.netcore webapi json返回值序列化null替换为空字符串
场景：数据库中部分表字段允许空值，则代码中实体类对应的字段类型为可空类型Nullable<>，如int?，DateTime?，null值字段序列化返回的值都为null，前端对应字段赋值需要做null值判断，随想到全局把null替换为""
网上找的方案都是重写了DefaultContractResolver，但是该方法只能解决string类型null→""的问题，对其他可空类型无效。
研究了下git 上Newtonsoft.Json和.netcore MVC的源码
最终使用自定义JsonOutputFormatter方式实现：
public void ConfigureServices(IServiceCollection services){services.AddMvc().SetCompatibilityVersion(CompatibilityVersion.Version_2_1); //过滤器services.AddMvc(config =>{var settings = new JsonSerializerSettings();settings.ContractResolver = new DefaultContractResolver();//统一设置JsonResult中的日期格式 settings.DateFormatString = "yyyy-MM-dd HH:mm:ss";config.OutputFormatters.Insert(0, new MyJsonOutputFormatter(settings));});//services.AddMvc().AddJsonOptions(options =>//{// //options.SerializerSettings.ContractResolver = new SubstituteNullWithEmptyStringContractResolver();// 统一设置JsonResult中的日期格式 // //options.SerializerSettings.DateFormatString = "yyyy-MM-dd HH:mm:ss";//});services.AddMvcCore().AddApiExplorer();}
public class MyJsonOutputFormatter : JsonOutputFormatter{public MyJsonOutputFormatter(JsonSerializerSettings serializerSettings) : base(serializerSettings, ArrayPool<char>.Shared){}public new JsonSerializerSettings SerializerSettings => base.SerializerSettings;protected override JsonWriter CreateJsonWriter(TextWriter writer){if (writer == null){throw new ArgumentNullException(nameof(writer));}var jsonWriter = new NullJsonWriter(writer){ArrayPool = new JsonArrayPool<char>(ArrayPool<char>.Shared),CloseOutput = false,AutoCompleteOnClose = false};return jsonWriter;}}public class NullJsonWriter : JsonTextWriter{public NullJsonWriter(TextWriter textWriter):base(textWriter){}public override void WriteNull(){this.WriteValue(String.Empty);}}
