Digital Certificate: How to import .cer file in to .truststore file using?

Instead of using sed to filter out the certificate, you can also pipe the openssl s_client output through openssl x509 -out certfile.txt, for example:

echo "" | openssl s_client -connect my.server.com:443 -showcerts 2>/dev/null | openssl x509 -out certfile.txt

# Copy the certificate into the directory Java_home\Jre\Lib\Security
# Change your directory to Java_home\Jre\Lib\Security>
# Import the certificate to a trust store.

keytool -import -alias ca -file somecert.cer -keystore cacerts -storepass changeit [Return]

Trust this certificate: [Yes]

changeit is the default truststore password

The way you import a .cer file into the trust store is the same way you'd import a .crt file from say an export from Firefox.

You do not have to put an alias and the password of the keystore, you can just type:

keytool -v -import -file somefile.crt  -alias somecrt -keystore my-cacerts

Preferably use the cacerts file that is already in your Java installation (jre\lib\security\cacerts) as it contains secure "popular" certificates.

Update regarding the differences of cer and crt (just to clarify) According to Apache with SSL - How to convert CER to CRT certificates? and user @Spawnrider

CER is a X.509 certificate in binary form, DER encoded.
CRT is a binary X.509 certificate, encapsulated in text (base-64) encoding.
It is not the same encoding.