My java web application is currently working on jre 1.5. I have upgraded it to jre 1.7. But found that the web pages are becoming unresponsive at times. What might be the reason?
There's nowhere near enough information in this post to know. What research have you done? Have you monitored CPU? Memory? Ran a profiler to get the bottleneck?
Also, think about what else changed. Did you upgrade your application server? Any jars?