Json处理时经常遇到一些null值的处理，这里可以通过SerializerFeature来实现，常用的枚举如下：

DisableCheckSpecialChar：一个对象的字符串属性中如果有特殊字符如双引号，将会在转成json时带有反斜杠转移符。如果不需要转义，可以使用这个属性。默认为false 
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null

实例：
 String jsonString=JSONObject.toJSONString(result, SerializerFeature.WriteMapNullValue);

package jsons.tostr;

import com.alibaba.fastjson.JSONObject;

import com.alibaba.fastjson.serializer.SerializerFeature;

 

public class TedaTools {

public static String toJsonString(Object obj) {

return JSONObject.toJSONString(obj, SerializerFeature.WriteMapNullValue, SerializerFeature.PrettyFormat,

SerializerFeature.WriteDateUseDateFormat, SerializerFeature.WriteNullStringAsEmpty,

SerializerFeature.WriteNullBooleanAsFalse, SerializerFeature.WriteNullListAsEmpty,

SerializerFeature.WriteNullNumberAsZero);

}

}

 

package com.alibaba.fastjson.serializer;

 

public enum SerializerFeature {

    QuoteFieldNames,

   

    UseSingleQuotes,

   

    WriteMapNullValue,

   

    WriteEnumUsingToString,

   

    WriteEnumUsingName,

   

    UseISO8601DateFormat,

   

    WriteNullListAsEmpty,

   

    WriteNullStringAsEmpty,

   

    WriteNullNumberAsZero,

   

    WriteNullBooleanAsFalse,

   

    SkipTransientField,

   

    SortField,

   

    @Deprecated

    WriteTabAsSpecial,

   

    PrettyFormat,

   

    WriteClassName,

   

    DisableCircularReferenceDetect,

   

    WriteSlashAsSpecial,

   

    BrowserCompatible,

   

    WriteDateUseDateFormat,

   

    NotWriteRootClassName,

   

    DisableCheckSpecialChar,

   

    BeanToArray,

   

    WriteNonStringKeyAsString,

    

   

    NotWriteDefaultValue,

    

   

    BrowserSecure,

    

   

    IgnoreNonFieldGetter

    ;

    SerializerFeature(){

        mask = (1 << ordinal());

    }

    private final int mask;

    public final int getMask() {

        return mask;

    }

    public static boolean isEnabled(int features, SerializerFeature feature) {

        return (features & feature.getMask()) != 0;

    }

    

    public static boolean isEnabled(int features, int fieaturesB, SerializerFeature feature) {

        int mask = feature.getMask();

        

        return (features & mask) != 0 || (fieaturesB & mask) != 0;

    }

    public static int config(int features, SerializerFeature feature, boolean state) {

        if (state) {

            features |= feature.getMask();

        } else {

            features &= ~feature.getMask();

        }

        return features;

    }

    

    public static int of(SerializerFeature[] features) {

        if (features == null) {

            return 0;

        }

        

        int value = 0;

        

        for (SerializerFeature feature: features) {

            value |= feature.getMask();

        }

        

        return value;

    }

}