OSGI bundle/plugin class loading

Being a programmer, I would ask you to take a look at this class.

Plugin:
org.eclipse.osgi_3.10.2.v20150203-1939.jar

Class:
BundleLoader

Below 2 methods will give lot of understanding:

Class<?> findClass(String name, boolean checkParent) throws ClassNotFoundException {

if (checkParent && parent != null && name.startsWith(JAVA_PACKAGE))

// 1) if startsWith "java." delegate to parent and terminate search

// we want to throw ClassNotFoundExceptions if a java.* class cannot be loaded from the parent.

return parent.loadClass(name);

return findClassInternal(name, checkParent);

}

private Class<?> findClassInternal(String name, boolean checkParent) throws ClassNotFoundException {

if (debug.DEBUG_LOADER)

Debug.println("BundleLoader[" + this + "].findClassInternal(" + name + ")"); //$NON-NLS-1$ //$NON-NLS-2$ //$NON-NLS-3$

String pkgName = getPackageName(name);

boolean bootDelegation = false;

// follow the OSGi delegation model

if (checkParent && parent != null && container.isBootDelegationPackage(pkgName))

// 2) if part of the bootdelegation list then delegate to parent and continue of failure

try {

return parent.loadClass(name);

} catch (ClassNotFoundException cnfe) {

// we want to continue

bootDelegation = true;

}

Class<?> result = null;

try {

result = (Class<?>) searchHooks(name, PRE_CLASS);

} catch (ClassNotFoundException e) {

throw e;

} catch (FileNotFoundException e) {

// will not happen

}

if (result != null)

return result;

// 3) search the imported packages

PackageSource source = findImportedSource(pkgName, null);

if (source != null) {

if (debug.DEBUG_LOADER) {

Debug.println("BundleLoader[" + this + "] loading from import package: " + source); //$NON-NLS-1$ //$NON-NLS-2$

}

// 3) found import source terminate search at the source

result = source.loadClass(name);

if (result != null)

return result;

throw new ClassNotFoundException(name + " cannot be found by " + this); //$NON-NLS-1$

}

// 4) search the required bundles

source = findRequiredSource(pkgName, null);

if (source != null) {

if (debug.DEBUG_LOADER) {

Debug.println("BundleLoader[" + this + "] loading from required bundle package: " + source); //$NON-NLS-1$ //$NON-NLS-2$

}

// 4) attempt to load from source but continue on failure

result = source.loadClass(name);

}

// 5) search the local bundle

if (result == null)

result = findLocalClass(name);

if (result != null)

return result;

// 6) attempt to find a dynamic import source; only do this if a required source was not found

if (source == null) {

source = findDynamicSource(pkgName);

if (source != null) {

result = source.loadClass(name);

if (result != null)

return result;

// must throw CNFE if dynamic import source does not have the class

throw new ClassNotFoundException(name + " cannot be found by " + this); //$NON-NLS-1$

}

}

if (result == null)

try {

result = (Class<?>) searchHooks(name, POST_CLASS);

} catch (ClassNotFoundException e) {

throw e;

} catch (FileNotFoundException e) {

// will not happen

}

// do buddy policy loading

if (result == null && policy != null)

result = policy.doBuddyClassLoading(name);

if (result != null)

return result;

// hack to support backwards compatibility for bootdelegation

// or last resort; do class context trick to work around VM bugs

if (parent != null && !bootDelegation && ((checkParent && container.getConfiguration().compatibilityBootDelegation) || isRequestFromVM()))

// we don't need to continue if a CNFE is thrown here.

try {

return parent.loadClass(name);

} catch (ClassNotFoundException e) {

// we want to generate our own exception below

}

throw new ClassNotFoundException(name + " cannot be found by " + this); //$NON-NLS-1$

}

Resources:

http://moi.vonos.net/java/osgi-classloaders/