Package io.permazen.util

Class ApplicationClassLoader

java.lang.Object

java.lang.ClassLoader

java.security.SecureClassLoader

java.net.URLClassLoader

io.permazen.util.ApplicationClassLoader

All Implemented Interfaces:

Closeable, AutoCloseable

public final class ApplicationClassLoader
extends URLClassLoader

An URLClassLoader whose classpath can be modified at runtime.

This is intended for use by applications that want to load classes using the usual system or context class loader, but need the ability to add URLs to the classpath that is searched. In JDK 9 and later, the system class loader can no longer be directly modified (this previously used an ugly reflection hack anyway). This class effectively restores that capability, by overriding addURL() and making it public.

This class also provides a way to lookup existing instances by parent; see getInstance(). These instances are cached using weak references to avoid a memory leak.

Instances work together to behave like a singleton; an URL added to any instance by addURL() is automagically added to all existing and future instances.

Method Summary

Modifier and Type	Method	Description
void	addFile(File file)	Append the specified file to the search classpath.
void	addURL(URL url)
static ApplicationClassLoader	getInstance()	Obtain the unique instance having the current thread's context class loader as its parent, creating it on demand if needed.
static ApplicationClassLoader	getInstance(ClassLoader parent)	Obtain the unique instance having the given ClassLoader as its parent, creating it on demand if needed.

Methods inherited from class java.net.URLClassLoader

close, definePackage, findClass, findResource, findResources, getPermissions, getResourceAsStream, getURLs, newInstance, newInstance

Methods inherited from class java.security.SecureClassLoader

defineClass, defineClass

Methods inherited from class java.lang.ClassLoader

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

Methods inherited from class java.lang.Object

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

Method Details

addFile

public void addFile(File file)

Append the specified file to the search classpath.

Parameters:

file - classpath component

Throws:

IllegalArgumentException - if file is null

addURL

public void addURL(URL url)

Overrides:

addURL in class URLClassLoader

Parameters:

url - the URL to be added to the search path of URLs

Throws:

IllegalArgumentException - if url cannot be converted into an URI

IllegalArgumentException - if url is null

getInstance

public static ApplicationClassLoader getInstance()

Obtain the unique instance having the current thread's context class loader as its parent, creating it on demand if needed.

getInstance

public static ApplicationClassLoader getInstance(ClassLoader parent)

Obtain the unique instance having the given ClassLoader as its parent, creating it on demand if needed.

Parameters:

parent - parent class loader, or null for the boot class loader

Returns:

corresponding ApplicationClassLoader, or parent if parent is itself already an ApplicationClassLoader