org.openmrs.util

Class OpenmrsClassLoader

java.lang.Object

java.lang.ClassLoader

java.security.SecureClassLoader

java.net.URLClassLoader

org.openmrs.util.OpenmrsClassLoader

All Implemented Interfaces:

Closeable, AutoCloseable

public class OpenmrsClassLoader
extends URLClassLoader

This classloader knows about the current ModuleClassLoaders and will attempt to load classes from them if needed

Constructor Summary

Constructors

Constructor and Description
OpenmrsClassLoader() Normal constructor.
OpenmrsClassLoader(ClassLoader parent) Creates the instance for the OpenmrsClassLoader

Method Summary

Modifier and Type	Method and Description
protected static void	clearReferences() This clears any references this classloader might have that will prevent garbage collection.
static void	destroyInstance() Destroy the current instance of the classloader.
static URL	expandURL(URL result, File folder) Expand the given URL into the given folder
URL	findResource(String name)
Enumeration<URL>	findResources(String name)
static void	flushInstance() All objects depending on the old classloader should be restarted here Should be called after destoryInstance() and after the service is restarted
static OpenmrsClassLoader	getInstance() Get the static/singular instance of the module class loader
static File	getLibCacheFolder() Get the temporary "work" directory for expanded jar files
InputStream	getResourceAsStream(String file) Searches all known module classloaders first, then parent classloaders
Enumeration<URL>	getResources(String packageName) Searches all known module classloaders first, then parent classloaders
Class<?>	loadClass(String name, boolean resolve) It attempts to load classes from the module class loaders first and then tries the web container class loader (parent class loader).
protected static boolean	loadedByThisOrChild(Class<?> clazz) Determine whether a class was loaded by this class loader or one of its child class loaders.
protected static void	nullInstance(Object instance) Used by clearReferences() upon application close.
static void	onShutdown()
static void	restoreState() This method should be called after restoring the instance
static void	saveState() This method should be called before destroying the instance
static void	setThreadsToNewClassLoader() Sets the class loader, for all threads referencing a destroyed openmrs class loader, to the current one.
String	toString()

Methods inherited from class java.net.URLClassLoader

addURL, close, definePackage, findClass, getPermissions, 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, findLibrary, findLoadedClass, findSystemClass, getClassLoadingLock, getPackage, getPackages, getParent, getResource, getSystemClassLoader, getSystemResource, getSystemResourceAsStream, getSystemResources, loadClass, registerAsParallelCapable, resolveClass, setClassAssertionStatus, setDefaultAssertionStatus, setPackageAssertionStatus, setSigners

Methods inherited from class java.lang.Object

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

Constructor Detail

OpenmrsClassLoader

public OpenmrsClassLoader(ClassLoader parent)

Creates the instance for the OpenmrsClassLoader

OpenmrsClassLoader

public OpenmrsClassLoader()

Normal constructor. Sets this class as the parent classloader

Method Detail

getInstance

public static OpenmrsClassLoader getInstance()

Get the static/singular instance of the module class loader

Returns:

OpenmrsClassLoader

loadClass

public Class<?> loadClass(String name,
                          boolean resolve)
                   throws ClassNotFoundException

It attempts to load classes from the module class loaders first and then tries the web container class loader (parent class loader).

Overrides:

loadClass in class ClassLoader

Throws:

ClassNotFoundException

See Also:

Should load class from cache second time Should not load class from cache if class loader has been disposed Should load class from parent first Should load class if two module class loaders have same packages

findResource

public URL findResource(String name)

Overrides:

findResource in class URLClassLoader

See Also:

URLClassLoader.findResource(java.lang.String)

findResources

public Enumeration<URL> findResources(String name)
                               throws IOException

Overrides:

findResources in class URLClassLoader

Throws:

IOException

See Also:

URLClassLoader.findResources(java.lang.String)

getResourceAsStream

public InputStream getResourceAsStream(String file)

Searches all known module classloaders first, then parent classloaders

Overrides:

getResourceAsStream in class URLClassLoader

See Also:

ClassLoader.getResourceAsStream(java.lang.String)

getResources

public Enumeration<URL> getResources(String packageName)
                              throws IOException

Searches all known module classloaders first, then parent classloaders

Overrides:

getResources in class ClassLoader

Throws:

IOException

See Also:

ClassLoader.getResources(java.lang.String)

toString

public String toString()

Overrides:

toString in class Object

See Also:

Object.toString()

destroyInstance

public static void destroyInstance()

Destroy the current instance of the classloader. Note**: After calling this and after the new service is set up, All classes using this instance should be flushed. This would allow all java classes that were loaded by the old instance variable to be gc'd and modules to load in new java classes

See Also:

flushInstance()

setThreadsToNewClassLoader

public static void setThreadsToNewClassLoader()

Sets the class loader, for all threads referencing a destroyed openmrs class loader, to the current one.

onShutdown

public static void onShutdown()

clearReferences

protected static void clearReferences()

This clears any references this classloader might have that will prevent garbage collection.

Borrowed from Tomcat's WebappClassLoader#clearReferences() (not javadoc linked intentionally)
The only difference between this and Tomcat's implementation is that this one only acts on openmrs objects and also clears out static java.* packages. Tomcat acts on all objects and does not clear our static java.* objects.

Since:

1.5

nullInstance

protected static void nullInstance(Object instance)

Used by clearReferences() upon application close.

Borrowed from Tomcat's WebappClassLoader.

Parameters:

instance - the object whose fields need to be nulled out

loadedByThisOrChild

protected static boolean loadedByThisOrChild(Class<?> clazz)

Determine whether a class was loaded by this class loader or one of its child class loaders.

Borrowed from Tomcat's WebappClassLoader

saveState

public static void saveState()

This method should be called before destroying the instance

See Also:

destroyInstance()

restoreState

public static void restoreState()

This method should be called after restoring the instance

See Also:

destroyInstance(), saveState()

flushInstance

public static void flushInstance()

All objects depending on the old classloader should be restarted here Should be called after destoryInstance() and after the service is restarted

See Also:

destroyInstance()

getLibCacheFolder

public static File getLibCacheFolder()

Get the temporary "work" directory for expanded jar files

Returns:

temporary location for storing the libraries

expandURL

public static URL expandURL(URL result,
                            File folder)

Expand the given URL into the given folder

Parameters:

result - URL of the file to expand

folder - File (directory) to place the expanded file

Returns:

the URL at the expanded location