12.2 WebSphere class loaders overview

Keep in mind when reading the following discussion that each JVM has its own setup of class loaders. In a WebSphere environment hosting multiple appservers (JVMs), this means the class loaders for the JVMs are completely separated even if they are running on the same physical machine. Also note that the Java Virtual Machine (JVM) uses class loaders called the extensions and application class loaders. As you will see, the WebSphere run time also uses class loaders called extensions and application class loader, but despite their names, they are not the same as the JVM ones.

WebSphere provides several custom delegated class loaders, as shown in Figure 12-2.

Figure 12-2 WebSphere class loaders hierarchy

The top box represents the Java (bootstrap, extensions, and application) class loaders. WebSphere loads just enough here to get itself bootstrapped and initialize the WebSphere extensions class loader.