Unable to Find Valid Certification Path to Requested Target while using Java on Server

SSL Certificates are small data files that digitally bind a cryptographic key to an organization’s details. 
When installed on a web server, it activates the padlock and the https protocol and allows secure connections from a web server to a browser. 

Typically, SSL is used to secure credit card transactions, data transfer, and logins, and more recently is becoming the norm when securing browsing of social media sites.

Even now, most the browsers show sites as "Not Secure" when they don't have SSL certificates

Maybe you also faced an issue like below:

org.springframework.web.client.ResourceAccessException: I/O error on GET request for "https://www.google.com":sun.security.validator.ValidatorException: 
PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: 
unable to find valid certification path to requested target; nested exception 
is javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: 
PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: 
unable to find valid certification path to requested target
    at org.springframework.web.client.RestTemplate.doExecute(RestTemplate.java:607)
    at org.springframework.web.client.RestTemplate.execute(RestTemplate.java:557)

It is because the certificate used by the HTTPS URL doesn’t exist in the Java Keystore. Hence, the SSL validation fails.

We can fix it downloading and adding site's certificate to Java keystore. Please follow below steps:

Save Exported file by name for example "google.cer". Now in terminal check is JAVA_HOME defined or not using below command

# echo $JAVA_HOME

If not defined above command will return empty string, in that case define it using

# export JAVA_HOME=/usr/java/jdk.1.8.0_12
# export PATH=$PATH:$JAVA_HOME

Now you can set certificate for your Java using below command

# sudo keytool -import -trustcacerts -file /path/to/google.cer -alias google -keystore $JAVA_HOME/jre/lib/security/cacerts -storepass changeit

if keytool not found then move to (cd) "$JAVA_HOME/bin" and execute the command again.

That is all you need to force java accept and work with Https site
You can remove defined certs from your Java as well using below command:

# sudo keytool -delete -alias google -keystore $JAVA_HOME/jre/lib/security/cacerts

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Thanks for reading!