Dan Lynn

In a grails application, I needed to persist a complicated expression tree to the database, but I didn’t want to have Hibernate generate a database table for the information as it would greatly affect read performance (lots of joins) and I don’t need to have relational access to subsets of the tree. I decided to serialize the entire tree into a BLOB.

After creating a Hibernate userType to handle the serialization/deserialization, I ran into a ClassNotFoundException when attempting to deserialize my object.  I found out that this is due to java using the “last defined ClassLoader” when deserializing with an ObjectInputStream, which might not be the right ClassLoader in a Groovy environment (see: http://jira.codehaus.org/browse/GROOVY-1627.

The solution? Subclass ObjectInputStream to allow you to pass in a predefined ClassLoader and override the resolveClass(ObjectStream classDesc) to use this ClassLoader parameter:

public class ClassLoaderAwareObjectInputStream extends ObjectInputStream {

 private ClassLoader myClassLoader;

 public ClassLoaderAwareObjectInputStream(ClassLoader myClassLoader) throws IOException, SecurityException {
 super();
 this.myClassLoader = myClassLoader;
 }

 public ClassLoaderAwareObjectInputStream(InputStream in, ClassLoader myClassLoader) throws IOException {
 super(in);
 this.myClassLoader = myClassLoader;
 }

 @Override
 protected Class resolveClass(ObjectStreamClass desc) throws IOException,
 ClassNotFoundException {
 String name = desc.getName();
 return Class.forName(name, false, myClassLoader);
 }
}

Thanks to Satish Gunnu for the tip.