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Jair da Silva Ferreira Jr
 Post subject: cache problem
PostPosted: Wed Oct 27, 2004 8:39 am 
Newbie

Joined: Thu Aug 12, 2004 10:27 am
Posts: 17
Hi,
I have a Category class that has a circular reference to itselft. I am using the second-level ehcache cache on this class. The problem is: when I load a Category instance by id, a strange NullPointerException happens in Category.hashCode() when the Category 'name' attribute is accessed in the second line of the Category.hashCode() method. This exception should not happen because name can't be null. This problem only happens when cache is enabled, Category._parent!=null and the Category instance is stored in the cache.
My guess is that hibernate is adding a Category instance to a Set before setting the Category name. Below are the exception stack trace, Category class, Category hibernate mapping and the ehcache configuration file. Please, what do I have to do to solve this problem? Any help would be appreciated.

Thank you very much.

Hibernate version: 2.1.6

Name and version of the database you are using:postgresql 7.2

NullPointerException stack trace:
Code:
java.lang.NullPointerException
   at my.package.Category.hashCode(Category.java:57)
   at java.util.HashMap.hash(HashMap.java:261)
   at java.util.HashMap.put(HashMap.java:379)
   at java.util.HashSet.add(HashSet.java:192)
   at net.sf.hibernate.collection.Set.initializeFromCache(Set.java:92)
   at net.sf.hibernate.impl.SessionImpl.initializeCollectionFromCache(SessionImpl.java:3963)
   at net.sf.hibernate.impl.SessionImpl.initializeCollection(SessionImpl.java:3262)
   at net.sf.hibernate.collection.PersistentCollection.forceInitialization(PersistentCollection.java:336)
   at net.sf.hibernate.impl.SessionImpl.initializeNonLazyCollections(SessionImpl.java:3123)
   at net.sf.hibernate.impl.SessionImpl.assembleCacheEntry(SessionImpl.java:2139)
   at net.sf.hibernate.impl.SessionImpl.doLoad(SessionImpl.java:2112)
   at net.sf.hibernate.impl.SessionImpl.doLoadByClass(SessionImpl.java:1991)
   at net.sf.hibernate.impl.SessionImpl.internalLoad(SessionImpl.java:1953)
   at net.sf.hibernate.type.ManyToOneType.resolveIdentifier(ManyToOneType.java:69)
   at net.sf.hibernate.type.ManyToOneType.assemble(ManyToOneType.java:108)
   at net.sf.hibernate.impl.CacheEntry.assemble(CacheEntry.java:56)
   at net.sf.hibernate.impl.CacheEntry.assemble(CacheEntry.java:48)
   at net.sf.hibernate.impl.SessionImpl.assembleCacheEntry(SessionImpl.java:2134)
   at net.sf.hibernate.impl.SessionImpl.doLoad(SessionImpl.java:2112)
   at net.sf.hibernate.impl.SessionImpl.doLoadByClass(SessionImpl.java:1991)
   at net.sf.hibernate.impl.SessionImpl.load(SessionImpl.java:1920)
   at org.apache.jsp.test_jsp._jspService(test_jsp.java:62)
   at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:137)
   at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
   at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:210)
   at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:295)
   at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:241)
   at javax.servlet.http.HttpServlet.service(HttpServlet.java:853)
   at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:247)
   at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
   at com.fabrica.hibernate.web.HibernateSessionFilter.doFilter(HibernateSessionFilter.java:26)
   at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:213)
   at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
   at my.package.web.LoggedUserFilter.doFilter(LoggedUserFilter.java:41)
   at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:213)
   at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:193)
   at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:256)
   at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
   at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
   at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
   at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
   at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
   at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
   at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
   at org.apache.catalina.core.StandardContext.invoke(StandardContext.java:2422)
   at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:180)
   at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
   at org.apache.catalina.valves.ErrorDispatcherValve.invoke(ErrorDispatcherValve.java:171)
   at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
   at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:163)
   at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:641)
   at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
   at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
   at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:174)
   at org.apache.catalina.core.StandardPipeline$StandardPipelineValveContext.invokeNext(StandardPipeline.java:643)
   at org.apache.catalina.core.StandardPipeline.invoke(StandardPipeline.java:480)
   at org.apache.catalina.core.ContainerBase.invoke(ContainerBase.java:995)
   at org.apache.coyote.tomcat4.CoyoteAdapter.service(CoyoteAdapter.java:199)
   at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:828)
   at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.processConnection(Http11Protocol.java:700)
   at org.apache.tomcat.util.net.TcpWorkerThread.runIt(PoolTcpEndpoint.java:584)
   at org.apache.tomcat.util.threads.ThreadPool$ControlRunnable.run(ThreadPool.java:683)
   at java.lang.Thread.run(Thread.java:534)


Category class
Code:
public class Category{
   
   private Long _id;
   private String _name;
   private Category _parent;
   private Set _children=new HashSet();

   public boolean equals(Object c){
      if(this==c){
         return true;
      }
      if(!(c instanceof Category)){
         return false;
      }
      
      final Category category=(Category)c;

      if(!getName().equals(category.getName())){
         return false;
      }
      if(!(getParent()==null ? category.getParent()==null : getParent().equals(category.getParent()))){
         return false;
      }
      return true;
   }
   
   public int hashCode(){
      int result=31;
      result=29*result+getName().hashCode();
      if(getParent()!=null){
         result=29*result+getParent().hashCode();
      }
      return result;
   }
   
   // other methods
}


Category hibernate mapping file
Code:
<?xml version="1.0"?>

<!DOCTYPE hibernate-mapping PUBLIC
    "-//Hibernate/Hibernate Mapping DTD 2.0//EN"
    "http://hibernate.sourceforge.net/hibernate-mapping-2.0.dtd">

<hibernate-mapping>
    <class
        name="my.package.Category"
        table="category"
        dynamic-update="false"
        dynamic-insert="false"
    >
        <cache usage="nonstrict-read-write" />

        <id
            name="id"
            column="id"
            type="long"
        >
            <generator class="increment">
            </generator>
        </id>

        <property
            name="name"
            type="java.lang.String"
            update="true"
            insert="true"
            access="property"
            column="name"
            length="50"
            not-null="true"
        />

        <many-to-one

            name="parent"
            class="my.package.Category"
            cascade="none"
            outer-join="auto"
            update="true"
            insert="true"
            access="property"
            column="parentId"
        />

        <set
            name="children"
            lazy="false"
            inverse="true"
            cascade="all-delete-orphan"
            sort="unsorted"
            order-by="name asc"
        >
            <cache
                usage="nonstrict-read-write"
             />

              <key
                  column="parentId"
              >
              </key>

              <one-to-many
                  class="my.package.Category"
              />
        </set>

    </class>

</hibernate-mapping>


ehcache configuration
Code:
<ehcache>

    <diskStore path="java.io.tmpdir"/>


    <defaultCache
        maxElementsInMemory="10000"
        eternal="false"
        timeToIdleSeconds="120"
        timeToLiveSeconds="120"
        overflowToDisk="false"
        />

   <cache name="my.package.Category"
        maxElementsInMemory="100"
        eternal="true"
        overflowToDisk="false"
        />
      
</ehcache>
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gavin
 Post subject:
PostPosted: Wed Oct 27, 2004 9:57 am 
Hibernate Team
Hibernate Team

Joined: Tue Aug 26, 2003 12:50 pm
Posts: 5130
Location: Melbourne, Australia
Submit this to JIRA, and I'll see if it can be fixed, I'm not sure if its possible.
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camel
 Post subject:
PostPosted: Fri Nov 19, 2004 4:45 am 
Newbie

Joined: Fri Nov 12, 2004 4:33 am
Posts: 7
Location: Austin, Texas
I see that this was submitted to JIRA and would be difficult to fix. I am having the exact same problem as the original poster. Interestingly, the Category class is almost the same as the Category example used throughout Hibernate in Action.

Can anyone suggest a workaround? (I have a layered app using session bean facade). Thanks

Here's the JIRA bug
http://opensource.atlassian.com/projects/hibernate/browse/HB-1286
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