业务场景：
统一返回格式参数中，如果包含 Null 值，调用方会不太好处理，需要替换为空字符串，示例：
{
"response":{
"code":200,
"msg":"Remote service error",
"result":null
}
}替换为：
{
"response":{
"code":200,
"msg":"Remote service error",
"result":""
}
}具体实现：
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Filters;
using Newtonsoft.Json;
using Newtonsoft.Json.Serialization;
using System;
using System.Collections.Generic;
using System.Linq;
using System.Reflection;
public class WebApiResultMiddleware : ActionFilterAttribute
{
public override void OnResultExecuting(ResultExecutingContext context)
{
if (context.HttpContext.Request.Path.HasValue)
{
if (context.HttpContext.Request.Path.Value.ToLower().IndexOf(".inside.") < 0)
{
if (context.Result is FileContentResult || context.Result is EmptyResult)
{
return;
}
if (context.Result is ObjectResult)
{
var objectResult = context.Result as ObjectResult;
var settings = new JsonSerializerSettings()
{
ContractResolver = new NullToEmptyStringResolver(),
DateFormatString = "yyyy-MM-dd HH:mm"
};
context.Result = new JsonResult(new { data = objectResult.Value }, settings);
}
else
{
context.Result = new ObjectResult(new { data = new { } });
}
}
}
}
}
public class NullToEmptyStringResolver : Newtonsoft.Json.Serialization.DefaultContractResolver
{
protected override IList<JsonProperty> CreateProperties(Type type, MemberSerialization memberSerialization)
{
return type.GetProperties()
.Select(p => {
var jp = base.CreateProperty(p, memberSerialization);
jp.ValueProvider = new NullToEmptyStringValueProvider(p);
return jp;
}).ToList();
}
}
public class NullToEmptyStringValueProvider : IValueProvider
{
PropertyInfo _MemberInfo;
public NullToEmptyStringValueProvider(PropertyInfo memberInfo)
{
_MemberInfo = memberInfo;
}
public object GetValue(object target)
{
object result = _MemberInfo.GetValue(target);
if (result == null) result = "";
return result;
}
public void SetValue(object target, object value)
{
_MemberInfo.SetValue(target, value);
}
}
本文转自田园里的蟋蟀博客园博客，原文链接：http://www.cnblogs.com/xishuai/p/asp-net-core-webapi-json-convert-empty-string-instead-of-null.html，如需转载请自行联系原作者
