how to check SSL certificate expiration date programmatically in Java

I need to extract expiration date from SSL certificate on web site in Java,should support both trusted and self-signed certificate,such as:1.trustedhttps://github.com2.self-signedhttps://mms.nw.ru/

I already copy some code as:

import java.net.URL;import java.security.SecureRandom;import java.security.cert.Certificate;import java.security.cert.CertificateException;import java.security.cert.X509Certificate;import javax.net.ssl.HostnameVerifier;import javax.net.ssl.HttpsURLConnection;import javax.net.ssl.KeyManager;import javax.net.ssl.SSLContext;import javax.net.ssl.SSLSession;import javax.net.ssl.TrustManager;import javax.net.ssl.X509TrustManager;public class SSLTest {    public static void main(String [] args) throws Exception {        // configure the SSLContext with a TrustManager        SSLContext ctx = SSLContext.getInstance("TLS");        ctx.init(new KeyManager[0], new TrustManager[] {new DefaultTrustManager()}, new SecureRandom());        SSLContext.setDefault(ctx);        URL url = new URL("https://github.com");//https://mms.nw.ru        HttpsURLConnection conn = (HttpsURLConnection) url.openConnection();        conn.setHostnameVerifier(new HostnameVerifier() {            @Override            public boolean verify(String arg0, SSLSession arg1) {                return true;            }        });        System.out.println(conn.getResponseCode());        Certificate[] certs = conn.getServerCertificates();        for (Certificate cert :certs){            System.out.println(cert.getType());            System.out.println(cert);        }        conn.disconnect();    }    private static class DefaultTrustManager implements X509TrustManager {        @Override        public void checkClientTrusted(X509Certificate[] arg0, String arg1) throws CertificateException {}        @Override        public void checkServerTrusted(X509Certificate[] arg0, String arg1) throws CertificateException {}        @Override        public X509Certificate[] getAcceptedIssuers() {            return null;        }    }}

The questions are:

1. How to parse the expiration date from the certificate, in my code the toString() did output the date,but it is hard to parse.

2. How to determine the certificate chain, eg, the github certificate with chains 3, how did i know which certificate to get the expiration date from?