Makes perfect sense, re: an improved web app. The testing of this is pretty straight forward.
Before the patch:
1. With a '+' or other non-encoded URL character in the real system path containing Hadoop, go to http://jt:50030/jobhistory.jsp.
2. Click on one of the job ids to view job history details.
3.a. Get a 500 response due to a FileNotFound exception ex. java.io.FileNotFoundException: File file:/Users/esammer/Applications/hadoop-0.20.1 152/logs/history/done/ (note the '+' in the Hadoop dir is a space).
After the patch:
1.5. Observe the '+' is encoded as %2B in the job id link.
3.b. Instead of 3.a., observe that the page loads successfully.
This is the test case I followed. This patch is very specific in that it deals with this singular link. The motivation behind doing a deep dive into the web app architecture is to address other places where user input or OS file system paths are used to build links for similar reasons. Let me know if this doesn't make sense.