java.lang.ClassLoader

java.lang.ClassLoader Class Reference

Detailed Description

A ClassLoader is used for loading classes.

VM Implementors Note

This class must be implemented by the VM. The documented methods and natives must be implemented to support other provided class implementations in this package.

Since:: 1.0

See also:: Class


Public Member Functions
final ClassLoader	getParent ()
	Returns the specified ClassLoader's parent.
URL	getResource (String resName)
	Answers an URL which can be used to access the resource described by resName, using the class loader's resource lookup algorithm.
Enumeration< URL >	getResources (String resName) throws IOException
	Answers an Enumeration of URL which can be used to access the resources described by resName, using the class loader's resource lookup algorithm.
InputStream	getResourceAsStream (String resName)
	Answers a stream on a resource found by looking up resName using the class loader's resource lookup algorithm.
Class<?>	loadClass (String className) throws ClassNotFoundException
	Invoked by the Virtual Machine when resolving class references.
void	setClassAssertionStatus (String cname, boolean enable)
	Sets the assertion status of a class.
void	setPackageAssertionStatus (String pname, boolean enable)
	Sets the assertion status of a package.
void	setDefaultAssertionStatus (boolean enable)
	Sets the default assertion status of a classloader.
void	clearAssertionStatus ()
	Clears the default, package and class assertion status of a classloader.
Static Public Member Functions
static ClassLoader	getSystemClassLoader ()
	Returns the system class loader.
static URL	getSystemResource (String resName)
	Answers an URL specifying a resource which can be found by looking up resName using the system class loader's resource lookup algorithm.
static Enumeration< URL >	getSystemResources (String resName) throws IOException
	Answers an Enumeration of URLs containing all resources which can be found by looking up resName using the system class loader's resource lookup algorithm.
static InputStream	getSystemResourceAsStream (String resName)
	Answers a stream on a resource found by looking up resName using the system class loader's resource lookup algorithm.
Protected Member Functions
	ClassLoader ()
	Constructs a new instance of this class with the system class loader as its parent.
	ClassLoader (ClassLoader parentLoader)
	Constructs a new instance of this class with the given class loader as its parent.
final Class<?>	defineClass (byte[] classRep, int offset, int length) throws ClassFormatError
	Constructs a new class from an array of bytes containing a class definition in class file format.
final Class<?>	defineClass (String className, byte[] classRep, int offset, int length) throws ClassFormatError
	Constructs a new class from an array of bytes containing a class definition in class file format.
final Class<?>	defineClass (String className, byte[] classRep, int offset, int length, ProtectionDomain protectionDomain) throws java.lang.ClassFormatError
	Constructs a new class from an array of bytes containing a class definition in class file format and assigns the new class to the specified protection domain.
final Class<?>	defineClass (String name, ByteBuffer b, ProtectionDomain protectionDomain) throws ClassFormatError
Class<?>	findClass (String className) throws ClassNotFoundException
	Overridden by subclasses, by default throws ClassNotFoundException.
final Class<?>	findLoadedClass (String className)
	Attempts to find and return a class which has already been loaded by the virtual machine.
final Class<?>	findSystemClass (String className) throws ClassNotFoundException
	Attempts to load a class using the system class loader.
Class<?>	loadClass (String className, boolean resolveClass) throws ClassNotFoundException
	Loads the class with the specified name, optionally linking the class after load.
final void	resolveClass (Class<?> clazz)
	Forces a class to be linked (initialized).
URL	findResource (String resName)
	Answers an URL which can be used to access the resource described by resName, using the class loader's resource lookup algorithm.
Enumeration< URL >	findResources (String resName) throws IOException
	Answers an Enumeration of URL which can be used to access the resources described by resName, using the class loader's resource lookup algorithm.
String	findLibrary (String libName)
	Answers the absolute path of the file containing the library associated with the given name, or null.
Package	getPackage (String name)
	Attempt to locate the requested package.
Package[]	getPackages ()
	Return all the packages known to this class loader.
Package	definePackage (String name, String specTitle, String specVersion, String specVendor, String implTitle, String implVersion, String implVendor, URL sealBase) throws IllegalArgumentException
	Define a new Package using the specified information.
final void	setSigners (Class<?> c, Object[] signers)
	Sets the signers of a class.
Package Functions
final boolean	isSystemClassLoader ()
	This method must be provided by the VM vendor, as it is used by other provided class implementations in this package.
final boolean	isAncestorOf (ClassLoader child)
final Object[]	getSigners (Class<?> c)
	Gets the signers of a class.
boolean	getClassAssertionStatus (String cname)
	Answers the assertion status of the named class Returns the assertion status of the class or nested class if it has been set.
boolean	getPackageAssertionStatus (String pname)
	Answers the assertion status of the named package Returns the assertion status of the named package or superpackage if that has been set.
boolean	getDefaultAssertionStatus ()
	Answers the default assertion status.
Static Package Functions
static final void	initializeClassLoaders ()
static final ClassLoader	getStackClassLoader (int depth)
static ClassLoader	callerClassLoader ()
	This method must be included, as it is used by System.load(), System.loadLibrary().
static void	loadLibraryWithClassLoader (String libName, ClassLoader loader)
	This method must be provided by the VM vendor, as it is called by java.lang.System.loadLibrary().
static void	loadLibraryWithPath (String libName, ClassLoader loader, String libraryPath)
	This method must be provided by the VM vendor, as it is called by java.lang.System.load().
Static Package Attributes
static ClassLoader	systemClassLoader
	The 'System' ClassLoader; also known as the bootstrap ClassLoader.

Constructor & Destructor Documentation

java.lang.ClassLoader.ClassLoader ( ) [protected]

Constructs a new instance of this class with the system class loader as its parent.

Exceptions:

SecurityException

if a security manager exists and it does not allow the creation of new ClassLoaders.

java.lang.ClassLoader.ClassLoader ( ClassLoader parentLoader ) [protected]

Constructs a new instance of this class with the given class loader as its parent.

Parameters:

parentLoader

The ClassLoader to use as the new class loaders parent.

Exceptions:

	SecurityException	if a security manager exists and it does not allow the creation of new ClassLoaders.
	NullPointerException	if the parent is null.

Member Function Documentation

static final void java.lang.ClassLoader.initializeClassLoaders ( ) [static, package]

TODO Document this method.

static ClassLoader java.lang.ClassLoader.getSystemClassLoader ( ) [static]

Returns the system class loader.

This is the parent for new ClassLoader instances, and is typically the class loader used to start the application. If a security manager is present, and the caller's class loader is not null and the caller's class loader is not the same as or an ancestor of the system class loader, then this method calls the security manager's checkPermission method with a RuntimePermission("getClassLoader") permission to ensure it's ok to access the system class loader. If not, a SecurityException will be thrown.

Returns:: The system classLoader.

Exceptions:

SecurityException

if a security manager exists and it does not allow access to the system class loader.

static URL java.lang.ClassLoader.getSystemResource ( String resName ) [static]

Answers an URL specifying a resource which can be found by looking up resName using the system class loader's resource lookup algorithm.

Returns:: A URL specifying a system resource or null.

Parameters:

resName

The name of the resource to find.

See also:: Class.getResource

static Enumeration<URL> java.lang.ClassLoader.getSystemResources ( String resName ) throws IOException [static]

Answers an Enumeration of URLs containing all resources which can be found by looking up resName using the system class loader's resource lookup algorithm.

Returns:: An Enumeration of URLs containing the system resources

Parameters:

resName

String the name of the resource to find.

Exceptions:

IOException

if an IO exception occurs

static InputStream java.lang.ClassLoader.getSystemResourceAsStream ( String resName ) [static]

Answers a stream on a resource found by looking up resName using the system class loader's resource lookup algorithm.

Basically, the contents of the java.class.path are searched in order, looking for a path which matches the specified resource.

Returns:: A stream on the resource or null.

Parameters:

resName

The name of the resource to find.

See also:: Class.getResourceAsStream

final Class<?> java.lang.ClassLoader.defineClass	(	byte[]	classRep,
		int	offset,
		int	length
	)			throws ClassFormatError `[protected]`

Constructs a new class from an array of bytes containing a class definition in class file format.

Parameters:

	classRep	A memory image of a class file.
	offset	The offset into the classRep.
	length	The length of the class file.

Deprecated:: Use defineClass(String, byte[], int, int)

final Class<?> java.lang.ClassLoader.defineClass	(	String	className,
		byte[]	classRep,
		int	offset,
		int	length
	)			throws ClassFormatError `[protected]`

Constructs a new class from an array of bytes containing a class definition in class file format.

Parameters:

	className	The name of the new class
	classRep	A memory image of a class file
	offset	The offset into the classRep
	length	The length of the class file

final Class<?> java.lang.ClassLoader.defineClass	(	String	className,
		byte[]	classRep,
		int	offset,
		int	length,
		ProtectionDomain	protectionDomain
	)			throws java.lang.ClassFormatError `[protected]`

Constructs a new class from an array of bytes containing a class definition in class file format and assigns the new class to the specified protection domain.

Parameters:

	className	The name of the new class.
	classRep	A memory image of a class file.
	offset	The offset into the classRep.
	length	The length of the class file.
	protectionDomain	The protection domain this class should belongs to.

final Class<?> java.lang.ClassLoader.defineClass	(	String	name,
		ByteBuffer	b,
		ProtectionDomain	protectionDomain
	)			throws ClassFormatError `[protected]`

Defines a new class for the name, bytecodes in the byte buffer and the protection domain.

Parameters:

	name	The name of the class to define.
	b	The byte buffer containing the bytecodes of the new class.
	protectionDomain	The protection domain this class belongs to.

Returns:: The defined class.

Exceptions:

ClassFormatError

if an invalid class file is defined.

Since:: 1.5

Class<?> java.lang.ClassLoader.findClass ( String className ) throws ClassNotFoundException [protected]

Overridden by subclasses, by default throws ClassNotFoundException.

This method is called by loadClass() after the parent ClassLoader has failed to find a loaded class of the same name.

Returns:: The class or null.

Parameters:

className

The name of the class to search for.

Exceptions:

ClassNotFoundException

if the class cannot be found.

final Class<?> java.lang.ClassLoader.findLoadedClass ( String className ) [protected]

Attempts to find and return a class which has already been loaded by the virtual machine.

Note that the class may not have been linked and the caller should call resolveClass() on the result if necessary.

Returns:: The class or null.

Parameters:

className

The name of the class to search for.

final Class<?> java.lang.ClassLoader.findSystemClass ( String className ) throws ClassNotFoundException [protected]

Attempts to load a class using the system class loader.

Note that the class has already been been linked.

Returns:: The class which was loaded.

Parameters:

className

The name of the class to search for.

Exceptions:

ClassNotFoundException

if the class cannot be found.

final ClassLoader java.lang.ClassLoader.getParent ( )

Returns the specified ClassLoader's parent.

Returns:: The class or null.

Exceptions:

SecurityException

if a security manager exists and it does not allow the parent loader to be retrieved.

URL java.lang.ClassLoader.getResource ( String resName )

Answers an URL which can be used to access the resource described by resName, using the class loader's resource lookup algorithm.

The default behavior is just to return null.

Returns:: The location of the resource.

Parameters:

resName

String the name of the resource to find.

See also:: Class.getResource(String)

Enumeration<URL> java.lang.ClassLoader.getResources ( String resName ) throws IOException

Answers an Enumeration of URL which can be used to access the resources described by resName, using the class loader's resource lookup algorithm.

The default behavior is just to return an empty Enumeration.

Returns:: The location of the resources.

Parameters:

resName

String the name of the resource to find.

Exceptions:

IOException

if an IO exception occurs

InputStream java.lang.ClassLoader.getResourceAsStream ( String resName )

Answers a stream on a resource found by looking up resName using the class loader's resource lookup algorithm.

The default behavior is just to return null.

Returns:: A stream on the resource or null.

Parameters:

resName

String the name of the resource to find.

See also:: Class.getResourceAsStream

Class<?> java.lang.ClassLoader.loadClass ( String className ) throws ClassNotFoundException

Invoked by the Virtual Machine when resolving class references.

Equivalent to loadClass(className, false);

Returns:: The Class object.

Parameters:

className

The name of the class to search for.

Exceptions:

ClassNotFoundException

if the class could not be found.

Class<?> java.lang.ClassLoader.loadClass	(	String	className,
		boolean	resolveClass
	)			throws ClassNotFoundException `[protected]`

Loads the class with the specified name, optionally linking the class after load.

Steps are: 1) Call findLoadedClass(className) to determine if class is loaded 2) Call loadClass(className, resolveClass) on the parent loader. 3) Call findClass(className) to find the class

Returns:: The Class object.

Parameters:

	className	The name of the class to search for.
	resolveClass	Indicates if class should be resolved after loading.

Exceptions:

ClassNotFoundException

if the class could not be found.

final void java.lang.ClassLoader.resolveClass ( Class<?> clazz ) [protected]

Forces a class to be linked (initialized).

If the class has already been linked this operation has no effect.

Parameters:

clazz

The Class to link.

Exceptions:

NullPointerException

if clazz is null.

final boolean java.lang.ClassLoader.isSystemClassLoader ( ) [package]

This method must be provided by the VM vendor, as it is used by other provided class implementations in this package.

A sample implementation of this method is provided by the reference implementation. This method is used by SecurityManager.classLoaderDepth(), currentClassLoader() and currentLoadedClass(). Answers true if the receiver is a system class loader.

Note that this method has package visibility only. It is defined here to avoid the security manager check in getSystemClassLoader, which would be required to implement this method anywhere else.

Returns:: true if the receiver is a system class loader

See also:: Class.getClassLoaderImpl()

final boolean java.lang.ClassLoader.isAncestorOf ( ClassLoader child ) [package]

Answers true if the receiver is ancestor of another class loader.

Note that this method has package visibility only. It is defined here to avoid the security manager check in getParent, which would be required to implement this method anywhere else.

Parameters:

child

A child candidate

Returns:: true if the receiver is ancestor of the parameter

URL java.lang.ClassLoader.findResource ( String resName ) [protected]

Answers an URL which can be used to access the resource described by resName, using the class loader's resource lookup algorithm.

The default behavior is just to return null. This should be implemented by a ClassLoader.

Returns:: The location of the resource.

Parameters:

resName

The name of the resource to find.

Enumeration<URL> java.lang.ClassLoader.findResources ( String resName ) throws IOException [protected]

Answers an Enumeration of URL which can be used to access the resources described by resName, using the class loader's resource lookup algorithm.

The default behavior is just to return an empty Enumeration.

Parameters:

resName

The name of the resource to find.

Returns:: The locations of the resources.

Exceptions:

IOException

when an error occurs

String java.lang.ClassLoader.findLibrary ( String libName ) [protected]

Answers the absolute path of the file containing the library associated with the given name, or null.

If null is answered, the system searches the directories specified by the system property "java.library.path".

Returns:: The library file name or null.

Parameters:

libName

The name of the library to find.

Package java.lang.ClassLoader.getPackage ( String name ) [protected]

Attempt to locate the requested package.

If no package information can be located, null is returned.

Parameters:

name

The name of the package to find

Returns:: The package requested, or null

Package [] java.lang.ClassLoader.getPackages ( ) [protected]

Return all the packages known to this class loader.

Returns:: All the packages known to this classloader

Package java.lang.ClassLoader.definePackage	(	String	name,
		String	specTitle,
		String	specVersion,
		String	specVendor,
		String	implTitle,
		String	implVersion,
		String	implVendor,
		URL	sealBase
	)			throws IllegalArgumentException `[protected]`

Define a new Package using the specified information.

Parameters:

	name	The name of the package
	specTitle	The title of the specification for the Package
	specVersion	The version of the specification for the Package
	specVendor	The vendor of the specification for the Package
	implTitle	The implementation title of the Package
	implVersion	The implementation version of the Package
	implVendor	The specification vendor of the Package
	sealBase	If sealBase is null, the package is left unsealed. Otherwise, the the package is sealed using this URL.

Returns:: The Package created

Exceptions:

IllegalArgumentException

if the Package already exists

final Object [] java.lang.ClassLoader.getSigners ( Class<?> c ) [package]

Gets the signers of a class.

Parameters:

The Class object

Returns:: signers The signers for the class

final void java.lang.ClassLoader.setSigners	(	Class<?>	c,
		Object[]	signers
	)			`[protected]`

Sets the signers of a class.

Parameters:

	c	The Class object
	signers	The signers for the class

static final ClassLoader java.lang.ClassLoader.getStackClassLoader ( int depth ) [static, package]

This must be provided by the VM vendor. It is used by SecurityManager.checkMemberAccess() with depth = 3. Note that checkMemberAccess() assumes the following stack when called:

    		< user code &gt; <- want this class
    		Class.getDeclared*();
    		Class.checkMemberAccess();
    		SecurityManager.checkMemberAccess(); <- current frame

Returns the ClassLoader of the method (including natives) at the specified depth on the stack of the calling thread. Frames representing the VM implementation of java.lang.reflect are not included in the list. Notes:

This method operates on the defining classes of methods on stack. NOT the classes of receivers.
The item at depth zero is the caller of this method

Parameters:

depth

the stack depth of the requested ClassLoader

Returns:: the ClassLoader at the specified depth

static ClassLoader java.lang.ClassLoader.callerClassLoader ( ) [static, package]

This method must be included, as it is used by System.load(), System.loadLibrary().

The reference implementation of this method uses the getStackClassLoader() method. Returns the ClassLoader of the method that called the caller. i.e. A.x() calls B.y() calls callerClassLoader(), A's ClassLoader will be returned. Returns null for the bootstrap ClassLoader.

Returns:: a ClassLoader or null for the bootstrap ClassLoader

static void java.lang.ClassLoader.loadLibraryWithClassLoader	(	String	libName,
		ClassLoader	loader
	)			`[static, package]`

This method must be provided by the VM vendor, as it is called by java.lang.System.loadLibrary().

System.loadLibrary() cannot call Runtime.loadLibrary() because this method loads the library using the ClassLoader of the calling method. Loads and links the library specified by the argument.

Parameters:

	libName	the name of the library to load
	loader	the classloader in which to load the library

Exceptions:

	UnsatisfiedLinkError	if the library could not be loaded
	SecurityException	if the library was not allowed to be loaded

static void java.lang.ClassLoader.loadLibraryWithPath	(	String	libName,
		ClassLoader	loader,
		String	libraryPath
	)			`[static, package]`

This method must be provided by the VM vendor, as it is called by java.lang.System.load().

System.load() cannot call Runtime.load() because the library is loaded using the ClassLoader of the calling method. Loads and links the library specified by the argument. No security check is done.

Parameters:

	libName	the name of the library to load
	loader	the classloader in which to load the library
	libraryPath	the library path to search, or null

Exceptions:

UnsatisfiedLinkError

if the library could not be loaded

void java.lang.ClassLoader.setClassAssertionStatus	(	String	cname,
		boolean	enable
	)

Sets the assertion status of a class.

Parameters:

	cname	Class name
	enable	Enable or disable assertion

void java.lang.ClassLoader.setPackageAssertionStatus	(	String	pname,
		boolean	enable
	)

Sets the assertion status of a package.

Parameters:

	pname	Package name
	enable	Enable or disable assertion

void java.lang.ClassLoader.setDefaultAssertionStatus ( boolean enable )

Sets the default assertion status of a classloader.

Parameters:

enable

Enable or disable assertion

void java.lang.ClassLoader.clearAssertionStatus ( )

Clears the default, package and class assertion status of a classloader.

boolean java.lang.ClassLoader.getClassAssertionStatus ( String cname ) [package]

Answers the assertion status of the named class Returns the assertion status of the class or nested class if it has been set.

Otherwise returns the assertion status of its package or superpackage if that has been set. Otherwise returns the default assertion status. Returns 1 for enabled and 0 for disabled.

Returns:: the assertion status.

Parameters:

cname

the name of class.

boolean java.lang.ClassLoader.getPackageAssertionStatus ( String pname ) [package]

Answers the assertion status of the named package Returns the assertion status of the named package or superpackage if that has been set.

Otherwise returns the default assertion status. Returns 1 for enabled and 0 for disabled.

Returns:: the assertion status.

Parameters:

pname

the name of package.

boolean java.lang.ClassLoader.getDefaultAssertionStatus ( ) [package]

Answers the default assertion status.

Returns:: boolean the default assertion status.

Member Data Documentation

ClassLoader java.lang.ClassLoader.systemClassLoader [static, package]

The 'System' ClassLoader; also known as the bootstrap ClassLoader.

See also:: getSystemClassLoader()

The documentation for this class was generated from the following file:

java/lang/ClassLoader.java

Genereated on Tue Dec 9 14:09:47 2008 by Doxygen.

java.lang.ClassLoader Class Reference

Detailed Description

VM Implementors Note

Public Member Functions

Static Public Member Functions

Protected Member Functions

Package Functions

Static Package Functions

Static Package Attributes

Constructor & Destructor Documentation

Member Function Documentation

Member Data Documentation