When i start my Weblogic 12 and deploy my app for first time everything runs good, but when I undeploy the app and deploy again it gives me a java heap space when the app works with streams at one point, but first time it is deployed it runs good. If I want to restart my app, I need to restart weblogic to have no error.
I don't know why first time everything is ok, and later when restart only the app, it gives me that error...
My guess is that you have some memory leaks.
I advice you to start jvisualvm (comes with jdk) and monitor and profile the memory for the java process started by weblogic.
Another option is to generate a heapdump and analize it with a tool like MAT http://www.eclipse.org/mat/