step 1. cover file.jks to file.p12
keytool -importkeystore -srckeystore filename.jks -destkeystore new.filename.p12 -srcstoretype jks -deststoretype pkcs12 step 2.1 cover file.p12 to pem with password
openssl pkcs12 -in new.filename.p12 -out file.pem
step 2.1 cover file.p12 to pem without password
openssl pkcs12 -nodes -in new.filename.p12 -out file.pem