How to write a servlet filter

Since you can call HttpServletResponse.getWriter() only once, it is a little bit tricky to add more output in servlet filter, because it is very likely your call to getWriter to be failed.

Come examples about filter can be found at:
http://download.oracle.com/docs/cd/A97329_03/web.902/a95878/filters.htm

Tips on svnmailer

svnmailer is a great tool to help admin monitor changes made in SVN repositories.
There're zillions of nice articles/docs on how to config it. So I won't bother adding one more here.
Only a couple of tips that I hope can help myself and you trouble-shooting it:

1. To remove =3D kind of characters in email
Looks like the current version of svnmailer (1.08x) and Python 2.4.3 will generate characters like =3D to replace special character = in the notification email. This is caused by the default encoding used by svnmailer (quoted-printable). The quick fix is to set it to utf8.
To apply the quick fix, open mailer.conf file, put the following setting in [defaults] section:

mail_transfer_encoding = 8bit

2. To test svnmailer without really committing anything into the repository:
After your configured svnmailer, you probably want to test the settings, but do not want to really commit anything into the repository. A quick command, which was actually suggested by svnmailer doc, is:

sudo -u apache ./post-commit [Repo Path] [Ver No.]

e.g.:

sudo -u apache ./post-commit /var/svn/2009 55

will send notification of change 55 of repository /var/svn/2009 to the designated email address.

Cheers!