Exception while exposing a bean in webservice using spring mvc

Question

I am using Spring 3.0.5.Release MVC for exposing a webservice and below is my servlet.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="
http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context 
http://www.springframework.org/schema/context/spring-context-3.0.xsd">

<!-- To enable @RequestMapping process on type level and method level -->
<context:component-scan base-package="com.pyramid.qls.progressReporter.service" />

<bean class="org.springframework.web.servlet.mvc.annotation.DefaultAnnotationHandlerMapping" />

<bean class="org.springframework.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">
  <property name="messageConverters">
    <list>
      <ref bean="marshallingConverter" />
      <ref bean="atomConverter"  />
      <ref bean="jsonConverter" />
    </list>
  </property>
</bean>

<bean id="marshallingConverter" class="org.springframework.http.converter.xml.MarshallingHttpMessageConverter">
  <constructor-arg ref="jaxbMarshaller" />
  <property name="supportedMediaTypes" value="application/xml"/>
</bean>

<bean id="atomConverter" class="org.springframework.http.converter.feed.AtomFeedHttpMessageConverter">
  <property name="supportedMediaTypes" value="application/atom+xml" />
</bean>

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

<!-- Client -->
<bean id="restTemplate" class="org.springframework.web.client.RestTemplate">
  <property name="messageConverters">
    <list>
      <ref bean="marshallingConverter" />
      <ref bean="atomConverter"  />
      <ref bean="jsonConverter" />
    </list>
  </property>
</bean>

<bean id="jaxbMarshaller" class="org.springframework.oxm.jaxb.Jaxb2Marshaller">
  <property name="classesToBeBound">
    <list>
      <value>com.pyramid.qls.progressReporter.impl.BatchProgressMetricsImpl</value>
      <value>com.pyramid.qls.progressReporter.datatype.InstrumentStats</value>
      <value>com.pyramid.qls.progressReporter.datatype.InstrumentInfo</value>
      <value>com.pyramid.qls.progressReporter.datatype.BatchProgressMetricsList</value>
      <value>com.pyramid.qls.progressReporter.datatype.LoadOnConsumer</value>
      <value>com.pyramid.qls.progressReporter.datatype.HighLevelTaskStats</value>
      <value>com.pyramid.qls.progressReporter.datatype.SessionStats</value>
      <value>com.pyramid.qls.progressReporter.datatype.TaskStats</value>
      <value>com.pyramid.qls.progressReporter.datatype.ComputeStats</value>
      <value>com.pyramid.qls.progressReporter.datatype.DetailedInstrumentStats</value>
      <value>com.pyramid.qls.progressReporter.datatype.ImntHistoricalStats</value>
    </list>
  </property>
</bean>

<bean id="QPRXmlView" class="org.springframework.web.servlet.view.xml.MarshallingView">
  <constructor-arg ref="jaxbMarshaller" />
</bean>

<bean class="org.springframework.web.servlet.view.ContentNegotiatingViewResolver">
  <property name="mediaTypes">
    <map>
      <entry key="xml" value="application/xml"/>
      <entry key="html" value="text/html"/>
    </map>
  </property>
  <property name="viewResolvers">
    <list>
      <bean class="org.springframework.web.servlet.view.BeanNameViewResolver"/>
      <bean id="viewResolver" class="org.springframework.web.servlet.view.UrlBasedViewResolver">
        <property name="viewClass" value="org.springframework.web.servlet.view.JstlView"/>
        <property name="prefix" value="/WEB-INF/jsp/"/>
        <property name="suffix" value=".jsp"/>
      </bean>
    </list>
  </property>
</bean>

<bean id="QPRController" class="com.pyramid.qls.progressReporter.service.QPRController">
  <property name="jaxb2Mashaller" ref="jaxbMarshaller" />
</bean>

</beans>  

Following is what i am doing in controller (QPRController)

@RequestMapping(value = "/clientMetrics/{clientId}", method = RequestMethod.GET)
public ModelAndView getBatchProgressMetrics(@PathVariable String clientId) {
  List<BatchProgressMetrics> batchProgressMetricsList = null;

  batchProgressMetricsList = batchProgressReporter.getBatchProgressMetricsForClient(clientId);
  BatchProgressMetricsList batchList = new BatchProgressMetricsList(batchProgressMetricsList);
  ModelAndView mav = new ModelAndView("QPRXmlView", BindingResult.MODEL_KEY_PREFIX + "batchProgressMetrics", batchList);
  return mav;
}  

This is what my batchprogressmetricsList looks like:

@XmlRootElement(name = "batchProgressMetrics")
public class BatchProgressMetricsList implements Serializable{

    private int count;
    private List<BatchProgressMetrics> batchProgressMetricsList;

    public BatchProgressMetricsList() {
    }

    public BatchProgressMetricsList(List<BatchProgressMetrics> batchProgressMetricsList) {
        this.batchProgressMetricsList = batchProgressMetricsList;
        this.count = batchProgressMetricsList.size();
    }

    public int getCount() {
        return count;
    }

    @XmlElement(name = "batchProgressMetrics1")
    public List<BatchProgressMetrics> getBatchProgressMetrics() {
        return batchProgressMetricsList;
    } 

Now i get the following:

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'QPRController' defined in ServletContext resource [/WEB-INF/rest-servlet.xml]: Cannot resolve reference to bean 'jaxbMarshaller' while setting bean property 'jaxb2Mashaller'; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'jaxbMarshaller' defined in ServletContext resource [/WEB-INF/rest-servlet.xml]: Invocation of init method failed; nested exception is org.springframework.oxm.UncategorizedMappingException: Unknown JAXB exception; nested exception is com.sun.xml.internal.bind.v2.runtime.IllegalAnnotationsException: 2 counts of IllegalAnnotationExceptions
com.pyramid.qls.progressReporter.iface.BatchProgressMetrics is an interface, and JAXB can't handle interfaces.
this problem is related to the following location:
    at com.pyramid.qls.progressReporter.iface.BatchProgressMetrics
    at public java.util.List com.pyramid.qls.progressReporter.datatype.BatchProgressMetricsList.getBatchProgressMetrics()
    at com.pyramid.qls.progressReporter.datatype.BatchProgressMetricsList
com.pyramid.qls.progressReporter.iface.BatchProgressMetrics does not have a no-arg default constructor.
this problem is related to the following location:
    at com.pyramid.qls.progressReporter.iface.BatchProgressMetrics
    at public java.util.List com.pyramid.qls.progressReporter.datatype.BatchProgressMetricsList.getBatchProgressMetrics()
    at com.pyramid.qls.progressReporter.datatype.BatchProgressMetricsList

        org.springframework.beans.factory.support.BeanDefinitionValueResolver.resolveReference(BeanDefinitionValueResolver.java:328)  

Previously i got this without the change.

SEVERE: Servlet.service() for servlet rest threw exception
javax.servlet.ServletException: Unable to locate object to be marshalled in model: {org.springframework.validation.BindingResult.batchProgressMetrics=  

Note that BatchProgressMetrics is an interface so my MAV is returning list of BatchProgressMetrics objects and i have entry for its impl in classes to be bound in servlet.xml.

Can you please help me as to what i am doing wrong. And yes if i send just batchProgressMetricsList.get(0) in MAV it just works fine.

Answer 1

This because the JAXB context doesn't know how to handle lists of objects, only the objects themselves. It makes sense when you think about it - the only way to represent a list in XML is to wrap it in a container element, and it has no information as to how to do that.

So you need to define a class which is the container for the list of BatchProgressMetrics, and return that in the model instead.