Scala example source code file (ASMTransformer.java)

This example Scala source code file (ASMTransformer.java) is included in my "Source Code Warehouse" project. The intent of this project is to help you more easily find Scala source code examples by using tags.

All credit for the original source code belongs to scala-lang.org; I'm just trying to make examples easier to find. (For my Scala work, see my Scala examples and tutorials.)

Scala tags/keywords

asm, asmtransformer, classfiletransformer, classloader, classreader, classwriter, profilervisitor, protectiondomain, runtimeexception, string, unexpected

The ASMTransformer.java Scala example source code

/* NEST (New Scala Test)
 * Copyright 2007-2013 LAMP/EPFL
 * @author Grzegorz Kossakowski
 */

package scala.tools.partest.javaagent;

import java.lang.instrument.ClassFileTransformer;
import java.security.ProtectionDomain;

import scala.tools.asm.ClassReader;
import scala.tools.asm.ClassWriter;

public class ASMTransformer implements ClassFileTransformer {

  private boolean shouldTransform(String className) {
    return
        // do not instrument instrumentation logic (in order to avoid infinite recursion)
        !className.startsWith("scala/tools/partest/instrumented/") &&
        !className.startsWith("scala/tools/partest/javaagent/") &&
        // we instrument all classes from empty package
        (!className.contains("/") ||
        // we instrument all classes from scala package
        className.startsWith("scala/") ||
        // we instrument all classes from `instrumented` package
        className.startsWith("instrumented/"));
  }

        public byte[] transform(final ClassLoader classLoader, final String className, Class<?> classBeingRedefined, ProtectionDomain protectionDomain, byte[] classfileBuffer) {
          if (shouldTransform(className)) {
            ClassWriter writer = new ClassWriter(ClassWriter.COMPUTE_MAXS) {
              @Override protected String getCommonSuperClass(final String type1, final String type2) {
                // Since we are not recomputing stack frame map, this should never be called we override this method because
                // default implementation uses reflection for implementation and might try to load the class that we are
                // currently processing. That leads to weird results like swallowed exceptions and classes being not
                // transformed.
                throw new RuntimeException("Unexpected call to getCommonSuperClass(" + type1 + ", " + type2 +
                    ") while transforming " + className);
              }
            };
                ProfilerVisitor visitor = new ProfilerVisitor(writer);
                ClassReader reader = new ClassReader(classfileBuffer);
                reader.accept(visitor, 0);
                return writer.toByteArray();
          } else {
            return classfileBuffer;
          }
        }
}