I'm going to say this with no references to back it up, but overall I believe PHP just has more support.
IMHO, PHP is far superior for developing web sites.
A little history of Java:
It was originally developed in the 1990s as a home control programming language. It failed because it was cumbersome and too complex.
In the late 1990s, it was touted as "the language that was going to dominate the web." It failed because at the time Sun Microsystems was pushing the use of Java applets, many of which were 20 meg or larger--at a time when almost all web users were on dial-up connections. It would literally take 20 minutes to an hour to download the applet so that people could use the web site.
The move to Java Server Pages (JSP) was a big improvement. That kept the Java code on the server-side, which minimized the performance problems. It is not widely used primarily due to the high cost of developing applications.
Very few web sites use JSP, primarily because of the expense of the programming staff and annual licensing issues with large scale applications.
I have worked on multi-million dollar web site projects. Based upon what I have seen over the years, I would never recommend the use of Java or JSP. Just my humble opinion. . .
FYI. FaceBook, one of the most heavily used web sites on the Internet was built using PHP.
"Democracy is two wolves and a lamb voting on what to have for lunch. Liberty is a well-armed lamb contesting the vote." -- Benjamin Franklin
PHP is the de facto Web 2.0 programming language.It has by far the best support.
ASP is a good language but it costs money to use exiting support for it,for some people in the industry it might be worth it to buy these modules but I think that most people would agree,that for web development,php is the way to go.
one more feature which has helped in quick growth of PHP is the availability of PHP based hosting service.
i have worked on ASP PHP and JSP all 3 and found that PHP is good if you want to implement something ASAP.
but JAVA rivals this by providing nearly everything in jar packages.