Package org.apache.struts2.util

Class ClassLoaderUtil

java.lang.Object

org.apache.struts2.util.ClassLoaderUtil

public class ClassLoaderUtil
extends Object

This class is extremely useful for loading resources and classes in a fault tolerant manner that works across different applications servers.

It has come out of many months of frustrating use of multiple application servers at Atlassian, please don't change things unless you're sure they're not going to break in one server or another!

Constructor Summary

Constructors

Constructor	Description
ClassLoaderUtil()

Method Summary

Modifier and Type	Method	Description
static URL	getResource(String resourceName, Class callingClass)	Load a given resource.
static InputStream	getResourceAsStream(String resourceName, Class callingClass)	This is a convenience method to load a resource as a stream.
static Iterator<URL>	getResources(String resourceName, Class callingClass, boolean aggregate)	Load all resources with a given name, potentially aggregating all results from the searched classloaders.
static Class	loadClass(String className, Class callingClass)	Load a class with a given name.
static void	printClassLoader()	Prints the current classloader hierarchy - useful for debugging.
static void	printClassLoader(ClassLoader cl)	Prints the classloader hierarchy from a given classloader - useful for debugging.

Methods inherited from class java.lang.Object

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

Constructor Details

ClassLoaderUtil

public ClassLoaderUtil()

Method Details

getResources

public static Iterator<URL> getResources(String resourceName,
 Class callingClass,
 boolean aggregate)
                                  throws IOException

Load all resources with a given name, potentially aggregating all results from the searched classloaders. If no results are found, the resource name is prepended by '/' and tried again.

This method will try to load the resources using the following methods (in order):

• From Thread.currentThread().getContextClassLoader()
• From ClassLoaderUtil.class.getClassLoader()
• callingClass.getClassLoader()

Parameters:

resourceName - The name of the resources to load

callingClass - The Class object of the calling object

aggregate - aggregate

Returns:

all resources found

Throws:

IOException - in case of IO errors

getResource

public static URL getResource(String resourceName,
 Class callingClass)

Load a given resource.

This method will try to load the resource using the following methods (in order):

• From Thread.currentThread().getContextClassLoader()
• From ClassLoaderUtil.class.getClassLoader()
• From the callingClass.getClassLoader()

Parameters:

resourceName - The name of the resource to load

callingClass - The Class object of the calling object

Returns:

the resource

getResourceAsStream

public static InputStream getResourceAsStream(String resourceName,
 Class callingClass)

This is a convenience method to load a resource as a stream. The algorithm used to find the resource is given in getResource()

Parameters:

resourceName - The name of the resource to load

callingClass - The Class object of the calling object

Returns:

resource as a stream

loadClass

public static Class loadClass(String className,
 Class callingClass)
                       throws ClassNotFoundException

Load a class with a given name.

It will try to load the class in the following order:

• From Thread.currentThread().getContextClassLoader()
• Using the basic Class.forName(java.lang.String)
• From ClassLoaderUtil.class.getClassLoader()
• From the callingClass.getClassLoader()

Parameters:

className - The name of the class to load

callingClass - The Class object of the calling object

Returns:

class with for the given name

Throws:

ClassNotFoundException - If the class cannot be found anywhere.

printClassLoader

public static void printClassLoader()

Prints the current classloader hierarchy - useful for debugging.

printClassLoader

public static void printClassLoader(ClassLoader cl)

Prints the classloader hierarchy from a given classloader - useful for debugging.

Parameters:

cl - the class loader