Class ProxyClassLoader

java.lang.Object

java.lang.ClassLoader

net.thevpc.common.prs.classloader.ProxyClassLoader

public class ProxyClassLoader
extends ClassLoader

A class loader that has multiple parents and uses them for loading classes and resources. It can be used in tree hierarchy, where it can exploit its capability to not throw ClassNotFoundException when communicating with other ProxyClassLoader. It itself doesn't load classes or resources, but allows subclasses to add such functionality.

Author:

Petr Nejedly, Jesse Glick (ProxyClassLoader)

Constructor Summary

Constructors

Constructor	Description
ProxyClassLoader(ClassLoader[] parents)	Create a multi-parented classloader.
ProxyClassLoader(String name, ClassLoader[] parents)
ProxyClassLoader(String name, ClassLoader[] parents, boolean transitive)	Create a multi-parented classloader.

Method Summary

Modifier and Type	Method	Description
void	append(ClassLoader[] classLoaders)	Add new parents dynamically.
protected Package	definePackage(String name, String specTitle, String specVersion, String specVendor, String implTitle, String implVersion, String implVendor, URL sealBase)	This is here just for locking serialization purposes.
void	destroy()	Try to destroy this classloader.
protected URL	findResource(String name)	This ClassLoader can't load anything itself.
protected final Enumeration	findResources(String name)	Finds all the resource with the given name.
String	getName()
protected Package	getPackage(String name)	Returns a Package that has been defined by this class loader or any of its parents.
Package	getPackageAccessibly(String name)
protected Package	getPackageFast(String name, String sname, boolean recurse)	Faster way to find a package.
protected Package[]	getPackages()	Returns all of the Packages defined by this class loader and its parents.
Package[]	getPackagesAccessibly()
final URL	getResource(String name)	Finds the resource with the given name.
protected boolean	isSpecialResource(String pkg)	Test whether a given resource name is something that any JAR might have, and for which the domain cache should be disabled.
protected final Class	loadClass(String name, boolean resolve)	Loads the class with the specified name.
protected boolean	shouldDelegateResource(String pkg, ClassLoader parent)	Test whether a given resource request (for a class or not) should be searched for in the specified parent classloader or not.
protected Class	simpleFindClass(String name, String fileName, String pkg)	This ClassLoader can't load anything itself.
protected Enumeration	simpleFindResources(String name)	This ClassLoader can't load anything itself.

Methods inherited from class ClassLoader

clearAssertionStatus, defineClass, defineClass, defineClass, defineClass, findClass, findClass, findLibrary, findLoadedClass, findResource, findSystemClass, getClassLoadingLock, getDefinedPackage, getDefinedPackages, getParent, getPlatformClassLoader, getResourceAsStream, getResources, getSystemClassLoader, getSystemResource, getSystemResourceAsStream, getSystemResources, getUnnamedModule, isRegisteredAsParallelCapable, loadClass, registerAsParallelCapable, resolveClass, resources, setClassAssertionStatus, setDefaultAssertionStatus, setPackageAssertionStatus, setSigners

Methods inherited from class Object

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

Constructor Details

ProxyClassLoader

public ProxyClassLoader(ClassLoader[] parents)

Create a multi-parented classloader. Loads recursively from parents.

Parameters:

parents - list of parent classloaders.

Throws:

IllegalArgumentException - if there are any nulls or duplicate parent loaders or cycles.

ProxyClassLoader

public ProxyClassLoader(String name,
 ClassLoader[] parents)

ProxyClassLoader

public ProxyClassLoader(String name,
 ClassLoader[] parents,
 boolean transitive)

Create a multi-parented classloader.

Parameters:

parents - list of parent classloaders.

transitive - whether other PCLs depending on this one will automatically search through its parent list

Throws:

IllegalArgumentException - if there are any nulls or duplicate parent loaders or cycles.

Since:

org.netbeans.core/1 > 1.6

Method Details

getName

public String getName()

Overrides:

getName in class ClassLoader

append

public void append(ClassLoader[] classLoaders)
            throws IllegalArgumentException

Add new parents dynamically.

Parameters:

classLoaders - the new parents to add (append to list)

Throws:

IllegalArgumentException - in case of a null or cyclic parent (duplicate OK)

destroy

public void destroy()

Try to destroy this classloader. Subsequent attempts to use it will log an error (at most one though).

loadClass

protected final Class loadClass(String name,
 boolean resolve)
                         throws ClassNotFoundException

Loads the class with the specified name. The implementation of this method searches for classes in the following order: Calls ClassLoader.findLoadedClass(String) to check if the class has * already been loaded. * Checks the caches whether another class from the same package * was already loaded and uses the same classloader * Tries to find the class using parent loaders in their order. * Calls the simpleFindClass(String, String, String) method to find * the class using this class loader. *

Overrides:

loadClass in class ClassLoader

Parameters:

name - the name of the class

resolve - if true then resolve the class

Returns:

the resulting Class object

Throws:

ClassNotFoundException - if the class could not be found

simpleFindClass

protected Class simpleFindClass(String name,
 String fileName,
 String pkg)

This ClassLoader can't load anything itself. Subclasses may override this method to do some class loading themselves. The implementation should not throw any exception, just return null if it can't load required class.

Parameters:

name - the name of the class

fileName - the expected filename of the classfile, like java/lang/Object.class for java.lang.Object The ClassLoader implementation may or may not use it, depending whether it is usefull to it.

pkg - the package name, in the format org/netbeans/modules/foo/

Returns:

the resulting Class object or null

getResource

public final URL getResource(String name)

Finds the resource with the given name. The implementation of this method searches for resources in the following order: Checks the caches whether another resource or class from the same * package was already loaded and uses the same classloader. * Tries to find the resources using parent loaders in their order. * Calls the findResource(String) method to find * the resources using this class loader. *

Overrides:

getResource in class ClassLoader

Parameters:

name - a "/"-separated path name that identifies the resource.

Returns:

a URL for reading the resource, or null if the resource could not be found.

See Also:

• findResource(String)

findResource

protected URL findResource(String name)

This ClassLoader can't load anything itself. Subclasses may override this method to do some resource loading themselves.

Overrides:

findResource in class ClassLoader

Parameters:

name - the resource name

Returns:

a URL for reading the resource, or null if the resource could not be found.

findResources

protected final Enumeration findResources(String name)
                                   throws IOException

Finds all the resource with the given name. The implementation of this method uses the simpleFindResources(String) method to find all the resources available from this classloader and adds all the resources from all the parents.

Overrides:

findResources in class ClassLoader

Parameters:

name - the resource name

Returns:

an Enumeration of URLs for the resources

Throws:

IOException - if I/O errors occur

simpleFindResources

protected Enumeration simpleFindResources(String name)
                                   throws IOException

This ClassLoader can't load anything itself. Subclasses may override this method to do some resource loading themselves, this implementation simply delegates to findResources method of the superclass that should return empty Enumeration.

Parameters:

name - the resource name

Returns:

an Enumeration of URLs for the resources

Throws:

IOException - if I/O errors occur

getPackage

protected Package getPackage(String name)

Returns a Package that has been defined by this class loader or any of its parents.

Overrides:

getPackage in class ClassLoader

Parameters:

name - the package name

Returns:

the Package corresponding to the given name, or null if not found

getPackageFast

protected Package getPackageFast(String name,
 String sname,
 boolean recurse)

Faster way to find a package.

Parameters:

name - package name in org.netbeans.modules.foo format

sname - package name in org/netbeans/modules/foo/ format

recurse - whether to also ask parents

definePackage

protected Package definePackage(String name,
 String specTitle,
 String specVersion,
 String specVendor,
 String implTitle,
 String implVersion,
 String implVendor,
 URL sealBase)
                         throws IllegalArgumentException

This is here just for locking serialization purposes. Delegates to super.definePackage with proper locking. Also tracks the package in our private cache, since getPackageFast(...,...,false) will not call super.getPackage.

Overrides:

definePackage in class ClassLoader

Throws:

IllegalArgumentException

getPackages

protected Package[] getPackages()

Returns all of the Packages defined by this class loader and its parents.

Overrides:

getPackages in class ClassLoader

Returns:

the array of Package objects defined by this ClassLoader

getPackageAccessibly

public Package getPackageAccessibly(String name)

getPackagesAccessibly

public Package[] getPackagesAccessibly()

isSpecialResource

protected boolean isSpecialResource(String pkg)

Test whether a given resource name is something that any JAR might have, and for which the domain cache should be disabled. The result must not change from one call to the next with the same argument. By default the domain cache is disabled only for META-INF/* JAR information.

Parameters:

pkg - the package component of the resource path ending with a slash, e.g. "org/netbeans/modules/foo/"

Returns:

true if it is a special resource, false for normal domain-cached resource

Since:

org.netbeans.core/1 1.3

shouldDelegateResource

protected boolean shouldDelegateResource(String pkg,
 ClassLoader parent)

Test whether a given resource request (for a class or not) should be searched for in the specified parent classloader or not. The result must not change from one call to the next with the same arguments. By default, always true. Subclasses may override to "mask" certain packages from view, possibly according to the classloader chain.

Parameters:

pkg - the package component of the resource path ending with a slash, e.g. "org/netbeans/modules/foo/"

parent - a classloader which is a direct or indirect parent of this one

Returns:

true if the request should be delegated to this parent; false to only search elsewhere (other parents, this loader's own namespace)

Since:

org.netbeans.core/1 1.3