Unfortunately, sometimes the only way to debug a program is by going through its long log files.
I searched for a decent log viewer for a while now, and haven't found a real solution. The only program that seemed to be most appropriate was Chainsaw with its Socket connector but after a few short uses the program proved to be buggy and unresponsive at best.
For my purposes, a log viewer should at least be able to mark log levels (for example with different colors) and perform easy filtering based on packages and free-text.
Is there any other (free) log viewer? I'm looking for anything that could work well with log4j.
You didn't mention an OS, so I'll mention this though it is only on Windows.
Bare Metal Software makes a product called BareTail that has a nice interface and works well. They have a free version with a startup nag screen, a licensed version with no nag, and a pro version with additional features. It has configurable highlighting based on matching lines against keywords.
They also have a BareGrep product too, which provides similar grep capabilities. Both are excellent and very stable and better than anything I've seen on Windows. I liked them so much I bought the bundle with both pro versions for $50.