The two main opensource IDE are Eclipse & Netbeans:
Eclipse is the jack of all trades with many plugins, you'll need to know which plugins to add in order to build your environment however it's really customizable to suit your needs.
Netbeans is the state of the art Java & JEE integration with less plugins and customization hence less cumbersome. As long as you only need to use its features you're on a smooth experience.
You should try both in order to define which one you prefer based on your tastes and needs (GWT/GAE support is better in Eclipse).
Comments
The two main opensource IDE are Eclipse & Netbeans:
Eclipse is the jack of all trades with many plugins, you'll need to know which plugins to add in order to build your environment however it's really customizable to suit your needs.
Netbeans is the state of the art Java & JEE integration with less plugins and customization hence less cumbersome. As long as you only need to use its features you're on a smooth experience.
You should try both in order to define which one you prefer based on your tastes and needs (GWT/GAE support is better in Eclipse).