关于java:Spring REST |

Spring REST | MappingJacksonHttpMessageConverter produces invalid JSON

我用Spring实现了一个RESTful Web服务。服务根据accept头以XML或JSON响应。以下是context.xml映射:

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  <bean id="xstreamMarshaller" class="org.springframework.oxm.xstream.XStreamMarshaller"/>
  <bean id="xmlMessageConverter"
        class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter">
    <constructor-arg ref="xstreamMarshaller"/>
    <property name="supportedMediaTypes" value="application/xml"/>
  </bean>

  <bean id="jsonHttpMessageConverter"
        class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter">
    <property name="prefixJson" value="false"/>
    <property name="supportedMediaTypes" value="application/json"/>
  </bean>

  <bean
    class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">
    <property name="messageConverters">
      <util:list id="beanList">
        <ref bean="xmlMessageConverter"/>
        <ref bean="jsonHttpMessageConverter"/>
      </util:list>
    </property>
  </bean>

以下是我的控制器方法:

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@Controller
@RequestMapping(value ="/entityService")
class RestfulEntityService {

  @Resource
  private EntityService entityService;

  @ResponseBody
  @RequestMapping(value ="/getAllEntities", method = RequestMethod.GET)
  public List<Entity> getAllEntities() {
    return entityService.getAllEntities();
  }
}

XML响应是有效的,但是,当客户机将accept头设置为application/json时,响应是无效的json。

下面是JSON响应示例:

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[{"id":3,"attributes":[{"id":18,"attributeValue":null,"attributeName":"mobile","attributeType":"varchar(40)","entity":{"id":3,"attributes":[{"id":18,"attributeValue":null,"attributeName":"mobile","attributeType":"varchar(40)","entity":{"id":3,"attributes":[{"id":18,"attributeValue":null,"attributeName":"mobile","attributeType":"varchar(40)","entity":{"id":3,"attributes": ..... repeats for a while and then stops..


您正在使用XStream序列化XML响应,而Jackson JSON序列化JSON响应。查看您发布的JSON输出,似乎有一个循环引用问题。我猜Entity有一个属性列表,每个属性都指向各自的实体。XStream使用xpath透明地处理循环引用,这允许在反序列化回对象时保留引用。Jackson从v1.6开始就能够处理循环引用,但是您需要通过使用@JsonManagedReference@JsonBackReference来注释序列化的实体来帮助它。我认为Jackson在允许在JSON序列化中返回引用方面是独一无二的。

请参阅Jackson关于使用声明性方法处理双向引用的文档以获取参考。