How to get the server certificate of a HTTPS Website?

If you created a URL object with "new java.net.URL(...)", you can use the getServerCertificates() method on the HttpsURLConnection class to get the server certificate of a HTTPS Website:

// Copyright (c) FYIcenter.com
import java.net.*;
import java.io.*;
import javax.net.ssl.*;
import java.security.cert.*;

public class GetServerCertificate {
   public static void main(String[] args) throws Exception {
     
    URL url = new URL("https://www.oracle.com/");
    System.out.println();
    System.out.println("URL Class Name: "+url.getClass().getName());

    URLConnection con = url.openConnection();
    System.out.println("Connection Class Name: "+con.getClass().getName());
    
    HttpsURLConnection scon = (HttpsURLConnection) con;
    scon.connect();
    Certificate[] certs = scon.getServerCertificates();
    System.out.println("Server Certificate: "+certs[0].toString());
   }
}

You can compile and run the above example in a command window:

\fyicenter>\local\jdk-1.8.0\bin\javac GetServerCertificate.java

\fyicenter>\local\jdk-1.8.0\bin\java GetServerCertificate

URL Class Name: java.net.URL
Connection Class Name: sun.net.www.protocol.https.HttpsURLConnectionImpl
Server Certificate: [
[
  Version: V3
  Subject: CN=www.oracle.com, OU=Content Management Services IT, O=Oracle Corporation, 
  L=Redwood Shores, ST=California, C=US
  Signature Algorithm: SHA256withRSA, OID = 1.2.840.113549.1.1.11

  Key:  Sun RSA public key, 2048 bits
  modulus: 266007053589262198503910002916415210613237870471654508456672717076127...
  public exponent: 65537
  Validity: [From: Thu Apr 13 20:00:00,
               To: Wed Mar 28 19:59:59 EDT 2018]
  Issuer: CN=GeoTrust SSL CA - G3, O=GeoTrust Inc., C=US
  SerialNumber: [    5d547be2 37a12187 1c8849d9 09f1e3ee]

  ...

⇒ SslSocketClient.java - SSL Socket Client Example

⇐ HttpsUrlInfo.java - HTTPS URL Information

⇑ Examples for jsse.jar - Java Secure Socket Extension

⇑⇑ FAQ for jsse.jar - Java Secure Socket Extension