Inside Class Loaders: Debugging

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Tutorial: Inside Class Loaders: Debugging

Inside Class Loaders: Debugging This article will show how to solve class-loading problems and to overcome some debugging limitations of the JDK class loaders.

Tutorial Details:

Tricks of the Trade to Investigate Class-Loading Problems
The biggest challenge in dealing with class-loading problems is that problems rarely manifest themselves during the class-loading process but rather during the usage of a class later on. In addition, the messages provided by the JDK are, to say the least, inadequate, and the toString() methods of the JDK class loaders are not overridden to provide more data.

ClassNotFoundException
Let's consider several different class-loading error scenarios. First, we want to figure out what to do when a class could not be found and the application throws a ClassNotFoundException
Here are some steps to resolve the issue:

Look for the line where your class loader's loadClass() call is involved (in our example, the last line).
Figure out what class loader is used there.
Figure out the parent class loaders recursively until you find the bootstrap class loader.
Figure out why the class cannot be found by any of these class loaders.
This problem is caused when a class loader is asked to load a particular class and it cannot be found. Here are few causes:

An archive, directory, or other source for the classes was not added to the class loader asked to load the class, or to its parent.
A class loader's parent is not set correctly.
The wrong class loader is used to load the class in question.

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