An always-running thread in Servelts

Question

• I need to built a thread/process that is always running, and can be queried through other servelts and JSP pages...
• This thread/process will be dealing with large files, so it will cache file blocks to reduce file accesses (plus some other processing)...
• So, that thread/process will be loaded and waiting for any queries coming, to answer... as long as the server is running.

I though about making a static class common between all the servelt classes, but I found out that will not work (tomcat deals with each new servelt as a totally new program)

So what are the other options I can try??

Answer 1

Other options in addition to the ones proposed by Morritz

1. Inside Tomcat: register a global object accessible by all servlets using the Global JNDI
2. Within the same JVM: start you shared resources (your static class, repository, etc...) and Tomcat programmatically (embedded) using a launcher like The Java Service Wrapper. You will need to define a small API implemented by your shared resource and usable by your servlets.
3. Distributed accross JVM: memcached, hazelcast, etc...

Answer 2

I think you have two options:

1. Use the ServletContext to access application-wide scope objects.
2. Use a more sophisticated solution, such as ehcache to put your data in memory.