Software environments continue to ratchet up security measures, the odds of having to deal with digital certificates in more than a superficial manner only increases over time.
Keytool is used for managing certificates in the Java world, keytool is an integral part of the Java Development Kit.
So suppose you have already used keytool to add certificates in JDK in your C drive or wherever your JDK is in your system but while running the application and hitting the endpoint you are still getting certificate not found or something similar error – the reason might be that in your apps RUN Configurations inside your IDE(STS or Eclipse), your application might not be pointing to actual runtime environment(JDK or JRE) where you added the certs!!!
So to solve these certs error just make sure to Right Click on your app > Run As > Run Configurations > JRE tab > Use Alternate JRE(select JDK where you have added certs) rather that default (Project execution env.)mentioned in STS ide.
Refer below image:
The Web Spark 