You can configure the application class loaders for an
application server. Class loaders enable applications that are deployed
on the application server to access repositories of available classes
and resources.
Before you begin
This topic assumes that an administrator created an application
server on a WebSphere® Application Server product.
About this task
Configure the class loaders of an application server to set
class-loader policy and mode values which affect all applications
that are deployed on the server. Use the administrative console to
configure the class loaders.
Procedure
- Click to
access an application server settings page.
- Specify the application class-loader policy for the application
server.
The application class-loader policy controls
the isolation of applications that run in the system (on the server).
An application class loader groups enterprise bean (EJB) modules,
shared libraries, resource adapter archives (RAR files), and dependency Java™ archive (JAR) files associated to an application.
Dependency JAR files are JAR files that contain code which can be
used by both enterprise beans and servlets. The application class-loader
policy controls whether an application class loader can be shared
by multiple applications or is unique for each application.
Use
the application server settings page to specify the application class-loader
policy for the server:
Option |
Description |
Single |
Applications are not isolated from each other. Uses a single
application class loader to load all of the EJB modules, shared libraries,
and dependency JAR files in the system. |
Multiple |
Applications are isolated from each other. Gives each application
its own class loader to load the EJB modules, shared libraries, and
dependency JAR files of that application. |
- Specify the application class-loader mode for the application
server.
The application class loading mode specifies
the class-loader mode when the application class-loader policy is Single.
On
the application server settings page, select either of the following
values:
Option |
Description |
Classes loaded with parent class loader first |
Causes the class loader to delegate the loading of classes
to its parent class loader before attempting to load the class from
its local class path. Classes loaded with parent class loader
first is the default value for class loading mode. This
value is also known as parent first.
|
Classes loaded with local class loader first (parent last) |
Causes the class loader to attempt to load classes from its
local class path before delegating the class loading to its parent.
Using this policy, an application class loader can override and provide
its own version of a class that exists in the parent class loader. |
- Specify the class-loader mode for the class loader.
- On the application server settings page, click to access the Class loader page.
- On the Class
loader page, click New to access the
settings page for a class loader.
- On the class loader settings page, specify the class
loader order.
The Classes loaded with parent
class loader first value causes the class loader to delegate
the loading of classes to its parent class loader before attempting
to load the class from its local class path.
The Classes
loaded with local class loader first (parent last) value
causes the class loader to attempt to load classes from its local
class path before delegating the class loading to its parent.
- Click OK.
An identifier is assigned to a class-loader instance.
The instance is added to the collection of class loaders shown on
the Class loader
page.
What to do next
Save the changes to the administrative configuration.