JDK comes with list of CA certificates per-installed. In my case I was trying to access Rest Service over HTTPS from my J2EE app which was using certificate provided by Trustwave which by default is not part of the JDK I was using i.e. 1.6
You can check which certificates are already installed in your JDK using following keytool command
keytool -list -v -keystore $JAVA_HOME/jre/lib/security/cacerts
I downloaded the missing Trustwave cert from
After downloading I imported the cert into the JDK using following command.
keytool -import -trustcacerts -alias twroot -file stca.cer -keystore $JAVA_HOME/jre/lib/security/cacerts
It will ask for a password to import the cert, if you haven't changed it by default it is changeit
Make sure you restart your web-server after importing the certificate.