Java Requires Chilkat v11.0.0+

Duplicate openssl pkey -in private.pem -pubout -out pubkey.pem

See more OpenSSL Examples

How to output the public part of a private key: Demonstrates how to duplicate this OpenSSL command:

openssl pkey -in private.pem -pubout -out pubkey.pem

Chilkat2 Java

import com.chilkatsoft.chilkat2.ChilkatException;
import com.chilkatsoft.chilkat2.PrivateKey;
import com.chilkatsoft.chilkat2.PublicKey;

public class ChilkatExample {

    public static void main(String[] args) {
        PrivateKey pkey = new PrivateKey();

        // Load the private key from an PEM file:
        try {
            pkey.loadPemFile("private.pem");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            return;
        }

        PublicKey pubKey = new PublicKey();
        pkey.toPublicKey(pubKey);

        try {
            pubKey.savePemFile(false, "pubKey.pem");
        } catch (ChilkatException e) {
            System.out.println(e.getLastErrorText());
            pubKey.close();
            return;
        }

        System.out.println("Success.");
    }
}