1.导入fastjson依赖

<dependency>
      <groupId>com.alibaba</groupId>
      <artifactId>fastjson</artifactId>
      <version>1.2.54</version>
    </dependency>

2.在spring-mvc.xml中配置 FastJsonHttpMessageConverter

<!--配置spring mvc的注解驱动-->
    <mvc:annotation-driven>
        
        <mvc:message-converters>
            <bean class="com.alibaba.fastjson.support.spring.FastJsonHttpMessageConverter">
                <property name="supportedMediaTypes">
                    <list>
                        <value>application/json</value>
                    </list>
                </property>


            </bean>
        </mvc:message-converters>
    </mvc:annotation-driven>

3.在转换json要展示null值的对象属性上添加相应的注解