springMVC,json視圖,返回的json數據有null值,怎麽過濾成空串

<bean class="org.springframework.web.servlet.view.json.MappingJacksonJsonView">

<property name="extractValueFromSingleKeyModel" value="true" />

<property name="objectMapper">

<bean class="org.codehaus.jackson.map.ObjectMapper">

<property name="serializationInclusion">

<value type="org.codehaus.jackson.map.annotate.JsonSerialize$Inclusion">NON_NULL</value>

</property>

</bean>

</property>

</bean>