Spring MVC with Jackson 2.2: “HttpMediaTypeNotAcce

Question

So I'm struggling to get my beans encoded in json... First I tried with codehaus' jackson 1.9.13 and Spring MVC 3.1.1. I had some issues until I managed to get to "Direct self-reference" exception. Looking this up I found I needed fasterxml's Jackson 2. Then I found (here) that I need Spring 3.1.2 because prior versions aren't supporting Jackson 2.

So, after all this... I'm still getting the same exception. My maven dependencies are indeed including Spring MVC 3.1.2 release as well as Jackson's 2 jars (and they are all in my build path)

<!-- Jackson JSON -->
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-databind</artifactId>
        <version>2.2.2</version>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-annotations</artifactId>
        <version>2.2.2</version>
    </dependency>
    <dependency>
        <groupId>com.fasterxml.jackson.core</groupId>
        <artifactId>jackson-core</artifactId>
        <version>2.2.2</version>
    </dependency>

Here is my controller method trying to send a bean:

@RequestMapping(value = "/WS/{id}")
public @ResponseBody Resource displayWS(@PathVariable final int id) {
    return this.service.findById(id);
}

Here is what I receive in my browser after the call:

HTTP Status 406
The resource identified by this request is only capable of generating responses with characteristics not acceptable according to the request "accept" headers ().

And here is the server log (JBoss 7.1.1):

12:10:59,691 TRACE [org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod] (http-localhost-127.0.0.1-8080-1) Error handling return value [type=com.steria.rm.model.InternalResource] [value=Luc MERTENS]
HandlerMethod details: 
Controller [com.steria.rm.controller.ResourceController]
Method [public com.steria.rm.model.Resource com.steria.rm.controller.ResourceController.displayWS(int)]
: org.springframework.web.HttpMediaTypeNotAcceptableException: Could not find acceptable representation
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:147) [spring-webmvc-3.1.2.RELEASE.jar:3.1.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.AbstractMessageConverterMethodProcessor.writeWithMessageConverters(AbstractMessageConverterMethodProcessor.java:80) [spring-webmvc-3.1.2.RELEASE.jar:3.1.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestResponseBodyMethodProcessor.handleReturnValue(RequestResponseBodyMethodProcessor.java:94) [spring-webmvc-3.1.2.RELEASE.jar:3.1.2.RELEASE]
    at org.springframework.web.method.support.HandlerMethodReturnValueHandlerComposite.handleReturnValue(HandlerMethodReturnValueHandlerComposite.java:74) [spring-web-3.1.2.RELEASE.jar:3.1.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.ServletInvocableHandlerMethod.invokeAndHandle(ServletInvocableHandlerMethod.java:110) [spring-webmvc-3.1.2.RELEASE.jar:3.1.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.invokeHandlerMethod(RequestMappingHandlerAdapter.java:617) [spring-webmvc-3.1.2.RELEASE.jar:3.1.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.annotation.RequestMappingHandlerAdapter.handleInternal(RequestMappingHandlerAdapter.java:578) [spring-webmvc-3.1.2.RELEASE.jar:3.1.2.RELEASE]
    at org.springframework.web.servlet.mvc.method.AbstractHandlerMethodAdapter.handle(AbstractHandlerMethodAdapter.java:80) [spring-webmvc-3.1.2.RELEASE.jar:3.1.2.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doDispatch(DispatcherServlet.java:923) [spring-webmvc-3.1.2.RELEASE.jar:3.1.2.RELEASE]
    at org.springframework.web.servlet.DispatcherServlet.doService(DispatcherServlet.java:852) [spring-webmvc-3.1.2.RELEASE.jar:3.1.2.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.processRequest(FrameworkServlet.java:882) [spring-webmvc-3.1.2.RELEASE.jar:3.1.2.RELEASE]
    at org.springframework.web.servlet.FrameworkServlet.doGet(FrameworkServlet.java:778) [spring-webmvc-3.1.2.RELEASE.jar:3.1.2.RELEASE]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:734) [jboss-servlet-api_3.0_spec-1.0.0.Final.jar:1.0.0.Final]
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:847) [jboss-servlet-api_3.0_spec-1.0.0.Final.jar:1.0.0.Final]
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:329) [jbossweb-7.0.13.Final.jar:]
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:248) [jbossweb-7.0.13.Final.jar:]
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:275) [jbossweb-7.0.13.Final.jar:]
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:161) [jbossweb-7.0.13.Final.jar:]
    at org.jboss.as.jpa.interceptor.WebNonTxEmCloserValve.invoke(WebNonTxEmCloserValve.java:50) [jboss-as-jpa-7.1.1.Final.jar:7.1.1.Final]
    at org.jboss.as.web.security.SecurityContextAssociationValve.invoke(SecurityContextAssociationValve.java:153) [jboss-as-web-7.1.1.Final.jar:7.1.1.Final]
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:155) [jbossweb-7.0.13.Final.jar:]
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102) [jbossweb-7.0.13.Final.jar:]
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109) [jbossweb-7.0.13.Final.jar:]
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:368) [jbossweb-7.0.13.Final.jar:]
    at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:877) [jbossweb-7.0.13.Final.jar:]
    at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:671) [jbossweb-7.0.13.Final.jar:]
    at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:930) [jbossweb-7.0.13.Final.jar:]
    at java.lang.Thread.run(Unknown Source) [rt.jar:1.7.0_21]

PS: InternalResource is a child of Resource.

So now, what is going on ? I've seen somewhere that this exception might be thrown for any reason that is not actually this one... Kind of swallowing anything and throwing this "high level" exception... Not sure if it's true tho.

I've tried with headers = "Accept=*/*", with produces = "application/json"... One at a time, both together, still not working...

Any idea guys?
PS: I know there are many similar posts but most if not all I've seen are prior 2012 which is the year of Jackson's 2 release (may)

Answer 1

Alright, I figured this out.

First, as suspected, Spring MVC wasn't calling Jackson to serialize the entities. As I found here, I needed to modify mvc:annotation-driven to

<mvc:annotation-driven>
    <mvc:message-converters register-defaults="false">
        <bean id="jacksonMessageConverter" class="org.springframework.http.converter.json.MappingJackson2HttpMessageConverter"/>
    </mvc:message-converters>
</mvc:annotation-driven>

After that was done, I was back to Direct self-reference exception... So after I looked that up for a good hour, I finally found I 'simply' needed to add an annotation to some classes.

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

This annotation means that if some object is repeated while in the serializer it will be serialized once then after that will only be referenced by an @id created by the serializer.