cert

http://docs.oracle.com/javase/7/docs/technotes/guides/net/properties.html
http://ant.apache.org/manual/proxy.html
http://docs.oracle.com/javase/1.5.0/docs/guide/security/jsse/JSSERefGuide.html#Debug
https://stackoverflow.com/questions/4062307/pkix-path-building-failed-unable-to-find-valid-certification-path-to-requested
https://stackoverflow.com/questions/9210514/unable-to-find-valid-certification-path-to-requested-target-error-even-after-c
https://stackoverflow.com/search?q=unable+to+find+valid+certification+path+to+requested+target
http://blog.csdn.net/lizeyang/article/details/18983843