se.jiderhamn.classloader.leak.prevention

Class ClassLoaderLeakPreventorListener

java.lang.Object

se.jiderhamn.classloader.leak.prevention.ClassLoaderLeakPreventorListener

All Implemented Interfaces:

EventListener, javax.servlet.ServletContextListener

public class ClassLoaderLeakPreventorListener
extends Object
implements javax.servlet.ServletContextListener

This class helps prevent classloader leaks.

Basic setup

Activate protection by adding this class as a context listener in your web.xml, like this:

  <listener>
     <listener-class>se.jiderhamn.classloader.leak.prevention.ClassLoaderLeakPreventor</listener-class>
  </listener> 
 

You should usually declare this listener before any other listeners, to make it "outermost".

Configuration

The context listener has a number of settings that can be configured with context parameters in web.xml, i.e.:

   <context-param>
     <param-name>ClassLoaderLeakPreventor.stopThreads</param-name>
     <param-value>false</param-value>
   </context-param>
 

The available settings are

Parameter name	Default value	Description
ClassLoaderLeakPreventor.stopThreads	true	Should threads tied to the web app classloader be forced to stop at application shutdown?
ClassLoaderLeakPreventor.stopTimerThreads	true	Should Timer threads tied to the web app classloader be forced to stop at application shutdown?
ClassLoaderLeakPreventor.executeShutdownHooks	true	Should shutdown hooks registered from the application be executed at application shutdown?
ClassLoaderLeakPreventor.threadWaitMs	5000 (5 seconds)	No of milliseconds to wait for threads to finish execution, before stopping them.
ClassLoaderLeakPreventor.shutdownHookWaitMs	10000 (10 seconds)	No of milliseconds to wait for shutdown hooks to finish execution, before stopping them. If set to -1 there will be no waiting at all, but Thread is allowed to run until finished.

License

This code is licensed under the Apache 2 license, which allows you to include modified versions of the code in your distributed software, without having to release your source code.

More info

For more info, see here.

Design goals

If you want to help improve this component, you should be aware of the design goals

Primary design goal: Zero dependencies. The component should build and run using nothing but the JDK and the Servlet API. Specifically we should not depend on any logging framework, since they are part of the problem. We also don't want to use any utility libraries, in order not to impose any further dependencies into any project that just wants to get rid of classloader leaks. Access to anything outside of the standard JDK (in order to prevent a known leak) should be managed with reflection.

Secondary design goal: Keep the runtime component in a single .java file. It should be possible to just add this one .java file into your own source tree.

Author:

Mattias Jiderhamn, 2012-2016

Field Summary

Fields

Modifier and Type	Field and Description
protected ClassLoaderLeakPreventor	classLoaderLeakPreventor
protected List<javax.servlet.ServletContextListener>	otherListeners Other ServletContextListeners to use also

Constructor Summary

Constructors

Constructor and Description
ClassLoaderLeakPreventorListener()

Method Summary

Modifier and Type	Method and Description
void	contextDestroyed(javax.servlet.ServletContextEvent servletContextEvent)
void	contextInitialized(javax.servlet.ServletContextEvent servletContextEvent)
protected static int	getIntInitParameter(javax.servlet.ServletContext servletContext, String parameterName, int defaultValue) Parse init parameter for integer value, returning default if not found or invalid
protected String	getLogPrefix()
protected void	info(String s) To "turn off" info logging override this method in a subclass and make that subclass method empty.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Field Detail

classLoaderLeakPreventor

protected ClassLoaderLeakPreventor classLoaderLeakPreventor

otherListeners

protected final List<javax.servlet.ServletContextListener> otherListeners

Other ServletContextListeners to use also

Constructor Detail

ClassLoaderLeakPreventorListener

public ClassLoaderLeakPreventorListener()

Method Detail

contextInitialized

public void contextInitialized(javax.servlet.ServletContextEvent servletContextEvent)

Specified by:

contextInitialized in interface javax.servlet.ServletContextListener

contextDestroyed

public void contextDestroyed(javax.servlet.ServletContextEvent servletContextEvent)

Specified by:

contextDestroyed in interface javax.servlet.ServletContextListener

getIntInitParameter

protected static int getIntInitParameter(javax.servlet.ServletContext servletContext,
                                         String parameterName,
                                         int defaultValue)

Parse init parameter for integer value, returning default if not found or invalid

getLogPrefix

protected String getLogPrefix()

info

protected void info(String s)

To "turn off" info logging override this method in a subclass and make that subclass method empty.