MapBackedClassLoader.java

/*
 * Copyright 2015 Red Hat, Inc. and/or its affiliates.
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *      http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package org.drools.android;

import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.security.AccessController;
import java.security.PrivilegedAction;
import java.security.ProtectionDomain;
import java.util.HashMap;
import java.util.Map;

public class MapBackedClassLoader extends MultiDexClassLoader {

    private static final long serialVersionUID = 510l;

    private static final ProtectionDomain PROTECTION_DOMAIN;

    private Map<String, byte[]> store;

    static {
        PROTECTION_DOMAIN = (ProtectionDomain) AccessController.doPrivileged(new PrivilegedAction() {
            public Object run() {
                return MapBackedClassLoader.class.getProtectionDomain();
            }
        });
    }

    public MapBackedClassLoader(final ClassLoader parentClassLoader) {
        this(parentClassLoader, new HashMap<String, byte[]>());
    }

    public MapBackedClassLoader(final ClassLoader parentClassLoader,
                                final Map store) {
        super(parentClassLoader);
        this.store = store;
    }

    public void addResource(String className,
                            byte[] bytes) {
        addClass(className,
                bytes);
    }

    private String convertResourcePathToClassName(final String pName) {
        return pName.replaceAll(".java$|.class$",
                "").replace('/',
                '.');
    }

    public void addClass(final String className,
                         byte[] bytes) {
        synchronized (this.store) {
            this.store.put(convertResourcePathToClassName(className),
                    bytes);
        }
    }

    public Class fastFindClass(final String name) {
        final Class clazz = findLoadedClass(name);

        if (clazz == null) {
            byte[] clazzBytes;
            synchronized (this.store) {
                clazzBytes = this.store.get(name);
            }

            if (clazzBytes != null) {
                return defineClass(name, clazzBytes);
            }
        }
        return clazz;
    }

    /**
     * Javadocs recommend that this method not be overloaded. We overload this so that we can prioritise the fastFindClass
     * over method calls to parent.loadClass(name, false); and c = findBootstrapClass0(name); which the default implementation
     * would first - hence why we call it "fastFindClass" instead of standard findClass, this indicates that we give it a
     * higher priority than normal.
     */
    public synchronized Class loadClass(final String name,
                                        final boolean resolve) throws ClassNotFoundException {
        Class clazz = fastFindClass(name);

        if (clazz == null) {
            final ClassLoader parent = getParent();
            if (parent != null) {
                clazz = Class.forName(name,
                        true,
                        parent);
            }
        }

        if (resolve) {
            resolveClass(clazz);
        }

        return clazz;
    }

    protected Class findClass(final String name) throws ClassNotFoundException {
        return fastFindClass(name);
    }

    public InputStream getResourceAsStream(final String name) {
        byte[] bytes = null;
        synchronized (this.store) {
            bytes = this.store.get(convertResourcePathToClassName(name));
        }

        if (bytes != null) {
            return new ByteArrayInputStream(bytes);
        } else {
            InputStream input = this.getParent().getResourceAsStream(name);
            if (input == null) {
                input = super.getResourceAsStream(name);
            }
            return input;
        }
    }

    public Map getStore() {
        return this.store;
    }
}