de.innovationgate.utils

Class DynamicClassLoadingChain

java.lang.Object

java.lang.ClassLoader

de.innovationgate.utils.DynamicClassLoadingChain

public class DynamicClassLoadingChain
extends java.lang.ClassLoader

Class to maintain a chain of URLClassLoaders, that may dynamically grow and where individual loaders may be updated.

The DynamicClassLoadingChain builds a chain of URLClassLoaders for the purpose of retrieving classes from all loaders while keeping individual loaders separate for addition and updating. The loaders registered are called "subloaders". New subloaders can be added at runtime, where each new classloader has the most recently added classloader as it's parent. So using the most recently added classloader - the "top loader" retrievable by getTopLoader() - you can load all classes provided by all class loaders in the chain.

Also at runtime individual class loaders in the chain may be replaced. At adding time you can provide a key with each new class loader that you can use later to address the loader to be replaced. Use method updateSubLoader(String, URL[]) for this. Replacing a class loader will implicitly recreate all class loaders down the child chain, but leave all class loaders up the parent chain untouched.

When adding a loader you can declare it "static" (when using updateSubLoader(String, URL[], boolean) and setting the last param to true). These loaders will be added to the chain in a way that will prevent them from being updated and rebuilt. They are inserted to the chain before all non-static loaders and updating or removing them will cause an IllegalStateException to be thrown. You can use static loaders for classes that need to be static in the classpath for their functionalities to work. For example if you have a singleton class that maintains state, rebuilding the loader of the class will drop the singleton instance and by the next use of it a new one will be created. By setting the loader to static you prevent such problems.

Nested Class Summary

Nested Classes

Modifier and Type	Class and Description
class	DynamicClassLoadingChain.SubLoader

Constructor Summary

Constructors

Constructor and Description
DynamicClassLoadingChain(java.lang.ClassLoader parent) Create a new chain.

Method Summary

Methods

Modifier and Type	Method and Description
void	clearAssertionStatus()
boolean	equals(java.lang.Object obj)
java.util.List<java.lang.String>	getChainKeys() Returns the keys of the classpath chain in the order of their loading priority (from parents to children)
java.net.URL	getResource(java.lang.String arg0)
java.io.InputStream	getResourceAsStream(java.lang.String arg0)
java.util.Enumeration<java.net.URL>	getResources(java.lang.String arg0)
DynamicClassLoadingChain.SubLoader	getSubLoader(java.lang.String key)
java.net.URL[]	getSubLoaderURLs(java.lang.String key) Retuns the url array registered for the subloader with the given key, in identical order as given to updateSubLoader(String, URL[])
java.lang.ClassLoader	getTopLoader() Returns the topmost subloader of the chain, which can be used to load classes from all currently registered subloaders
int	hashCode()
boolean	hasSubLoader(java.lang.String key)
java.lang.Class<?>	loadClass(java.lang.String arg0)
void	removeSubLoader(java.lang.String key) Removes the subloader with the given key from the chain.
void	setClassAssertionStatus(java.lang.String arg0, boolean arg1)
void	setDefaultAssertionStatus(boolean arg0)
void	setPackageAssertionStatus(java.lang.String arg0, boolean arg1)
java.lang.String	toString()
void	updateSubLoader(java.lang.String key, java.net.URL[] urls) Creates or updates a subloader for the given key.
void	updateSubLoader(java.lang.String key, java.net.URL[] urls, boolean isstatic) Creates or updates a subloader for the given key.

Methods inherited from class java.lang.ClassLoader

getParent, getSystemClassLoader, getSystemResource, getSystemResourceAsStream, getSystemResources

Methods inherited from class java.lang.Object

getClass, notify, notifyAll, wait, wait, wait

Constructor Detail

DynamicClassLoadingChain

public DynamicClassLoadingChain(java.lang.ClassLoader parent)

Create a new chain.

Parameters:

parent - The parent class loader to be used by the first subloader registered

Method Detail

updateSubLoader

public void updateSubLoader(java.lang.String key,
                   java.net.URL[] urls,
                   boolean isstatic)
                     throws java.lang.IllegalStateException

Creates or updates a subloader for the given key.

Parameters:

key - The of the loader

urls - URLs to JARs or Java class folders that should be loaderd by this subloader

isstatic - True if the loader should be static, i.e. should never be updated

Throws:

java.lang.IllegalStateException - When trying to update a subloader that is static

updateSubLoader

public void updateSubLoader(java.lang.String key,
                   java.net.URL[] urls)

Creates or updates a subloader for the given key. This operation always creates non-static subloaders

Parameters:

key - The of the loader

urls - URLs to JARs or Java class folders that should be loaderd by this subloader

getSubLoaderURLs

public java.net.URL[] getSubLoaderURLs(java.lang.String key)

Retuns the url array registered for the subloader with the given key, in identical order as given to updateSubLoader(String, URL[])

Parameters:

key - The key of the subloader to use

Returns:

The URLs of the subloader or null if no subloader of this name exists

removeSubLoader

public void removeSubLoader(java.lang.String key)

Removes the subloader with the given key from the chain. This operation implictly rebuilts all child class loaders of the removed one

Parameters:

key - The key of the loader to remove

Throws:

java.lang.IllegalStateException - When trying to update a subloader that is static

getTopLoader

public java.lang.ClassLoader getTopLoader()

Returns the topmost subloader of the chain, which can be used to load classes from all currently registered subloaders

getChainKeys

public java.util.List<java.lang.String> getChainKeys()

Returns the keys of the classpath chain in the order of their loading priority (from parents to children)

clearAssertionStatus

public void clearAssertionStatus()

Overrides:

clearAssertionStatus in class java.lang.ClassLoader

equals

public boolean equals(java.lang.Object obj)

Overrides:

equals in class java.lang.Object

getResource

public java.net.URL getResource(java.lang.String arg0)

Overrides:

getResource in class java.lang.ClassLoader

getResourceAsStream

public java.io.InputStream getResourceAsStream(java.lang.String arg0)

Overrides:

getResourceAsStream in class java.lang.ClassLoader

getResources

public java.util.Enumeration<java.net.URL> getResources(java.lang.String arg0)
                                                 throws java.io.IOException

Overrides:

getResources in class java.lang.ClassLoader

Throws:

java.io.IOException

hashCode

public int hashCode()

Overrides:

hashCode in class java.lang.Object

loadClass

public java.lang.Class<?> loadClass(java.lang.String arg0)
                             throws java.lang.ClassNotFoundException

Overrides:

loadClass in class java.lang.ClassLoader

Throws:

java.lang.ClassNotFoundException

setClassAssertionStatus

public void setClassAssertionStatus(java.lang.String arg0,
                           boolean arg1)

Overrides:

setClassAssertionStatus in class java.lang.ClassLoader

setDefaultAssertionStatus

public void setDefaultAssertionStatus(boolean arg0)

Overrides:

setDefaultAssertionStatus in class java.lang.ClassLoader

setPackageAssertionStatus

public void setPackageAssertionStatus(java.lang.String arg0,
                             boolean arg1)

Overrides:

setPackageAssertionStatus in class java.lang.ClassLoader

toString

public java.lang.String toString()

Overrides:

toString in class java.lang.Object

hasSubLoader

public boolean hasSubLoader(java.lang.String key)

getSubLoader

public DynamicClassLoadingChain.SubLoader getSubLoader(java.lang.String key)