java.lang.ClassLoader Maven / Gradle / Ivy
/*
This is not an official specification document, and usage is restricted.
NOTICE
(c) 2005-2007 Sun Microsystems, Inc. All Rights Reserved.
Neither this file nor any files generated from it describe a complete
specification, and they may only be used as described below. For
example, no permission is given for you to incorporate this file, in
whole or in part, in an implementation of a Java specification.
Sun Microsystems Inc. owns the copyright in this file and it is provided
to you for informative, as opposed to normative, use. The file and any
files generated from it may be used to generate other informative
documentation, such as a unified set of documents of API signatures for
a platform that includes technologies expressed as Java APIs. The file
may also be used to produce "compilation stubs," which allow
applications to be compiled and validated for such platforms.
Any work generated from this file, such as unified javadocs or compiled
stub files, must be accompanied by this notice in its entirety.
This work corresponds to the API signatures of JSR 219: Foundation
Profile 1.1. In the event of a discrepency between this work and the
JSR 219 specification, which is available at
http://www.jcp.org/en/jsr/detail?id=219, the latter takes precedence.
*/
package java.lang;
import java.io.InputStream;
import java.io.IOException;
import java.io.File;
import java.lang.reflect.Constructor;
import java.lang.reflect.InvocationTargetException;
import java.net.MalformedURLException;
import java.net.URL;
import java.security.AccessController;
import java.security.AccessControlContext;
import java.security.CodeSource;
import java.security.Policy;
import java.security.PrivilegedAction;
import java.security.PrivilegedActionException;
import java.security.PrivilegedExceptionAction;
import java.security.ProtectionDomain;
import java.util.Enumeration;
import java.util.Hashtable;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Set;
import java.util.Stack;
import java.util.Map;
import java.util.Vector;
/**
* A class loader is an object that is responsible for loading classes. The
* class ClassLoader is an abstract class. Given the name of a
* class, a class loader should attempt to locate or generate data that
* constitutes a definition for the class. A typical strategy is to transform
* the name into a file name and then read a "class file" of that name
* from a file system.
*
*
Every {@link Class Class} object contains a {@link
* Class#getClassLoader() reference} to the ClassLoader that defined
* it.
*
*
Class objects for array classes are not created by class
* loaders, but are created automatically as required by the Java runtime.
* The class loader for an array class, as returned by {@link
* Class#getClassLoader()} is the same as the class loader for its element
* type; if the element type is a primitive type, then the array class has no
* class loader.
*
*
Applications implement subclasses of ClassLoader in order to
* extend the manner in which the Java virtual machine dynamically loads
* classes.
*
*
Class loaders may typically be used by security managers to indicate
* security domains.
*
*
The ClassLoader class uses a delegation model to search for
* classes and resources. Each instance of ClassLoader has an
* associated parent class loader. When requested to find a class or
* resource, a ClassLoader instance will delegate the search for the
* class or resource to its parent class loader before attempting to find the
* class or resource itself. The virtual machine's built-in class loader,
* called the "bootstrap class loader", does not itself have a parent but may
* serve as the parent of a ClassLoader instance.
*
*
Normally, the Java virtual machine loads classes from the local file
* system in a platform-dependent manner. For example, on UNIX systems, the
* virtual machine loads classes from the directory defined by the
* CLASSPATH environment variable.
*
*
However, some classes may not originate from a file; they may originate
* from other sources, such as the network, or they could be constructed by an
* application. The method {@link #defineClass(String, byte[], int, int)
* defineClass} converts an array of bytes into an instance of class
* Class. Instances of this newly defined class can be created using
* {@link Class#newInstance Class.newInstance}.
*
*
The methods and constructors of objects created by a class loader may
* reference other classes. To determine the class(es) referred to, the Java
* virtual machine invokes the {@link #loadClass loadClass} method of
* the class loader that originally created the class.
*
*
For example, an application could create a network class loader to
* download class files from a server. Sample code might look like:
*
*
* ClassLoader loader = new NetworkClassLoader(host, port);
* Object main = loader.loadClass("Main", true).newInstance();
* . . .
*
*
* The network class loader subclass must define the methods {@link
* #findClass findClass} and loadClassData to load a class
* from the network. Once it has downloaded the bytes that make up the class,
* it should use the method {@link #defineClass defineClass} to
* create a class instance. A sample implementation is:
*
*
* class NetworkClassLoader extends ClassLoader {
* String host;
* int port;
*
* public Class findClass(String name) {
* byte[] b = loadClassData(name);
* return defineClass(name, b, 0, b.length);
* }
*
* private byte[] loadClassData(String name) {
* // load the class data from the connection
* . . .
* }
* }
*
*
* @version 1.159, 07/27/05
* @see #resolveClass(Class)
* @since 1.0
*/
public abstract class ClassLoader
{
/**
* Creates a new class loader using the specified parent class loader for
* delegation.
*
* If there is a security manager, its {@link
* SecurityManager#checkCreateClassLoader()
* checkCreateClassLoader} method is invoked. This may result in
* a security exception.
*
* @param parent
* The parent class loader
*
* @throws SecurityException
* If a security manager exists and its
* checkCreateClassLoader method doesn't allow creation
* of a new class loader.
*
* @since 1.2
*/
protected ClassLoader(java.lang.ClassLoader parent) { }
/**
* Creates a new class loader using the ClassLoader returned by
* the method {@link #getSystemClassLoader()
* getSystemClassLoader()} as the parent class loader.
*
* If there is a security manager, its {@link
* SecurityManager#checkCreateClassLoader()
* checkCreateClassLoader} method is invoked. This may result in
* a security exception.
*
* @throws SecurityException
* If a security manager exists and its
* checkCreateClassLoader method doesn't allow creation
* of a new class loader.
*/
protected ClassLoader() { }
/**
* Loads the class with the specified name. This method searches for
* classes in the same manner as the {@link #loadClass(String, boolean)}
* method. It is invoked by the Java virtual machine to resolve class
* references. Invoking this method is equivalent to invoking {@link
* #loadClass(String, boolean) loadClass(name, false)}.
*
* @param name
* The name of the class
*
* @return The resulting Class object
*
* @throws ClassNotFoundException
* If the class was not found
*/
public java.lang.Class loadClass(java.lang.String name)
throws java.lang.ClassNotFoundException
{
return null;
}
/**
* Loads the class with the specified name. The default implementation
* of this method searches for classes in the following order:
*
*
*
* Invoke {@link #findLoadedClass(String)} to check if the class
* has already been loaded.
Invoke the {@link #loadClass(String) loadClass} method
* on the parent class loader. If the parent is null the class
* loader built-in to the virtual machine is used, instead.
Invoke the {@link #findClass(String)} method to find the
* class.
*
* If the class was found using the above steps, and the
* resolve flag is true, this method will then invoke the {@link
* #resolveClass(Class)} method on the resulting Class object.
*
*
Subclasses of ClassLoader are encouraged to override {@link
* #findClass(String)}, rather than this method.
*
* @param name
* The name of the class
*
* @param resolve
* If true then resolve the class
*
* @return The resulting Class object
*
* @throws ClassNotFoundException
* If the class could not be found
*/
protected synchronized java.lang.Class loadClass(java.lang.String name,
boolean resolve) throws java.lang.ClassNotFoundException
{
return null;
}
/**
* Finds the specified class. This method should be overridden by class
* loader implementations that follow the delegation model for loading
* classes, and will be invoked by the {@link #loadClass
* loadClass} method after checking the parent class loader for
* the requested class. The default implementation throws a
* ClassNotFoundException.
*
* @param name
* The name of the class
*
* @return The resulting Class object
*
* @throws ClassNotFoundException
* If the class could not be found
*
* @since 1.2
*/
protected java.lang.Class findClass(java.lang.String name)
throws java.lang.ClassNotFoundException
{
return null;
}
/**
* Converts an array of bytes into an instance of class Class.
* Before the Class can be used it must be resolved.
*
* This method assigns a default {@link java.security.ProtectionDomain
* ProtectionDomain} to the newly defined class. The
* ProtectionDomain is effectively granted the same set of
* permissions returned when {@link
* java.security.Policy#getPermissions(java.security.CodeSource)
* Policy.getPolicy().getPermissions(new CodeSource(null, null))}
* is invoked. The default domain is created on the first invocation of
* {@link #defineClass(String, byte[], int, int) defineClass},
* and re-used on subsequent invocations.
*
*
To assign a specific ProtectionDomain to the class, use
* the {@link #defineClass(String, byte[], int, int,
* java.security.ProtectionDomain) defineClass} method that takes a
* ProtectionDomain as one of its arguments.
*
* @param name
* The expected name of the class, or null
* if not known, using '.' and not '/' as the
* separator and without a trailing .class suffix.
*
* @param b
* The bytes that make up the class data. The bytes in positions
* off through off+len-1 should have the format
* of a valid class file as defined by the Java Virtual
* Machine Specification.
*
* @param off
* The start offset in b of the class data
*
* @param len
* The length of the class data
*
* @return The Class object that was created from the specified
* class data.
*
* @throws ClassFormatError
* If the data did not contain a valid class
*
* @throws IndexOutOfBoundsException
* If either off or len is negative, or if
* off+len is greater than b.length.
*
* @throws SecurityException
* If an attempt is made to add this class to a package that
* contains classes that were signed by a different set of
* certificates than this class (which is unsigned), or if the
* class name begins with "java.".
*
* @see #loadClass(String, boolean)
* @see #resolveClass(Class)
* @see java.security.CodeSource
* @see java.security.SecureClassLoader
*
* @since 1.1
*/
protected final java.lang.Class defineClass(java.lang.String name, byte[] b,
int off, int len) throws java.lang.ClassFormatError
{
return null;
}
/**
* Converts an array of bytes into an instance of class Class,
* with an optional ProtectionDomain. If the domain is
* null, then a default domain will be assigned to the class as
* specified in the documentation for {@link #defineClass(String, byte[],
* int, int)}. Before the class can be used it must be resolved.
*
* The first class defined in a package determines the exact set of
* certificates that all subsequent classes defined in that package must
* contain. The set of certificates for a class is obtained from the
* {@link java.security.CodeSource CodeSource} within the
* ProtectionDomain of the class. Any classes added to that
* package must contain the same set of certificates or a
* SecurityException will be thrown. Note that if the
* name argument is null, this check is not performed.
* You should always pass in the name of the class you are defining as
* well as the bytes. This ensures that the class you are defining is
* indeed the class you think it is.
*
*
The specified class name cannot begin with "java.", since
* all classes in the "java.* packages can only be defined by the
* bootstrap class loader. If the name parameter is not null, it
* must be equal to the name of the class specified by the byte array
* "b", otherwise a {@link NoClassDefFoundError} will be
* thrown.
*
* @param name
* The expected name of the class, or null if not known,
* using '.' and not '/' as the separator and
* without a trailing ".class" suffix.
*
* @param b
* The bytes that make up the class data. The bytes in positions
* off through off+len-1 should have the format
* of a valid class file as defined by the Java Virtual
* Machine Specification.
*
* @param off
* The start offset in b of the class data
*
* @param len
* The length of the class data
*
* @param protectionDomain
* The ProtectionDomain of the class
*
* @return The Class object created from the data,
* and optional ProtectionDomain.
*
* @throws ClassFormatError
* If the data did not contain a valid class
*
* @throws NoClassDefFoundError
* If name is not equal to the name of the class
* specified by b
*
* @throws IndexOutOfBoundsException
* If either off or len is negative, or if
* off+len is greater than b.length.
*
* @throws SecurityException
* If an attempt is made to add this class to a package that
* contains classes that were signed by a different set of
* certificates than this class, or if the class name begins with
* "java.".
*/
protected final java.lang.Class defineClass(java.lang.String name, byte[] b,
int off, int len, ProtectionDomain protectionDomain)
throws java.lang.ClassFormatError
{
return null;
}
/**
* Links the specified class. This (misleadingly named) method may be
* used by a class loader to link a class. If the class c has
* already been linked, then this method simply returns. Otherwise, the
* class is linked as described in the "Execution" chapter of the Java Language Specification.
*
*
* @param c
* The class to link
*
* @throws NullPointerException
* If c is null.
*
* @see #defineClass(String, byte[], int, int)
*/
protected final void resolveClass(java.lang.Class c) { }
/**
* Finds a class with the specified name, loading it if necessary.
*
* This method loads the class through the system class loader (see
* {@link #getSystemClassLoader()}). The Class object returned
* might have more than one ClassLoader associated with it.
* Subclasses of ClassLoader need not usually invoke this method,
* because most class loaders need to override just {@link
* #findClass(String)}.
*
* @param name
* The name of the class that is to be found
*
* @return The Class object for the specified name
*
* @throws ClassNotFoundException
* If the class could not be found
*
* @see #ClassLoader(ClassLoader)
* @see #getParent()
*/
protected final java.lang.Class findSystemClass(java.lang.String name)
throws java.lang.ClassNotFoundException
{
return null;
}
/**
* Returns the class with the given name if this loader has been recorded
* by the Java virtual machine as an initiating loader of a class with
* that name. Otherwise null is returned.
*
* @param name
* The class name
*
* @return The Class object, or null if the class has
* not been loaded
*
* @since 1.1
*/
protected final java.lang.Class findLoadedClass(java.lang.String name) {
return null;
}
/**
* Sets the signers of a class. This should be invoked after defining a
* class.
*
* @param c
* The Class object
*
* @param signers
* The signers for the class
*
* @since 1.1
*/
protected final void setSigners(java.lang.Class c, java.lang.Object[]
signers)
{ }
/**
* Finds the resource with the given name. A resource is some data
* (images, audio, text, etc) that can be accessed by class code in a way
* that is independent of the location of the code.
*
* The name of a resource is a '/'-separated path name that
* identifies the resource.
*
*
This method will first search the parent class loader for the
* resource; if the parent is null the path of the class loader
* built-in to the virtual machine is searched. That failing, this method
* will invoke {@link #findResource(String)} to find the resource.
*
* @param name
* The resource name
*
* @return 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.
*
* @since 1.1
*/
public URL getResource(java.lang.String name) {
return null;
}
/**
* Finds all the resources with the given name. A resource is some data
* (images, audio, text, etc) that can be accessed by class code in a way
* that is independent of the location of the code.
*
* The name of a resource is a /-separated path name that
* identifies the resource.
*
*
The search order is described in the documentation for {@link
* #getResource(String)}.
*
* @param name
* The resource name
*
* @return An enumeration of {@link java.net.URL 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 #findResources(String)
*
* @since 1.2
*/
public final Enumeration getResources(java.lang.String name)
throws IOException
{
return null;
}
/**
* Finds the resource with the given name. Class loader implementations
* should override this method to specify where to find resources.
*
* @param name
* The resource name
*
* @return A URL object for reading the resource, or
* null if the resource could not be found
*
* @since 1.2
*/
protected URL findResource(java.lang.String name) {
return null;
}
/**
* Returns an enumeration of {@link java.net.URL URL} objects
* representing all the resources with the given name. Class loader
* implementations should override this method to specify where to load
* resources from.
*
* @param name
* The resource name
*
* @return An enumeration of {@link java.net.URL URL} objects for
* the resources
*
* @throws IOException
* If I/O errors occur
*
* @since 1.2
*/
protected Enumeration findResources(java.lang.String name)
throws IOException
{
return null;
}
/**
* Find a resource of the specified name from the search path used to load
* classes. This method locates the resource through the system class
* loader (see {@link #getSystemClassLoader()}).
*
* @param name
* The resource name
*
* @return A {@link java.net.URL URL} object for reading the
* resource, or null if the resource could not be found
*
* @since 1.1
*/
public static URL getSystemResource(java.lang.String name) {
return null;
}
/**
* Finds all resources of the specified name from the search path used to
* load classes. The resources thus found are returned as an
* {@link java.util.Enumeration Enumeration} of {@link
* java.net.URL URL} objects.
*
* The search order is described in the documentation for {@link
* #getSystemResource(String)}.
*
* @param name
* The resource name
*
* @return An enumeration of resource {@link java.net.URL URL}
* objects
*
* @throws IOException
* If I/O errors occur
*
* @since 1.2
*/
public static Enumeration getSystemResources(java.lang.String name)
throws IOException
{
return null;
}
/**
* Returns an input stream for reading the specified resource.
*
* The search order is described in the documentation for {@link
* #getResource(String)}.
*
* @param name
* The resource name
*
* @return An input stream for reading the resource, or null
* if the resource could not be found
*
* @since 1.1
*/
public InputStream getResourceAsStream(java.lang.String name) {
return null;
}
/**
* Open for reading, a resource of the specified name from the search path
* used to load classes. This method locates the resource through the
* system class loader (see {@link #getSystemClassLoader()}).
*
* @param name
* The resource name
*
* @return An input stream for reading the resource, or null
* if the resource could not be found
*
* @since 1.1
*/
public static InputStream getSystemResourceAsStream(java.lang.String name) {
return null;
}
/**
* Returns the parent class loader for delegation. Some implementations may
* use null to represent the bootstrap class loader. This method
* will return null in such implementations if this class loader's
* parent is the bootstrap class loader.
*
* If a security manager is present, and the invoker's class loader is
* not null and is not an ancestor of this class loader, then this
* method invokes the security manager's {@link
* SecurityManager#checkPermission(java.security.Permission)
* checkPermission} method with a {@link
* RuntimePermission#RuntimePermission(String)
* RuntimePermission("getClassLoader")} permission to verify
* access to the parent class loader is permitted. If not, a
* SecurityException will be thrown.
*
* @return The parent ClassLoader
*
* @throws SecurityException
* If a security manager exists and its checkPermission
* method doesn't allow access to this class loader's parent class
* loader.
*
* @since 1.2
*/
public final java.lang.ClassLoader getParent() {
return null;
}
/**
* Returns the system class loader for delegation. This is the default
* delegation parent for new ClassLoader instances, and is
* typically the class loader used to start the application.
*
* This method is first invoked early in the runtime's startup
* sequence, at which point it creates the system class loader and sets it
* as the context class loader of the invoking Thread.
*
*
The default system class loader is an implementation-dependent
* instance of this class.
*
*
If the system property "java.system.class.loader" is defined
* when this method is first invoked then the value of that property is
* taken to be the name of a class that will be returned as the system
* class loader. The class is loaded using the default system class loader
* and must define a public constructor that takes a single parameter of
* type ClassLoader which is used as the delegation parent. An
* instance is then created using this constructor with the default system
* class loader as the parameter. The resulting class loader is defined
* to be the system class loader.
*
*
If a security manager is present, and the invoker's class loader is
* not null and the invoker's class loader is not the same as or
* an ancestor of the system class loader, then this method invokes the
* security manager's {@link
* SecurityManager#checkPermission(java.security.Permission)
* checkPermission} method with a {@link
* RuntimePermission#RuntimePermission(String)
* RuntimePermission("getClassLoader")} permission to verify
* access to the system class loader. If not, a
* SecurityException will be thrown.
*
* @return The system ClassLoader for delegation, or
* null if none
*
* @throws SecurityException
* If a security manager exists and its checkPermission
* method doesn't allow access to the system class loader.
*
* @throws IllegalStateException
* If invoked recursively during the construction of the class
* loader specified by the "java.system.class.loader"
* property.
*
* @throws Error
* If the system property "java.system.class.loader"
* is defined but the named class could not be loaded, the
* provider class does not define the required constructor, or an
* exception is thrown by that constructor when it is invoked. The
* underlying cause of the error can be retrieved via the
* {@link Throwable#getCause()} method.
*
* @revised 1.4
*/
public static java.lang.ClassLoader getSystemClassLoader() {
return null;
}
/**
* Defines a package by name in this ClassLoader. This allows
* class loaders to define the packages for their classes. Packages must
* be created before the class is defined, and package names must be
* unique within a class loader and cannot be redefined or changed once
* created.
*
* @param name
* The package name
*
* @param specTitle
* The specification title
*
* @param specVersion
* The specification version
*
* @param specVendor
* The specification vendor
*
* @param implTitle
* The implementation title
*
* @param implVersion
* The implementation version
*
* @param implVendor
* The implementation vendor
*
* @param sealBase
* If not null, then this package is sealed with
* respect to the given code source {@link java.net.URL
* URL} object. Otherwise, the package is not sealed.
*
* @return The newly defined Package object
*
* @throws IllegalArgumentException
* If package name duplicates an existing package either in this
* class loader or one of its ancestors
*
* @since 1.2
*/
protected java.lang.Package definePackage(java.lang.String name,
java.lang.String specTitle, java.lang.String specVersion,
java.lang.String specVendor, java.lang.String implTitle,
java.lang.String implVersion, java.lang.String implVendor, URL sealBase)
throws java.lang.IllegalArgumentException
{
return null;
}
/**
* Returns a Package that has been defined by this class loader
* or any of its ancestors.
*
* @param name
* The package name
*
* @return The Package corresponding to the given name, or
* null if not found
*
* @since 1.2
*/
protected java.lang.Package getPackage(java.lang.String name) {
return null;
}
/**
* Returns all of the Packages defined by this class loader and
* its ancestors.
*
* @return The array of Package objects defined by this
* ClassLoader
*
* @since 1.2
*/
protected java.lang.Package[] getPackages() {
return null;
}
/**
* Returns the absolute path name of a native library. The VM invokes this
* method to locate the native libraries that belong to classes loaded with
* this class loader. If this method returns null, the VM
* searches the library along the path specified as the
* "java.library.path" property.
*
* @param libname
* The library name
*
* @return The absolute path of the native library
*
* @see System#loadLibrary(String)
* @see System#mapLibraryName(String)
*
* @since 1.2
*/
protected java.lang.String findLibrary(java.lang.String libname) {
return null;
}
/**
* Sets the default assertion status for this class loader. This setting
* determines whether classes loaded by this class loader and initialized
* in the future will have assertions enabled or disabled by default.
* This setting may be overridden on a per-package or per-class basis by
* invoking {@link #setPackageAssertionStatus(String, boolean)} or {@link
* #setClassAssertionStatus(String, boolean)}.
*
* @param enabled
* true if classes loaded by this class loader will
* henceforth have assertions enabled by default, false
* if they will have assertions disabled by default.
*
* @since 1.4
*/
public synchronized void setDefaultAssertionStatus(boolean enabled) { }
/**
* Sets the package default assertion status for the named package. The
* package default assertion status determines the assertion status for
* classes initialized in the future that belong to the named package or
* any of its "subpackages".
*
* A subpackage of a package named p is any package whose name begins
* with "p.". For example, javax.swing.text is a
* subpackage of javax.swing, and both java.util and
* java.lang.reflect are subpackages of java.
*
*
In the event that multiple package defaults apply to a given class,
* the package default pertaining to the most specific package takes
* precedence over the others. For example, if javax.lang and
* javax.lang.reflect both have package defaults associated with
* them, the latter package default applies to classes in
* javax.lang.reflect.
*
*
Package defaults take precedence over the class loader's default
* assertion status, and may be overridden on a per-class basis by invoking
* {@link #setClassAssertionStatus(String, boolean)}.
*
* @param packageName
* The name of the package whose package default assertion status
* is to be set. A null value indicates the unnamed
* package that is "current" (Java Language
* Specification, section 7.4.2).
*
* @param enabled
* true if classes loaded by this classloader and
* belonging to the named package or any of its subpackages will
* have assertions enabled by default, false if they will
* have assertions disabled by default.
*
* @since 1.4
*/
public synchronized void setPackageAssertionStatus(java.lang.String
packageName, boolean enabled)
{ }
/**
* Sets the desired assertion status for the named top-level class in this
* class loader and any nested classes contained therein. This setting
* takes precedence over the class loader's default assertion status, and
* over any applicable per-package default. This method has no effect if
* the named class has already been initialized. (Once a class is
* initialized, its assertion status cannot change.)
*
* If the named class is not a top-level class, this invocation will
* have no effect on the actual assertion status of any class, and its
* return value is undefined.
*
* @param className
* The fully qualified class name of the top-level class whose
* assertion status is to be set.
*
* @param enabled
* true if the named class is to have assertions
* enabled when (and if) it is initialized, false if the
* class is to have assertions disabled.
*
* @since 1.4
*/
public synchronized void setClassAssertionStatus(java.lang.String className,
boolean enabled)
{ }
/**
* Sets the default assertion status for this class loader to
* false and discards any package defaults or class assertion
* status settings associated with the class loader. This method is
* provided so that class loaders can be made to ignore any command line or
* persistent assertion status settings and "start with a clean slate."
*
*
* @since 1.4
*/
public synchronized void clearAssertionStatus() { }
}