Java in a Nutshell, 5th Edition [Electronic resources] نسخه متنی

This class adds protected methods to
those defined by ClassLoader. The
defineClass( ) method is passed the bytes of a
class file as a byte[ ] or, in Java 5.0, as a
ByteBuffer and a CodeSource
object that represents the source of that class. It calls the
getPermissions( ) method to obtain a
PermissionCollection for that
CodeSource and then uses the
CodeSource and
PermissionCollection to create a
ProtectionDomain, which is passed to the
defineClass( ) method of its superclass.

The default implementation of the getPermissions(
) method uses the default Policy to
determine the appropriate set of permissions for a given code source.
The value of SecureClassLoader is that subclasses
can use its defineClass( ) method to load classes
without having to work explicitly with the
ProtectionDomain and Policy
classes. A subclass of SecureClassLoader can
define its own security policy by overriding getPermissions(
). In Java 1.2 and later, any application that implements a
custom class loader should do so by extending
SecureClassLoader, instead of subclassing
ClassLoader directly. Most applications can use
java.net.URLClassLoader, however, and never have
to subclass this class.

Figure 14-35. java.security.SecureClassLoader

public class

SecureClassLoader extends ClassLoader {
// Protected Constructors
protected

SecureClassLoader ( );
protected

SecureClassLoader (ClassLoader

parent );
// Protected Instance Methods

5.0 protected final Class<?>

defineClass (String

name ,
java.nio.ByteBuffer

b , CodeSource

cs );
protected final Class<?>

defineClass (String

name , byte[ ]

b , int

off ,
int

len , CodeSource

cs );
protected PermissionCollection

getPermissions (CodeSource

codesource );
}

Subclasses

java.net.URLClassLoader