There are times when a nice quick and simple way of diagnosing memory usage is required. Sure there are lots of amazing and powerful tools, however what follows is a very simple solution!
<%@ page import="java.lang.management.*, java.util.*" %>
<%response.setContentType("text/plain");
Iterator iter = ManagementFactory.getMemoryPoolMXBeans().iterator();
while(iter.hasNext()) {
MemoryPoolMXBean item = (MemoryPoolMXBean) iter.next();
MemoryUsage mu = item.getUsage();
long used = mu.getUsed();
long committed = mu.getCommitted();
long max = mu.getMax();
long usedMB = (long)(used/(1024*1024));
long committedMB = (long)(committed/(1024*1024));
long maxMB = (long)(max/(1024*1024));
%>
MEMORY TYPE: <%=item.getName()%>
Used: <%=used%> (<%=usedMB%>MB)
Committed: <%=committed%> (<%=committedMB%>MB)
Max: <%=max%> (<%=maxMB%>MB)
<%}%>
Whilst this won't fix issues like java.lang.OutOfMemoryError: PermGen space it will help show whether other areas of memory are also having an issue and possibly allow you to get early sight of the problem.