1/*
2 * Copyright (C) 2011 The Android Open Source Project
3 *
4 * Licensed under the Apache License, Version 2.0 (the "License");
5 * you may not use this file except in compliance with the License.
6 * You may obtain a copy of the License at
7 *
8 *      http://www.apache.org/licenses/LICENSE-2.0
9 *
10 * Unless required by applicable law or agreed to in writing, software
11 * distributed under the License is distributed on an "AS IS" BASIS,
12 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
13 * See the License for the specific language governing permissions and
14 * limitations under the License.
15 */
16
17package dalvik.system;
18
19import java.io.File;
20import java.net.URL;
21import java.util.Enumeration;
22
23/**
24 * Base class for common functionality between various dex-based
25 * {@link ClassLoader} implementations.
26 */
27public class BaseDexClassLoader extends ClassLoader {
28    /** originally specified path (just used for {@code toString()}) */
29    private final String originalPath;
30
31    /** structured lists of path elements */
32    private final DexPathList pathList;
33
34    /**
35     * Constructs an instance.
36     *
37     * @param dexPath the list of jar/apk files containing classes and
38     * resources, delimited by {@code File.pathSeparator}, which
39     * defaults to {@code ":"} on Android
40     * @param optimizedDirectory directory where optimized dex files
41     * should be written; may be {@code null}
42     * @param libraryPath the list of directories containing native
43     * libraries, delimited by {@code File.pathSeparator}; may be
44     * {@code null}
45     * @param parent the parent class loader
46     */
47    public BaseDexClassLoader(String dexPath, File optimizedDirectory,
48            String libraryPath, ClassLoader parent) {
49        super(parent);
50
51        this.originalPath = dexPath;
52        this.pathList =
53            new DexPathList(this, dexPath, libraryPath, optimizedDirectory);
54    }
55
56    @Override
57    protected Class<?> findClass(String name) throws ClassNotFoundException {
58        Class clazz = pathList.findClass(name);
59
60        if (clazz == null) {
61            throw new ClassNotFoundException(name);
62        }
63
64        return clazz;
65    }
66
67    @Override
68    protected URL findResource(String name) {
69        return pathList.findResource(name);
70    }
71
72    @Override
73    protected Enumeration<URL> findResources(String name) {
74        return pathList.findResources(name);
75    }
76
77    @Override
78    public String findLibrary(String name) {
79        return pathList.findLibrary(name);
80    }
81
82    /**
83     * Returns package information for the given package.
84     * Unfortunately, instances of this class don't really have this
85     * information, and as a non-secure {@code ClassLoader}, it isn't
86     * even required to, according to the spec. Yet, we want to
87     * provide it, in order to make all those hopeful callers of
88     * {@code myClass.getPackage().getName()} happy. Thus we construct
89     * a {@code Package} object the first time it is being requested
90     * and fill most of the fields with dummy values. The {@code
91     * Package} object is then put into the {@code ClassLoader}'s
92     * package cache, so we see the same one next time. We don't
93     * create {@code Package} objects for {@code null} arguments or
94     * for the default package.
95     *
96     * <p>There is a limited chance that we end up with multiple
97     * {@code Package} objects representing the same package: It can
98     * happen when when a package is scattered across different JAR
99     * files which were loaded by different {@code ClassLoader}
100     * instances. This is rather unlikely, and given that this whole
101     * thing is more or less a workaround, probably not worth the
102     * effort to address.
103     *
104     * @param name the name of the class
105     * @return the package information for the class, or {@code null}
106     * if there is no package information available for it
107     */
108    @Override
109    protected synchronized Package getPackage(String name) {
110        if (name != null && !name.isEmpty()) {
111            Package pack = super.getPackage(name);
112
113            if (pack == null) {
114                pack = definePackage(name, "Unknown", "0.0", "Unknown",
115                        "Unknown", "0.0", "Unknown", null);
116            }
117
118            return pack;
119        }
120
121        return null;
122    }
123
124    @Override
125    public String toString() {
126        return getClass().getName() + "[" + originalPath + "]";
127    }
128}
129