Hello Reza,
Please, find here in the documentation how to implement SSO based on Kerberos/SPNEGO for applications running on AS JAVA server:
Kerberos and SAP NetWeaver AS for Java - User Authentication and Single Sign-On - SAP Library
Here is also the wiki on this topic:
SPNego Kerberos Authentication - SAP Netweaver Application Server Java - SCN Wiki
Regards,
Donka Dimitrova