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The AspectJ weaver applies aspects to Java classes. It can be used as a Java agent in order to apply load-time weaving (LTW) during class-loading and also contains the AspectJ runtime classes.
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/* *******************************************************************
 * Copyright (c) 2005 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:
 *   Ron Bodkin		Initial implementation
 * ******************************************************************/
package org.aspectj.weaver.ltw;

import java.lang.reflect.InvocationTargetException;
import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.List;
import java.util.Map;

import org.aspectj.apache.bcel.classfile.JavaClass;
import org.aspectj.bridge.IMessageHandler;
import org.aspectj.weaver.Dump.IVisitor;
import org.aspectj.weaver.ICrossReferenceHandler;
import org.aspectj.weaver.ReferenceType;
import org.aspectj.weaver.ReferenceTypeDelegate;
import org.aspectj.weaver.ResolvedType;
import org.aspectj.weaver.bcel.BcelWorld;
import org.aspectj.weaver.loadtime.IWeavingContext;
import org.aspectj.weaver.reflect.AnnotationFinder;
import org.aspectj.weaver.reflect.IReflectionWorld;
import org.aspectj.weaver.reflect.ReflectionBasedReferenceTypeDelegateFactory;
import org.aspectj.weaver.reflect.ReflectionWorld;

/**
 * @author adrian
 * @author Ron Bodkin
 *
 *         For use in LT weaving
 *
 *         Backed by both a BcelWorld and a ReflectionWorld
 *
 *         Needs a callback when a woven class is defined This is the trigger for us to ditch the class from Bcel and cache it in
 *         the reflective world instead.
 *
 *         Create by passing in a classloader, message handler
 */
public class LTWWorld extends BcelWorld implements IReflectionWorld {

	private AnnotationFinder annotationFinder;
	private IWeavingContext weavingContext;
	private String classLoaderString;

	private String classLoaderParentString;

	protected final static Class concurrentMapClass;

	private static final boolean ShareBootstrapTypes = false;
	protected static Map/* > */bootstrapTypes;

	static {
		if (ShareBootstrapTypes) {
			concurrentMapClass = makeConcurrentMapClass();
			bootstrapTypes = makeConcurrentMap();
		} else {
			concurrentMapClass = null;
		}
	}

	/**
	 * Build a World from a ClassLoader, for LTW support
	 */
	public LTWWorld(ClassLoader loader, IWeavingContext weavingContext, IMessageHandler handler, ICrossReferenceHandler xrefHandler) {
		super(loader, handler, xrefHandler);
		this.weavingContext = weavingContext;
		try {
			classLoaderString = loader.toString();
		} catch (Throwable t) {
			// Possibly some state in the loader isn't initialized but is used in the toString()
			classLoaderString = loader.getClass().getName()+":"+Integer.toString(System.identityHashCode(loader));
		}
		classLoaderParentString = (loader.getParent() == null ? "" : loader.getParent().toString());
		setBehaveInJava5Way(true);
		annotationFinder = ReflectionWorld.makeAnnotationFinderIfAny(loader, this);
	}

	public ClassLoader getClassLoader() {
		return weavingContext.getClassLoader();
	}

	// TEST
	// this is probably easier: just mark anything loaded while loading aspects as not
	// expendible... it also fixes a possible bug whereby non-rewoven aspects are deemed expendible
	// 
	// protected boolean isExpendable(ResolvedType type) {
	// return ((type != null) && !loadingAspects && !type.isAspect() && (!type
	// .isPrimitiveType()));
	// }

	/**
	 * Override
	 */
	@Override
	protected ReferenceTypeDelegate resolveDelegate(ReferenceType ty) {

		// use reflection delegates for all bootstrap types
		ReferenceTypeDelegate bootstrapLoaderDelegate = resolveIfBootstrapDelegate(ty);
		if (bootstrapLoaderDelegate != null) {
			return bootstrapLoaderDelegate;
		}

		return super.resolveDelegate(ty);
	}

	protected ReferenceTypeDelegate resolveIfBootstrapDelegate(ReferenceType ty) {
		// first check for anything available in the bootstrap loader: these types are just defined from that without allowing
		// nondelegation
		// if (!ShareBootstrapTypes) return null;
		// String name = ty.getName();
		// Reference bootRef = (Reference) bootstrapTypes.get(name);
		// if (bootRef != null) {
		// ReferenceTypeDelegate rtd = (ReferenceTypeDelegate) bootRef.get();
		// if (rtd != null) {
		// return rtd;
		// }
		// }
		//
		// char fc = name.charAt(0);
		// if (fc == 'j' || fc == 'c' || fc == 'o' || fc == 's') { // cheaper than imminent string startsWith tests
		// if (name.startsWith("java") || name.startsWith("com.sun.") || name.startsWith("org.w3c") ||
		// name.startsWith("sun.") || name.startsWith("org.omg")) {
		// ReferenceTypeDelegate bootstrapLoaderDelegate = resolveReflectionTypeDelegate(ty, null);
		// if (bootstrapLoaderDelegate != null) {
		// // it's always fine to load these bytes: there's no weaving into them
		// // and since the class isn't initialized, all we are doing at this point is loading the bytes
		// // processedRefTypes.put(ty, this); // has no effect - and probably too aggressive if we did store
		// // these in the type map
		//
		// // should we share these, like we do the BCEL delegates?
		// bootstrapTypes.put(ty.getName(), new WeakReference(bootstrapLoaderDelegate));
		// }
		// return bootstrapLoaderDelegate;
		// }
		// }
		return null;
	}

	/**
	 * Helper method to resolve the delegate from the reflection delegate factory.
	 */
	private ReferenceTypeDelegate resolveReflectionTypeDelegate(ReferenceType ty, ClassLoader resolutionLoader) {
		ReferenceTypeDelegate res = ReflectionBasedReferenceTypeDelegateFactory.createDelegate(ty, this, resolutionLoader);
		return res;
	}

	/**
	 * Remove this class from the typeMap. Call back to be made from a publishing class loader The class loader should, ideally,
	 * make this call on each not yet working
	 *
	 * @param clazz
	 */
	public void loadedClass(Class clazz) {
	}

	private static final long serialVersionUID = 1;

	public AnnotationFinder getAnnotationFinder() {
		return this.annotationFinder;
	}

	/*
	 * (non-Javadoc)
	 *
	 * @see org.aspectj.weaver.reflect.IReflectionWorld#resolve(java.lang.Class)
	 */
	public ResolvedType resolve(Class aClass) {
		return ReflectionWorld.resolve(this, aClass);
	}

	private static Map makeConcurrentMap() {
		if (concurrentMapClass != null) {
			try {
				return (Map) concurrentMapClass.getDeclaredConstructor().newInstance();
			} catch (InstantiationException | IllegalAccessException | NoSuchMethodException | InvocationTargetException ignored) {}
			// fall through if exceptions
		}
		return Collections.synchronizedMap(new HashMap<>());
	}

	private static Class makeConcurrentMapClass() {
		String betterChoices[] = { "java.util.concurrent.ConcurrentHashMap",
				"edu.emory.mathcs.backport.java.util.concurrent.ConcurrentHashMap",
				"EDU.oswego.cs.dl.util.concurrent.ConcurrentHashMap" };
		for (String betterChoice : betterChoices) {
			try {
				return Class.forName(betterChoice);
			} catch (ClassNotFoundException cnfe) {
				// try the next one
			} catch (SecurityException se) {
				// you get one of these if you dare to try to load an undefined class in a
				// package starting with java like java.util.concurrent
			}
		}
		return null;
	}

	@Override
	public boolean isRunMinimalMemory() {
		if (isRunMinimalMemorySet()) {
			return super.isRunMinimalMemory();
		}
		return false;
	}

	// One type is completed at a time, if multiple need doing then they
	// are queued up
	private boolean typeCompletionInProgress = false;
	private List typesForCompletion = new ArrayList<>();

	@Override
	protected void completeBinaryType(ResolvedType ret) {
		if (isLocallyDefined(ret.getName())) {
			if (typeCompletionInProgress) {
				typesForCompletion.add(ret);
			} else {
				try {
					typeCompletionInProgress = true;
					completeHierarchyForType(ret);
				} finally {
					typeCompletionInProgress = false;
				}
				while (typesForCompletion.size() != 0) {
					ResolvedType rt = typesForCompletion.get(0);
					completeHierarchyForType(rt);
					typesForCompletion.remove(0);
				}
			}
		} else {
			if (!ret.needsModifiableDelegate()) {
				ret = completeNonLocalType(ret);
			}
		}
	}

	private void completeHierarchyForType(ResolvedType ret) {
		getLint().typeNotExposedToWeaver.setSuppressed(true);
		weaveInterTypeDeclarations(ret);
		getLint().typeNotExposedToWeaver.setSuppressed(false);
	}

	protected boolean needsCompletion() {
		return true;
	}

	@Override
	public boolean isLocallyDefined(String classname) {
		return weavingContext.isLocallyDefined(classname);
	}

	protected ResolvedType completeNonLocalType(ResolvedType ret) {
		if (ret.isMissing()) {
			return ret; // who knows ?!?
		}
		ResolvedType toResolve = ret;
		if (ret.isParameterizedType() || ret.isGenericType()) {
			toResolve = toResolve.getGenericType();
		}
		ReferenceTypeDelegate rtd = resolveReflectionTypeDelegate((ReferenceType) toResolve, getClassLoader());
		((ReferenceType) ret).setDelegate(rtd);
		return ret;
	}

	@Override
	public void storeClass(JavaClass clazz) {
		ensureRepositorySetup();
		delegate.storeClass(clazz);
	}

	@Override
	public void accept(IVisitor visitor) {
		visitor.visitObject("Class loader:");
		visitor.visitObject(classLoaderString);
		visitor.visitObject("Class loader parent:");
		visitor.visitObject(classLoaderParentString);
		super.accept(visitor);
	}

	public boolean isLoadtimeWeaving() {
		return true;
	}

}