Module java.base
Package java.net

Class URLClassLoader

java.lang.Object
java.lang.ClassLoader
java.security.SecureClassLoader
java.net.URLClassLoader
All Implemented Interfaces:
Closeable,AutoCloseable
Direct Known Subclasses:
MLet
public classURLClassLoaderextendsSecureClassLoaderimplementsCloseable
This class loader is used to load classes and resources from a search path of URLs referring to both JAR files and directories. Anyjar: scheme URL (seeJarURLConnection) is assumed to refer to a JAR file. Anyfile: 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 amulti-release JAR file that is referred to by a given URL.

The AccessControlContext of the thread that created the instance of URLClassLoader will be used when subsequently loading classes and resources.

The classes that are loaded are by default granted permission only to access the URLs specified when the URLClassLoader was created.

Since:
1.2

  • 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. Anyjar: scheme URL is assumed to refer to a JAR file. Anyfile: 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.

      If there is a security manager, this method first calls the security manager'scheckCreateClassLoader method to ensure creation of a class loader is allowed.

      Parameters:
      urls - the URLs from which to load classes and resources
      parent - the parent class loader for delegation
      Throws:
      SecurityException - if a security manager exists and itscheckCreateClassLoader method doesn't allow creation of a class loader.
      NullPointerException - ifurls or any of its elements isnull.
      See Also:

    • URLClassLoader

      public URLClassLoader(URL[] urls)
      Constructs a new URLClassLoader for the specified URLs using the default delegation parentClassLoader. 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.

      If there is a security manager, this method first calls the security manager'scheckCreateClassLoader method to ensure creation of a class loader is allowed.

      Parameters:
      urls - the URLs from which to load classes and resources
      Throws:
      SecurityException - if a security manager exists and itscheckCreateClassLoader method doesn't allow creation of a class loader.
      NullPointerException - ifurls or any of its elements isnull.
      See Also:

    • 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.

      If there is a security manager, this method first calls the security manager'scheckCreateClassLoader method to ensure creation of a class loader is allowed.

      Parameters:
      urls - the URLs from which to load classes and resources
      parent - the parent class loader for delegation
      factory - the URLStreamHandlerFactory to use when creating URLs
      Throws:
      SecurityException - if a security manager exists and itscheckCreateClassLoader method doesn't allow creation of a class loader.
      NullPointerException - ifurls or any of its elements isnull.
      See Also:

    • URLClassLoader

      public URLClassLoader(String name,URL[] urls,ClassLoader parent)
      Constructs a new namedURLClassLoader 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.
      Parameters:
      name - class loader name; ornull if not named
      urls - the URLs from which to load classes and resources
      parent - the parent class loader for delegation
      Throws:
      IllegalArgumentException - if the given name is empty.
      NullPointerException - ifurls or any of its elements isnull.
      SecurityException - if a security manager exists and itsSecurityManager.checkCreateClassLoader() method doesn't allow creation of a class loader.
      Since:
      9

    • URLClassLoader

      public URLClassLoader(String name,URL[] urls,ClassLoader parent,URLStreamHandlerFactory factory)
      Constructs a new namedURLClassLoader 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.
      Parameters:
      name - class loader name; ornull if not named
      urls - the URLs from which to load classes and resources
      parent - the parent class loader for delegation
      factory - the URLStreamHandlerFactory to use when creating URLs
      Throws:
      IllegalArgumentException - if the given name is empty.
      NullPointerException - ifurls or any of its elements isnull.
      SecurityException - if a security manager exists and itscheckCreateClassLoader method doesn't allow creation of a class loader.
      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 forClassLoader.getResource(String).

      Overrides:
      getResourceAsStream in class ClassLoader
      Parameters:
      name - The resource name
      Returns:
      An input stream for reading the resource, ornull if the resource could not be found
      Throws:
      NullPointerException - Ifname isnull
      Since:
      1.7

    • close

      public void close() throwsIOException
      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 theclose method is invoked, then the result of that load is undefined.

      The method makes a best effort attempt to close all opened files, by catchingIOExceptions 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.
      SecurityException - if a security manager is set, and it deniesRuntimePermission("closeClassLoader")
      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 isnull 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) throwsClassNotFoundException
      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 - ifname isnull.

    • definePackage

      protected Package definePackage(String name,Manifest man,URL url)
      Defines a new package by name in thisURLClassLoader. The attributes contained in the specifiedManifest 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 - theManifest containing package version and sealing information
      url - the code source url for the package, or null if none
      Returns:
      the newly definedPackage 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:
      aURL for the resource, ornull if the resource could not be found, or if the loader is closed.

    • findResources

      public Enumeration<URL> findResources(String name) throwsIOException
      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:
      AnEnumeration ofURLs. 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 the permissions for the given codesource object. The implementation of this method first calls super.getPermissions and then adds permissions based on the URL of the codesource.

      If the protocol of this URL is "jar", then the permission granted is based on the permission that is required by the URL of the Jar file.

      If the protocol is "file" and there is an authority component, then permission to connect to and accept connections from that authority may be granted. If the protocol is "file" and the path specifies a file, then permission to read that file is granted. If protocol is "file" and the path is a directory, permission is granted to read all files and (recursively) all files and subdirectories contained in that directory.

      If the protocol is not "file", then permission to connect to and accept connections from the URL's host is granted.

      Overrides:
      getPermissions in class SecureClassLoader
      Parameters:
      codesource - the codesource
      Returns:
      the permissions granted to the codesource
      Throws:
      NullPointerException - ifcodesource isnull.

    • newInstance

      public static URLClassLoader newInstance(URL[] urls,ClassLoader parent)
      Creates a new instance of URLClassLoader for the specified URLs and parent class loader. If a security manager is installed, theloadClass method of the URLClassLoader returned by this method will invoke theSecurityManager.checkPackageAccess method before loading the class.
      Parameters:
      urls - the URLs to search for classes and resources
      parent - the parent class loader for delegation
      Returns:
      the resulting class loader
      Throws:
      NullPointerException - ifurls or any of its elements isnull.

    • newInstance

      public static URLClassLoader newInstance(URL[] urls)
      Creates a new instance of URLClassLoader for the specified URLs and default parent class loader. If a security manager is installed, theloadClass method of the URLClassLoader returned by this method will invoke theSecurityManager.checkPackageAccess before loading the class.
      Parameters:
      urls - the URLs to search for classes and resources
      Returns:
      the resulting class loader
      Throws:
      NullPointerException - ifurls or any of its elements isnull.