One option is to use wayback machine, which seems to contain the document (here's direct link to pdf version). However I would also be interested to find out what Oracle did with it and do they intend to get rid of it.
There's a discussion on Oracle forums about this being raised to OTN support, but no response is mentioned.
Update on 17.6.2014: There's now a forum posting added to the site explaining the following:
Those Java Code Conventions were written in 1999 and have not been
maintained since.
The information might not be up to date; links within the documents
might not work. That is why the pages were removed. Unfortunately
there are other sites that point to that document which were not
updated.
To avoid confusions we have re-posted the original document –with an
appropriate disclaimer about the information not being up to date-
while we clean up those other sites.
Try Code Conventions for the Java Programming Language
And indeed, seems the page has been restored.
与恶龙缠斗过久,自身亦成为恶龙;凝视深渊过久,深渊将回以凝视…