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java.net

Class URLClassLoader

java.lang.Object
|
+--java.lang.ClassLoader
   |
   +--java.security.SecureClassLoader
      |
      +--java.net.URLClassLoader


public class URLClassLoader

extends SecureClassLoader

A secure class loader that can load classes and resources from multiple locations. Given an array of URLs this class loader will retrieve classes and resources by fetching them from possible remote locations. Each URL is searched in order in which it was added. If the file portion of the URL ends with a '/' character then it is interpreted as a base directory, otherwise it is interpreted as a jar file from which the classes/resources are resolved.

New instances can be created by two static newInstance() methods or by three public contructors. Both ways give the option to supply an initial array of URLs and (optionally) a parent classloader (that is different from the standard system class loader).

Normally creating a URLClassLoader throws a SecurityException if a SecurityManager is installed and the checkCreateClassLoader() method does not return true. But the newInstance() methods may be used by any code as long as it has permission to acces the given URLs. URLClassLoaders created by the newInstance() methods also explicitly call the checkPackageAccess() method of SecurityManager if one is installed before trying to load a class. Note that only subclasses of URLClassLoader can add new URLs after the URLClassLoader had been created. But it is always possible to get an array of all URLs that the class loader uses to resolve classes and resources by way of the getURLs() method.

Open issues:

Since:Authors:

Constructor Summary

URLClassLoader(java.net.URL[] urls)

Creates a URLClassLoader that gets classes from the supplied URLs.
URLClassLoader(java.net.URL[] urls, java.lang.ClassLoader parent)

Creates a URLClassLoader that gets classes from the supplied URLs.
URLClassLoader(java.net.URL[] urls, java.lang.ClassLoader parent, java.net.URLStreamHandlerFactory factory)

Creates a URLClassLoader that gets classes from the supplied URLs.

Method Summary

voidaddURL(java.net.URL newUrl)

Adds a new location to the end of the internal URL store.
java.lang.PackagedefinePackage(java.lang.String name, java.util.jar.Manifest manifest, java.net.URL url)

Defines a Package based on the given name and the supplied manifest information.
java.lang.ClassfindClass(final String className)

Finds (the first) class by name from one of the locations.
java.net.URLfindResource(java.lang.String resourceName)

Finds the first occurrence of a resource that can be found.
java.util.EnumerationfindResources(java.lang.String resourceName)

Finds all the resources with a particular name from all the locations.
java.security.PermissionCollectiongetPermissions(java.security.CodeSource source)

Returns the permissions needed to access a particular code source.
java.net.URL[]getURLs()

Returns all the locations that this class loader currently uses the resolve classes and resource.
static java.net.URLClassLoadernewInstance(java.net.URL[] urls)

Creates a new instance of a URLClassLoader that gets classes from the supplied URLs.
static java.net.URLClassLoadernewInstance(java.net.URL[] urls, final ClassLoader parent)

Creates a new instance of a URLClassLoader that gets classes from the supplied URLs and with the supplied loader as parent class loader.

Constructor Details

URLClassLoader

public URLClassLoader(java.net.URL[] urls)

Creates a URLClassLoader that gets classes from the supplied URLs. To determine if this classloader may be created the constructor of the super class (SecureClassLoader) is called first, which can throw a SecurityException. Then the supplied URLs are added in the order given to the URLClassLoader which uses these URLs to load classes and resources (after using the default parent ClassLoader).

Parameters:

Throws:

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URLClassLoader

public URLClassLoader(java.net.URL[] urls, java.lang.ClassLoader parent)

Creates a URLClassLoader that gets classes from the supplied URLs. To determine if this classloader may be created the constructor of the super class (SecureClassLoader) is called first, which can throw a SecurityException. Then the supplied URLs are added in the order given to the URLClassLoader which uses these URLs to load classes and resources (after using the supplied parent ClassLoader).

Parameters:

Throws:

See Also:


URLClassLoader

public URLClassLoader(java.net.URL[] urls, java.lang.ClassLoader parent, java.net.URLStreamHandlerFactory factory)

Creates a URLClassLoader that gets classes from the supplied URLs. To determine if this classloader may be created the constructor of the super class (SecureClassLoader) is called first, which can throw a SecurityException. Then the supplied URLs are added in the order given to the URLClassLoader which uses these URLs to load classes and resources (after using the supplied parent ClassLoader). It will use the supplied URLStreamHandlerFactory to get the protocol handlers of the supplied URLs.

Parameters:

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Method Details

addURL

protected void addURL(java.net.URL newUrl)

Adds a new location to the end of the internal URL store.

Parameters:


definePackage

protected Package definePackage(java.lang.String name, java.util.jar.Manifest manifest, java.net.URL url)

Defines a Package based on the given name and the supplied manifest information. The manifest indicates the tile, version and vendor information of the specification and implementation and wheter the package is sealed. If the Manifest indicates that the package is sealed then the Package will be sealed with respect to the supplied URL.

Parameters:

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findClass

protected Class findClass(final String className)

Finds (the first) class by name from one of the locations. The locations are searched in the order they were added to the URLClassLoader.

Parameters:

Returns:

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findResource

public URL findResource(java.lang.String resourceName)

Finds the first occurrence of a resource that can be found.

Parameters:

Returns:


findResources

public Enumeration findResources(java.lang.String resourceName)

Finds all the resources with a particular name from all the locations.

Parameters:

Returns:

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getPermissions

protected PermissionCollection getPermissions(java.security.CodeSource source)

Returns the permissions needed to access a particular code source. These permissions includes those returned by SecureClassLoader.getPermissions() and the actual permissions to access the objects referenced by the URL of the code source. The extra permissions added depend on the protocol and file portion of the URL in the code source. If the URL has the "file" protocol ends with a '/' character then it must be a directory and a file Permission to read everything in that directory and all subdirectories is added. If the URL had the "file" protocol and doesn't end with a '/' character then it must be a normal file and a file permission to read that file is added. If the URL has any other protocol then a socket permission to connect and accept connections from the host portion of the URL is added.

Parameters:

Returns:

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getURLs

public URL[] getURLs()

Returns all the locations that this class loader currently uses the resolve classes and resource. This includes both the initially supplied URLs as any URLs added later by the loader.

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newInstance

public static URLClassLoader newInstance(java.net.URL[] urls)

Creates a new instance of a URLClassLoader that gets classes from the supplied URLs. This class loader will have as parent the standard system class loader.

Parameters:

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newInstance

public static URLClassLoader newInstance(java.net.URL[] urls, final ClassLoader parent)

Creates a new instance of a URLClassLoader that gets classes from the supplied URLs and with the supplied loader as parent class loader.

Parameters:

Throws: