Why Does Object Casting Fail in WebSphere Portal Despite `getClass()` Confirmation?

Exception During Object Casting in WebSphere Portal Framework

When attempting to cast an object to a particular class within the WebSphere Portal Server framework, a user encountered a ClassCastException, despite the object's class being confirmed as the target class using the .getClass() method.

Analysis

The issue arises from the fact that in WebSphere Portal Server, classes may be loaded by different classloaders. When an object is dynamically loaded and stored in a session, it is associated with a specific classloader. Subsequently, trying to cast the object to the same class loaded by a different classloader will result in a ClassCastException.

Solution

To resolve this issue, one of the following approaches can be considered:

1. Setting the Context Class Loader: Use the Thread.currentThread().setContextClassLoader(...) method to ensure that the thread's context class loader is set to the appropriate classloader that loaded the target class. This allows the cast to succeed.
2. Assuring Class Loading by a Common Parent: Verify that both the dynamic class and the target class are loaded by the same classloader parent. By ensuring that the class hierarchies originate from a common source, the cast can be performed without exception.
3. Serializing and Deserializing the Object: Although a less desirable solution, serializing the object to a byte stream and then deserializing it can create a new instance of the object loaded by the desired classloader. However, it's important to note that this approach may have performance implications.

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