JSON.toJSONString 空对象也可以转化为JSON字符串

通过阿里巴巴 fastjson json 空对象转json null ,
导入maven依赖

　　　　　　　　<dependency><groupId>com.alibaba</groupId><artifactId>fastjson</artifactId><version>1.2.23</version></dependency>

RequestDTOitem requestDTO= new RequestDTO();String jsonObject =   JSON.toJSONString(requestDTO, SerializerFeature.WriteMapNullValue,SerializerFeature.WriteNullListAsEmpty,SerializerFeature.WriteNullStringAsEmpty,SerializerFeature.WriteNullBooleanAsFalse);System.out.println(JSON.toJSONString());//QuoteFieldNames———-输出key时是否使用双引号,默认为true//WriteMapNullValue——–是否输出值为null的字段,默认为false//WriteNullNumberAsZero—-数值字段如果为null,输出为0,而非null//WriteNullListAsEmpty—–List字段如果为null,输出为[],而非null//WriteNullStringAsEmpty—字符类型字段如果为null,输出为”“,而非null//WriteNullBooleanAsFalse–Boolean字段如果为null,输出为false,而非nul