关于前后端交互 json转换值为null的操作_json ""转换为null-优快云博客

SpringmvcJSON转换器MappingJackson2HttpMessageConverter设置对值为null的处理n 空值

我们在使用springmvc中的 @ResponseBody 注解返回JSON时可以配置Json转换器如下:


<bean id="mappingJackson2HttpMessageConverter"
class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
<property name="supportedMediaTypes">
<list>
<value>application/json;charset=UTF-8</value>
</list>
</property>
</bean>

有时我们返回的字段存在null的情况我们需要对其进行处理,objectMapper提供了默认的几种处理方式配置如下:

<bean id="mappingJacksonHttpMessageConverter"
class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
<property name="supportedMediaTypes">
<list>
<value>application/json;charset=UTF-8</value>
</list>
</property>
<property name="objectMapper">
<bean class="com.fasterxml.jackson.databind.ObjectMapper">
<property name="serializationInclusion">
<value type="com.fasterxml.jackson.annotation.JsonInclude.Include">NON_NULL</value>
</property>
</bean>
</property>
</bean>

这种是将字段为null的清理掉不在结果Json中显示出来,其余的还有以下几种配置:

ALWAYS, NON_NULL, NON_DEFAULT, NON_EMPTY

有些特殊情况,我们不能将null字段直接去除,而是需要给予一个默认的值,则可以设置如下配置:

<bean id="mappingJacksonHttpMessageConverter"
class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter">
<property name="supportedMediaTypes">
<list>
<value>application/json;charset=UTF-8</value>
</list>
</property>
<property name="objectMapper">
<bean class="com.fasterxml.jackson.databind.ObjectMapper">
<property name="serializerProvider">
<bean class="com.fasterxml.jackson.databind.ser.DefaultSerializerProvider.Impl">
<property name="nullValueSerializer">
<bean class="cn.com.mx.gome.flash.component.GomeSearchJsonSerializer"></bean>
</property>
</bean>
</property>
</bean>
</property>
</bean>

自定义的null处理类如下;

import java.io.IOException;
import java.util.ArrayList;
import java.util.List;
import com.fasterxml.jackson.core.JsonGenerator;
import com.fasterxml.jackson.core.JsonProcessingException;
import com.fasterxml.jackson.databind.JsonSerializer;
import com.fasterxml.jackson.databind.SerializerProvider;
public class GomeSearchJsonSerializer extends JsonSerializer<Object> {
@Override
public void serialize(Object value, JsonGenerator jgen, SerializerProvider provider)
throws IOException, JsonProcessingException {
// jgen.writeString("");
jgen.writeObject(new JsonNullDef());
}
}
class JsonNullDef{
private List<String> def = new ArrayList<>();
public List<String> getDef() {
return def;
}
public void setDef(List<String> def) {
this.def = def;
}
}