You have the classic deadlock associated with Runtime.exec() and ProcessBuilder. You are waiting for the process to complete but it can't complete because either the process stdout or stderr buffer becomes full. The process then suspends until there is room in the buffer to place more output but since you do not process either the stdout or stderr to make more room available until the process completes you have a deadlock.

You need to read ALL the sections of http://www.javaworld.com/article/2071275/core-java/when-runtime-exec---won-t.html and implement ALL the recommendations.