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JMockit is a Java toolkit for developer (unit/integration) testing. It contains mocking APIs and other tools, 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) 2006-2012 Rogério Liesenfeld
 * This file is subject to the terms of the MIT license (see LICENSE.txt).
 */
package mockit.internal.startup;

import java.io.*;
import java.lang.instrument.*;

import mockit.external.asm4.*;
import mockit.internal.*;
import mockit.internal.util.*;

final class ToolLoader extends ClassVisitor
{
   private final String toolClassName;
   private boolean loadClassFileTransformer;

   ToolLoader(String toolClassName) { this.toolClassName = toolClassName; }

   void loadTool()
   {
      ClassReader cr;

      try {
         cr = ClassFile.readClass(toolClassName);
      }
      catch (IOException ignore) {
         System.out.println("JMockit: external tool class \"" + toolClassName + "\" not available in classpath");
         return;
      }

      try {
         cr.accept(this, ClassReader.SKIP_DEBUG);
         System.out.println("JMockit: loaded external tool " + toolClassName);
      }
      catch (IllegalStateException ignore) {}
   }

   @Override
   public void visit(int version, int access, String name, String signature, String superName, String[] interfaces)
   {
      if (interfaces != null && containsClassFileTransformer(interfaces)) {
         loadClassFileTransformer = true;
      }
   }

   private boolean containsClassFileTransformer(String[] interfaces)
   {
      for (String anInterface : interfaces) {
         if ("java/lang/instrument/ClassFileTransformer".equals(anInterface)) {
            return true;
         }
      }

      return false;
   }

   @Override
   public void visitEnd()
   {
      if (loadClassFileTransformer) {
         createAndInstallSpecifiedClassFileTransformer();
      }
      else {
         setUpStartupMock();
      }
   }

   private void createAndInstallSpecifiedClassFileTransformer()
   {
      Class transformerClass = Utilities.loadClass(toolClassName);
      ClassFileTransformer transformer = Utilities.newInstance(transformerClass);

      Startup.instrumentation().addTransformer(transformer);
   }

   private void setUpStartupMock()
   {
      Class mockClass;

      try {
         mockClass = Class.forName(toolClassName);
      }
      catch (ClassNotFoundException e) {
         throw new RuntimeException(e);
      }

      try {
         new RedefinitionEngine(null, mockClass).setUpStartupMock();
      }
      catch (TypeNotPresentException e) {
         // OK, ignores the startup mock if the necessary third-party class files are not in the classpath.
         System.out.println(e);
      }
   }
}