org.datanucleus

Class ClassLoaderResolverImpl

java.lang.Object

org.datanucleus.ClassLoaderResolverImpl

All Implemented Interfaces:

ClassLoaderResolver

public class ClassLoaderResolverImpl
extends Object
implements ClassLoaderResolver

A basic implementation of a ClassLoaderResolver. A ClassLoaderResolver provides a series of methods for resolving classes from their names. It supports up to 3 class loaders, based loosely on JDO Spec section 12.5. The class loaders will be used in this order:

• The loader that loaded the class or instance referred to in the API that caused this class to be loaded.
  • In case of query, this is the loader of the candidate class, or the loader of the object passed to the newQuery
  • In case of navigation from a persistent instance, this is the loader of the class of the instance.
  • In the case of getExtent with subclasses, this is the loader of the candidate class.
  • In the case of getObjectById, this is the loader of the object id instance.
  • Other cases do not have an explicit loader.
• The loader returned in the current context by Thread.getContextClassLoader().
• The loader returned by Thread.getContextClassLoader() at the time of creating an ExecutionContext.
• The loader registered for dynamically creating and loading classes at runtime.

TODO Provide a way of flushing a classname from the cached classes so we can reload a class

Field Summary

Fields

Modifier and Type	Field and Description
protected ClassLoader	contextLoader ClassLoader initialised by the context (ExecutionContext).
protected int	contextLoaderHashCode Hash code cache for performance improvement
protected Map<String,Class>	loadedClasses Cache for loaded classes
protected Map<String,URL>	resources Cache for resources
protected ClassLoader	runtimeLoader ClassLoader registered to load runtime created classes.
protected int	runtimeLoaderHashCode Hash code cache for performance improvement
protected Map<String,Class>	unloadedClasses Cache for loaded classes
protected ClassLoader	userRegisteredLoader ClassLoader registered to load classes (e.g set in the persistence properties as the primary loader).
protected int	userRegisteredLoaderHashCode Hash code cache for performance improvement

Constructor Summary

Constructors

Constructor and Description
ClassLoaderResolverImpl() Constructor for non-PersistenceManager cases so there is no PM context loader.
ClassLoaderResolverImpl(ClassLoader ctxLoader) Constructor for ExecutionContext cases.

Method Summary

Modifier and Type	Method and Description
Class	classForName(String name) JDO's Class Loading mechanism (Spec 1.0.1 Chapter 12.5).
Class	classForName(String name, boolean initialize) JDO's Class Loading mechanism (Spec 1.0.1 Chapter 12.5)
Class	classForName(String name, ClassLoader primary) JDO's Class Loading mechanism (Spec 1.0.1 Chapter 12.5).
Class	classForName(String name, ClassLoader primary, boolean initialize) JDO's Class Loading mechanism (Spec 1.0.1 Chapter 12.5)
URL	getResource(String resourceName, ClassLoader primary) Finds the resource with the given name.
Enumeration	getResources(String resourceName, ClassLoader primary) Finds all the resources with the given name.
boolean	isAssignableFrom(Class class_1, String class_name_2) Utility to check the assignability of 2 classes in accordance with JDO's Class Loading mechanism.
boolean	isAssignableFrom(String class_name_1, Class class_2) Utility to check the assignability of 2 classes in accordance with JDO's Class Loading mechanism.
boolean	isAssignableFrom(String class_name_1, String class_name_2) Utility to check the assignability of 2 classes in accordance with JDO's Class Loading mechanism.
void	registerUserClassLoader(ClassLoader loader) ClassLoader registered by users to load classes.
void	setPrimary(ClassLoader primary) Sets the primary classloader for the current thread
void	setRuntimeClassLoader(ClassLoader loader) ClassLoader registered to load classes created at runtime.
String	toString()
void	unsetPrimary() Unsets the primary classloader for the current thread

Methods inherited from class java.lang.Object

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

Field Detail

contextLoader

protected final ClassLoader contextLoader

ClassLoader initialised by the context (ExecutionContext).

contextLoaderHashCode

protected int contextLoaderHashCode

Hash code cache for performance improvement

runtimeLoader

protected ClassLoader runtimeLoader

ClassLoader registered to load runtime created classes.

runtimeLoaderHashCode

protected int runtimeLoaderHashCode

Hash code cache for performance improvement

userRegisteredLoader

protected ClassLoader userRegisteredLoader

ClassLoader registered to load classes (e.g set in the persistence properties as the primary loader).

userRegisteredLoaderHashCode

protected int userRegisteredLoaderHashCode

Hash code cache for performance improvement

loadedClasses

protected Map<String,Class> loadedClasses

Cache for loaded classes

unloadedClasses

protected Map<String,Class> unloadedClasses

Cache for loaded classes

resources

protected Map<String,URL> resources

Cache for resources

Constructor Detail

ClassLoaderResolverImpl

public ClassLoaderResolverImpl(ClassLoader ctxLoader)

Constructor for ExecutionContext cases.

Parameters:

ctxLoader - Loader from ExecutionContext initialisation time.

ClassLoaderResolverImpl

public ClassLoaderResolverImpl()

Constructor for non-PersistenceManager cases so there is no PM context loader.

Method Detail

classForName

public Class classForName(String name,
                          ClassLoader primary)

JDO's Class Loading mechanism (Spec 1.0.1 Chapter 12.5). Try 3 loaders, starting with user-supplied loader, then try the current thread's loader, and finally try the PM context loader. This method does not initialize the class

Specified by:

classForName in interface ClassLoaderResolver

Parameters:

name - Name of the Class to be loaded

primary - primary ClassLoader to use (or null)

Returns:

The class given the name, using the required loader.

Throws:

ClassNotResolvedException - if the class can't be found in the classpath

classForName

public Class classForName(String name,
                          ClassLoader primary,
                          boolean initialize)

JDO's Class Loading mechanism (Spec 1.0.1 Chapter 12.5)

Specified by:

classForName in interface ClassLoaderResolver

Parameters:

name - Name of the Class to be loaded

primary - the primary ClassLoader to use (or null)

initialize - whether to initialize the class or not.

Returns:

The Class given the name, using the specified ClassLoader

Throws:

ClassNotResolvedException - if the class can't be found in the classpath

classForName

public Class classForName(String name)

JDO's Class Loading mechanism (Spec 1.0.1 Chapter 12.5). This method does not initialize the class

Specified by:

classForName in interface ClassLoaderResolver

Parameters:

name - Name of the Class to be loaded

Returns:

The class given the name, using the required loader.

classForName

public Class classForName(String name,
                          boolean initialize)

JDO's Class Loading mechanism (Spec 1.0.1 Chapter 12.5)

Specified by:

classForName in interface ClassLoaderResolver

Parameters:

name - Name of the Class to be loaded

initialize - whether to initialize the class or not.

Returns:

The Class given the name, using the specified ClassLoader

Throws:

ClassNotResolvedException - if the class can't be found in the classpath

isAssignableFrom

public boolean isAssignableFrom(String class_name_1,
                                String class_name_2)

Utility to check the assignability of 2 classes in accordance with JDO's Class Loading mechanism. This will check class_1.isAssignableFrom(class_2);

Specified by:

isAssignableFrom in interface ClassLoaderResolver

Parameters:

class_name_1 - Name of first class

class_name_2 - Name of second class

Returns:

Whether Class 2 is assignable from Class 1

isAssignableFrom

public boolean isAssignableFrom(String class_name_1,
                                Class class_2)

Utility to check the assignability of 2 classes in accordance with JDO's Class Loading mechanism. This will check class_1.isAssignableFrom(class_2);

Specified by:

isAssignableFrom in interface ClassLoaderResolver

Parameters:

class_name_1 - Name of first class

class_2 - Second class

Returns:

Whether Class 2 is assignable from Class 1

isAssignableFrom

public boolean isAssignableFrom(Class class_1,
                                String class_name_2)

Utility to check the assignability of 2 classes in accordance with JDO's Class Loading mechanism. This will check class_1.isAssignableFrom(class_2);

Specified by:

isAssignableFrom in interface ClassLoaderResolver

Parameters:

class_1 - First class

class_name_2 - Name of second class

Returns:

Whether Class 2 is assignable from Class 1

setRuntimeClassLoader

public void setRuntimeClassLoader(ClassLoader loader)

ClassLoader registered to load classes created at runtime.

Specified by:

setRuntimeClassLoader in interface ClassLoaderResolver

Parameters:

loader - The ClassLoader in which classes are defined

registerUserClassLoader

public void registerUserClassLoader(ClassLoader loader)

ClassLoader registered by users to load classes. One ClassLoader can be registered, and if one ClassLoader is already registered, the registered ClassLoader is replaced by loader.

Specified by:

registerUserClassLoader in interface ClassLoaderResolver

Parameters:

loader - The ClassLoader in which classes are loaded

getResources

public Enumeration getResources(String resourceName,
                                ClassLoader primary)
                         throws IOException

Finds all the resources with the given name.

Specified by:

getResources in interface ClassLoaderResolver

Parameters:

resourceName - the resource name. If resourceName starts with "/", remove it before searching.

primary - the primary ClassLoader to use (or null)

Returns:

An enumeration of URL objects for the resource. If no resources could be found, the enumeration will be empty. Resources that the class loader doesn't have access to will not be in the enumeration.

Throws:

IOException - If I/O errors occur

See Also:

ClassLoader.getResources(java.lang.String)

getResource

public URL getResource(String resourceName,
                       ClassLoader primary)

Finds the resource with the given name.

Specified by:

getResource in interface ClassLoaderResolver

Parameters:

resourceName - the path to resource name relative to the classloader root path. If resourceName starts with "/", remove it before searching.

primary - the primary ClassLoader to use (or null)

Returns:

A URL object for reading the resource, or null if the resource could not be found or the invoker doesn't have adequate privileges to get the resource.

See Also:

ClassLoader.getResource(java.lang.String)

setPrimary

public void setPrimary(ClassLoader primary)

Sets the primary classloader for the current thread

Specified by:

setPrimary in interface ClassLoaderResolver

Parameters:

primary - the primary classloader

unsetPrimary

public void unsetPrimary()

Unsets the primary classloader for the current thread

Specified by:

unsetPrimary in interface ClassLoaderResolver

toString

public String toString()

Overrides:

toString in class Object