SpringmvcJSON转换器MappingJackson2HttpMessageConverter设置对值为null的处理

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:

<!-- 请求信息转换器,负责读取和写入json格式的数据 --><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;      }          }  

大家可以根据自己的需求来设置null的自定义值.

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