Question: I connected with VPN to setup the inventory API to get product list and it works fine. Once I get the result from the web-service and i bind to UI. And also I integrated PayPal with my application for make Express checkout when I make a call for payment I'm facing this error. I use servlet for back-end process. Can any one say how to fix this issue?

```
javax.net.ssl.SSLHandshakeException: sun.security.validator.ValidatorException: 
PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException:
unable to find valid certification path to requested target

```

Answer: 
Whenever we are trying to connect to URL, 

if server at the other site is running on https protocol and is mandating that we should communicate via information provided in certificate then 
 we have following option:

1) ask for the certificate(download the certificate), import this certificate in trustore. Default trustore java uses can be found in \Java\jdk1.6.0\_29\jre\lib\security\cacerts, then if we retry to connect to the URL connection would be accepted.

2) In normal business cases, we might be connecting to internal URLS in organizations and we know that they are correct.
 In such cases, you trust that it is the correct URL, In such cases above, code can be used which will not mandate to store the certificate to connect to particular URL.

**for the point no 2 we have to follow below steps :**

1) write below method which sets HostnameVerifier for HttpsURLConnection which returns true for all cases meaning we are trusting the trustStore.

```
  // trusting all certificate 
 public void doTrustToCertificates() throws Exception {
        Security.addProvider(new com.sun.net.ssl.internal.ssl.Provider());
        TrustManager[] trustAllCerts = new TrustManager[]{
                new X509TrustManager() {
                    public X509Certificate[] getAcceptedIssuers() {
                        return null;
                    }

                    public void checkServerTrusted(X509Certificate[] certs, String authType) throws CertificateException {
                        return;
                    }

                    public void checkClientTrusted(X509Certificate[] certs, String authType) throws CertificateException {
                        return;
                    }
                }
        };

        SSLContext sc = SSLContext.getInstance("SSL");
        sc.init(null, trustAllCerts, new SecureRandom());
        HttpsURLConnection.setDefaultSSLSocketFactory(sc.getSocketFactory());
        HostnameVerifier hv = new HostnameVerifier() {
            public boolean verify(String urlHostName, SSLSession session) {
                if (!urlHostName.equalsIgnoreCase(session.getPeerHost())) {
                    System.out.println("Warning: URL host '" + urlHostName + "' is different to SSLSession host '" + session.getPeerHost() + "'.");
                }
                return true;
            }
        };
        HttpsURLConnection.setDefaultHostnameVerifier(hv);
    }

```

2) write below method, which calls doTrustToCertificates before trying to connect to URL

```
    // connecting to URL
    public void connectToUrl(){
     doTrustToCertificates();//  
     URL url = new URL("https://www.example.com");
     HttpURLConnection conn = (HttpURLConnection)url.openConnection(); 
     System.out.println("ResponseCode ="+conn.getResponseCode());
   }

```

This call will return response code = 200 means connection is successful.

For more detail and sample example you can refer to [URL](http://blog.hexican.com/2010/12/sending-soap-messages-through-https-using-saaj/).
I believe that you are trying to connect to a something using SSL but that something is providing a certificate which is not verified by root certification authorities such as verisign.. In essence by default secure connections can only be established if the person trying to connect knows the counterparties keys or some other verndor such as verisign can step in and say that the public key being provided is indeed right..

ALL OS's trust a handful of certification authorities and smaller certificate issuers need to be certified by one of the large certifiers making a chain of certifiers if you get what I mean...

Anyways coming back to the point.. I had a similiar problem when programming a java applet and a java server ( Hopefully some day I will write a complete blogpost about how I got all the security to work :) ) 

In essence what I had to do was to extract the public keys from the server and store it in a keystore inside my applet and when I connected to the server I used this key store to create a trust factory and that trust factory to create the ssl connection. There are alterante procedures as well such as adding the key to the JVM's trusted host and modifying the default trust store on start up.. 

I did this around two months back and dont have source code on me right now.. use google and you should be able to solve this problem. If you cant message me back and I can provide you the relevent source code for the project .. Dont know if this solves your problem since you havent provided the code which causes these exceptions. Furthermore I was working wiht applets thought I cant see why it wont work on Serverlets...

P.S I cant get source code before the weekend since external SSH is disabled in my office :(