FastJson生成json时,显示Null属性

FastJson生成json时，默认不会输出null字段。
移动端，有时候，需要后端提供完整的字段说明。

Map < String , Object > jsonMap = new HashMap< String , Object>();
jsonMap.put("a",1);
jsonMap.put("b","");
jsonMap.put("c",null);
jsonMap.put("d","wuzhuti.cn");

String str = JSONObject.toJSONString(jsonMap);
System.out.println(str);
//输出结果:{"a":1,"b":"",d:"wuzhuti.cn"}

从输出结果可以看出，null对应的key已经被过滤掉；这明显不是我们想要的结果，这时我们就需要用到fastjson的SerializerFeature序列化属性也就是这个方法：JSONObject.toJSONString(Object object, SerializerFeature... features)

Fastjson的SerializerFeature序列化属性

--来自oschina bfleeee博客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

Map < String , Object > jsonMap = new HashMap< String , Object>();
jsonMap.put("a",1);
jsonMap.put("b","");
jsonMap.put("c",null);
jsonMap.put("d","wuzhuti.cn");

String str = JSONObject.toJSONString(jsonMap,SerializerFeature.WriteMapNullValue);
System.out.println(str);
//输出结果:{"a":1,"b":"","c":null,"d":"wuzhuti.cn"}

Spring配置FastJson
<mvc:annotation-driven>
<mvc:message-converters>
<bean class="com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter">
<property name="supportedMediaTypes">
<list>
<value>application/json;charset=UTF-8</value>
</list>
</property>
<property name="features">
<list>
<value>DisableCircularReferenceDetect </value>
<value>WriteMapNullValue</value>
<value>WriteNullListAsEmpty</value>
<value>WriteNullStringAsEmpty</value>
<value>WriteNullNumberAsZero</value>
<value>WriteNullBooleanAsFalse</value>
</list>
</property>
</bean>
</mvc:message-converters>
</mvc:annotation-driven>

//模型
public class TopicVo implements Serializable {

private static final long serialVersionUID = 1L;

private Long id;

private String name;

private String nullName;
private Integer intName;
private Long longName;
private Double doubleName;
private Map mapName;
private List listName;
private Map mapNameWithValue = Maps.newHashMap();
private Map mapNameWithValue2 = Maps.newHashMap();
{
mapNameWithValue2.put("a", "a");
}
}

//json数据，空的转换成了null或者0或者空[]

{
"doubleName": 0,
"id": 17,
"intName": 0,
"listName": [],
"longName": 0,
"mapName": null,
"mapNameWithValue": {},
"mapNameWithValue2": {
"a": "a"
},
"name": "好像的",
"nullName": ""
}

完整的选项

package com.alibaba.fastjson.serializer;

/**
* @author wenshao[szujobs@hotmail.com]
*/
public enum SerializerFeature {
QuoteFieldNames,
/**
*
*/
UseSingleQuotes,
/**
*
*/
WriteMapNullValue,
/**
* 用枚举toString()值输出
*/
WriteEnumUsingToString,
/**
* 用枚举name()输出
*/
WriteEnumUsingName,
/**
*
*/
UseISO8601DateFormat,
/**
* @since 1.1
*/
WriteNullListAsEmpty,
/**
* @since 1.1
*/
WriteNullStringAsEmpty,
/**
* @since 1.1
*/
WriteNullNumberAsZero,
/**
* @since 1.1
*/
WriteNullBooleanAsFalse,
/**
* @since 1.1
*/
SkipTransientField,
/**
* @since 1.1
*/
SortField,
/**
* @since 1.1.1
*/
@Deprecated
WriteTabAsSpecial,
/**
* @since 1.1.2
*/
PrettyFormat,
/**
* @since 1.1.2
*/
WriteClassName,

/**
* @since 1.1.6
*/
DisableCircularReferenceDetect,

/**
* @since 1.1.9
*/
WriteSlashAsSpecial,

/**
* @since 1.1.10
*/
BrowserCompatible,

/**
* @since 1.1.14
*/
WriteDateUseDateFormat,

/**
* @since 1.1.15
*/
NotWriteRootClassName,

/**
* @since 1.1.19
*/
DisableCheckSpecialChar,

/**
* @since 1.1.35
*/
BeanToArray,

/**
* @since 1.1.37
*/
WriteNonStringKeyAsString,

/**
* @since 1.1.42
*/
NotWriteDefaultValue,

/**
* @since 1.2.6
*/
BrowserSecure,

/**
* @since 1.2.7
*/
IgnoreNonFieldGetter
;

参考资料：https://wuzhuti.cn/2175.html