Is there any open source automated testing tool for middleware application? if yes, can anyone please provide links for that?

There are many, but after 7 years, have you found the best choice ever?

You can try Black Duck products mainy BlackDuck Protex. Click on this link for more information. 

Link : https://www.blackducksoftware.com/products/black-duck-suite/protex

Try Selenium. 

http://www.seleniumhq.org/

SoapUI is very useful testing tool for Soap and Rest services. you can use the freeware Open Source version and you can try the pro version free for14 days. 

Note: the Pro version adds up a lot of useful functionaries and it is not that expensive 

http://www.soapui.org/ 

No short answer for your question. There are a lot of open source tools available out on the internet. You might need to do a POC(Proof Of Concept) on these tools to see which tool meets your needs. From past experience from quite a few POC's on open source tools we were unable to find anything which matched our needs under the requirements/resources/timelines that we had to adhere; so we opted for a well known Paid Tool after going through a few demo's.

This doesnt mean i am discouraging you to use open source tools but it all depends on your requirements. 

Quoting from wikipedia you can check out the link for more tools:

http://en.wikipedia.org/wiki/List_of_GUI_testing_tools

www.opensourcetesting.org