ByteCodeLoader.java revision 2224:2a8815d86b93 
1/*
2 * Copyright (c) 2013, 2016, Oracle and/or its affiliates. All rights reserved.
3 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
4 *
5 * This code is free software; you can redistribute it and/or modify it
6 * under the terms of the GNU General Public License version 2 only, as
7 * published by the Free Software Foundation.
8 *
9 * This code is distributed in the hope that it will be useful, but WITHOUT
10 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
11 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
12 * version 2 for more details (a copy is included in the LICENSE file that
13 * accompanied this code).
14 *
15 * You should have received a copy of the GNU General Public License version
16 * 2 along with this work; if not, write to the Free Software Foundation,
17 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
18 *
19 * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
20 * or visit www.oracle.com if you need additional information or have any
21 * questions.
22 */
23
24package jdk.test.lib;
25
26import java.security.SecureClassLoader;
27
28/**
29 * {@code ByteCodeLoader} can be used for easy loading of byte code already
30 * present in memory.
31 *
32 * {@code InMemoryCompiler} can be used for compiling source code in a string
33 * into byte code, which then can be loaded with {@code ByteCodeLoader}.
34 *
35 * @see InMemoryCompiler
36 */
37public class ByteCodeLoader extends SecureClassLoader {
38    private final String className;
39    private final byte[] byteCode;
40    private volatile Class<?> holder;
41
42    /**
43     * Creates a new {@code ByteCodeLoader} ready to load a class with the
44     * given name and the given byte code.
45     *
46     * @param className The name of the class
47     * @param byteCode The byte code of the class
48     */
49    public ByteCodeLoader(String className, byte[] byteCode) {
50        this.className = className;
51        this.byteCode = byteCode;
52    }
53
54    @Override
55    public Class<?> loadClass(String name) throws ClassNotFoundException {
56        if (!name.equals(className)) {
57            return super.loadClass(name);
58        }
59        if (holder == null) {
60            synchronized(this) {
61                if (holder == null) {
62                    holder = findClass(name);
63                }
64            }
65        }
66        return holder;
67    }
68
69    @Override
70    protected Class<?> findClass(String name) throws ClassNotFoundException {
71        if (!name.equals(className)) {
72            throw new ClassNotFoundException(name);
73        }
74
75        return defineClass(name, byteCode, 0, byteCode.length);
76    }
77
78    /**
79     * Utility method for creating a new {@code ByteCodeLoader} and then
80     * directly load the given byte code.
81     *
82     * @param className The name of the class
83     * @param byteCode The byte code for the class
84     * @throws ClassNotFoundException if the class can't be loaded
85     * @return A {@see Class} object representing the class
86     */
87    public static Class<?> load(String className, byte[] byteCode) throws ClassNotFoundException {
88        return new ByteCodeLoader(className, byteCode).loadClass(className);
89    }
90}
91