Programmatically Import CA trust cert into existing keystore file without using keytool

The following code inserts the CA cert file yourcert.cer into your keystore without using keytool:

import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.security.Key;
import java.security.KeyStore;
import java.security.cert.Certificate;
import java.io.IOException;
import java.io.InputStream;
import java.io.DataInputStream;
import java.io.ByteArrayInputStream;
import java.security.spec.*;
import java.security.cert.Certificate;
import java.security.cert.CertificateFactory;
import java.util.Collection;

public class ImportCA {

    public static void main(String[] argv) throws Exception {
        String certfile = "yourcert.cer"; /*your cert path*/
        FileInputStream is = new FileInputStream("yourKeyStore.keystore");

        KeyStore keystore = KeyStore.getInstance(KeyStore.getDefaultType());
        keystore.load(is, "yourKeyStorePass".toCharArray());

        String alias = "youralias";
        char[] password = "yourKeyStorePass".toCharArray();

        //////

        CertificateFactory cf = CertificateFactory.getInstance("X.509");
        InputStream certstream = fullStream (certfile);
        Certificate certs =  cf.generateCertificate(certstream);

        ///
        File keystoreFile = new File("yourKeyStorePass.keystore");
        // Load the keystore contents
        FileInputStream in = new FileInputStream(keystoreFile);
        keystore.load(in, password);
        in.close();

        // Add the certificate
        keystore.setCertificateEntry(alias, certs);

        // Save the new keystore contents
        FileOutputStream out = new FileOutputStream(keystoreFile);
        keystore.store(out, password);
        out.close();
    }

    private static InputStream fullStream ( String fname ) throws IOException {
        FileInputStream fis = new FileInputStream(fname);
        DataInputStream dis = new DataInputStream(fis);
        byte[] bytes = new byte[dis.available()];
        dis.readFully(bytes);
        ByteArrayInputStream bais = new ByteArrayInputStream(bytes);
        return bais;
    }
}

Download certs from links and store into specific path.. then load that file into trustStore during runtime using below code.. i hope this exaple will help you..

KeyStore keyStore = KeyStore.getInstance("JKS");
String fileName = "D:\\certs_path\\cacerts"; // cerrtification file path
System.setProperty("javax.net.ssl.trustStore", fileName);