The Java software development kit documentation can be downloaded from java.sun.com, in the form of a ZIP file with tens of thousands of linked HTML file. This seems like an ideal canonical form for this documentation, but it is inconvenient to use, and inconvenient to have so many files sitting around.
If your development machine runs Windows, a Windows HTML Help is more convenient; it consists of a handful of files (mostly one large CHM file) and offers good search and browse features. It can be unpacked or moved around far more quickly. Franck Allimant processes the HTML from Sun for each new Java release, and makes the CHMs etc. available on his web site. Recommended.
Allimant has been doing this for quite a few years now; I suspect it was unauthorized at first, but some kind of peace was made with Sun, which now links to the site.