code: public byte[] transform(ClassLoader loader,
                              String className,
                              Class<?> classBeingRedefined,
                              ProtectionDomain protectionDomain,
                              byte[] classfileBuffer) throws IllegalClassFormatException {
  
          // Don't modify our own package
          if (className.startsWith(Transformer.class.getPackage().getName().replaceAll("\\.", "/"))) {
              return null;
          }
  
          // Don't modify the java.util.logging classes
          if (className.startsWith("java/util/logging/")) {
              return null;
          }
  
          boolean include = false;
          for (String s : includesList) {
              if (className.startsWith(s) || s.equals("/")) {
                  include = true;
                  break;
              }
          }
  
          for (String s : excludesList) {
              if (className.startsWith(s) || s.equals("/")) {
                  include = false;
                  break;
              }
          }
  
          if (include == false) {
              return null;
          }
  
          String internalPackageName = className.replaceAll("/[^/]+$", "");
          PackageInfo packageInfo = getPackageInfo(internalPackageName);
          if (packageInfo == null && loader != null) {
              String packageInfoResourceName = internalPackageName + "/package-info.class";
              InputStream is = loader.getResourceAsStream(packageInfoResourceName);
              packageInfo = processPackageInfo(is);
              addPackageInfo(packageInfo);
          }
  
          try {
              return transform(new ByteArrayInputStream(classfileBuffer));
          } catch (Throwable t) {
              t.printStackTrace();
              return null;
          }
      }
docs: Instrument the classes.