I wanted to add what might be very pertinent information for projects using maven and eclipse / wtp. What I did to get the Javadocs to attach nicely was the following 2 steps.
1) I am using glassfish so using the glassfish plugin site I installed the java ee 6 (or 7) documentation. You can easily view this documentation with Help->Java EE 6 docs. I copied the URL from here.
2) Opened my projects build path and went to the libraries tab. Opened the Maven Dependencies and found the java ee 6 api entry (this should be part of the maven project). Opened this up and was able to add a location for the javadocs for the api. I pasted the file:/// url I had copied.
Then I verified this worked by using the ctrl + shift plus mouse pointer hover over some of the java ee 6 classes and methods.
I hope this information will be useful to other who searched and got here but didn't find the solution they were looking for (or for those who now use Maven!).