Feature Requests item #1524019, was opened at 2006-07-17 21:12
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Category: None
Group: None
Status: Open
Priority: 5
Submitted By: Ittay Dror (ittayd)
Assigned to: Nobody/Anonymous (nobody)
Summary: working with plugins (classloaders)
Initial Comment:
We're using plugins similar to Eclipse's to decouple
functionality. Each plugin's classes run in their own
class loader. specifically, a plugin can have a MyPage
class (this is done by having our implementation of
Application that iterates over the XXXPage classes for
each plugin and uses mount and url coding strategy to
make the XXXPage accessible from a url)
We've encountered a problem in onNewBrowserWindow(). it
uses Objects.cloneObject(), which uses serialization to
implement deep copy. It serializes the object and then
uses ObjectInputStream to reconstruct the object.
ObjectInputStream resolves classes by using a class
loader that is associated with the execution stack. At
the point of cloning, the execution stack contains only
wicket / tomcat classes, so the class loader it finds
is WebClassLoader. This class loader knows only of the
classes under WEB-INF. so when it encounters a class
name that belongs to a plugin (and hence is not in
WEB-INF, but in the plugin's jar, in a separate
folder), it fails to resolve it.
This can be solved by changing cloneObject to use the
class loader associated with the object to be cloned.
This class loader is guarenteed to work (since the
instance of the object is used, then all classes of
objects contained in this object (as fields) are
resolveable by the object - through its associated
class loader)
more specifically, it means using a subclass of
ObjectInputStream that resolves classes using the
object's class loader.
here is the revised method (the important change is the
overrided resolveClass in the annonymous class):
public static Object cloneObject(final Object object)
{
if (object == null)
{
return null;
}
else
{
try
{
final ByteArrayOutputStream out = new
ByteArrayOutputStream(256);
ObjectOutputStream oos = new
ObjectOutputStream(out);
oos.writeObject(object);
ObjectInputStream ois = new
ObjectInputStream(new ByteArrayInputStream(out
.toByteArray())) {
protected Class
resolveClass(ObjectStreamClass desc) throws IOException,
ClassNotFoundException {
String className = desc.getName();
return Class.forName(className,
true, object.getClass().getClassLoader());
}
};
return ois.readObject();
}
catch (ClassNotFoundException e)
{
throw new
WicketRuntimeException("Internal error cloning object", e);
}
catch (IOException e)
{
throw new
WicketRuntimeException("Internal error cloning object", e);
}
}
}
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