You can configure whether your application and web modules
use their own class loaders to load classes or use different class
loaders, as well as configure the reloading of classes when application
files are updated. Class loaders enable an application to access repositories
of available classes and resources.
Before you begin
This topic assumes that your application or module is already
deployed on a server.
The following note applies to the xmi file references in this topic:
Supported configurations: For IBM®
extension and binding files, the
.xmi or
.xml file name
extension is different depending on whether you are using a pre-Java EE 5 application or module or a
Java™ EE 5 or later application or module. An IBM extension or binding file is named
ibm-*-ext.xmi or
ibm-*-bnd.xmi where * is the type of extension or binding file such as
app,
application,
ejb-jar, or
web. The following conditions apply:
- For an application or module that uses a Java EE version
prior to version 5, the file extension must be .xmi.
- For an application or module that uses Java EE 5 or
later, the file extension must be .xml. If .xmi files are
included with the application or module, the product ignores the .xmi
files.
However, a Java EE 5 or later module can exist within
an application that includes pre-Java EE 5 files and uses the .xmi file name
extension.
The ibm-webservices-ext.xmi,
ibm-webservices-bnd.xmi, ibm-webservicesclient-bnd.xmi,
ibm-webservicesclient-ext.xmi, and ibm-portlet-ext.xmi
files continue to use the .xmi file extensions.
About this task
Class loaders affect whether your application and its
modules find the resources that they need to run effectively. You
can select whether your application and web modules use their own
class loaders to load classes, or use a parent class loader.
An
application class loader groups Enterprise JavaBeans (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.
An application class
loader is the parent of a web application archive (WAR) class loader.
By default, a web module has its own WAR class loader to load the
contents of the web module. The WAR class-loader policy value of an
application class loader determines whether the WAR class loader or
the application class loader is used to load the contents of the Web
module.
You can also select whether classes are reloaded when
application files are updated. For EJB modules or any non-web modules,
enabling class reloading causes the application server run time to
stop and start the application to reload application classes. For
web modules such as servlets and JavaServer Pages (JSP) files, a web
container reloads a web module only when the IBM extension reloadingEnabled in the ibm-web-ext.xmi file
is set to true
.
To configure use of class loaders
by your application and web modules, use the Class loading and update detection page
of the administrative console.
Attention: If an application is running, changing an application
setting causes the application to restart. On stand-alone servers, the application restarts after
you save the change. On multiple-server products, the application restarts after you save the change
and files synchronize on the node where the application is installed. To control when
synchronization occurs on multiple-server products, deselect Synchronize changes with
nodes on the Console preferences page.
Procedure
- Click to
access the Class loading and update detection page.
- Specify whether to reload application classes when the
application or its files are updated.
By default, class
reloading is not enabled. Select Override class reloading
settings for web and EJB modules to choose to reload application
classes. You might specify different values for EJB modules and for
web modules such as servlets and JSP files.
- Specify the number of seconds to scan the application's
file system for updated files.
The value specified for Polling
interval for updated files takes effect only if class
reloading is enabled. The default is the value of the reloading interval
attribute in the IBM extension (META-INF/ibm-application-ext.xmi)
file of the enterprise application (EAR file). You might specify different
values for EJB modules and for web modules such as servlets and JSP
files.
To enable reloading, specify an integer value that is
greater than zero (for example, 1 to 2147483647).
To disable
reloading, specify zero (0).
- Specify the class loader order for the application.
The application class loader order specifies whether the
class loader searches in the parent class loader or in the application
class loader first to load a class. The default is to search in the
parent class loader before searching in the application class loader
to load a class.
Select either of the following values for Class
loader order:
Option |
Description |
Classes loaded with parent class loader first |
Causes the class loader to search in the parent class loader
first to load a class. This value is the standard for Development
Kit class loaders and WebSphere® Application Server class
loaders. |
Classes loaded with local class loader first (parent last) |
Causes the class loader to search in the application class
loader first to load a class. By specifying Classes loaded
with local class loader first (parent last) , your application
can override classes contained in the parent class loader.Attention: Specifying the Classes loaded with local
class loader first (parent last) value might result in LinkageErrors
or ClassCastException messages if you have mixed use of overridden
classes and non-overridden classes.
|
- Specify whether to use a single or multiple class loaders
to load web application archives (WAR files) of your application.
By default, web modules have their own WAR class loader to
load the contents of the WEB-INF/classes and WEB-INF/lib directories.
The default WAR class loader value is Class loader for each
WAR file in application
, which uses a separate class loader
to load each WAR file. Setting the value to Single class loader
for application
causes the application class loader to load
the web module contents as well as the EJB modules, shared libraries,
RAR files, and dependency JAR files associated to the application.
The application class loader is the parent of the WAR class loader.
Select
either of the following values for WAR class loader policy:
Option |
Description |
Class loader for each WAR file in application |
Uses a different class loader for each WAR file. |
Single class loader for application |
Uses a single class loader to load all of the WAR files in
your application. |
- Click OK.
Results
The application or module configuration is changed. The
application or stand-alone web module is restarted so the changes
take effect.
What to do next
If the application or module
is deployed on a cluster and you have no more configuration changes
to make, click Rollout Update on the Enterprise
applications page to propagate the changed configuration on all cluster
members of the cluster on which the application or module is deployed. Rollout
Update sequentially updates the configuration on the nodes
that contain cluster members.
Save changes to your administrative
configuration.
On multiple-server
products, the application binaries are transferred to nodes when the
configuration changes on the deployment manager synchronize with configurations
for individual nodes on which the application will run.