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AspectJ tools most notably contains the AspectJ compiler (AJC). AJC applies aspects to Java classes during compilation, fully replacing Javac for plain Java classes and also compiling native AspectJ or annotation-based @AspectJ syntax. Furthermore, AJC can weave aspects into existing class files in a post-compile binary weaving step. This library is a superset of AspectJ weaver and hence also of AspectJ runtime.

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/*******************************************************************************
 * Copyright (c) 2012 Contributors.
 * All rights reserved.
 * This program and the accompanying materials are made available
 * under the terms of the Eclipse Public License v 2.0
 * which accompanies this distribution and is available at
 * https://www.eclipse.org/org/documents/epl-2.0/EPL-2.0.txt
 *
 * Contributors:
 *   John Kew (vmware)         initial implementation
 *******************************************************************************/

package org.aspectj.weaver.tools.cache;

import java.net.URL;
import java.net.URLClassLoader;
import java.util.Collections;
import java.util.LinkedList;
import java.util.List;
import java.util.zip.CRC32;

/**
 * Naive default class and classloader hashing implementation useful
 * for some multi-classloader environments.
 * 
 * This implementation creates classloader scopes of the form:

 * "ExampleClassLoaderName.[crc hash]"
 * 
 * 
 * And weaved class keys of the form:

 * "com.foo.BarClassName.[bytes len][crc].weaved"
 * 
 * 
 * And generated class keys of the form:

 * "com.foo.BarClassName$AjClosure.generated
 * 
 */
public class DefaultCacheKeyResolver implements CacheKeyResolver {
	public static final String GENERATED_SUFFIX = ".generated";
	public static final String WEAVED_SUFFIX = ".weaved";

	/**
	 * Create a scope from a set of urls and aspect urls. Creates scope
	 * of the form "ExampleClassLoaderName.[md5sum]" or
	 * "ExampleClassLoaderName.[crc]"
	 *
	 * @param cl	  the classloader which uses the cache, can be null
	 * @param aspects the aspects
	 * @return a unique string for URLClassloaders, otherwise a non-unique classname
	 */
	public String createClassLoaderScope(ClassLoader cl, List aspects) {
		String name = cl != null ? cl.getClass().getSimpleName() : "unknown";

		List hashableStrings = new LinkedList<>();
		StringBuilder hashable = new StringBuilder(256);

		// Add the list of loader urls to the hash list
		if (cl instanceof URLClassLoader) {
			URL[] urls = ((URLClassLoader) cl).getURLs();
			for (URL url : urls) {
				hashableStrings.add(url.toString());
			}
		}

		hashableStrings.addAll(aspects);
		Collections.sort(hashableStrings);
		for (String url : hashableStrings) {
			hashable.append(url);
		}
		String hash = null;
		byte[] bytes = hashable.toString().getBytes();
		hash = crc(bytes);

		return name + '.' + hash;
	}

	private String crc(byte[] input) {
		CRC32 crc32 = new CRC32();
		crc32.update(input);
		return String.valueOf(crc32.getValue());
	}

	public String getGeneratedRegex() {
		return ".*" + GENERATED_SUFFIX;
	}

	public String getWeavedRegex() {
		return ".*" + WEAVED_SUFFIX;
	}


	/**
	 * Converts a cache key back to a className
	 *
	 * @param key to convert
	 * @return className, e.g. "com.foo.Bar"
	 */
	public String keyToClass(String key) {
		if (key.endsWith(GENERATED_SUFFIX)) {
			return key.replaceAll(GENERATED_SUFFIX + "$", "");
		}
		if (key.endsWith(WEAVED_SUFFIX)) {
			return key.replaceAll("\\.[^.]+" + WEAVED_SUFFIX, "");
		}
		return key;
	}

	public CachedClassReference weavedKey(String className, byte[] original_bytes) {
		String hash = crc(original_bytes);
		return new CachedClassReference(className + "." + hash + WEAVED_SUFFIX, className);

	}

	public CachedClassReference generatedKey(String className) {
		return new CachedClassReference(className + GENERATED_SUFFIX, className);
	}

}