应用场景
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。如果我们有实现定义好的实体类，再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字符串然后动态生成实体类，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
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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的。
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
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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，完整地项目地址可以参考：dynamic_demo项目
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