Class URLClassLoader

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

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()`	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.
`protected final Class<?>`	`defineClass(byte[] b, int off, int len)`	Deprecated. Replaced by `defineClass(String, byte[], int, int)`
`protected final Class<?>`	`defineClass(String name, byte[] b, int off, int len)`	Converts an array of bytes into an instance of class `Class`.
`protected final Class<?>`	`defineClass(String name, byte[] b, int off, int len, ProtectionDomain protectionDomain)`	Converts an array of bytes into an instance of class `Class`, with a given `ProtectionDomain`.
`protected final Class<?>`	`defineClass(String name, ByteBuffer b, ProtectionDomain protectionDomain)`	Converts a `ByteBuffer` into an instance of class `Class`, with the given `ProtectionDomain`.
`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 `ClassLoader`.
`protected Class<?>`	`findClass(String moduleName, String name)`	Finds the class with the given binary name in a module defined to this class loader.
`protected String`	`findLibrary(String libname)`	Returns the absolute path name of a native library.
`protected final Class<?>`	`findLoadedClass(String name)`	Returns the class with the given binary name if this loader has been recorded by the Java virtual machine as an initiating loader of a class with that binary name.
`protected URL`	`findResource(String moduleName, String name)`	Returns a URL to a resource in a module defined to this class loader.
`protected final Class<?>`	`findSystemClass(String name)`	Finds a class with the specified binary name, loading it if necessary.
`protected Object`	`getClassLoadingLock(String className)`	Returns the lock object for class loading operations.
`final Package`	`getDefinedPackage(String name)`	Returns a `Package` of the given name that has been defined by this class loader.
`final Package[]`	`getDefinedPackages()`	Returns all of the `Package`s that have been defined by this class loader.
`String`	`getName()`	Returns the name of this class loader or `null` if this class loader is not named.
`protected Package`	`getPackage(String name)`	Deprecated. If multiple class loaders delegate to each other and define classes with the same package name, and one such loader relies on the lookup behavior of `getPackage` to return a `Package` from a parent loader, then the properties exposed by the `Package` may not be as expected in the rest of the program.
`protected Package[]`	`getPackages()`	Returns all of the `Package`s that have been defined by this class loader and its ancestors.
`final ClassLoader`	`getParent()`	Returns the parent class loader for delegation.
`static ClassLoader`	`getPlatformClassLoader()`	Returns the platform class loader.
`URL`	`getResource(String name)`	Finds the resource with the given name.
`Enumeration<URL>`	`getResources(String name)`	Finds all the resources with the given name.
`static ClassLoader`	`getSystemClassLoader()`	Returns the system class loader.
`static URL`	`getSystemResource(String name)`	Find a resource of the specified name from the search path used to load classes.
`static InputStream`	`getSystemResourceAsStream(String name)`	Open for reading, a resource of the specified name from the search path used to load classes.
`static Enumeration<URL>`	`getSystemResources(String name)`	Finds all resources of the specified name from the search path used to load classes.
`final Module`	`getUnnamedModule()`	Returns the unnamed `Module` for this class loader.
`final boolean`	`isRegisteredAsParallelCapable()`	Returns `true` if this class loader is registered as parallel capable, otherwise `false`.
`Class<?>`	`loadClass(String name)`	Loads the class with the specified binary name.
`protected Class<?>`	`loadClass(String name, boolean resolve)`	Loads the class with the specified binary name.
`protected static boolean`	`registerAsParallelCapable()`	Registers the caller as parallel capable.
`protected final void`	`resolveClass(Class<?> c)`	Links the specified class.
`Stream<URL>`	`resources(String name)`	Returns a stream whose elements are the URLs of all the resources with the given name.
`void`	`setClassAssertionStatus(String className, boolean enabled)`	Sets the desired assertion status for the named top-level class in this class loader and any nested classes contained therein.
`void`	`setDefaultAssertionStatus(boolean enabled)`	Sets the default assertion status for this class loader.
`void`	`setPackageAssertionStatus(String packageName, boolean enabled)`	Sets the package default assertion status for the named 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()`	Creates and returns a copy of this object.
`boolean`	`equals(Object obj)`	Indicates whether some other object is "equal to" this one.
`protected void`	`finalize()`	Deprecated, for removal: This API element is subject to removal in a future version. Finalization is deprecated and subject to removal in a future release.
`final Class<?>`	`getClass()`	Returns the runtime class of this `Object`.
`int`	`hashCode()`	Returns a hash code value for this object.
`final void`	`notify()`	Wakes up a single thread that is waiting on this object's monitor.
`final void`	`notifyAll()`	Wakes up all threads that are waiting on this object's monitor.
`String`	`toString()`	Returns a string representation of the object.
`final void`	`wait()`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted.
`final void`	`wait(long timeoutMillis)`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.
`final void`	`wait(long timeoutMillis, int nanos)`	Causes the current thread to wait until it is awakened, typically by being notified or interrupted, or until a certain amount of real time has elapsed.

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

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.

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