This code directly writes an HTTP parameter to JSP output, which allows for a cross site scripting vulnerability. See http://en.wikipedia.org/wiki/Cross-site_scripting for more information.

FindBugs looks only for the most blatant, obvious cases of cross site scripting. If FindBugs found any, you almost certainly have more cross site scripting vulnerabilities that FindBugs doesn't report. If you are concerned about cross site scripting, you should seriously consider using a commercial static analysis or pen-testing tool.