This ClassLoader
provides a useful way to load untrusted Java code from a search path
of arbitrary URLs, where each URL represents a directory or JAR file
to search. Use the inherited loadClass( ) method
to load a named class with a URLClassLoader.
Classes loaded by a URLClassLoader have whatever
permissions are granted to their
java.security.CodeSource by the system
java.security.Policy, plus they have one
additional permission that allows the class loader to read any
resource files associated with the class. If the class is loaded from
a local file: URL that represents a directory, the
class is given permission to read all files and directories below
that directory. If the class is loaded from a local
file: URL that represents a JAR file, the class is
given permission to read that JAR file. If the class is loaded from a
URL that represents a resource on another host, that class is given
permission to connect to and accept network connections from that
host. Note, however, that loaded classes are not granted this
additional permission if the code that created the
URLClassLoader in the first place would not have
had that permission.You can obtain a
URLClassLoader by calling one of the
URLClassLoader( ) constructors or one of the
static newInstance( ) methods. If you call
newInstance( ), the loadClass(
) method of the returned URLClassLoader
performs an additional check to ensure that the caller has permission
to access the specified package.
Figure 12-28. java.net.URLClassLoader
 public class URLClassLoader extends java.security.SecureClassLoader {
// Public Constructors
public URLClassLoader (URL[ ] urls );
public URLClassLoader (URL[ ] urls , ClassLoader parent );
public URLClassLoader (URL[ ] urls , ClassLoader parent ,
URLStreamHandlerFactory factory );
// Public Class Methods
public static URLClassLoader newInstance (URL[ ] urls );
public static URLClassLoader newInstance (URL[ ] urls , ClassLoader parent );
// Public Instance Methods
public URL[ ] getURLs ( );
// Protected Methods Overriding SecureClassLoader
protected java.security.PermissionCollection getPermissions (java.security.
CodeSource codesource );
// Public Methods Overriding ClassLoader
public URL findResource (String name );
public java.util.Enumeration<URL> findResources (String name )
throws java.io.IOException;
// Protected Methods Overriding ClassLoader
protected Class<?> findClass (String name ) throws ClassNotFoundException;
// Protected Instance Methods
protected void addURL (URL url );
protected Package definePackage (String name , java.util.jar.Manifest man ,
URL url ) throws IllegalArgumentException;
}
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