Sun GlassFish Enterprise Server v3 Application Development Guide

The Class Loader Hierarchy

Class loaders in the Enterprise Server runtime follow a delegation hierarchy that is fully described in Table 2–1.

Table 2–1 Sun GlassFish Enterprise Server Class Loaders


Class Loader	Description
Bootstrap	The Bootstrap class loader loads the basic runtime classes provided by the JVM software.
Extension	The Extension class loader loads classes from JAR files present in the system extensions directory, `domain-dir/lib/ext`. It is parent to the Public API class loader. See Using the Java Optional Package Mechanism.
Public API	The Public API class loader makes available all classes specifically exported by the Enterprise Server runtime for use by deployed applications. This includes, but is not limited to, Java EE APIs and other Sun GlassFish APIs. It is parent to the Common class loader.
Common	The Common class loader loads JAR files in the `as-install/lib` directory, then classes in the `domain-dir/lib/classes` directory, followed by JAR files in the `domain-dir/lib` directory. Using `domain-dir/lib/classes` or `domain-dir/lib` is recommended whenever possible, and required for custom login modules and realms. It is parent to the Connector class loader. See Using the Common Class Loader.
Connector	The Connector class loader is a single class loader instance that loads individually deployed connector modules, which are shared across all applications. It is parent to the Applib class loader and the LifeCycleModule class loader.
LifeCycleModule	The LifeCycleModule class loader is created once per lifecycle module. Each lifecycle module’s classpath is used to construct its own class loader. For more information on lifecycle modules, see Chapter 13, Developing Lifecycle Listeners.
Applib	The Applib class loader loads the library classes, specified during deployment, for a specific enabled module or Java EE application; see Application-Specific Class Loading. One instance of this class loader is present in each class loader universe; see Class Loader Universes. It is parent to the Archive class loader. When multiple deployed applications use the same library, they share the same instance of the library. One library cannot reference classes from another library.
Archive	The Archive class loader loads classes from the WAR, EAR, and JAR files or directories (for directory deployment) of applications or modules deployed to the Enterprise Server. This class loader also loads any application-specific classes generated by the Enterprise Server runtime, such as stub classes or servlets generated by JSP pages.