https://jingyan.baidu.com/article/a948d6515d3e850a2dcd2ee6.html
http://javarevisited.blogspot.hk/2012/09/difference-between-truststore-vs-keyStore-Java-SSL.html
http://javarevisited.blogspot.hk/2012/03/add-list-certficates-java-keystore.html#axzz4oc9zMps6