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:
原文出处：https://www.cnblogs.com/kugar/p/12334210.html
