List of useful libraries (mostly free) for common tasks, so you don’t have to write your own. Use your browser search to find the probably-useful library you need.
Java Web Server, supports JSP, Servlets and Java EE.
Apache Jakarta Commons FileUpload
Servlet-side Library for easy management of file uploads.
Apache Jakarta Commons HttpClient
Make HTTP connections.
Apache Jakarta Commons Net
Support network protocols such as FTP, SMTP, POP3, etc.
Draw and render 3D models in Java.
Send/Receive email easily. Protocol independant, but ships with IMAP, SMTP and POP3.