Given Joshua's previous trouble with spies (in Numbers chapters 13-14 - an event that led to the Jews wandering in the wilderness for four decades!), it's surprising that he chose to employ spies again. Rashi on verse 4 quotes the Midrash Tanchuma that the two spies he sent were Kalev (Caleb), who was one of the "good" spies with Joshua, and Pinchas, who stood up for G-d and was rewarded (in Numbers 25).