Spring with Castor - Null Pointer Exception when initialising Application Context

Question

Hi,

I'm trying to register my castor mapping files with spring and I appear to be getting a null pointer exception.

In my application context I have:

   <bean id="xmlContext" class="org.castor.spring.xml.XMLContextFactoryBean">
  <property name="mappingLocations">
       <list>
          <value>DistributionSamplerMappings.xml</value>
       </list>
    </property>
    <property name="castorProperties">
            <props>
                <prop key="org.exolab.castor.xml.strictelements">false</prop>
            </props>
       </property>
 </bean>

 <bean id="marshaller"
       class="org.castor.spring.xml.CastorMarshallerFactoryBean">
    <property name="xmlContext"><ref local="xmlContext"/></property>
 </bean>

 <bean id="unmarshaller"
        class="org.castor.spring.xml.CastorUnmarshallerFactoryBean">
        <property name="xmlContext"> <ref local="xmlContext"/></property>
        <property name="ignoreExtraElements"><value>true</value></property>
        <property name="ignoreExtraAttributes"><value>true</value></property>
    </bean>

Where DistributionSamplerMappings.xml lives in the same dir as the application context.

I've tried using the spring-xml jar 1.2.1 and 1.5.3. but none of them seem to help.

The exception being thrown back is:

SEVERE: Context initialization failed
org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'xmlContext' defined in ServletContext resource [/WEB-INF/applicationContext.xml]: Invocation of init method failed; nested exception is java.lang.NullPointerException
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1338)
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:473)
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory$1.run(AbstractAutowireCapableBeanFactory.java:409)
 at java.security.AccessController.doPrivileged(Native Method)
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:380)
 at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:264)
 at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:222)
 at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:261)
 at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:185)
 at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:164)
 at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:423)
 at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:728)
 at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:380)
 at org.springframework.web.context.ContextLoader.createWebApplicationContext(ContextLoader.java:255)
 at org.springframework.web.context.ContextLoader.initWebApplicationContext(ContextLoader.java:199)
 at org.springframework.web.context.ContextLoaderListener.contextInitialized(ContextLoaderListener.java:45)
 at org.apache.catalina.core.StandardContext.listenerStart(StandardContext.java:3830)
 at org.apache.catalina.core.StandardContext.start(StandardContext.java:4337)
 at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1045)
 at org.apache.catalina.core.StandardHost.start(StandardHost.java:719)
 at org.apache.catalina.core.ContainerBase.start(ContainerBase.java:1045)
 at org.apache.catalina.core.StandardEngine.start(StandardEngine.java:443)
 at org.apache.catalina.core.StandardService.start(StandardService.java:516)
 at org.apache.catalina.core.StandardServer.start(StandardServer.java:710)
 at org.apache.catalina.startup.Catalina.start(Catalina.java:566)
 at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
 at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
 at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
 at java.lang.reflect.Method.invoke(Unknown Source)
 at org.apache.catalina.startup.Bootstrap.start(Bootstrap.java:288)
 at org.apache.catalina.startup.Bootstrap.main(Bootstrap.java:413)
Caused by: java.lang.NullPointerException
 at org.castor.spring.xml.XMLContextFactoryBean.afterPropertiesSet(XMLContextFactoryBean.java:118)
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.invokeInitMethods(AbstractAutowireCapableBeanFactory.java:1369)
 at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.initializeBean(AbstractAutowireCapableBeanFactory.java:1335)
 ... 30 more

I'm using Spring 2.5.6 and Castor 1.3.1.

Looking around I find I'm not the only one who has had this problem, but I don't seem to be able to find a solution.

Any help would be much appreciated.

Answer 1

First, look at the code - line 118 of the XMLContextFactoryBean is the last one here. It suggests that somehow mappingResource is null. That suggests that getClass().getClassLoader().getResource(mappingLocation) is returning a null, so perhaps it can't find your file.

                mappingLocation = (String) iter.next();
                URL mappingResource = getClass().getClassLoader()
                        .getResource(mappingLocation);
                mapping.loadMapping(new InputSource(mappingResource
                        .openStream()));  // NPE occurs on this line.

Now if you want the class loader to find a file, you need to put the file in the same place that it would look for classes. Putting your DistributionSamplerMappings.xml in the same directory as applicationContext isn't good enough. Try WEB-INF/classes, or whichever is the classes folder that has the root of your compiled classes inside it. If you're using Eclipse, you can do this by putting the file inside your source folder -- it looks a bit untidy, since you'd rather have config info elsewhere, but at least it will work.

Answer 2

This exception can also occur if a mapped class doesn't have a default public constructor.