Objectively speaking, there are good employers and there are bad employers, and Japan is no exception.
We must understand Japanese work culture and their expectation of foreign workers. A hardworking boss will demand the same hardworking attitude from his workers. Japanese are not only very hardworking people, they are also very detail in their works. Thus if a foreign worker from a country that is not known for hardworking and paying no attention to details of their works will not face well from their Japanese employee. The foreign workers will complain the hard demands from their boss is discrimination.
However, this does not mean foreign workers don't face discrimination, the Yakuza nowadays control many large corporations in Japan, they even have big influence over the country's politicians. Exploitation of foreign workers is thus not unexpected. The unfortunate workers hired by the Yakuza controlled companies would face long hours doing hard and dirty jobs with little pay, and harsh living accommodation.