To customize the webapp class loader for all the webapps

Question

How to customize the webapp class loader for all the webapps in tomcat using a common webappclassloader?

I saw that I can extend class loader and add it in the context tag for each and every webapp, is there a way to put this as common classloader for all the webapps and also where I should place this classloader .class file?

Thanks

Answer 1

You can place the custom class loader in $CATALINA_HOME/lib.

To replace the default loader for all webapps, a convenient solution is modifying $CATALINA_HOME/conf/context.xml

<?xml version='1.0' encoding='utf-8'?>
<Context>
    <Loader className="test.loader.MyWebappLoader" /><!-- add this element -->
</Context>

Here is a sample code:

package test.loader;
import org.apache.catalina.loader.WebappLoader;
public class MyWebappLoader extends WebappLoader {
    public MyWebappLoader() {
        System.err.println("!! create MyWebappLoader !!");
    }
    public MyWebappLoader(ClassLoader parent) {
        super(parent);
        System.err.println("!! create MyWebappLoader !!");
    }
}

For more detail, you can read Tomcat document - The Loader Component. It work on Tomcat 7~9.