JAMon allows developers to easily monitor production applications.
Edit by : The Java Application Monitor (JAMon) is a free, simple, high performance, thread safe, Java API that allows developers to easily monitor production applications.

JAMon can be used to determine application performance bottlenecks, user/application interactions, track application scalability, and more.
JAMon 1.0 gathers aggregate performance statistics such as hits, Execution times (total, average, minimum, maximum, standard deviation), as well as concurrency information such as simultaneous application requests.
JAMon 2.7 comes with several ways to monitor your application that require no application code changes. Usually all that is required is to add a line to an xml file, and make the jamon jar file available. Some examples:
-JDBC/SQL monitoring via the JAMon JDBC proxy driver (works with any other JDBC driver),
Log4j monitoring via the JAMon log4j Appender,
-HTTP Monitoring. Monitor requests/responses to Tomcat, Jetty, JBoss or any other JAVA web container.
-EJB3 monitoring using the JAMon EJB interceptor.
JAMon 2.0 aggregates ANY numeric entity (such as bytes sent, dollars purchased, phone call duration) associated with a key (label and units).
JAMon 2.1 adds the ability to track both summary statistics and detils for Interfaces/JDBC/SQL/Exceptions.
JAMon 2.2 adds the ability to track JDBC/SQL/Exceptions vi the new JAMonDriver JDBC Driver using a URL (not changing code)
JAMon 2.3 minor bug fixes
JAMon 2.4/2.5 Introduction of JAMon Buffer Listeners to track Details of Interest such as extreme values, or most recent values
JAMon 2.6 log4j monitoring. Track stats on log4j method calls, as well as have the ability to tail data written to log4j through the JAMon web application.
JAMon 2.7 Add the ability to flexibly monitor Tomcat, Jetty, Jboss. More flexible detail tracking was added. Also better exception tracking was added.
JAMon data can also be programmatically accessed or queried and your program can take actions on the results you can free download JAMon 2.7 now.