java.net

Class URLClassLoader

java.lang.Object

java.lang.ClassLoader

java.security.SecureClassLoader

java.net.URLClassLoader

public class URLClassLoader
extends SecureClassLoader

This class loader is responsible for loading classes and resources from a list of URLs which can refer to either directories or JAR files. Classes loaded by this URLClassLoader are granted permission to access the URLs contained in the URL search list.

Field Summary

Fields inherited from class java.lang.ClassLoader

proxyCache

Constructor Summary

Constructors

Constructor and Description
URLClassLoader(URL[] urls) Constructs a new URLClassLoader instance.
URLClassLoader(URL[] urls, ClassLoader parent) Constructs a new URLClassLoader instance.
URLClassLoader(URL[] searchUrls, ClassLoader parent, URLStreamHandlerFactory factory) Constructs a new URLClassLoader instance.

Method Summary

Modifier and Type	Method and Description
protected void	addURL(URL url) Adds the specified URL to the search list.
protected Package	definePackage(String packageName, Manifest manifest, URL url) Defines a new package using the information extracted from the specified manifest.
protected Class<?>	findClass(String className) Tries to locate and load the specified class using the known URLs.
URL	findResource(String name) Returns an URL referencing the specified resource or null if the resource could not be found.
Enumeration<URL>	findResources(String name) Returns all known URLs which point to the specified resource.
protected PermissionCollection	getPermissions(CodeSource codesource) Gets all permissions for the specified codesource.
URL[]	getURLs() Returns the search list of this URLClassLoader.
static URLClassLoader	newInstance(URL[] urls) Returns a new URLClassLoader instance for the given URLs and the system ClassLoader as its parent.
static URLClassLoader	newInstance(URL[] urls, ClassLoader parentCl) Returns a new URLClassLoader instance for the given URLs and the specified ClassLoader as its parent.

Methods inherited from class java.security.SecureClassLoader

defineClass, defineClass

Methods inherited from class java.lang.ClassLoader

clearAssertionStatus, defineClass, defineClass, defineClass, defineClass, definePackage, findLibrary, findLoadedClass, findSystemClass, getPackage, getPackages, getParent, getResource, getResourceAsStream, getResources, getSystemClassLoader, getSystemResource, getSystemResourceAsStream, getSystemResources, loadClass, loadClass, resolveClass, setClassAssertionStatus, setDefaultAssertionStatus, setPackageAssertionStatus, setSigners

Methods inherited from class java.lang.Object

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

Constructor Detail

URLClassLoader

public URLClassLoader(URL[] urls)

Constructs a new URLClassLoader instance. The newly created instance will have the system ClassLoader as its parent. URLs that end with "/" are assumed to be directories, otherwise they are assumed to be JAR files.

Parameters:

urls - the list of URLs where a specific class or file could be found.

URLClassLoader

public URLClassLoader(URL[] urls,
                      ClassLoader parent)

Constructs a new URLClassLoader instance. The newly created instance will have the system ClassLoader as its parent. URLs that end with "/" are assumed to be directories, otherwise they are assumed to be JAR files.

Parameters:

urls - the list of URLs where a specific class or file could be found.

parent - the class loader to assign as this loader's parent.

URLClassLoader

public URLClassLoader(URL[] searchUrls,
                      ClassLoader parent,
                      URLStreamHandlerFactory factory)

Constructs a new URLClassLoader instance. The newly created instance will have the specified ClassLoader as its parent and use the specified factory to create stream handlers. URLs that end with "/" are assumed to be directories, otherwise they are assumed to be JAR files.

Parameters:

searchUrls - the list of URLs where a specific class or file could be found.

parent - the ClassLoader to assign as this loader's parent.

factory - the factory that will be used to create protocol-specific stream handlers.

Method Detail

addURL

protected void addURL(URL url)

Adds the specified URL to the search list.

Parameters:

url - the URL which is to add.

findResources

public Enumeration<URL> findResources(String name)
                               throws IOException

Returns all known URLs which point to the specified resource.

Overrides:

findResources in class ClassLoader

Parameters:

name - the name of the requested resource.

Returns:

the enumeration of URLs which point to the specified resource.

Throws:

IOException - if an I/O error occurs while attempting to connect.

getPermissions

protected PermissionCollection getPermissions(CodeSource codesource)

Gets all permissions for the specified codesource. First, this method retrieves the permissions from the system policy. If the protocol is "file:/" then a new permission, FilePermission, granting the read permission to the file is added to the permission collection. Otherwise, connecting to and accepting connections from the URL is granted.

Overrides:

getPermissions in class SecureClassLoader

Parameters:

codesource - the code source object whose permissions have to be known.

Returns:

the list of permissions according to the code source object.

getURLs

public URL[] getURLs()

Returns the search list of this URLClassLoader.

Returns:

the list of all known URLs of this instance.

newInstance

public static URLClassLoader newInstance(URL[] urls)

Returns a new URLClassLoader instance for the given URLs and the system ClassLoader as its parent.

Parameters:

urls - the list of URLs that is passed to the new URLClassLoader.

Returns:

the created URLClassLoader instance.

newInstance

public static URLClassLoader newInstance(URL[] urls,
                                         ClassLoader parentCl)

Returns a new URLClassLoader instance for the given URLs and the specified ClassLoader as its parent.

Parameters:

urls - the list of URLs that is passed to the new URLClassLoader.

parentCl - the parent class loader that is passed to the new URLClassLoader.

Returns:

the created URLClassLoader instance.

findClass

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

Tries to locate and load the specified class using the known URLs. If the class could be found, a class object representing the loaded class will be returned.

Overrides:

findClass in class ClassLoader

Parameters:

className - the name of the class to look for.

Returns:

the Class object that is found.

Throws:

ClassNotFoundException - if the specified class cannot be loaded.

findResource

public URL findResource(String name)

Returns an URL referencing the specified resource or null if the resource could not be found.

Overrides:

findResource in class ClassLoader

Parameters:

name - the name of the requested resource.

Returns:

the URL which points to the given resource.

definePackage

protected Package definePackage(String packageName,
                                Manifest manifest,
                                URL url)
                         throws IllegalArgumentException

Defines a new package using the information extracted from the specified manifest.

Parameters:

packageName - the name of the new package.

manifest - the manifest containing additional information for the new package.

url - the URL to the code source for the new package.

Returns:

the created package.

Throws:

IllegalArgumentException - if a package with the given name already exists.