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Top Description Fields Constructors Methods
java.net

public Class URLClassLoader

extends SecureClassLoader
implements Closeable
Class Inheritance
All Implemented Interfaces
java.io.Closeable, java.lang.AutoCloseable
Known Direct Subclasses
jdk.internal.jrtfs.JrtFileSystemProvider.JrtFsLoader
Imports
java.io.Closeable, .IOException, .InputStream, java.security.CodeSigner, .CodeSource, .Permissions, .PermissionCollection, .SecureClassLoader, java.util.Enumeration, .List, .NoSuchElementException, .Objects, .Set, .WeakHashMap, java.util.jar.Attributes, .Attributes.Name, .JarFile, .Manifest, jdk.internal.loader.Resource, .URLClassPath, jdk.internal.access.SharedSecrets, jdk.internal.perf.PerfCounter
This class loader is used to load classes and resources from a search path of URLs referring to both JAR files and directories. Any jar: scheme URL (see java.net.JarURLConnection) is assumed to refer to a JAR file. Any file: scheme URL that ends with a '/' is assumed to refer to a directory. Otherwise, the URL is assumed to refer to a JAR file which will be opened as needed.

This class loader supports the loading of classes and resources from the contents of a multi-release JAR file that is referred to by a given URL.

Author
David Connelly
Since
1.2

Field Summary

Modifier and TypeField and Description
private final WeakHashMap<Closeable, Void>
closeables

private final URLClassPath
ucp

Constructor Summary

AccessConstructor and Description
public
URLClassLoader(URL[]
the URLs from which to load classes and resources
urls, ClassLoader
the parent class loader for delegation, can be null for the bootstrap class loader
parent)

Constructs a new URLClassLoader for the given URLs.

public
URLClassLoader(URL[]
the URLs from which to load classes and resources
urls)

Constructs a new URLClassLoader for the specified URLs using the system class loader as the parent.

public
URLClassLoader(URL[]
the URLs from which to load classes and resources
urls, ClassLoader
the parent class loader for delegation, can be null for the bootstrap class loader
parent, URLStreamHandlerFactory
the URLStreamHandlerFactory to use when creating URLs
factory)

Constructs a new URLClassLoader for the specified URLs, parent class loader, and URLStreamHandlerFactory.

public
URLClassLoader(String
class loader name; or null if not named
name, URL[]
the URLs from which to load classes and resources
urls, ClassLoader
the parent class loader for delegation, can be null for the bootstrap class loader
parent)

Constructs a new named URLClassLoader for the specified URLs.

public
URLClassLoader(String
class loader name; or null if not named
name, URL[]
the URLs from which to load classes and resources
urls, ClassLoader
the parent class loader for delegation, can be null for the bootstrap class loader
parent, URLStreamHandlerFactory
the URLStreamHandlerFactory to use when creating URLs
factory)

Constructs a new named URLClassLoader for the specified URLs, parent class loader, and URLStreamHandlerFactory.

Method Summary

Modifier and TypeMethod and Description
protected void
addURL(URL
the URL to be added to the search path of URLs
url)

Appends the specified URL to the list of URLs to search for classes and resources.

public void
close()

Implements java.io.Closeable.close.

Closes this URLClassLoader, so that it can no longer be used to load new classes or resources that are defined by this loader.

private Class<?>
defineClass(String name, Resource res)

protected Package

Returns:

the newly defined Package object
definePackage(String
the package name
name, Manifest
the Manifest containing package version and sealing information
man, URL
the code source url for the package, or null if none
url)

Defines a new package by name in this URLClassLoader.

protected Class<?>

Returns:

the resulting class
findClass(final String
the name of the class
name)

Overrides java.lang.ClassLoader.findClass.

Finds and loads the class with the specified name from the URL search path.

public URL

Returns:

a URL for the resource, or null if the resource could not be found, or if the loader is closed.
findResource(final String
the name of the resource
name)

Overrides java.lang.ClassLoader.findResource.

Finds the resource with the specified name on the URL search path.

public Enumeration<URL>

Returns:

An Enumeration of URLs. If the loader is closed, the Enumeration contains no elements.
findResources(final String
the resource name
name)

Overrides java.lang.ClassLoader.findResources.

Returns an Enumeration of URLs representing all of the resources on the URL search path having the specified name.

private Package
getAndVerifyPackage(String pkgname, Manifest man, URL url)

protected PermissionCollection

Returns:

an empty Permission collection
getPermissions(CodeSource
the CodeSource
codesource)

Overrides java.security.SecureClassLoader.getPermissions.

Returns an empty Permission collection.

public InputStream

Returns:

An input stream for reading the resource, or null if the resource could not be found
getResourceAsStream(String
The resource name
name)

Overrides java.lang.ClassLoader.getResourceAsStream.

Returns an input stream for reading the specified resource.

public URL[]

Returns:

the search path of URLs for loading classes and resources.
getURLs()

Returns the search path of URLs for loading classes and resources.

private boolean
isSealed(String name, Manifest man)

public static URLClassLoader

Returns:

the resulting class loader
newInstance(final URL[]
the URLs to search for classes and resources
urls, final ClassLoader
the parent class loader for delegation
parent)

Creates a new instance of URLClassLoader for the specified URLs and parent class loader.

public static URLClassLoader

Returns:

the resulting class loader
newInstance(final URL[]
the URLs to search for classes and resources
urls)

Creates a new instance of URLClassLoader for the specified URLs and default parent class loader.

Inherited from java.security.SecureClassLoader:
defineClassdefineClass

Field Detail

closeablesback to summary
private final WeakHashMap<Closeable, Void> closeables
ucpback to summary
private final URLClassPath ucp

Constructor Detail

URLClassLoaderback to summary
public URLClassLoader(URL[] urls, ClassLoader parent)

Constructs a new URLClassLoader for the given URLs. The URLs will be searched in the order specified for classes and resources after first searching in the specified parent class loader. Any jar: scheme URL is assumed to refer to a JAR file. Any file: scheme URL that ends with a '/' is assumed to refer to a directory. Otherwise, the URL is assumed to refer to a JAR file which will be downloaded and opened as needed.

API Note

If parent is specified as null (for the bootstrap class loader) then there is no guarantee that all platform classes are visible. See Run-time Built-in Class Loaders for information on the bootstrap class loader and other built-in class loaders.

Parameters
urls:URL[]

the URLs from which to load classes and resources

parent:ClassLoader

the parent class loader for delegation, can be null for the bootstrap class loader

Exceptions
NullPointerException:
if urls or any of its elements is null.
URLClassLoaderback to summary
public URLClassLoader(URL[] urls)

Constructs a new URLClassLoader for the specified URLs using the system class loader as the parent. The URLs will be searched in the order specified for classes and resources after first searching in the parent class loader. Any URL that ends with a '/' is assumed to refer to a directory. Otherwise, the URL is assumed to refer to a JAR file which will be downloaded and opened as needed.

Parameters
urls:URL[]

the URLs from which to load classes and resources

Exceptions
NullPointerException:
if urls or any of its elements is null.
URLClassLoaderback to summary
public URLClassLoader(URL[] urls, ClassLoader parent, URLStreamHandlerFactory factory)

Constructs a new URLClassLoader for the specified URLs, parent class loader, and URLStreamHandlerFactory. The parent argument will be used as the parent class loader for delegation. The factory argument will be used as the stream handler factory to obtain protocol handlers when creating new jar URLs.

API Note

If parent is specified as null (for the bootstrap class loader) then there is no guarantee that all platform classes are visible. See Run-time Built-in Class Loaders for information on the bootstrap class loader and other built-in class loaders.

Parameters
urls:URL[]

the URLs from which to load classes and resources

parent:ClassLoader

the parent class loader for delegation, can be null for the bootstrap class loader

factory:URLStreamHandlerFactory

the URLStreamHandlerFactory to use when creating URLs

Exceptions
NullPointerException:
if urls or any of its elements is null.
URLClassLoaderback to summary
public URLClassLoader(String name, URL[] urls, ClassLoader parent)

Constructs a new named URLClassLoader for the specified URLs. The URLs will be searched in the order specified for classes and resources after first searching in the specified parent class loader. Any URL that ends with a '/' is assumed to refer to a directory. Otherwise, the URL is assumed to refer to a JAR file which will be downloaded and opened as needed.

API Note

If parent is specified as null (for the bootstrap class loader) then there is no guarantee that all platform classes are visible. See Run-time Built-in Class Loaders for information on the bootstrap class loader and other built-in class loaders.

Parameters
name:String

class loader name; or null if not named

urls:URL[]

the URLs from which to load classes and resources

parent:ClassLoader

the parent class loader for delegation, can be null for the bootstrap class loader

Exceptions
IllegalArgumentException:
if the given name is empty.
NullPointerException:
if urls or any of its elements is null.
Since
9
URLClassLoaderback to summary
public URLClassLoader(String name, URL[] urls, ClassLoader parent, URLStreamHandlerFactory factory)

Constructs a new named URLClassLoader for the specified URLs, parent class loader, and URLStreamHandlerFactory. The parent argument will be used as the parent class loader for delegation. The factory argument will be used as the stream handler factory to obtain protocol handlers when creating new jar URLs.

API Note

If parent is specified as null (for the bootstrap class loader) then there is no guarantee that all platform classes are visible. See Run-time Built-in Class Loaders for information on the bootstrap class loader and other built-in class loaders.

Parameters
name:String

class loader name; or null if not named

urls:URL[]

the URLs from which to load classes and resources

parent:ClassLoader

the parent class loader for delegation, can be null for the bootstrap class loader

factory:URLStreamHandlerFactory

the URLStreamHandlerFactory to use when creating URLs

Exceptions
IllegalArgumentException:
if the given name is empty.
NullPointerException:
if urls or any of its elements is null.
Since
9

Method Detail

addURLback to summary
protected void addURL(URL url)

Appends the specified URL to the list of URLs to search for classes and resources.

If the URL specified is null or is already in the list of URLs, or if this loader is closed, then invoking this method has no effect.

Parameters
url:URL

the URL to be added to the search path of URLs

closeback to summary
public void close() throws IOException

Implements java.io.Closeable.close.

Closes this URLClassLoader, so that it can no longer be used to load new classes or resources that are defined by this loader. Classes and resources defined by any of this loader's parents in the delegation hierarchy are still accessible. Also, any classes or resources that are already loaded, are still accessible.

In the case of jar: and file: URLs, it also closes any files that were opened by it. If another thread is loading a class when the close method is invoked, then the result of that load is undefined.

The method makes a best effort attempt to close all opened files, by catching IOExceptions internally. Unchecked exceptions and errors are not caught. Calling close on an already closed loader has no effect.

Exceptions
IOException:
if closing any file opened by this class loader resulted in an IOException. Any such exceptions are caught internally. If only one is caught, then it is re-thrown. If more than one exception is caught, then the second and following exceptions are added as suppressed exceptions of the first one caught, which is then re-thrown.
Since
1.7
defineClassback to summary
private Class<?> defineClass(String name, Resource res) throws IOException
definePackageback to summary
protected Package definePackage(String name, Manifest man, URL url)

Defines a new package by name in this URLClassLoader. The attributes contained in the specified Manifest will be used to obtain package version and sealing information. For sealed packages, the additional URL specifies the code source URL from which the package was loaded.

Parameters
name:String

the package name

man:Manifest

the Manifest containing package version and sealing information

url:URL

the code source url for the package, or null if none

Returns:Package

the newly defined Package object

Exceptions
IllegalArgumentException:
if the package name is already defined by this class loader
findClassback to summary
protected Class<?> findClass(final String name) throws ClassNotFoundException

Overrides java.lang.ClassLoader.findClass.

Finds and loads the class with the specified name from the URL search path. Any URLs referring to JAR files are loaded and opened as needed until the class is found.

Parameters
name:String

the name of the class

Returns:Class<?>

the resulting class

Exceptions
ClassNotFoundException:
if the class could not be found, or if the loader is closed.
NullPointerException:
if name is null.
findResourceback to summary
public URL findResource(final String name)

Overrides java.lang.ClassLoader.findResource.

Finds the resource with the specified name on the URL search path.

Parameters
name:String

the name of the resource

Returns:URL

a URL for the resource, or null if the resource could not be found, or if the loader is closed.

findResourcesback to summary
public Enumeration<URL> findResources(final String name) throws IOException

Overrides java.lang.ClassLoader.findResources.

Returns an Enumeration of URLs representing all of the resources on the URL search path having the specified name.

Parameters
name:String

the resource name

Returns:Enumeration<URL>

An Enumeration of URLs. If the loader is closed, the Enumeration contains no elements.

Annotations
@Override
Exceptions
IOException:
if an I/O exception occurs
getAndVerifyPackageback to summary
private Package getAndVerifyPackage(String pkgname, Manifest man, URL url)
getPermissionsback to summary
protected PermissionCollection getPermissions(CodeSource codesource)

Overrides java.security.SecureClassLoader.getPermissions.

Returns an empty Permission collection.

Parameters
codesource:CodeSource

the CodeSource

Returns:PermissionCollection

an empty Permission collection

Annotations
@Override
Exceptions
NullPointerException:
if codesource is null.
getResourceAsStreamback to summary
public InputStream getResourceAsStream(String name)

Overrides java.lang.ClassLoader.getResourceAsStream.

Returns an input stream for reading the specified resource. If this loader is closed, then any resources opened by this method will be closed.

The search order is described in the documentation for getResource(String).

Parameters
name:String

The resource name

Returns:InputStream

An input stream for reading the resource, or null if the resource could not be found

Exceptions
NullPointerException:
If name is null
Since
1.7
getURLsback to summary
public URL[] getURLs()

Returns the search path of URLs for loading classes and resources. This includes the original list of URLs specified to the constructor, along with any URLs subsequently appended by the addURL() method.

Returns:URL[]

the search path of URLs for loading classes and resources.

isSealedback to summary
private boolean isSealed(String name, Manifest man)
newInstanceback to summary
public static URLClassLoader newInstance(final URL[] urls, final ClassLoader parent)

Creates a new instance of URLClassLoader for the specified URLs and parent class loader.

Parameters
urls:URL[]

the URLs to search for classes and resources

parent:ClassLoader

the parent class loader for delegation

Returns:URLClassLoader

the resulting class loader

Exceptions
NullPointerException:
if urls or any of its elements is null.
newInstanceback to summary
public static URLClassLoader newInstance(final URL[] urls)

Creates a new instance of URLClassLoader for the specified URLs and default parent class loader.

Parameters
urls:URL[]

the URLs to search for classes and resources

Returns:URLClassLoader

the resulting class loader

Exceptions
NullPointerException:
if urls or any of its elements is null.