WAS v8.5 > Develop applications

Class loading

Class loaders are part of the JVM code and are responsible for finding and loading class files. Class loaders enable applications deployed on servers to access repositories of available classes and resources. Application developers and deployers must consider the location of class and resource files, and the class loaders used to access those files, to make the files available to deployed applications. Class loaders affect the packaging of applications and the runtime behavior of packaged applications of deployed applications.

This topic describes how to configure class loaders for application files or modules that are installed on an application server.

To better understand class loaders in WebSphere Application Server, read Class loaders. The topic Class loading: Resources for learning refers to additional sources.

Configure class loaders for application files or modules that are installed on an application server using the dmgr console. You configure class loaders to ensure that deployed application files and modules can access the classes and resources they need to run successfully.

1. If an installed application module uses a resource, create a resource provider that specifies the directory name of the resource drivers.

   Do not specify the resource JAR file names. All JAR files in the specified directory are added into the class path of the WAS extensions class loader. If a resource driver requires a native library (.dll or .so file), specify the name of the directory containing the library in the native path of the resource configuration.

2. Class-loader values for an application server.

3. Class-loader values for an installed enterprise application.

4. Class-loader mode for an installed web module.

5. If deployed application uses shared library files, associate the shared library files with the application. Use a library reference to associate a shared library file with the application.

   1. If we have not done so already, define shared libraries for library files the applications need.
   2. Define a library reference for each shared library the application uses.

After configuring class loaders, ensure the application performs as desired. To diagnose and fix problems with class loaders, refer to Troubleshooting class loaders.

Subtopics

• Class loaders
  Class loaders find and load class files. Class loaders enable applications deployed on servers to access repositories of available classes and resources. Application developers and deployers must consider the location of class and resource files, and the class loaders used to access those files, to make the files available to deployed applications.
• Configure class loaders of a server
  We can configure the application class loaders for an application server. Class loaders enable applications deployed on the application server to access repositories of available classes and resources.
• Class loader page
  Use this page to manage class-loader instances on an application server. A class loader determines whether an application class loader or a parent class loader finds and loads Java class files for an application.
• Class loader settings
  Use this page to configure a class loader for applications that reside on an application server.
• Configure application class loaders
  We can set values that control the class-loading behavior of an installed enterprise application. Class loaders enable an application to access repositories of available classes and resources.
• Configure web module class loaders
  We can set values that control the class-loading behavior of an installed web module.
• Class loading: Resources for learning
  Additional information and guidance on class loading is available on various Internet sites.
• Class loaders
  Class loaders find and load class files. Class loaders enable applications deployed on servers to access repositories of available classes and resources. Application developers and deployers must consider the location of class and resource files, and the class loaders used to access those files, to make the files available to deployed applications.
• Configure class loaders of a server
  You can configure the application class loaders for an application server. Class loaders enable applications deployed on the application server to access repositories of available classes and resources.
• Class loader page
  Use this page to manage class-loader instances on an application server. A class loader determines whether an application class loader or a parent class loader finds and loads Java class files for an application.
• Configure application class loaders
  You can set values that control the class-loading behavior of an installed enterprise application. Class loaders enable an application to access repositories of available classes and resources.
• Configure web module class loaders
  We can set values that control the class-loading behavior of an installed web module.
• Class loading: Resources for learning
  Additional information and guidance on class loading is available on various Internet sites.

Related concepts:

Mail, URLs, and other J2EE resources

Related

Create shared libraries
Associate shared libraries with applications or modules
Troubleshoot class loaders
Assemble applications
Manage shared libraries

Reference:

Enterprise application settings
Web module deployment settings
Java EE client application class loading

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