how to verify the validity of SSL certificate in an Android application

Host name validation can be customizez by setting a custom X509HostnameVerifier on the SSLSocketFactory. Some implementations are already available in android: AllowAllHostnameVerifier, BrowserCompatHostnameVerifier, StrictHostnameVerifier /* ... */

public class MyHostnameVerifier extends AbstractVerifier {
  boolean verify(String hostname, SSLSession session) {
    X509Certificate[] chain = session.getPeerCertificateChain();
    /* made some checks... */
    return checked;
  }
}
sslSocketFactory.setHostnameVerifier(new MyHostnameVerifier());