Clean Up Your Mess: Managing Temp Files in Java Apps

was always taught to leave a place cleaner than when I got there, and I hold my applications to the same standard. However, a recent Java project I worked on was doing just the opposite, dumping temporary files on the user's system and never cleaning them up. Fearing the inevitable tech support call after the application filled the user's hard disk, I had to fix the problem.

The scenario was simple enough: like many applications, mine had to create temporary files on the user's system during its execution and it then—in theory—would clean them up at exit. The requirement for temporary files (short-lived files normally created in a designated temporary directory) varies from project to project. Applications requiring large batch processing may use temporary files as an intermediate step, while other apps use them to buffer input and output (I/O) from a network or a device. In my case, the temporary files, commonly called temp files, were actually Java Archives (JARs) created at runtime and loaded dynamically into the application (which I later found exasperated the situation). As the project deadline approached, I had to find the problem and, more importantly, develop a solution.