列化{counts}次花费时间：{(t2 - t1).TotalMilliseconds}");

t1 = DateTime.Now;
for (int i = 0; i < counts; i++)
{
string nnnnn = Newtonsoft.Json.JsonConvert.SerializeObject(item);
}
t2 = DateTime.Now;

Console.WriteLine($"第2次序列化{counts}次花费时间：{(t2 - t1).TotalMilliseconds}");

t1 = DateTime.Now;
for (int i = 0; i < counts; i++)
{
if (i % 2 == 1)
{
string output2 = "{ "aaaa":"1","bbb":"哈哈哈哈","ccc":"和hi黑欸"} ";
testjson2 res2 = new testjson2();
res2 = (testjson2)Newtonsoft.Json.JsonConvert.DeserializeObject(output2, typeof(testjson2));
}
else
{
string output1 = "{ "aa":"1","bb":"哈哈哈哈","cc":"和hi黑欸"} ";
testjson res1 = new testjson();
res1 = (testjson)Newtonsoft.Json.JsonConvert.DeserializeObject(output1, typeof(testjson));
}
}
t2 = DateTime.Now;

Console.WriteLine($"第2次反序列化{counts}次(反复切换类),花费时间：{(t2 - t1).TotalMilliseconds}");

}

public class testjson
{
public string aa { get; set; }
public string bb { get; set; }
public string cc { get; set; }

}

public class testjson2
{
public string aaa { get; set; }
public string bbb { get; set; }
public string ccc { get; set; }

}
}
}

测试结果：首次反序列化都要120毫秒，首次序列化也要20多毫秒，反过先做序列化也是首次120毫秒左右，首次反序列化20毫秒左右。再后续一万次的时间也只要20毫秒左右，序列化相对来说比反序列化要快一些。

也就是说 jsonconvert "首次"调用的时候可能在100毫秒左右，然后"首次"调用序列化或者反序列化需要20毫秒左右，再往后的调用耗时就几乎可以忽略不计了。

目前我的猜想是首次调用做了一些初始化的工作，具体的后续去看下newtonsoftd的源码再分析，待续....