Introspection: JConsole vs VisualVM vs JRockit Mission Control

Java VisualVM comes with the JDK since JDK 6 update 7.

Common Java Problems:
OutOfMemory
...

http://java.sun.com/developer/technicalArticles/J2SE/monitoring/

http://blogs.sun.com/jmxetc/entry/troubleshooting_connection_problems_in_jconsole