400 lines
12 KiB
Java
400 lines
12 KiB
Java
// ClassLoader.java - Define policies for loading Java classes.
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/* Copyright (C) 1998, 1999 Cygnus Solutions
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This file is part of libgcj.
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This software is copyrighted work licensed under the terms of the
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Libgcj License. Please consult the file "LIBGCJ_LICENSE" for
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details. */
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package java.lang;
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import java.io.InputStream;
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import java.net.URL;
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import java.net.URLConnection;
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import java.util.Stack;
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/**
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* The class <code>ClassLoader</code> is intended to be subclassed by
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* applications in order to describe new ways of loading classes,
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* such as over the network.
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*
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* @author Kresten Krab Thorup
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*/
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public abstract class ClassLoader {
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static private ClassLoader system;
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private ClassLoader parent;
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public ClassLoader getParent ()
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{
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/* FIXME: security */
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return parent;
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}
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public static native ClassLoader getSystemClassLoader ();
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/**
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* Creates a <code>ClassLoader</code> with no parent.
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* @exception java.lang.SecurityException if not allowed
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*/
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protected ClassLoader()
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{
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this (null);
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}
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/**
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* Creates a <code>ClassLoader</code> with the given parent.
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* The parent may be <code>null</code>.
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* The only thing this
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* constructor does, is to call
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* <code>checkCreateClassLoader</code> on the current
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* security manager.
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* @exception java.lang.SecurityException if not allowed
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*/
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protected ClassLoader(ClassLoader parent)
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{
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SecurityManager security = System.getSecurityManager ();
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if (security != null)
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security.checkCreateClassLoader ();
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this.parent = parent;
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}
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/**
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* Loads and link the class by the given name.
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* @param name the name of the class.
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* @return the class loaded.
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* @see ClassLoader#loadClass(String,boolean)
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* @exception java.lang.ClassNotFoundException
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*/
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public Class loadClass(String name)
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throws java.lang.ClassNotFoundException, java.lang.LinkageError
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{
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return loadClass (name, false);
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}
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/**
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* Loads the class by the given name. The default implementation
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* will search for the class in the following order (similar to jdk 1.2)
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* <ul>
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* <li> First <code>findLoadedClass</code>.
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* <li> If parent is non-null, <code>parent.loadClass</code>;
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* otherwise <code>findSystemClass</code>.
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* <li> <code>findClass</code>.
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* </ul>
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* If <code>link</code> is true, <code>resolveClass</code> is then
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* called. <p> Normally, this need not be overridden; override
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* <code>findClass</code> instead.
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* @param name the name of the class.
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* @param link if the class should be linked.
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* @return the class loaded.
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* @exception java.lang.ClassNotFoundException
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* @deprecated
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*/
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protected Class loadClass(String name, boolean link)
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throws java.lang.ClassNotFoundException, java.lang.LinkageError
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{
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Class c = findLoadedClass (name);
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if (c == null)
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{
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try {
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if (parent != null)
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return parent.loadClass (name, link);
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else
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c = findSystemClass (name);
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} catch (ClassNotFoundException ex) {
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/* ignore, we'll try findClass */;
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}
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}
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if (c == null)
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c = findClass (name);
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if (c == null)
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throw new ClassNotFoundException (name);
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if (link)
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resolveClass (c);
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return c;
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}
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/** Find a class. This should be overridden by subclasses; the
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* default implementation throws ClassNotFoundException.
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*
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* @param name Name of the class to find.
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* @return The class found.
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* @exception java.lang.ClassNotFoundException
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*/
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protected Class findClass (String name)
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throws ClassNotFoundException
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{
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throw new ClassNotFoundException ();
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}
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/**
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* Defines a class, given the class-data. According to the JVM, this
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* method should not be used; instead use the variant of this method
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* in which the name of the class being defined is specified
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* explicitly.
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* <P>
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* If the name of the class, as specified (implicitly) in the class
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* data, denotes a class which has already been loaded by this class
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* loader, an instance of
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* <code>java.lang.ClassNotFoundException</code> will be thrown.
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*
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* @param data bytes in class file format.
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* @param off offset to start interpreting data.
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* @param len length of data in class file.
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* @return the class defined.
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* @exception java.lang.ClassNotFoundException
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* @exception java.lang.LinkageError
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* @see ClassLoader#defineClass(String,byte[],int,int) */
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protected final Class defineClass(byte[] data, int off, int len)
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throws java.lang.ClassNotFoundException, java.lang.LinkageError
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{
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return defineClass (null, data, off, len);
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}
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/**
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* Defines a class, given the class-data. This is preferable
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* over <code>defineClass(byte[],off,len)</code> since it is more
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* secure. If the expected name does not match that of the class
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* file, <code>ClassNotFoundException</code> is thrown. If
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* <code>name</code> denotes the name of an already loaded class, a
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* <code>LinkageError</code> is thrown.
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* <p>
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*
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* FIXME: How do we assure that the class-file data is not being
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* modified, simultaneously with the class loader running!? If this
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* was done in some very clever way, it might break security.
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* Right now I am thinking that defineclass should make sure never to
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* read an element of this array more than once, and that that would
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* assure the ``immutable'' appearance. It is still to be determined
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* if this is in fact how defineClass operates.
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*
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* @param name the expected name.
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* @param data bytes in class file format.
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* @param off offset to start interpreting data.
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* @param len length of data in class file.
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* @return the class defined.
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* @exception java.lang.ClassNotFoundException
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* @exception java.lang.LinkageError
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*/
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protected final synchronized Class defineClass(String name,
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byte[] data,
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int off,
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int len)
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throws java.lang.ClassNotFoundException, java.lang.LinkageError
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{
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if (data==null || data.length < off+len || off<0 || len<0)
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throw new ClassFormatError ("arguments to defineClass "
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+ "are meaningless");
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// as per 5.3.5.1
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if (name != null && findLoadedClass (name) != null)
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throw new java.lang.LinkageError ("class "
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+ name
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+ " already loaded");
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try {
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// Since we're calling into native code here,
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// we better make sure that any generated
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// exception is to spec!
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return defineClass0 (name, data, off, len);
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} catch (java.lang.LinkageError x) {
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throw x; // rethrow
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} catch (java.lang.ClassNotFoundException x) {
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throw x; // rethrow
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} catch (java.lang.VirtualMachineError x) {
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throw x; // rethrow
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} catch (java.lang.Throwable x) {
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// This should never happen, or we are beyond spec.
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throw new InternalError ("Unexpected exception "
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+ "while defining class "
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+ name + ": "
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+ x.toString ());
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}
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}
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/** This is the entry point of defineClass into the native code */
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private native Class defineClass0 (String name,
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byte[] data,
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int off,
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int len)
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throws java.lang.ClassNotFoundException, java.lang.LinkageError;
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/** This is called by defineClass0, once the "raw" and uninitialized
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* class object has been created, and handles exceptions generated
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* while actually defining the class (_Jv_DefineClass). defineClass0
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* holds the lock on the new class object, so it needs to capture
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* these exceptions. */
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private static Throwable defineClass1 (Class klass, byte[] data,
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int offset, int length)
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{
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try {
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defineClass2 (klass, data, offset, length);
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} catch (Throwable x) {
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return x;
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}
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return null;
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}
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/** This is just a wrapper for _Jv_DefineClass */
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private static native void defineClass2 (Class klass, byte[] data,
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int offset, int length)
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throws Throwable;
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/**
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* Link the given class. This will bring the class to a state where
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* the class initializer can be run. Linking involves the following
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* steps:
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* <UL>
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* <LI> Prepare (allocate and internalize) the constant strings that
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* are used in this class.
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* <LI> Allocate storage for static fields, and define the layout
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* of instance fields.
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* <LI> Perform static initialization of ``static final'' int,
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* long, float, double and String fields for which there is a
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* compile-time constant initializer.
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* <LI> Create the internal representation of the ``vtable''.
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* </UL>
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* For <code>gcj</code>-compiled classes, only the first step is
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* performed. The compiler will have done the rest already.
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* <P>
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* This is called by the system automatically,
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* as part of class initialization; there is no reason to ever call
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* this method directly.
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* <P>
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* For historical reasons, this method has a name which is easily
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* misunderstood. Java classes are never ``resolved''. Classes are
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* linked; whereas method and field references are resolved.
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*
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* @param clazz the class to link.
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* @exception java.lang.LinkageError
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*/
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protected final void resolveClass(Class clazz)
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throws java.lang.LinkageError
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{
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resolveClass0(clazz);
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}
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static void resolveClass0(Class clazz)
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throws java.lang.LinkageError
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{
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synchronized (clazz)
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{
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try {
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linkClass0 (clazz);
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} catch (Throwable x) {
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markClassErrorState0 (clazz);
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if (x instanceof Error)
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throw (Error)x;
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else
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throw new java.lang.InternalError
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("unexpected exception during linking: " + x);
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}
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}
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}
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/** Internal method. Calls _Jv_PrepareClass and
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* _Jv_PrepareCompiledClass. This is only called from resolveClass. */
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private static native void linkClass0(Class clazz)
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throws java.lang.LinkageError;
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/** Internal method. Marks the given clazz to be in an erroneous
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* state, and calls notifyAll() on the class object. This should only
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* be called when the caller has the lock on the class object. */
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private static native void markClassErrorState0(Class clazz);
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/**
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* Returns a class found in a system-specific way, typically
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* via the <code>java.class.path</code> system property. Loads the
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* class if necessary.
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*
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* @param name the class to resolve.
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* @return the class loaded.
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* @exception java.lang.LinkageError
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* @exception java.lang.ClassNotFoundException
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*/
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protected Class findSystemClass(String name)
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throws java.lang.ClassNotFoundException, java.lang.LinkageError
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{
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return getSystemClassLoader ().loadClass (name);
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}
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/*
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* Does currently nothing.
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*/
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protected final void setSigners(Class claz, Object[] signers) {
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/* claz.setSigners (signers); */
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}
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/**
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* If a class named <code>name</code> was previously loaded using
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* this <code>ClassLoader</code>, then it is returned. Otherwise
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* it returns <code>null</code>. (Unlike the JDK this is native,
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* since we implement the class table internally.)
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* @param name class to find.
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* @return the class loaded, or null.
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*/
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protected native Class findLoadedClass(String name);
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public static final InputStream getSystemResourceAsStream(String name) {
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return getSystemClassLoader().getResourceAsStream (name);
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}
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public static final URL getSystemResource(String name) {
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return getSystemClassLoader().getResource (name);
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}
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/**
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* Return an InputStream representing the resource name.
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* This is essentially like
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* <code>getResource(name).openStream()</code>, except
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* it masks out any IOException and returns null on failure.
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* @param name resource to load
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* @return an InputStream, or null
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* @see java.lang.ClassLoader#getResource(String)
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* @see java.io.InputStream
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*/
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public InputStream getResourceAsStream(String name)
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{
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try {
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URL res = getResource (name);
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if (res == null) return null;
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return res.openStream ();
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} catch (java.io.IOException x) {
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return null;
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}
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}
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/**
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* Return an java.io.URL representing the resouce <code>name</code>.
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* The default implementation just returns <code>null</code>.
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* @param name resource to load
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* @return a URL, or null if there is no such resource.
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* @see java.lang.ClassLoader#getResourceAsBytes(String)
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* @see java.lang.ClassLoader#getResourceAsStream(String)
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* @see java.io.URL
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*/
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public URL getResource(String name) {
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return null;
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}
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}
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