Quartz

• Quartz

Quartz is a full-featured, open source job scheduling service that can be integrated with, or used along side virtually any Java application - from the smallest stand-alone application to the largest e-commerce system.
Quartz can be used to create simple or complex schedules for executing tens, hundreds, or even tens-of-thousands of jobs
http://quartz-scheduler.org/

JRebel

JRebel, formerly known as JavaRebel, is a plug-in for the Java Virtual Machine (JVM) that enables instant reloading of changes made to a Java class file.
JRebel is an alternative solution to updating classes which does not require a debugging session to be started
Instead it monitors the file system for changes and updates the classes in-memory.
This means that only classes compiled to ".class" files will be updated and changes to classes in JAR files will be ignored.
JRebel imposes a performance overhead on the application and should not be used in production or performance tests. It is meant to be a development tool only.

Starting from version 1.4, the Java Virtual Machine includes a hot swapping feature that allows developers to update the code on-the-fly during debugging
However hot swapping was limited to updating method bodies only, and trying to add methods and fields to classes would not succeed.

https://en.wikipedia.org/wiki/JRebel

Messaging

• RabbitMQ?

Robust messaging for applications
Easy to use
Runs on all major operating systems
Supports a huge number of developer platforms
Open source and commercially supported
http://www.rabbitmq.com/

• zeromq

The socket library that acts as a concurrency framework.
Faster than TCP, for clustered products and supercomputing.
Carries messages across inproc, IPC, TCP, and multicast.
http://www.zeromq.org/

• Apache ActiveMQ

Apache ActiveMQ ™ is the most popular and powerful open source messaging and Integration Patterns server.
http://activemq.apache.org/