Now there is a position of java software engineer, which requires Japanese. Can I go (but I don't know Japanese now, but it takes time to practice, and)

You can go if you like. If it is outsourced by Japan, you don't have to go. You can't learn anything. It's a toss-up. I went to Japan when I just graduated. Many things are within my ability and are often delayed by Japanese problems. Also approved, hehe. がんばれ ください