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How to set my custom class loader to be the default?

Answer 1

+2 A:

You can set the system default class loader as a JVM argument:

java -Djava.system.class.loader
    =com.test.YourCustomClassLoader com.test.YourMainClass

As Tomcat starts as a java application, you can set this parameter too, at the %TOMCAT_HOME%\bin\run.bat or $TOMCAT_HOME/bin/run.sh executable.

Edit for completion: If you set your classloader as de System class loader, it will be used to load Tomcat component classes, the different libraries, and your own classes. If you want your class loader to be used only for your application classes (including libraries and so), you should configure a Loader element for your context. The Loader element must be defined inside your Context element, wich can be defined at a context.xml file. More information:

Apache Tomcat: Class Loader HOW-TO: defines how the ClassLoaders work in Tomcat.
Tomcat Configuration Reference: The Context Container: how to define your Context element
Tomcat Configuration Reference: The Loader Component: How to define your custom Loader element for your own Context.

Tomas Narros 2010-09-27 07:09:37

For some reason it got me java.lang.Error: java.lang.IllegalStateException: recursive invocation. This is what I did: subclassing ClassLoader, supplying c'tor that take a ClassLoader as parameter, configured it using the -Djava.system.class.loader, and... Boom! Error occurred during initialization of VM :-( Did I miss anything?

Seffy 2010-09-27 07:44:58

Without a sight on your code, I can't tell you for sure.

Tomas Narros 2010-09-27 07:56:01

I have tested it with a little Main Application I have, and it's run OK.

Tomas Narros 2010-09-27 07:56:49

package com.demo.presale;public class MyClassLoader extends ClassLoader{ public MyClassLoader( ClassLoader parent ) { } protected Class loadClass( String name, boolean resolve ) throws ClassNotFoundException { Class c = super.loadClass( name, resolve ); System.out.println( "name: " + name + ", class: " + c); return c; }}

Seffy 2010-09-27 08:04:43

And the exception:java.lang.IllegalStateException: recursive invocation at java.lang.ClassLoader.initSystemClassLoader(ClassLoader.java:1312) at java.lang.ClassLoader.getSystemClassLoader(ClassLoader.java:1295) at java.lang.ClassLoader.<init>(ClassLoader.java:228) at com.demo.presale.MyClassLoader.<init>(MyClassLoader.java:7) at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)

Seffy 2010-09-27 08:12:10

In my test code, the overriden Constructor calls the parent class constructor. It checks some permissions, and sets the "initialized" attribute as true. I have also overriden the default constructor, calling the parent constructor too: package com.test; public class MyCustomClassLoader extends ClassLoader { public MyCustomClassLoader() { super(); } public MyCustomClassLoader(ClassLoader parent) { super(parent); } /* rest of the code is quite the same as yours */ }

Tomas Narros 2010-09-27 08:12:39

Thanks! It's working now :-)

Seffy 2010-09-27 08:18:02

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How to set my custom class loader to be the default?

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