Hi, Is there a way to encode lowercase digits for Code 39 generation in Java application? I have little knowledge on barcode specification. After trying to encode lowercase letters many times, the Code 39 barcode images are still invalid. Any advice on this is greatly appreciated.

You can use a third party control called Java Code 39 barcode generator SDK to do this.  When you put this in Google, you can find much information like this. It's easy to use. You just follow the detailed tutorial of generating barcode in Java.