Johnson spent part of last season on loan at Cardiff City.
He told the Daily Star Sunday: “I want to show Fulham fans that I am here to score goals and play an important role.
“Pre-season went really well for me. The manager told me that he signed me for a reason and that I have everything that he is looking for.
“It’s just a matter of me putting those aspects into practice. My nine months at Cardiff City gave me the chance to get used to English football. It has opened my eyes to another style of football.”