由于开发功能的需要,又懒得新建太多的class,所以ValueTuple是个比较好的偷懒方法,但是,由于WebApi需要返回序列化后的json,默认的序列化只能将ValueTuple定义的各个属性序列化成Item1...n
但是微软还是良心的为序列化留下入口,编译器会在每个返回ValueTuple<>的函数或者属性上,增加一个TupleElementNamesAttribute特性,该类的TransformNames就是存着所设置的属性的名称(强烈需要记住:是每个使用到ValueTuple的函数或者属性才会添加,而不是加在有使用ValueTuple的类上),比如 (string str1,string str2) 那么 TransformNames=["str1","str2"],那么现在有如下一个class
public class A<T1,T2> { public T1 Prop1{set;get;}
public T2 Prop2{set;get;}
public (string str5,int int2) Prop3{set;get;} }
经过测试,如下一个函数
public A<(string str1,string str2),(string str3,string str4)> testApi(){}
这样一个函数testApi 的会加上 TupleElementNamesAttribute 特性,,TransformNames=["str1","str2","str3","str4","str5","int2"],注意了,,这里只会添加一个TupleElementNamesAttribute特性,然后把A里所有的名字按定义的顺序包含进去.
然后我们需要定义一个JsonConverter,用来专门针对一个函数或一个属性的返回值进行了序列化
public class ValueTupleConverter : JsonConverter { private string[] _tupleNames = null; private NamingStrategy _strategy = null; //也可以直接在这里传入特性 public ValueTupleConverter(TupleElementNamesAttribute tupleNames, NamingStrategy strategy = null) { _tupleNames = tupleNames.TransformNames.ToArrayEx(); _strategy = strategy; } //这里在构造函数里把需要序列化的属性或函数返回类型的names传进来 public ValueTupleConverter(string[] tupleNames, NamingStrategy strategy = null) { _tupleNames = tupleNames; _strategy = strategy; } public override void WriteJson(JsonWriter writer, object value, JsonSerializer serializer) { if (value != null && value is ITuple v) { writer.WriteStartObject(); for (int i = 0; i < v.Length; i++) { var pname = _tupleNames[i]; //根据规则,设置属性名 writer.WritePropertyName(_strategy?.GetPropertyName(pname, true) ?? pname); if (v[i] == null) { writer.WriteNull(); } else { serializer.Serialize(writer, v[i]); } } writer.WriteEndObject(); } } public override object ReadJson(JsonReader reader, Type objectType, object existingValue, JsonSerializer serializer) { //只需要实现序列化,,不需要反序列化,因为只管输出,所以,这个写不写无所谓 throw new NotImplementedException(); } public override bool CanConvert(Type objectType) { return objectType.IsValueTuple(); } }
接下来说说实现的原理:
1.newtonsoft.json的组件里,有一个ContactResolver类,用于对不同的类的解析,类库中自带的DefaultContractResolver默认定义了将类解析成各个JsonProperty,利用这个类,可用于将ValueTuple的定义的名字当做属性,返回给序列化器
2.asp.net core的Formatter,可以对Action输出的对象进行格式化,一般用于比如json的格式化器或者xml格式化器的定义,利用格式化器,在Action最后输出的时候,配合ContractResolver进行序列化
下面的实现中,很多地方需要判断是否为ValueTuple,为了节省代码,因此,先写一个Helper:
public static class ValueTupleHelper { private static ConcurrentDictionary<Type,bool> _cacheIsValueTuple=new ConcurrentDictionary<Type, bool>(); public static bool IsValueTuple(this Type type) { return _cacheIsValueTuple.GetOrAdd(type, x => x.IsValueType && x.IsGenericType && (x.FullName.StartsWith("System.ValueTuple") || x.FullName ?.StartsWith("System.ValueTuple`") == true) ); } }
那么开始来定义一个ContractResolver,实现的原理请看注释
public class CustomContractResolver : DefaultContractResolver { private MethodInfo _methodInfo = null; private IContractResolver _parentResolver = null; public CustomContractResolver(MethodInfo methodInfo, IContractResolver? parentContractResolver = null) { _methodInfo = methodInfo; _parentResolver = parentContractResolver; } public override JsonContract ResolveContract(Type type) { if (!type.GetProperties() .Where(x => x.CanRead && x.PropertyType.IsValueTuple()) .Any()) //如果Type类中不包含可读的ValueTuple类型的属性,则调用预定义的Resolver处理,当前Resolver只处理包含ValueTuple的类 { return _parentResolver?.ResolveContract(type); } var rc = base.ResolveContract(type); return rc; } public MethodInfo Method => _methodInfo; protected override JsonProperty CreateProperty(MemberInfo member, MemberSerialization memberSerialization) { //CreateProperty函数的结果,不需要额外加缓存,因为每个Method的返回Type,只会调用一次 JsonProperty property = base.CreateProperty(member, memberSerialization); //先调用默认的CreateProperty函数,创建出默认JsonProperty var pi = member as PropertyInfo; if (property.PropertyType.IsValueTuple()) { var attr = pi.GetCustomAttribute<TupleElementNamesAttribute>(); //获取定义在属性上的特性 if (attr != null) { //如果该属性是已经编译时有添加了TupleElementNamesAttribute特性的,,则不需要从method获取 //这里主要是为了处理 (string str1,int int2) Prop3 这种情况 property.Converter = new ValueTupleConverter(attr, this.NamingStrategy); } else { //从输入的method获取,并且需要计算当前属性所属的泛型是在第几个,然后计算出在TupleElementNamesAttribute.Names中的偏移 //这个主要是处理比如T2 Prop2 T2=ValueTuple的这种情况 var mAttr = (TupleElementNamesAttribute)_methodInfo.ReturnTypeCustomAttributes.GetCustomAttributes(typeof(TupleElementNamesAttribute), true).FirstOrDefault(); //用来获取valueTuple的各个字段名称 var basePropertyClass = pi.DeclaringType.GetGenericTypeDefinition(); //属性定义的泛型基类 如 A<T1,T2> var basePropertyType = basePropertyClass.GetProperty(pi.Name)!.PropertyType; //获取基类属性的返回类型 就是T1 ,比如获取在A<(string str1,string str2),(string str3,string str4)> 中 Prop1 返回的类型是对应基类中的T1还是T2 var index = basePropertyType.GenericParameterPosition;//获取属性所在的序号,用于计算 mAttr.Names中的偏移量 var skipNamesCount = (pi.DeclaringType as TypeInfo).GenericTypeArguments .Take(index) .Sum(x => x.IsValueTuple() ? x.GenericTypeArguments.Length : 0); ; //计算TupleElementNamesAttribute.TransformNames中当前类的偏移量 var names = mAttr.TransformNames .Skip(skipNamesCount) .Take(pi.PropertyType.GenericTypeArguments.Length) .ToArrayEx(); //获取当前类的所有name property.Converter = new ValueTupleConverter(names, this.NamingStrategy); //传入converter } property.GetIsSpecified = x => true; property.ItemConverter = property.Converter; //传入converter property.ShouldSerialize = x => true; property.HasMemberAttribute = false; } return property; } protected override JsonConverter? ResolveContractConverter(Type objectType) //该函数可用于返回特定类型类型的JsonConverter { var type = base.ResolveContractConverter(objectType); //这里主要是为了忽略一些在class上定义了JsonConverter的情况,因为有些比如 A<T1,T2> 在序列化的时候,并无法知道ValueTuple定义的属性名,这里添加忽略是为了跳过已定义过的JsonConverter //如有需要,可在这里多添加几个 if (type is ResultReturnConverter) { return null; } else { return type; } } }
为了能兼容用于预先定义的ContractResolver,因此,先定义一个CompositeContractResolver,用于合并多个ContractResolver,可看可不看:
/// <summary> /// 合并多个IContractResolver,,并只返回第一个返回非null的Contract,如果所有列表中的ContractResolver都返回null,则调用DefaultContractResolver返回默认的JsonContract /// </summary> public class CompositeContractResolver : IContractResolver, IEnumerable<IContractResolver> { private readonly IList<IContractResolver> _contractResolvers = new List<IContractResolver>(); private static DefaultContractResolver _defaultResolver = new DefaultContractResolver(); private ConcurrentDictionary<Type, JsonContract> _cacheContractResolvers=new ConcurrentDictionary<Type, JsonContract>(); /// <summary> /// 返回列表中第一个返回非null的Contract,如果所有列表中的ContractResolver都返回null,则调用DefaultContractResolver返回默认的JsonContract /// </summary> /// <param name="type"></param> /// <returns></returns> public JsonContract ResolveContract(Type type) { return _cacheContractResolvers.GetOrAdd(type, m => { for (int i = 0; i < _contractResolvers.Count; i++) { var contact = _contractResolvers[i].ResolveContract(type); if (contact != null) { return contact; } } return _defaultResolver.ResolveContract(type); }); } public void Add(IContractResolver contractResolver) { if (contractResolver == null) return; _contractResolvers.Add(contractResolver); } public IEnumerator<IContractResolver> GetEnumerator() { return _contractResolvers.GetEnumerator(); } IEnumerator IEnumerable.GetEnumerator() { return GetEnumerator(); } }
接下来,就该定义OutputFormatter了
public class ValueTupleOutputFormatter : TextOutputFormatter { private static ConcurrentDictionary<Type, bool> _canHandleType = new ConcurrentDictionary<Type, bool>(); //缓存一个Type是否能处理,提高性能,不用每次都判断 private static ConcurrentDictionary<MethodInfo, JsonSerializerSettings> _cacheSettings = new ConcurrentDictionary<MethodInfo, JsonSerializerSettings>(); //用于缓存不同的函数的JsonSerializerSettings,各自定义,避免相互冲突 private Action<ValueTupleContractResolver> _resolverConfigFunc = null; /// <summary> /// /// </summary> /// <param name="resolverConfigFunc">用于在注册Formatter的时候对ContractResolver进行配置修改,比如属性名的大小写之类的</param> public ValueTupleOutputFormatter(Action<ValueTupleContractResolver> resolverConfigFunc = null) { SupportedMediaTypes.Add("application/json"); SupportedMediaTypes.Add("text/json"); SupportedEncodings.Add(Encoding.UTF8); SupportedEncodings.Add(Encoding.Unicode); _resolverConfigFunc = resolverConfigFunc; } protected override bool CanWriteType(Type type) { return _canHandleType.GetOrAdd(type, t => { return type.GetProperties() //判断该类是否包含有ValueTuple的属性 .Where(x => x.CanRead && (CustomAttributeExtensions.GetCustomAttribute<TupleElementNamesAttribute>((MemberInfo) x) != null || x.PropertyType.IsValueTuple())) .Any(); }); } public override async Task WriteResponseBodyAsync(OutputFormatterWriteContext context, Encoding selectedEncoding) { var acce = (IActionContextAccessor)context.HttpContext.RequestServices.GetService(typeof(IActionContextAccessor)); #if NETCOREAPP2_1 var ac = acce.ActionContext.ActionDescriptor as ControllerActionDescriptor; #endif #if NETCOREAPP3_0 var endpoint = acce.ActionContext.HttpContext.GetEndpoint(); var ac = endpoint.Metadata.GetMetadata<ControllerActionDescriptor>(); //用来获取当前Action对应的函数信息 #endif var settings = _cacheSettings.GetOrAdd(ac.MethodInfo, m => //这里主要是为了配置settings,每个methodinfo对应一个自己的settings,当然也就是每个MethodInfo一个CustomContractResolver,防止相互冲突 { var orgSettings = JsonConvert.DefaultSettings?.Invoke(); //获取默认的JsonSettings var tmp = orgSettings != null ? cloneSettings(orgSettings) : new JsonSerializerSettings(); //如果不存在默认的,则new一个,如果已存在,则clone一个新的 var resolver = new ValueTupleContractResolver(m, tmp.ContractResolver is CompositeContractResolver ? null : tmp.ContractResolver); //创建自定义ContractResolver,传入函数信息 _resolverConfigFunc?.Invoke(resolver); //调用配置函数 if (tmp.ContractResolver != null) //如果已定义过ContractResolver,则使用CompositeContractResolver进行合并 { if (tmp.ContractResolver is CompositeContractResolver c) //如果定义的是CompositeContractResolver,则直接插入到最前 { c.Insert(0, resolver); } else { tmp.ContractResolver = new CompositeContractResolver() { resolver, tmp.ContractResolver }; } } else { tmp.ContractResolver = new CompositeContractResolver() { resolver }; } return tmp; }); var json = JsonConvert.SerializeObject(context.Object, Formatting.None, settings); //调用序列化器进行序列化 await context.HttpContext.Response.Body.WriteAsync(selectedEncoding.GetBytes(json)); } private JsonSerializerSettings cloneSettings(JsonSerializerSettings settings) { var tmp = new JsonSerializerSettings(); var properties = settings.GetType().GetProperties(); foreach (var property in properties) { var pvalue = property.GetValue(settings); if (pvalue is ICloneable p2) { property.SetValue(tmp, p2.Clone()); } else { property.SetValue(tmp, pvalue); } } return tmp; } }
到此,该定义的类都定义完了,下面是注册方法:在Start.cs中:
public void ConfigureServices(IServiceCollection services) { services.AddControllersWithViews(opt => { opt.OutputFormatters.Insert(0,new ValueTupleOutFormatter(x => { x.NamingStrategy= new CamelCaseNamingStrategy(true,true); //这里主要是为了演示对CustomContractResolver的配置,设置了所有属性首字母小写 })); }).AddNewtonsoftJson(); }
注册完成后,用下面的Action可测试:
public class ApiTestController : ControllerBase { [FromBodyJson()] public IActionResult test1(List<(string productid,int qty)> details) { return Content("success"); } public ResultReturn<(string str1, int int3)> Test() { return new SuccessResultReturn<(string str1, int int3)>(("2222",222)); } public Test<(string Y1, string Y2), (string str1, string t2)> Test2() { return new Test< (string Y1, string Y2),(string str1, string t2)>(("111","22222"),("3333","44444") ); } }
总结一下,上面实现的原理是: 自定义一个OutputFormatter,在WriteResponseBodyAsync中,可以获取到当前的Action对应的MethodInfo,然后利用编译器在所有返回ValueTuple的地方,都加了TupleElementNamesAttribute的功能,获取到使用时定义的ValueTuple各个Item的名字,再利用ContractResolver的CreateProperty功能,将定义的各个Item转换为对应的name.然后使用newtonsoft的序列化器,进行json序列化.
以上代码只能处理返回时,返回的类型为ValueTuple<T1...n>或者返回的类型中包含了ValueTuple<T1....n>的属性,但是对于函数内,不用于返回的,则无法处理,比如
public object Test2() { var s= new Test< (string Y1, string Y2),(string str1, string t2)>(("111","22222"),("3333","44444") ); JsonConvert.SerializeObject(s); return null; }
这种情况的变量s的序列化就没办法了
部分代码地址: