Execute CURL command with CA CERT file in JAVA

Question

I have an http POST request which I need to send from my JAVA webservice to a job queueing service. My request in the following CURL format works:

curl 
--cacert ca-cert.txt 
-u user:password 
-H "content-type:application/json" 
-X POST  
-d '{"properties":{"delivery_mode":2},"routing_key":"test","payload":"HI","payload_encoding":"string"}' 
https://testserver.com:15671/api/exchanges/%2f/amq.default/publish

I'm trying to translate this to JAVA code. I cannot seem to find any Java library that except a ca-cert variable/file as a parameter. I found some hints that I need to make some sort of "keystore" object, however am not sure what this means.

I found a source online which suggests to something like this:

String command = "enter curl command";
Process process = Runtime.getRuntime().exec(command);

however, when I try this it does not work! Any suggestions?