Question

I have a Spring web project and I need load some classes after application context has been initialized because those classes will eventually used in future. Thus, I try to preload them before use to improve performance.

How to do it ?

Please help.

Thanks.

Answer 1

To load a class into JVM it is enough simply to call Class.forName('com.foo.bar.MyClassToPreLoad') method.
You can do it e.g. in your own implementation of javax.servlet.ServletContextListener and then register it in web.xml

<listener>
    <listener-class>com.foo.bar.MyClassPreloadingContextListener</listener-class>
</listener>

Or you can do it in any of your Spring beans implementing org.springframework.beans.factory.InitializingBean interface. Or if you don’t want to implement interface you can do it in any bean method without arguments and register it as a init-method for this bean:

<bean class="com.foo.bar.MyClassPreloadingBean" init-method="preloadClasses"/>

See http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/beans.html#beans-factory-lifecycle-initializingbean for details.

Or http://static.springsource.org/spring/docs/3.0.x/spring-framework-reference/html/beans.html#beans-postconstruct-and-predestroy-annotations if you prefer annotation based configuration.

Hope it helps.