I need to convert a .cer file to a .jks file.
I saw a few questions about it, but haven't seen a solution to what I need.
I don't need it in order to add it to my local certificates, but as a file to upload to a server. I also need to do it only once, and not programmatically. There's this thread Converting .cer to .jks using java and the author says he had done it successfully, but I couldn't comment to his last reply as I don't have enough reputation, nor could I send him a personal message and ask him.
So if anyone knows of a simple way to do so, I'll be glad to hear.
keytool comes with the JDK installation (in the bin folder):
keytool -importcert -file "your.cer" -keystore your.jks -alias "<anything>"
This will create a new keystore and add just your certificate to it.
So, you can't convert a certificate to a keystore: you add a certificate to a keystore.
Just to be sure that this is really the "conversion" you need, please note that jks files are keystores, a file format used to store more than one certificate and allows you to retrieve them programmatically using the Java security API, it's not a one-to-one conversion between equivalent formats.
So, if you just want to import that certificate in a new ad-hoc keystore you can do it with Keystore Explorer, a graphical tool. You'll be able to modify the keystore and the certificates contained therein like you would have done with the java terminal utilities like keytool (but in a more accessible way).
Export a certificate from a keystore:
keytool -export -alias mydomain -file mydomain.crt -keystore keystore.jks
Use the following will help
keytool -import -v -trustcacerts -alias keyAlias -file server.cer -keystore cacerts.jks -keypass changeit
来源：https://stackoverflow.com/questions/30352681/convert-cer-certificate-to-jks