getting SSLHandshakeException during https call from weblogic 10.3.6 server to iplanet webserver

Our requirement is that Application deployed in APP tier – i.e. weblogic 10.3.6  is required to call HTTPS URL to an application which is deployed in iplanet 7 webserver. Both weblogic and iplanet are installed in same server/same LAN .
Now when we are trying to call the web application which is deployed on web server from app server through https url, we are getting SSLHandshakeException as below,

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
            at sun.security.ssl.Alerts.getSSLException(Alerts.java:192)
            at sun.security.ssl.SSLSocketImpl.fatal(SSLSocketImpl.java:1916)
            at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:279)
            at sun.security.ssl.Handshaker.fatalSE(Handshaker.java:273)
            at sun.security.ssl.ClientHandshaker.serverCertificate(ClientHandshaker.java:1469)
            at sun.security.ssl.ClientHandshaker.processMessage(ClientHandshaker.java:213)
            at sun.security.ssl.Handshaker.processLoop(Handshaker.java:913)
            at sun.security.ssl.Handshaker.process_record(Handshaker.java:849)
            at sun.security.ssl.SSLSocketImpl.readRecord(SSLSocketImpl.java:1035)
            at sun.security.ssl.SSLSocketImpl.performInitialHandshake(SSLSocketImpl.java:1344)
            at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1371)
            at sun.security.ssl.SSLSocketImpl.startHandshake(SSLSocketImpl.java:1355)
            at sun.net.www.protocol.https.HttpsClient.afterConnect(HttpsClient.java:559)
            at sun.net.www.protocol.https.AbstractDelegateHttpsURLConnection.connect(AbstractDelegateHttpsURLConnection.java:185)
            at sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1301)
            at java.net.HttpURLConnection.getResponseCode(HttpURLConnection.java:468)
            at sun.net.www.protocol.https.HttpsURLConnectionImpl.getResponseCode(HttpsURLConnectionImpl.java:338)
           

we used explicit hostname verification and sun http handler instead of weblogic, but still same problem.

After going through blogs and references, found that we need to add identity certificate of weblogic server to trusted certificates list of iplanet web server. But we don't know how to import the identity certificate of weblogic server to webserver.  Advise is greatly appreciated.