Spring @ResponseBody Json Cyclic Reference

问题

I am trying to use Spring 3.x @ResponseBody to generate json/xml response, I am using JPA 2.0 ORM when there is many-many relation b/w tables then json is throwing LazyInitializationException

If I give "eager fetch" then it is going into cyclic reference.

回答1:

I recently encountered a similar problem: Jackson - serialization of entities with birectional relationships (avoiding cycles)

So the solution is to upgrade to Jackson 2.0, and add to classes the following annotation:

@JsonIdentityInfo(generator = ObjectIdGenerators.IntSequenceGenerator.class, 
                  property = "@id")
public class SomeEntityClass ...

Then the problem is that Spring doesn't work with Jackson 2.0. This has been solved in the following way:

<bean id="jacksonMessageConverter"
          class="own.implementation.of.MappingJacksonHttpMessageConverter"/>

<bean class="org.springframework.web.servlet.mvc
             .annotation.AnnotationMethodHandlerAdapter">
        <property name="messageConverters">
            <list>
                <ref bean="jacksonMessageConverter"/>
            </list>
        </property>
        <property name="requireSession" value="false"/>
    </bean>

And the own.implementation.of.MappingJacksonHttpMessageConverter is based on this:

http://www.jarvana.com/jarvana/view/org/springframework/spring-web/3.0.0.RELEASE/spring-web-3.0.0.RELEASE-sources.jar!/org/springframework/http/converter/json/MappingJacksonHttpMessageConverter.java?format=ok

But use ObjectMapper and other Jackson classes from Jackson 2.0 instead of Jackson 1.*

回答2:

Judging by your comments, just create a custom Serializer.

Your JsonSerializer. You can have these for each object type you're trying to serialize.

public class MyObjectJsonSerializer extends JsonSerializer<MyObject> {

@Override
public Class<MyObject> handledType() {
    return MyObject.class;
}

@Override
public void serialize(MyObject myObject, JsonGenerator jgen, SerializerProvider provider) throws IOException, JsonProcessingException {
    jgen.writeStartObject();
    jgen.writeNumberField("id", myObject.getId());
    // whatever else you need
    jgen.writeEndObject();
}

}

Your ObjectMapper.

public class MyObjectMapper extends ObjectMapper {

public MyObjectMapper() {
    SimpleModule module = new SimpleModule("My Module", new Version(1, 0, 0, "SNAPSHOT"));
    module.addSerializer(new MyObjectJsonSerializer());

    this.registerModule(module);
}

}

And then in your spring-config.xml.

<mvc:annotation-driven>
    <mvc:message-converters>
        <bean class="org.springframework.http.converter.json.MappingJacksonHttpMessageConverter">
            <property name="objectMapper" ref="myObjectMapper" />
        </bean>
    </mvc:message-converters>
</mvc:annotation-driven>

<bean id="myObjectMapper" class="com.manne.app.objectmapper.MyObjectMapper" />

回答3:

Sounds like you are serializing an ORM-managed object to JSON, but haven't initialized all of the child associations, leading to the LazyInitializationException, as your Controller doesn't have a handle to the DB connection. 2 choices:

1. Initialize all of the objects' child associations in the DAO layer
2. Convert the ORM-managed object to a TO and pass that to the Controller for conversion to JSON

来源：https://stackoverflow.com/questions/9727279/spring-responsebody-json-cyclic-reference