How to maintain session in android?

Can anybody tell me how to maintain session for a user login. For example when the user sign- in to an application they have to be signed in unless the user logouts or uninstall the application similar to gmail in android.

Make one class for your SharedPreferences

public class Session {

    private SharedPreferences prefs;

    public Session(Context cntx) {
        // TODO Auto-generated constructor stub
        prefs = PreferenceManager.getDefaultSharedPreferences(cntx);
    }

    public void setusename(String usename) {
        prefs.edit().putString("usename", usename).commit();
    }

    public String getusename() {
        String usename = prefs.getString("usename","");
        return usename;
    }
}

Now after making this class when you want to use it, use like this: make object of this class like

private Session session;//global variable 
session = new Session(cntx); //in oncreate 
//and now we set sharedpreference then use this like

session.setusename("USERNAME");

now whenever you want to get the username then same work is to be done for session object and call this

session.getusename();

Do same for password