Proxying a Request to Localhost in Java

It can be very convenient when developing to server based application to run them using "localhost" in order to maintain consistency between developer machines. This is normally a good idea but there is a small case where this can cause problems.

Consider if you are running a local http proxy on your machine in order to capture your HTTP traffic. (Cough perhaps even the one in JDeveloper I work on). Then you might run into Java bug 6737819. Basically by default JDK 1.6 was hard coded not to send any request to localhost via a proxy which of course was a bit of a pain. Luckily a workaround was put in where you could put the string "~localhost" in your nonProxyHosts entry to turn of this feature:

java -client -classpath classes -Dhttp.proxyHost=localhost 
-Dhttp.proxyPort=8099 -Dhttp.nonProxyHosts=~localhost 
-Dhttps.proxyHost=localhost 
-Dhttps.proxyPort=8099 client.Example 

Now moving forward to JDK 1.7 this workaround no longer works; but you need to take care to define nonProxyHosts as an empty string:

 java -client -classpath classes -Dhttp.proxyHost=localhost -Dhttp.proxyPort=8099
 -Dhttp.nonProxyHosts= -Dhttps.proxyHost=localhost 
-Dhttps.proxyPort=8099 client.Example  

If you define this any anything other than an empty string the DefaultProxySelector though beware because internally it will append / or use the http.nonProxyHosts value from ../jre/lib/net.properties".

Just a minor complication that is not obvious from the published API.