json格式转换（json转换成C#类）

最近碰到一个问题，就是想把json字符串中的字段名称都改成首字母小写，当然这个json是非常大的，手动改不理智，那有没有什么办法通过什么方式直接将json字符串的首字母都改成小写的呢？一开始是想通过Newtonsoft.Json.dll这个类库，直接反序列化为动态的类(dynamic)，然后重新序列化成json字符串时指定：ContractResolver = new CamelCasePropertyNamesContractResolver()，但是还是行不通。如果我们有事先定义好的实体类，在序列化的时候通过上面的设置是可以输出首字母小写的json字符串，基于这个考虑，是否可以通过原json字符串动态生成实体类，再通过反序列化成该实体类，最后把得到的对象再序列化成json字符串，是否可达目的呢。请往下看。

动态生成实体类

创建一个控制台项目：dotnet new console -o JsonToObject新建一个json文件，里面就是需要转换的json内容读取json内容，拼接json中涉及到的所有的类的定义

Action<string> Write = Console.WriteLine; var jsonString = File.ReadAllText("demo.json");//读取json文件里的内容 var jObject = JObject.Parse(jsonString);//Newtonsoft.Json中的JObject.Parse转换成json对象 Dictionary<string, string> classDicts = new Dictionary<string, string>();//key为类名，value为类中的所有属性定义的字符串 classDicts.Add("Root", GetClassDefinion(jObject));//拼接顶层的类 foreach (var item in jObject.Properties()) { classDicts.Add(item.Name, GetClassDefinion(item.Value)); GetClasses(item.Value, classDicts); } //下面是将所有的类定义完整拼接起来 StringBuilder sb = new StringBuilder(1024); sb.AppendLine("using System;"); sb.AppendLine("using System.Collections.Generic;"); sb.AppendLine("namespace JsonToObject"); sb.AppendLine("{"); foreach (var item in classDicts) { sb.Append($"public class {item.Key}" + Environment.NewLine); sb.Append("{" + Environment.NewLine); sb.Append(item.Value); sb.Append("}" + Environment.NewLine); } sb.AppendLine("}"); Write(sb.ToString()); //递归遍历json节点，把需要定义的类存入classes void GetClasses(JToken jToken, Dictionary<string, string> classes) { if (jToken is JValue) { return; } var childToken = jToken.First; while (childToken != null) { if (childToken.Type == JTokenType.Property) { var p = (JProperty)childToken; var valueType = p.Value.Type; if (valueType == JTokenType.Object) { classes.Add(p.Name, GetClassDefinion(p.Value)); GetClasses(p.Value, classes); } else if (valueType == JTokenType.Array) { foreach (var item in (JArray)p.Value) { if (item.Type == JTokenType.Object) { if (!classes.ContainsKey(p.Name)) { classes.Add(p.Name, GetClassDefinion(item)); } GetClasses(item, classes); } } } } childToken = childToken.Next; } } //获取类中的所有的属性 string GetClassDefinion(JToken jToken) { StringBuilder sb = new(256); var subValueToken = jToken.First(); while (subValueToken != null) { if (subValueToken.Type == JTokenType.Property) { var p = (JProperty)subValueToken; var valueType = p.Value.Type; if (valueType == JTokenType.Object) { sb.Append("public " + p.Name + " " + p.Name + " {get;set;}" + Environment.NewLine); } else if (valueType == JTokenType.Array) { var arr = (JArray)p.Value; //a.First switch (arr.First().Type) { case JTokenType.Object: sb.Append($"public List<{p.Name}> " + p.Name + " {get;set;}" + Environment.NewLine); break; case JTokenType.Integer: sb.Append($"public List<int> " + p.Name + " {get;set;}" + Environment.NewLine); break; case JTokenType.Float: sb.Append($"public List<float> " + p.Name + " {get;set;}" + Environment.NewLine); break; case JTokenType.String: sb.Append($"public List<string> " + p.Name + " {get;set;}" + Environment.NewLine); break; case JTokenType.Boolean: sb.Append($"public List<bool> " + p.Name + " {get;set;}" + Environment.NewLine); break; default: break; } } else { switch (valueType) { case JTokenType.Integer: sb.Append($"public int " + p.Name + " {get;set;}" + Environment.NewLine); break; case JTokenType.Float: sb.Append($"public float " + p.Name + " {get;set;}" + Environment.NewLine); break; case JTokenType.String: sb.Append($"public string " + p.Name + " {get;set;}" + Environment.NewLine); break; case JTokenType.Boolean: sb.Append($"public bool " + p.Name + " {get;set;}" + Environment.NewLine); break; default: break; } } } subValueToken = subValueToken.Next; } return sb.ToString(); }现在有了类的定义字符串，接下来就可以动态编译成实体类

Write("Let's compile!"); Write("Parsing the code into the SyntaxTree"); SyntaxTree syntaxTree = CSharpSyntaxTree.ParseText(sb.ToString()); string assemblyName = Path.GetRandomFileName(); var refPaths = new[] { typeof(object).GetTypeInfo().Assembly.Location, typeof(Console).GetTypeInfo().Assembly.Location, Path.Combine(Path.GetDirectoryName(typeof(System.Runtime.GCSettings).GetTypeInfo().Assembly.Location), "System.Runtime.dll") }; MetadataReference[] references = refPaths.Select(r => MetadataReference.CreateFromFile(r)).ToArray(); Write("Adding the following references"); foreach (var r in refPaths) Write(r); Write("Compiling ..."); CSharpCompilation compilation = CSharpCompilation.Create( assemblyName, syntaxTrees: new[] { syntaxTree }, references: references, options: new CSharpCompilationOptions(OutputKind.DynamicallyLinkedLibrary)); using (var ms = new MemoryStream()) { EmitResult result = compilation.Emit(ms); if (!result.Success) { Write("Compilation failed!"); IEnumerable<Diagnostic> failures = result.Diagnostics.Where(diagnostic => diagnostic.IsWarningAsError || diagnostic.Severity == DiagnosticSeverity.Error); foreach (Diagnostic diagnostic in failures) { Console.Error.WriteLine("t{0}: {1}", diagnostic.Id, diagnostic.GetMessage()); } } else { Write("Compilation successful! Now instantiating and executing the code ..."); ms.Seek(0, SeekOrigin.Begin); Assembly assembly = AssemblyLoadContext.Default.LoadFromStream(ms); var type = assembly.GetType("JsonToObject.Root"); var instance = assembly.CreateInstance("JsonToObject.Root"); //反射获取静态的 DeserializeObject方法 var deserializeObject = typeof(JsonConvert).GetGenericMethod("DeserializeObject", BindingFlags.Public | BindingFlags.Static, new Type[] { typeof(string), typeof(JsonSerializerSettings) }); var genericDeserializeObject = deserializeObject.MakeGenericMethod(type); //执行反序列化 var root = genericDeserializeObject.Invoke(null, new object[] { jsonString, null }); //输出序列化的结果 Write(JsonConvert.SerializeObject(root, new JsonSerializerSettings { ContractResolver = new CamelCasePropertyNamesContractResolver() })); } }

通过反射获取静态方法的扩展

public static class Extension { public static MethodInfo GetGenericMethod(this Type targetType, string name, BindingFlags flags, params Type[] parameterTypes) { var methods = targetType.GetMethods(flags).Where(m => m.Name == name && m.IsGenericMethod); var flag = false; foreach (MethodInfo method in methods) { var parameters = method.GetParameters(); if (parameters.Length != parameterTypes.Length) continue; for (var i = 0; i < parameters.Length; i++) { if (parameters[i].ParameterType != parameterTypes[i]) { break; } if (i == parameters.Length - 1) { flag = true; } } if (flag) { return method; } } return null; } }

至此，我们已经实现了文章开头说的将json字符串的首字母都变成小写

总结

本文主要涉及以下的内容

如何通过json字符串拼接类的定义如何通过动态编译的方式动态生成类反射动态调用反序列化的方法希望本文能够对大家有所帮助，完整的项目地址可以参考：dynamic_demo（https://github.com/likeshan168/test_demo/tree/main/dynamic_demo）项目