PHP is perhaps the most popular language used with websites with database-driven content. However, since you already know Java, all you need to do is to install a server/container as Tomcat and start coding JSP (JavaServer Pages) and Servlets. Here are some tutorials about JSP:
http://www.jsptut.com/
http://www.apl.jhu.edu/~hall/java/Servlet-Tutorial/
There's also a good ebook that you will want to have:
http://www.theserverside.com/books/a...lknerJones.zip
This book is just awesome. The problem is, you will need to register before downloading. Not a big deal, really.
Basically, to have a server up and running, all you will need is a computer (with Linux or any other OS) and
Apache tomcat Web server:
http://tomcat.apache.org/
MySQL:
http://www.mysql.com/
Java - MySQL drivers:
http://www.mysql.com/products/connector/
And a working Java Runtime Enviroment. Get the one from Sun's website. I've just started getting into JSP/Servlets, so if you get stuck let me know

.
That's for the server part. To develop your pages, I recommend Eclipse WTP. It has support for many advanced features, like starting and stopping Tomcat, among other finessess and plugins. I can give a hand to set up Eclipse WTP if you need it.
Now, I'm not saying you should not use PHP (or any other language for that matter), but since you already know Java, it feels pointless to learn yet another language since Java is very robust, very well supported and it really shines on the web side
Best of luck!