The first time a WebSphere Application Server process starts, the name of each run-time class loaded and the name of the JAR file containing the class are written to a preload file. The names of non-runtime classes such as custom services, resource classes such as db2_classes.jar, classes on the JVM classpath, and application classes are not written to the preload file. Subsequent startups of the process use the preload file to start the process more quickly because the runtime goes directly to the stored file to load a class rather than searching through the configured classloaders to locate the class.
Preload files have the extension .preload and are located in the instance/properties/preload directory, where instance is the name of your application server instance. The following WebSphere Application Server processes have preload files:
| Process | Preload file name |
|---|---|
| Application server | cell_name.node_name.server_name.preload |
| startserver | WsServerLauncher.preload |
| launchClient | launchClient.preload |
A server process uses a cell_name.node_name.server_name.preload file, where cell_name is the name of your WebSphere Application Server cell, node_name is the name of your application server node, and server_name is the name of your application server.
New classes required during startup of a process are added to the preload file. Any classes removed from a process are ignored during subsequent startups. Although it is not necessary, an administrator can delete the preload file and force a refresh that removes the ignored classes from the file.
Enable and disable class preloading
By default, class preloading is enabled. If you want to disable it, use the administrative console to specify a value of false for the ibm.websphere.preload.classes JVM custom property.
If you disable class preloading and later want to re-enable it, remove the ibm.websphere.preload.classes property for the JVM, or change the value of the property from false to true.
For information on setting JVM properties with the administrative console, see Set JVM custom properties in Administration.