I just cut HtmlUnit’s build time by about 20% by changing four lines of code. How? HtmlUnit keeps a small cache of web requests in a HashMap, keyed on the request URL. The problem with this is twofold:
- The URL.hashCode() method is synchronized.
- The URL.hashCode() method triggers DNS lookups for the URL hosts.
The impact of item 2 was magnified by the fact that some of the HtmlUnit unit tests use a mock web connection to connect to fake URLs. DNS (non)resolution of these fake URLs took an especially long time.
The fix was to key the map entries on the value of URL.toString() instead. Apparently I’m not the first person to stumble across this problem. So think twice before coding your next HashMap<URL, XXX> 
