if (optionalFileName == null && Boolean.getBoolean(ICookable.SYSTEM_PROPERTY_SOURCE_DEBUGGING_ENABLE)) {
String dirName = System.getProperty(ICookable.SYSTEM_PROPERTY_SOURCE_DEBUGGING_DIR);
File dir = dirName == null ? null : new File(dirName);
File temporaryFile = File.createTempFile("janino", ".java", dir);
temporaryFile.deleteOnExit();
in = new TeeReader(
in, // in
new FileWriter(temporaryFile), // out
true // closeWriterOnEOF
);
optionalFileName = temporaryFile.getAbsolutePath();