import java.io.File;
import java.io.FileInputStream;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.OutputStream;
import java.nio.file.Files;
import java.security.KeyStore;
import java.security.MessageDigest;
import java.security.cert.CertificateException;
import java.security.cert.X509Certificate;
import java.util.Date;

import javax.net.ssl.SSLContext;
import javax.net.ssl.SSLException;
import javax.net.ssl.SSLSocket;
import javax.net.ssl.SSLSocketFactory;
import javax.net.ssl.TrustManager;
import javax.net.ssl.TrustManagerFactory;
import javax.net.ssl.X509TrustManager;

/**
 * Class used to add the server's certificate to the KeyStore with your trusted
 * certificates.
 */
public class InstallCert {
  public static void main(String[] args) throws Exception {
    String host = "다운받을인증서 사이트 주소";
    int port = 443;// 다운받을인증서 사이트 포트
    char[] passphrase = "changeit".toCharArray(); // 자바 인증서 기본 암호
    char SEP = File.separatorChar;

    File cacerts = new File(System.getProperty("java.home") + SEP + "lib" + SEP + "security" + SEP + "cacerts");
    System.out.println("Loading KeyStore " + cacerts.getAbsolutePath() + "...");
    InputStream in = new FileInputStream(cacerts);
    KeyStore ks = KeyStore.getInstance(KeyStore.getDefaultType());
    ks.load(in, passphrase);
    in.close();
    SSLContext context = SSLContext.getInstance("TLS");
    TrustManagerFactory tmf = TrustManagerFactory.getInstance(TrustManagerFactory.getDefaultAlgorithm());
    tmf.init(ks);
    X509TrustManager defaultTrustManager = (X509TrustManager) tmf.getTrustManagers()[0];
    SavingTrustManager tm = new SavingTrustManager(defaultTrustManager);
    context.init(null, new TrustManager[] { tm }, null);
    SSLSocketFactory factory = context.getSocketFactory();
    System.out.println("Opening connection to " + host + ":" + port + "...");
    SSLSocket socket = (SSLSocket) factory.createSocket(host, port);
    socket.setSoTimeout(10000);
    try {
      System.out.println("Starting SSL handshake...");
      socket.startHandshake();
      socket.close();
      System.out.println();
      System.out.println("No errors, certificate is already trusted");
      return;
    } catch (SSLException e) {
      System.out.println();
      e.printStackTrace(System.out);
    }
    X509Certificate[] chain = tm.chain;
    if (chain == null) {
      System.out.println("Could not obtain server certificate chain");
      return;
    }
    System.out.println();
    System.out.println("Server sent " + chain.length + " certificate(s):");
    System.out.println();
    MessageDigest sha1 = MessageDigest.getInstance("SHA1");
    MessageDigest md5 = MessageDigest.getInstance("MD5");
    for (int i = 0; i < chain.length; i++) {
      X509Certificate cert = chain[i];
      System.out.println(" " + (i + 1) + " Subject " + cert.getSubjectDN());
      System.out.println("   Issuer  " + cert.getIssuerDN());
      sha1.update(cert.getEncoded());
      System.out.println("   sha1    " + toHexString(sha1.digest()));
      md5.update(cert.getEncoded());
      System.out.println("   md5     " + toHexString(md5.digest()));
      System.out.println();

      String alias = host + "-" + (i + 1);
      ks.setCertificateEntry(alias, cert);
      OutputStream out = new FileOutputStream("jssecacerts");
      ks.store(out, passphrase);
      out.close();
      System.out.println();
      System.out.println(cert);
      System.out.println();
      System.out.println("Added certificate to keystore 'jssecacerts' using alias '" + alias + "'");
      StringBuffer command = new StringBuffer();
      command.append("keytool -exportcert -keystore ");
      command.append(new File("jssecacerts").getAbsolutePath());
      command.append(" -storepass changeit -file output.cert -alias ");
      command.append(alias);
      Runtime.getRuntime().exec(command.toString());

      Files.copy(cacerts.toPath(), new File(cacerts.getAbsolutePath() + ".bak." + new Date().getTime()).toPath());

      command = new StringBuffer();
      command.append("keytool -importcert -noprompt -keystore ");
      command.append(cacerts.getAbsolutePath());
      command.append(" -storepass changeit -file output.cert -alias ");
      command.append(alias);
      System.out.println(command.toString());
      Runtime.getRuntime().exec(command.toString());
    }

  }

  private static final char[] HEXDIGITS = "0123456789abcdef".toCharArray();

  private static String toHexString(byte[] bytes) {
    StringBuilder sb = new StringBuilder(bytes.length * 3);
    for (int b : bytes) {
      b &= 0xff;
      sb.append(HEXDIGITS[b >> 4]);
      sb.append(HEXDIGITS[b & 15]);
      sb.append(' ');
    }
    return sb.toString();
  }

  private static class SavingTrustManager implements X509TrustManager {
    private final X509TrustManager tm;
    private X509Certificate[] chain;

    SavingTrustManager(X509TrustManager tm) {
      this.tm = tm;
    }

    public X509Certificate[] getAcceptedIssuers() {
      return new X509Certificate[0];
    }

    public void checkClientTrusted(X509Certificate[] chain, String authType) throws CertificateException {
      throw new UnsupportedOperationException();
    }

    public void checkServerTrusted(X509Certificate[] chain, String authType) throws CertificateException {
      this.chain = chain;
      tm.checkServerTrusted(chain, authType);
    }
  }
}