After installing the latest WebLogic Release, at startup it asks for the username and password.
Just go to user_domains/MYDOMAIN where MYDOMAIN is the domain that you want to start.
Goto Servers/SERVER where SERVER is the SERVER that you want to start.
Create, if does not exist a security directory
On the security directory create a file named boot.properties with the following entries:
Just put your un-encripted password. At startup the password will be encrypted.