Java Virtual Machine Statistics Monitoring Tool

To diagnose heap issues
jstat  -gcutil  <id> 2s

Option                 Displays...
class                     Statistics on the behavior of the class loader.
compiler               Statistics of the behavior of the HotSpot Just-in-Time compiler.
gc                         Statistics of the behavior of the garbage collected heap.
gccapacity            Statistics of the capacities of the generations and their corresponding spaces.
gccause                Summary of garbage collection statistics (same as -gcutil), with the cause of the                                    last and current (if applicable) garbage collection events.
gcnew                  Statistics of the behavior of the new generation.
gcnewcapacity     Statistics of the sizes of the new generations and its corresponding spaces.
gcold                    Statistics of the behavior of the old and permanent generations.
gcoldcapacity       Statistics of the sizes of the old generation.
gcpermcapacity Statistics of the sizes of the permanent generation.
gcutil                    Summary of garbage collection statistics.
printcompilation HotSpot compilation method statistics.

http://docs.oracle.com/javase/7/docs/technotes/tools/share/jstat.html