Robert M. Grant , A Historical Introduction to the New Testament, , Chapter 11 The Gospel of John
The author was probably not the son of Zebedee but a Jerusalem disciple of Jesus who wrote his gospel around the time of the Roman-Jewish war of 66-70 (probably not long after it) in order to present faith in Christ to bewildered and distressed Jewish sectarians. These sectarians lived either in Palestine itself or in the Dispersion.