code: public InputStream openSource(String packageName, String fileName) throws IOException {
          SourceFile sourceFile = findSourceFile(packageName, fileName);
          return sourceFile.getInputStream();
      }
docs: Open an input stream on a source file in given package.
  
  @param packageName
  the name of the package containing the class whose source file
  is given
  @param fileName
  the unqualified name of the source file
  @return an InputStream on the source file
  @throws IOException
  if a matching source file cannot be found