Develop Reference

Extract metadata from a MP3/OGG with Java

In my final project for this course, I need to use Java to make an aplication with real use. I chose to make a music library, but I need to extract metadata from all MP3/OGG files in the library folder.
For MP3 files I think with jid3 (https://blinkenlights.org/jid3/) it's ok, but... What can I make with OGG files? Is there any Java library for both files types?
Thanks! And sorry for my english.

See you that, Juanjo. http://diariodeuninformaticorenegado.hol.es/es/portfolio/ragml-rename-automatic-and-generate-music-library/ !! :D
This program generate a html library of a directory.

Extracting contents from a webpage and comparing using Java

I am developing a Java project in which i have a sub-module where i need to extract contents [text, image, color] from a webpage and compare it with another webpage. I am planning to use WinHTTrack software for downloading the webpage locally, but the problem is it doesn't save it as HTML. How can i download a webpage with HTML extension using softwares such as WinHTTrack [or just saving the webpage through ctrl+s is enogh.?]. Also i am planning to use HTML Parsers to extract the 3 content types[text, image, color],after downloading the webpage locally. So which parser to go with.?

WEll I use Httrack and it fetches html files as well. You are probably taking winhttrack project file as the only output file, but if you check inside the project directory there are html files (together with images, etc). I would suggest using - http://htmlparser.sourceforge.net/. It is a java library and since your project is a Java project it should be fairly easy to use it. You can also save the whole website locally using org.htmlparser.parserapplications.SiteCapturer (and specify whether resources such as images should be captured as well). Hope it helps.

Writing to text file in GAE

Has anyone figured out a way to write to text file on the server-side using Google App Engine (GAE). I understand the limitation of not being able to use FileWriter, but I was wondering if there was a work around. Thanks!

Not only can you not use FileWriter, you can not write to files at all, since you do not have access to the filesystem from within the GAE. It's impossible by design.
As a "work-around" (which I hesistate designating as such since this is a technically valid solution), you can emulate a filesystem using the GAE datastore using GAEVFS: http://code.google.com/p/gaevfs/

Try the blob store. Now, you can write to the blob store like you write files to the file system.
https://developers.google.com/appengine/docs/java/blobstore/overview#Writing_Files_to_the_Blobstore

Multiple file upload (even folder)

I'm looking for an easy to use (free) "module" that can upload multiple files / folders.
It must:
Support image files
be user-friendly
be customizable
It may be written in:
RoR (Ruby On Rails)
Java
Flash
Thanks in advance.

Have a look here http://jimneath.org/2008/04/17/paperclip-attaching-files-in-rails the article explains how to use Paperclip
Or you could try SWFUpload , a Javascript & Flash solution for file uploads

Uploading multiple files and folders in one go is not supported by HTML, which means that your options are Flash or a Java applet. Ruby on Rails isn't going to help you because it's a server-side framework that generates HTML.

What is the best way of opening PDFs from a JSP?

I would like some guidance on the best way of launching PDFs from a browser.
I have a JSP that takes some parameters and based on this downloads a PDF from my Documentum server. The files are stored on my local file system. I then provide the user with a bunch of links to the PDFs so they can click on them to launch the PDF.
Is there a best practice method of doing this?
Thanks.

There is nothing special to do: a link is sufficient. But you can add target="_new" if you want the browser to open the pdf in a new window.
Just make sure that the content-type returned for the pdf is application/pdf.