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 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); } }
在 Startup 代码里面 修改
//services.AddMvc().AddJsonOptions(option => { // //配置大小写问题，默认是首字母小写,该配置根据项目需要更改 // //option.SerializerSettings.ContractResolver = new Newtonsoft.Json.Serialization.DefaultContractResolver(); // //配置序列化时时间格式为时间戳 // //option.SerializerSettings.ContractResolver = new NullToEmptyStringResolver(); // option.SerializerSettings.DateFormatString = "yyyy-MM-dd HH:mm:ss"; //}); services.AddMvc(config => { var settings = new JsonSerializerSettings(); //设置首字母小写，如果不需要 则改为 DefaultContractResolver settings.ContractResolver = new CamelCasePropertyNamesContractResolver(); //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)); });