org.jboss.modules

Class ConcurrentClassLoader

java.lang.Object

java.lang.ClassLoader

org.jboss.modules.ConcurrentClassLoader

Direct Known Subclasses:

ModuleClassLoader

public abstract class ConcurrentClassLoader
extends ClassLoader

A classloader which can delegate to multiple other classloaders without risk of deadlock. A concurrent class loader should only ever be delegated to by another concurrent class loader; however a concurrent class loader may delegate to a standard hierarchical class loader. In other words, holding a lock on another class loader while invoking a method on this class loader may cause an unexpected deadlock.

Author:

David M. Lloyd

Field Summary

Fields

Modifier and Type	Field and Description
protected static Enumeration<URL>	EMPTY_ENUMERATION An empty enumeration, for subclasses to use if desired.

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	ConcurrentClassLoader() Construct a new instance, using our class loader as the parent.
protected	ConcurrentClassLoader(ConcurrentClassLoader parent) Construct a new instance with the given parent class loader, which must be a concurrent class loader, or null to create a root concurrent class loader.

Method Summary

Methods

Modifier and Type	Method and Description
protected Class<?>	defineOrLoadClass(String className, byte[] bytes, int off, int len) Atomically define or load the named class.
protected Class<?>	defineOrLoadClass(String className, byte[] bytes, int off, int len, ProtectionDomain protectionDomain) Atomically define or load the named class.
protected Package	definePackage(String name, String specTitle, String specVersion, String specVendor, String implTitle, String implVersion, String implVendor, URL sealBase) Defines a package by name in this ConcurrentClassLoader.
protected Class<?>	findClass(String className) Implementation of ClassLoader.findClass(String).
protected Class<?>	findClass(String className, boolean exportsOnly, boolean resolve) Find a class, possibly delegating to other loader(s).
protected Package	findLoadedPackage(String name) Load a package from this class loader only.
protected URL	findResource(String name) Never used.
protected URL	findResource(String name, boolean exportsOnly) Find the resource with the given name and exported status.
protected InputStream	findResourceAsStream(String name, boolean exportsOnly) Finds the resource with the given name and exported status, returning the resource content as a stream.
protected Enumeration<URL>	findResources(String name) Never used.
protected Enumeration<URL>	findResources(String name, boolean exportsOnly) Finds the resources with the given name and exported status.
protected Package	getPackage(String name) Load a package which is visible to this class loader.
protected Package	getPackageByName(String name) Perform the actual work to load a package which is visible to this class loader.
protected Package[]	getPackages() Get all defined packages which are visible to this class loader.
URL	getResource(String name) Finds the resource with the given name.
InputStream	getResourceAsStream(String name) Returns an input stream for reading the specified resource.
Enumeration<URL>	getResources(String name) Finds all available resources with the given name.
Class<?>	loadClass(String className) Loads the class with the specified binary name.
Class<?>	loadClass(String className, boolean resolve) Loads the class with the specified binary name.
Class<?>	loadExportedClass(String className) Same as loadClass(String), except only exported classes will be considered.
Class<?>	loadExportedClass(String className, boolean resolve) Same as loadClass(String,boolean), except only exported classes will be considered.

Methods inherited from class java.lang.ClassLoader

clearAssertionStatus, defineClass, defineClass, defineClass, defineClass, findLibrary, findLoadedClass, findSystemClass, getClassLoadingLock, getParent, getSystemClassLoader, getSystemResource, getSystemResourceAsStream, getSystemResources, registerAsParallelCapable, resolveClass, setClassAssertionStatus, setDefaultAssertionStatus, setPackageAssertionStatus, setSigners

Methods inherited from class java.lang.Object

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

Field Detail

EMPTY_ENUMERATION

protected static final Enumeration<URL> EMPTY_ENUMERATION

An empty enumeration, for subclasses to use if desired.

Constructor Detail

ConcurrentClassLoader

protected ConcurrentClassLoader(ConcurrentClassLoader parent)

Construct a new instance with the given parent class loader, which must be a concurrent class loader, or null to create a root concurrent class loader.

Parameters:

parent - the parent class loader

ConcurrentClassLoader

protected ConcurrentClassLoader()

Construct a new instance, using our class loader as the parent.

Method Detail

loadClass

public final Class<?> loadClass(String className)
                         throws ClassNotFoundException

Loads the class with the specified binary name. Equivalent to calling loadClass(className, false).

Overrides:

loadClass in class ClassLoader

Parameters:

className - The binary name of the class

Returns:

the resulting Class instance

Throws:

ClassNotFoundException - if the class was not found

loadClass

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

Loads the class with the specified binary name.

Overrides:

loadClass in class ClassLoader

Parameters:

className - The binary name of the class

resolve - true if the class should be linked after loading

Returns:

the resulting Class instance

Throws:

ClassNotFoundException

loadExportedClass

public final Class<?> loadExportedClass(String className)
                                 throws ClassNotFoundException

Same as loadClass(String), except only exported classes will be considered.

Parameters:

className - the class name

Returns:

the class

Throws:

ClassNotFoundException - if the class isn't found

loadExportedClass

public final Class<?> loadExportedClass(String className,
                         boolean resolve)
                                 throws ClassNotFoundException

Same as loadClass(String,boolean), except only exported classes will be considered.

Parameters:

className - the class name

resolve - true if the class should be linked after loading

Returns:

the class

Throws:

ClassNotFoundException - if the class isn't found

findClass

protected Class<?> findClass(String className,
                 boolean exportsOnly,
                 boolean resolve)
                      throws ClassNotFoundException

Find a class, possibly delegating to other loader(s). This method should never synchronize across a delegation method call of any sort. The default implementation always throws ClassNotFoundException.

If a class is to be defined by this method, it should be done via one of the atomic defineOrLoadClass methods rather than defineClass() in order to avoid spurious exceptions.

Parameters:

className - the class name

exportsOnly - true if only exported classes should be considered

resolve - true if the class should be linked after loading

Returns:

the class

Throws:

ClassNotFoundException - if the class is not found

defineOrLoadClass

protected final Class<?> defineOrLoadClass(String className,
                         byte[] bytes,
                         int off,
                         int len)

Atomically define or load the named class. If the class is already defined, the existing class is returned.

Parameters:

className - the class name to define or load

bytes - the bytes to use to define the class

off - the offset into the byte array at which the class bytes begin

len - the number of bytes in the class

Returns:

the class

defineOrLoadClass

protected final Class<?> defineOrLoadClass(String className,
                         byte[] bytes,
                         int off,
                         int len,
                         ProtectionDomain protectionDomain)

Atomically define or load the named class. If the class is already defined, the existing class is returned.

Parameters:

className - the class name to define or load

bytes - the bytes to use to define the class

off - the offset into the byte array at which the class bytes begin

len - the number of bytes in the class

protectionDomain - the protection domain for the defined class

Returns:

the class

findClass

protected final Class<?> findClass(String className)
                            throws ClassNotFoundException

Implementation of ClassLoader.findClass(String).

Overrides:

findClass in class ClassLoader

Parameters:

className - the class name

Returns:

the result of findClass(className, false, false)

Throws:

ClassNotFoundException

getResource

public final URL getResource(String name)

Finds the resource with the given name. The name of a resource is a '/'-separated path name that identifies the resource. If the resource name starts with "java/" then the parent class loader is used. Otherwise, this method delegates to findResource(String, boolean).

Overrides:

getResource in class ClassLoader

Parameters:

name - the name of the resource

Returns:

the resource URL, or null if no such resource exists or the invoker does not have adequate permission to access it

getResources

public final Enumeration<URL> getResources(String name)
                                    throws IOException

Finds all available resources with the given name.

Overrides:

getResources in class ClassLoader

Parameters:

name - the resource name

Returns:

an enumeration over all the resource URLs; if no resources could be found, the enumeration will be empty

Throws:

IOException - if an I/O error occurs

See Also:

getResource(String)

findResource

protected URL findResource(String name,
               boolean exportsOnly)

Find the resource with the given name and exported status.

Parameters:

name - the resource name

exportsOnly - true to consider only exported resources or false to consider all resources

Returns:

the resource URL

See Also:

getResource(String)

findResource

protected final URL findResource(String name)

Never used. ClassLoader.getResource(String) and related methods can cause a loop condition when this method is implemented; use findResource(String, boolean) instead.

Overrides:

findResource in class ClassLoader

Parameters:

name - ignored

Returns:

null always

findResources

protected Enumeration<URL> findResources(String name,
                             boolean exportsOnly)
                                  throws IOException

Finds the resources with the given name and exported status.

Parameters:

name - the resource name

exportsOnly - true to consider only exported resources or false to consider all resources

Returns:

the resource enumeration

Throws:

IOException - if an I/O error occurs

See Also:

getResources(String)

findResources

protected final Enumeration<URL> findResources(String name)

Never used. ClassLoader.getResources(String) and related methods can cause a loop condition when this method is implemented; use findResources(String, boolean) instead. By default, returns an empty enumeration.

Overrides:

findResources in class ClassLoader

Parameters:

name - ignored

Returns:

an empty enumeration

findResourceAsStream

protected InputStream findResourceAsStream(String name,
                               boolean exportsOnly)

Finds the resource with the given name and exported status, returning the resource content as a stream.

Parameters:

name - the resource name

exportsOnly - true to consider only exported resources or false to consider all resources

Returns:

the resource stream, or null if the resource is not found

getResourceAsStream

public final InputStream getResourceAsStream(String name)

Returns an input stream for reading the specified resource. If the resource starts with "java/", then this method delegates to the parent class loader. Otherwise, this method delegates to findResourceAsStream(String, boolean).

Overrides:

getResourceAsStream in class ClassLoader

Parameters:

name - the resource name

Returns:

the resource stream, or null if the resource is not found

getPackage

protected final Package getPackage(String name)

Load a package which is visible to this class loader.

Overrides:

getPackage in class ClassLoader

Parameters:

name - the package name

Returns:

the package, or null if no such package is visible to this class loader

getPackageByName

protected Package getPackageByName(String name)

Perform the actual work to load a package which is visible to this class loader. By default, uses a simple parent-first delegation strategy.

Parameters:

name - the package name

Returns:

the package, or null if no such package is visible to this class loader

getPackages

protected Package[] getPackages()

Get all defined packages which are visible to this class loader.

Overrides:

getPackages in class ClassLoader

Returns:

the packages

findLoadedPackage

protected final Package findLoadedPackage(String name)

Load a package from this class loader only.

Parameters:

name - the package name

Returns:

the package or null if no such package is defined by this class loader

definePackage

protected Package definePackage(String name,
                    String specTitle,
                    String specVersion,
                    String specVendor,
                    String implTitle,
                    String implVersion,
                    String implVendor,
                    URL sealBase)
                         throws IllegalArgumentException

Defines a package by name in this ConcurrentClassLoader. If the package was already defined, the existing package is returned instead.

Overrides:

definePackage in class ClassLoader

Parameters:

name - the package name

specTitle - the specification title

specVersion - the specification version

specVendor - the specification vendor

implTitle - the implementation title

implVersion - the implementation version

implVendor - the implementation vendor

sealBase - if not null, then this package is sealed with respect to the given code source URL

Returns:

the newly defined package, or the existing one if one was already defined

Throws:

IllegalArgumentException