co.cask.cdap.internal.asm.ByteCodeClassLoader.java Source code

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Here is the source code for co.cask.cdap.internal.asm.ByteCodeClassLoader.java

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/*
 * Copyright  2014 Cask Data, Inc.
 *
 * 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 co.cask.cdap.internal.asm;

import com.google.common.collect.Maps;

import java.util.Map;

/**
 * A {@link ClassLoader} for loading known bytecode.
 */
public class ByteCodeClassLoader extends ClassLoader {

    /**
     * Map from class name to bytecode.
     */
    protected final Map<String, byte[]> bytecodes;
    protected final Map<String, Class<?>> typeClasses;

    public ByteCodeClassLoader(ClassLoader parent) {
        super(parent);
        this.bytecodes = Maps.newHashMap();
        this.typeClasses = Maps.newHashMap();
    }

    /**
     * Adds a class definition for this ClassLoader. When the class as given in the definition is
     * loaded for the first time, the byte code inside the definition will be used to load the class.
     *
     * @param classDef The class definition
     */
    public final synchronized ByteCodeClassLoader addClass(ClassDefinition classDef) {
        bytecodes.put(classDef.getClassName(), classDef.getBytecode());
        for (Class<?> cls : classDef.getPreservedClasses()) {
            typeClasses.put(cls.getName(), cls);
        }
        return this;
    }

    @Override
    public Class<?> loadClass(String className) throws ClassNotFoundException {
        return loadClass(className, true);
    }

    @Override
    public synchronized Class<?> loadClass(String className, boolean resolveIt) throws ClassNotFoundException {

        Class<?> result = findLoadedClass(className);
        if (result != null) {
            return result;
        }

        // See if it is a known type. If yes, return it.
        result = typeClasses.get(className);
        if (result != null) {
            return result;
        }

        // Tries to load it from this classloader
        byte[] bytecode = bytecodes.get(className);
        if (bytecode != null) {
            result = defineClass(className, bytecode, 0, bytecode.length);
            if (resolveIt) {
                resolveClass(result);
            }
            return result;
        }

        // Load with parent classloader
        return super.loadClass(className, resolveIt);
    }
}