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JMockit is a Java toolkit for automated developer testing. It contains mocking/faking APIs and a code coverage tool, supporting both JUnit and TestNG. The mocking APIs allow all kinds of Java code, without testability restrictions, to be tested in isolation from selected dependencies.

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/*
 * Copyright (c) 2006 JMockit developers
 * This file is subject to the terms of the MIT license (see LICENSE.txt).
 */
package mockit.internal.state;

import java.lang.instrument.*;
import java.security.*;
import java.util.*;
import javax.annotation.*;

import mockit.internal.startup.*;

/**
 * Holds a map of internal class names to the corresponding class files (bytecode arrays), for the classes
 * that have already been loaded during the test run.
 * These classfiles are not necessarily the same as those stored in the corresponding ".class" files
 * available from the runtime classpath.
 * If any third-party {@link ClassFileTransformer}s are active, those original classfiles may have been modified before
 * being loaded by the JVM.
 * JMockit installs a ClassFileTransformer of its own which saves all potentially modified classfiles
 * here.
 * 
 * This bytecode cache allows classes to be mocked and un-mocked correctly, even in the presence of other
 * bytecode modification agents such as the AspectJ load-time weaver.
 */
public final class CachedClassfiles implements ClassFileTransformer
{
   @Nonnull public static final CachedClassfiles INSTANCE = new CachedClassfiles();

   @Nonnull private final Map> classLoadersAndClassfiles;
   @Nullable private Class classBeingCached;

   private CachedClassfiles() {
      classLoadersAndClassfiles = new WeakHashMap<>(2);
   }

   @Nullable @Override
   public byte[] transform(
      @Nullable ClassLoader loader, String classDesc, @Nullable Class classBeingRedefinedOrRetransformed,
      @Nullable ProtectionDomain protectionDomain, @Nonnull byte[] classfileBuffer
   ) {
      if (classDesc != null) { // can be null for Java 8 lambdas
         if (classBeingRedefinedOrRetransformed != null && classBeingRedefinedOrRetransformed == classBeingCached) {
            addClassfile(loader, classDesc, classfileBuffer);
            classBeingCached = null;
         }
      }

      return null;
   }

   private void addClassfile(@Nullable ClassLoader loader, @Nonnull String classDesc, @Nonnull byte[] classfile) {
      Map classfiles = getClassfiles(loader);
      classfiles.put(classDesc, classfile);
   }

   @Nonnull
   private Map getClassfiles(@Nullable ClassLoader loader) {
      Map classfiles = classLoadersAndClassfiles.get(loader);

      if (classfiles == null) {
         classfiles = new HashMap<>(100);
         classLoadersAndClassfiles.put(loader, classfiles);
      }

      return classfiles;
   }

   @Nullable
   private byte[] findClassfile(@Nonnull Class aClass) {
      String className = aClass.getName();

      // Discards an invalid numerical suffix from a synthetic Java 8 class, if detected.
      int p = className.indexOf('/');
      if (p > 0) className = className.substring(0, p);

      Map classfiles = getClassfiles(aClass.getClassLoader());
      return classfiles.get(className.replace('.', '/'));
   }

   @Nullable
   public static synchronized byte[] getClassfile(@Nonnull String classDesc) {
      return INSTANCE.findClassfile(classDesc);
   }

   @Nullable
   private byte[] findClassfile(@Nonnull String classDesc) {
      byte[] classfile = null;

      for (Map classfiles : classLoadersAndClassfiles.values()) {
         classfile = classfiles.get(classDesc);

         if (classfile != null) {
            return classfile;
         }
      }

      Class desiredClass = Startup.getClassIfLoaded(classDesc);

      if (desiredClass != null) {
         classBeingCached = desiredClass;
         Startup.retransformClass(desiredClass);
         ClassLoader classLoader = desiredClass.getClassLoader();
         classfile = INSTANCE.findClassfile(classLoader, classDesc);
      }

      return classfile;
   }

   @Nullable
   private synchronized byte[] findClassfile(@Nullable ClassLoader loader, @Nonnull String classDesc) {
      Map classfiles = getClassfiles(loader);
      return classfiles.get(classDesc);
   }

   @Nullable
   public static synchronized byte[] getClassfile(@Nonnull Class aClass) {
      byte[] cached = INSTANCE.findClassfile(aClass);
      if (cached != null) return cached;

      INSTANCE.classBeingCached = aClass;
      Startup.retransformClass(aClass);
      return INSTANCE.findClassfile(aClass);
   }

   @Nullable
   public static byte[] getClassfile(@Nullable ClassLoader loader, @Nonnull String internalClassName) {
      return INSTANCE.findClassfile(loader, internalClassName);
   }

   public static void addClassfile(@Nonnull Class aClass, @Nonnull byte[] classfile) {
      INSTANCE.addClassfile(aClass.getClassLoader(), aClass.getName().replace('.', '/'), classfile);
   }
}