春季休息| MappingJacksonHttpMessageConverter 生成无效的 JSON
我已经使用 Spring 实现了 RESTful Web 服务。服务根据 Accept 标头以 XML 或 JSON 形式进行响应。这是 context.xml 映射：
<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>
这是我的控制器方法：
@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，当客户端将 Accept 标头设置为 application/json 时，响应是无效的 JSON。
以下是 JSON 响应示例：
[{"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..
I've implemented a RESTful web service with Spring. The service responds in XML or JSON based on the Accept header. Here's the context.xml mapping:
<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>
Here is my controller method:
@Controller
@RequestMapping(value = "/entityService")
class RestfulEntityService {
@Resource
private EntityService entityService;
@ResponseBody
@RequestMapping(value = "/getAllEntities", method = RequestMethod.GET)
public List<Entity> getAllEntities() {
return entityService.getAllEntities();
}
}
The XML response is valid, however, when the client sets the Accept header to application/json, the response is invalid JSON.
Here is the JSON response sample:
[{"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..
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您正在使用 XStream 序列化 XML 响应和 Jackson JSON 用于序列化 JSON 响应。查看您发布的 JSON 输出，似乎存在循环引用问题。我猜测 Entity 有一个属性列表，每个属性都指向各自的实体。 XStream 通过使用 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 自 v1.6 起就能够处理循环引用，但您需要通过使用
@JsonManagedReference和@JsonBackReference注释序列化实体来帮助它。我认为 Jackson 的独特之处在于允许在 JSON 序列化中进行反向引用。请参阅 Jackson 关于使用声明性方法处理双向引用的文档以供参考。
You're using XStream to serialize XML responses and Jackson JSON to serialize JSON responses. Looking at the JSON output you posted, it seems like there's a circular reference issue at hand. I'm guessing
Entityhas a list of attributes, each pointing to their respective entity. XStream handles circular references transparently by using XPath, this allows to preserve references when deserializing back to objects. Jackson is able to handle circular references since v1.6, but you need to help it by annotating your serialized entities with@JsonManagedReferenceand@JsonBackReference. I think Jackson is unique in allowing back references in JSON serialization.See Jackson's documentation on handling bi-directional references using declarative methods for reference.