java.net.URLClassLoader

All Implemented Interfaces:: Closeable, AutoCloseable

public class URLClassLoader extends SecureClassLoader implements Closeable

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 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.

Since:: 1.2

Constructor Summary

Constructors

Constructor

Description

URLClassLoader(String name, URL[] urls, ClassLoader parent)

Constructs a new named URLClassLoader for the specified URLs.

URLClassLoader(String name, URL[] urls, ClassLoader parent, URLStreamHandlerFactory factory)

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

URLClassLoader(URL[] urls)

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

URLClassLoader(URL[] urls, ClassLoader parent)

Constructs a new URLClassLoader for the given URLs.

URLClassLoader(URL[] urls, ClassLoader parent, URLStreamHandlerFactory factory)

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

Modifier and Type

Method

Description

protected void

addURL(URL url)

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

void

close()

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

protected Package

definePackage(String name, Manifest man, URL url)

Defines a new package by name in this URLClassLoader.

protected Class<?>

findClass(String name)

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

URL

findResource(String name)

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

Enumeration<URL>

findResources(String name)

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

protected PermissionCollection

getPermissions(CodeSource codesource)

Returns an empty Permission collection.

InputStream

getResourceAsStream(String name)

Returns an input stream for reading the specified resource.

URL[]

getURLs()

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

static URLClassLoader

newInstance(URL[] urls)

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

static URLClassLoader

newInstance(URL[] urls, ClassLoader parent)

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

Methods declared in class SecureClassLoader
defineClass, defineClass

Modifier and Type

Method

Description

protected final Class<?>

defineClass(String name, byte[] b, int off, int len, CodeSource cs)

Converts an array of bytes into an instance of class Class, with an optional CodeSource.

protected final Class<?>

defineClass(String name, ByteBuffer b, CodeSource cs)

Converts a ByteBuffer into an instance of class Class, with an optional CodeSource.

Methods declared in class ClassLoader
clearAssertionStatus, defineClass, defineClass, defineClass, defineClass, definePackage, findClass, findLibrary, findLoadedClass, findResource, findSystemClass, getClassLoadingLock, getDefinedPackage, getDefinedPackages, getName, getPackage, getPackages, getParent, getPlatformClassLoader, getResource, getResources, getSystemClassLoader, getSystemResource, getSystemResourceAsStream, getSystemResources, getUnnamedModule, isRegisteredAsParallelCapable, loadClass, loadClass, registerAsParallelCapable, resolveClass, resources, setClassAssertionStatus, setDefaultAssertionStatus, setPackageAssertionStatus, setSigners

Modifier and Type

Method

Description

void

clearAssertionStatus()

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

protected final Class<?>

defineClass(byte[] classRep, int offset, int length)

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

protected final Class<?>

defineClass(String className, byte[] classRep, int offset, int length)

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

protected final Class<?>

defineClass(String className, byte[] classRep, int offset, int length, ProtectionDomain protectionDomain)

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.

protected final Class<?>

defineClass(String name, ByteBuffer buffer, ProtectionDomain domain)

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.

protected Package

definePackage(String name, String specTitle, String specVersion, String specVendor, String implTitle, String implVersion, String implVendor, URL sealBase)

Define a new Package using the specified information.

protected Class<?>

findClass(String moduleName, String className)

Overridden by subclasses that support the loading from modules.

protected String

findLibrary(String libName)

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

protected final Class<?>

findLoadedClass(String className)

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

protected URL

findResource(String moduleName, String resName)

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

protected final Class<?>

findSystemClass(String className)

Attempts to load a class using the system class loader.

protected Object

getClassLoadingLock(String className)

Answers the lock object for class loading in parallel.

final Package

getDefinedPackage(String name)

Answers a package of given name defined by this ClassLoader.

final Package[]

getDefinedPackages()

Answers all the packages defined by this classloader.

String

getName()

Get the name given when creating the ClassLoader instance, or null if none was provided.

protected Package

getPackage(String name)

Deprecated.
Use getDefinedPackage(String)

protected Package[]

getPackages()

Answers all the packages known to this class loader.

final ClassLoader

getParent()

Returns the specified ClassLoader's parent.

static ClassLoader

getPlatformClassLoader()

Return the Platform classloader.

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)

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

static ClassLoader

getSystemClassLoader()

Convenience operation to obtain a reference to 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 InputStream

getSystemResourceAsStream(String resName)

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

static Enumeration<URL>

getSystemResources(String resName)

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

final Module

getUnnamedModule()

Answers the unnamed Module of this class loader.

final boolean

isRegisteredAsParallelCapable()

Indicating if this class loader is registered as parallel capable or not

Class<?>

loadClass(String className)

Invoked by the Virtual Machine when resolving class references.

protected Class<?>

loadClass(String className, boolean resolveClass)

Attempts to load the type className in the running VM, optionally linking the type after a successful load.

protected static boolean

registerAsParallelCapable()

Attempts to register the ClassLoader as being capable of parallel class loading.

protected final void

resolveClass(Class<?> clazz)

Forces a class to be linked (initialized).

Stream<URL>

resources(String name)

Answers a stream of URL which can be used to access the resources described by name, using the class loader's resource lookup algorithm.

void

setClassAssertionStatus(String cname, boolean enable)

Sets the assertion status of a class.

void

setDefaultAssertionStatus(boolean enable)

Sets the default assertion status of a classloader

void

setPackageAssertionStatus(String pname, boolean enable)

Sets the assertion status of a package.

protected final void

setSigners(Class<?> c, Object[] signers)

Sets the signers of a class.

Methods declared in class Object
clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Modifier and Type

Method

Description

protected Object

clone()

Answers a new instance of the same class as the receiver, whose slots have been filled in with the values in the slots of the receiver.

boolean

equals(Object o)

Compares the argument to the receiver, and answers true if they represent the same object using a class specific comparison.

protected void

finalize()

Deprecated, for removal: This API element is subject to removal in a future version.
May cause performance issues, deadlocks and hangs.

final Class<? extends Object>

getClass()

Answers the unique instance of java.lang.Class which represents the class of the receiver.

int

hashCode()

Answers an integer hash code for the receiver.

final void

notify()

Causes one thread which is waiting on the receiver to be made ready to run.

final void

notifyAll()

Causes all threads which are waiting on the receiver to be made ready to run.

String

toString()

Answers a string containing a concise, human-readable description of the receiver.

final void

wait()

Causes the thread which sent this message to be made not ready to run pending some change in the receiver (as indicated by notify or notifyAll).

final void

wait(long time)

Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.

final void

wait(long time, int frac)

Causes the thread which sent this message to be made not ready to run either pending some change in the receiver (as indicated by notify or notifyAll) or the expiration of the timeout.

Constructor Details
- URLClassLoader
  
  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 - the URLs from which to load classes and resources
  
  parent - the parent class loader for delegation, can be null for the bootstrap class loader
  
  Throws:
  
  NullPointerException - if urls or any of its elements is null.
- URLClassLoader
  
  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 - the URLs from which to load classes and resources
  
  Throws:
  
  NullPointerException - if urls or any of its elements is null.
- URLClassLoader
  
  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 - the URLs from which to load classes and resources
  
  parent - the parent class loader for delegation, can be null for the bootstrap class loader
  
  factory - the URLStreamHandlerFactory to use when creating URLs
  
  Throws:
  
  NullPointerException - if urls or any of its elements is null.
- URLClassLoader
  
  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 - class loader name; or null if not named
  
  urls - the URLs from which to load classes and resources
  
  parent - the parent class loader for delegation, can be null for the bootstrap class loader
  
  Throws:
  
  IllegalArgumentException - if the given name is empty.
  
  NullPointerException - if urls or any of its elements is null.
  
  Since:
  
  9
- URLClassLoader
  
  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 - class loader name; or null if not named
  
  urls - the URLs from which to load classes and resources
  
  parent - the parent class loader for delegation, can be null for the bootstrap class loader
  
  factory - the URLStreamHandlerFactory to use when creating URLs
  
  Throws:
  
  IllegalArgumentException - if the given name is empty.
  
  NullPointerException - if urls or any of its elements is null.
  
  Since:
  
  9
Method Details
- getResourceAsStream
  public InputStream getResourceAsStream(String name)
  
  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 ClassLoader.getResource(String).
  
  Overrides:
  
  getResourceAsStream in class ClassLoader
  
  Parameters:
  
  name - The resource name
  
  Returns:
  
  An input stream for reading the resource, or null if the resource could not be found
  
  Throws:
  
  NullPointerException - If name is null
  
  Since:
  
  1.7
  
  See Also:
  
  Class.getResourceAsStream(String)
- close
  
  public void close() throws IOException
  
  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.
  
  Specified by:
  
  close in interface AutoCloseable
  
  Specified by:
  
  close in interface Closeable
  
  Throws:
  
  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
- addURL
  
  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 - the URL to be added to the search path of URLs
- getURLs
  
  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:
  
  the search path of URLs for loading classes and resources.
- findClass
  
  protected Class<?> findClass(String name) throws ClassNotFoundException
  
  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.
  
  Overrides:
  
  findClass in class ClassLoader
  
  Parameters:
  
  name - the name of the class
  
  Returns:
  
  the resulting class
  
  Throws:
  
  ClassNotFoundException - if the class could not be found, or if the loader is closed.
  
  NullPointerException - if name is null.
- definePackage
  
  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 - the package name
  
  man - the Manifest containing package version and sealing information
  
  url - the code source url for the package, or null if none
  
  Returns:
  
  the newly defined Package object
  
  Throws:
  
  IllegalArgumentException - if the package name is already defined by this class loader
- findResource
  
  public URL findResource(String name)
  
  Finds the resource with the specified name on the URL search path.
  
  Overrides:
  
  findResource in class ClassLoader
  
  Parameters:
  
  name - the name of the resource
  
  Returns:
  
  a URL for the resource, or null if the resource could not be found, or if the loader is closed.
- findResources
  
  public Enumeration<URL> findResources(String name) throws IOException
  
  Returns an Enumeration of URLs representing all of the resources on the URL search path having the specified name.
  
  Overrides:
  
  findResources in class ClassLoader
  
  Parameters:
  
  name - the resource name
  
  Returns:
  
  An Enumeration of URLs. If the loader is closed, the Enumeration contains no elements.
  
  Throws:
  
  IOException - if an I/O exception occurs
- getPermissions
  
  protected PermissionCollection getPermissions(CodeSource codesource)
  
  Returns an empty Permission collection.
  
  Overrides:
  
  getPermissions in class SecureClassLoader
  
  Parameters:
  
  codesource - the CodeSource
  
  Returns:
  
  an empty Permission collection
  
  Throws:
  
  NullPointerException - if codesource is null.
- newInstance
  
  public static URLClassLoader newInstance(URL[] urls, ClassLoader parent)
  
  Creates a new instance of URLClassLoader for the specified URLs and parent class loader.
  
  Parameters:
  
  urls - the URLs to search for classes and resources
  
  parent - the parent class loader for delegation
  
  Returns:
  
  the resulting class loader
  
  Throws:
  
  NullPointerException - if urls or any of its elements is null.
- newInstance
  
  public static URLClassLoader newInstance(URL[] urls)
  
  Creates a new instance of URLClassLoader for the specified URLs and default parent class loader.
  
  Parameters:
  
  urls - the URLs to search for classes and resources
  
  Returns:
  
  the resulting class loader
  
  Throws:
  
  NullPointerException - if urls or any of its elements is null.

Class URLClassLoader

Constructor Summary

Method Summary

Methods declared in class SecureClassLoader

Methods declared in class ClassLoader

Methods declared in class Object

Constructor Details

URLClassLoader

URLClassLoader

URLClassLoader

URLClassLoader

URLClassLoader

Method Details

getResourceAsStream

close

addURL

getURLs

findClass

definePackage

findResource

findResources

getPermissions

newInstance

newInstance