The issue: You are probably missing the certificate for the specific site you work with.
Solution: You need to add export the certificate for the site mentioned above, After exporting it, add it to the cacerts file of java (default file) which located usually here : "c:\Program Files\Java\jdk1.6.0_23\jre\lib\security".
(the default java password for this file is 'changeit').
* If you need the export procedure, tell me, it's simple i can guide you.
In the code, add this lines :
System.setProperty("javax.net.ssl.trustStore", "path_to_cacerts_file/cacerts"); // for example c:\cert\cacerts
System.setProperty("javax.net.ssl.trustStorePassword", "changeit"); //unless you change it
You can also create your own certificate storage file and direct java to it instead.
Helpful link to keytool can be found here.