Serkan,
You can use SDML in Java. The com.syclo.sap.User class has an eval method that allows this. For example, if you wanted to retrieve the user's client language, you could do:
String lang = User.eval("<<user.client.Language>>");
Other tags that might work are <<id>> and <<password>>. Those are the tags I found in old SQL scripts.
You can use the System function USERID from a rule to get the userid on the client. The password is also kept in the java user object in a protected variable called _password. You may need to change the visibility of this variable to public so you can access it freely. I would then bring this down in a fetch or a CT or DT so you can access it from the client. Make sure you keep your editor application encrypted so the password cannot be hacked.
Jason Latko - Senior Product Developer at SAP