classloader.java

一个开源的JAVA虚拟机

/*
    libaegisvm - The Aegis Virtual Machine for executing Java bytecode
    by Philip W. L. Fong
    Copyright (C) 2001-2002

    This library is free software; you can redistribute it and/or
    modify it under the terms of the GNU Lesser General Public
    License as published by the Free Software Foundation; either
    version 2.1 of the License, or (at your option) any later version.

    This library is distributed in the hope that it will be useful,
    but WITHOUT ANY WARRANTY; without even the implied warranty of
    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
    Lesser General Public License for more details.

    You should have received a copy of the GNU Lesser General Public
    License along with this library; if not, write to the Free Software
    Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA

*/

package java.lang;

import aegis.*;
import java.io.*;
import java.net.*;
import java.util.*;
import java.security.*;

/**
 * \todo Should be turned into an inner class of ClassLoader.
 */
class ClassHashTable {
    Class[] values;
    String[] keys;
    int size;
    ClassHashTable() {
	values = new Class[16];
	keys = new String[16];
	size = 0;
    }
    void expand() {
	int oldCapacity = values.length;
	int newCapacity;
	Class[] newValues;
	String[] newKeys;
	int mask;
	if (oldCapacity == (1 << 30))
	    throw new aegis.ImplementationLimitError();
	newCapacity = oldCapacity << 1;
	newValues = new Class[newCapacity];
	newKeys = new String[newCapacity];
	mask = newCapacity - 1;
	for (int i = 0; i < oldCapacity; i++) {
	    if (keys[i] != null) {
		int index = keys[i].hashCode() & mask;
		while (newKeys[index] != null)
		    index = (index + 1) & mask;
		newValues[index] = values[i];
		newKeys[index] = keys[i];
	    }
	}
	values = newValues;
	keys = newKeys;
    }
    void put(String classname, Class C) {
	int capacity = keys.length;
	int mask, index;
	if (size + 1 > capacity / 2)
	    expand();
	mask = capacity - 1;
	index = classname.hashCode() & mask;
	while (keys[index] != null)
	    index = (index + 1) & mask;
	keys[index] = classname;
	values[index] = C;
	++size;
    }
    Class get(String classname) {
	int mask = keys.length - 1;
	int index = classname.hashCode() & mask;
	while (keys[index] != null) {
	    if (classname.compareTo(keys[index]) == 0)
		return values[index];
	    index = (index + 1) & mask;
	}
	return null;
    }
}

public abstract class ClassLoader {
    private Namespace   namespace;  // The Aegis VM internal is dependent
    private ClassLoader parent;     // on the exact layout of these fields
    private ClassHashTable table;
    public static ClassLoader getSystemClassLoader() {
	return SystemClassLoader.theSystemClassLoader;
    }
    protected final Class findSystemClass(String name)
	throws ClassNotFoundException {
	return SystemClassLoader.theSystemClassLoader.loadClass(name);
    }
    protected Class findClass(String name) throws ClassNotFoundException {
	throw new ClassNotFoundException();
    }
    protected final Class findLoadedClass(String name) {
	if (name == null)
	    throw new NullPointerException();
	return table.get(name);
    }
    private static native Class defineClass(ClassLoader loader, String name,
					    byte[] b, int off, int len);
    /**
     * \todo Security checks.
     */
    protected final Class defineClass(String name, byte[] b, int off, int len)
	throws ClassFormatError {
	Class C;
	if (name == null || b == null)
	    throw new NullPointerException();
	if (off < 0 || off > b.length || len < 0 || len > b.length - off)
	    throw new IndexOutOfBoundsException();
	// security check goes here
	C = defineClass(this, name, b, off, len);
	table.put(name, C);
	return C;
    }
    /**
     * \todo Not implemented yet.
     */
    protected final Class defineClass(String name, byte[] b, int off, int len,
				      ProtectionDomain protectionDomain)
	throws ClassFormatError {
	throw new FeatureNotYetImplementedError();
    }
    private static native Class bootstrapLoadClass(String name);
    protected final native void resolveClass(Class C);
    protected Class loadClass(String name, boolean resolve) 
	throws ClassNotFoundException {
	Class C;
	C = findLoadedClass(name);
	if (C == null) {
	    try {
		if (parent == null)
		    C = bootstrapLoadClass(name);
		else
		    C = parent.loadClass(name);
		if (C == null)
		    throw new ClassNotFoundException();
	    } catch (ClassNotFoundException ex) {
		C = findClass(name);
		if (C == null)
		    throw new ClassNotFoundException();
	    }
	}
	if (resolve)
	    resolveClass(C);
	return C;
    }
    public Class loadClass(String name) throws ClassNotFoundException {
	return loadClass(name, false);
    }
    /**
     * \todo Security check.
     */
    public final ClassLoader getParent() {
	// Bug: security checks goes here
	return parent;
    }
    private static native Namespace createNamespace(ClassLoader parent,
						    ClassLoader loader);
    /**
     * \todo Not implemented yet.
     */
    protected final void setSigners(Class c, Object[] signers) {
	throw new FeatureNotYetImplementedError();
    }
    /**
     * \todo Not implemented yet.
     */
    public URL getResource(String name) {
	throw new FeatureNotYetImplementedError();
    }
    /**
     * \todo Not implemented yet.
     */
    public final Enumeration getResources(String name) throws IOException {
	throw new FeatureNotYetImplementedError();
    }
    /**
     * \todo Not implemented yet.
     */
    protected Enumeration findResources(String name) throws IOException {
	throw new FeatureNotYetImplementedError();
    }
    /**
     * \todo Not implemented yet.
     */
    protected URL findResource(String name) {
	throw new FeatureNotYetImplementedError();
    }
    /**
     * \todo Not implemented yet.
     */
    public static URL getSystemResource(String name) {
	throw new FeatureNotYetImplementedError();
    }
    /**
     * \todo Not implemented yet.
     */
    public static Enumeration getSystemResources(String name)
	throws IOException {
	throw new FeatureNotYetImplementedError();
    }
    /**
     * \todo Not implemented yet.
     */
    public InputStream getResourceAsStream(String name) {
	throw new FeatureNotYetImplementedError();
    }
    /**
     * \todo Not implemented yet.
     */
    public static InputStream getSystemResourceAsStream(String name) {
	throw new FeatureNotYetImplementedError();
    }
    /**
     * \todo Not implemented yet.
     */
    protected Package definePackage(String name,
				    String specTitle,
				    String specVersion,
				    String specVendor,
				    String implTitle,
				    String implVersion,
				    String implVendor,
				    URL sealBase)
	throws IllegalArgumentException {
	throw new FeatureNotYetImplementedError();
    }
    /**
     * \todo Not implemented yet.
     */
    protected Package getPackage(String name) {
	throw new FeatureNotYetImplementedError();
    }
    /**
     * \todo Not implemented yet.
     */
    protected Package[] getPackages() {
	throw new FeatureNotYetImplementedError();
    }
    protected String findLibrary(String libname) {
	return null;
    }
    /**
     * \todo Security checks.
     */
    protected ClassLoader(ClassLoader parent) {
	// security checks goes here
	this.parent = parent;
	namespace = createNamespace(parent, this);
	table = new ClassHashTable();
    }
    protected ClassLoader(){
	this(getSystemClassLoader());
    }
}