Even after a nearly six-month Mets hiatus, Johan Santana won’t have to sell his team on the idea his left shoulder is sturdy upon his expected arrival at spring training today. The left-hander has done his convincing gradually, over the course of the winter. “He says he feels great,” manager Terry Collins told The Post yesterday after a meeting with his coaches at Tradition Field. “He is well-rested and said [the layoff] was real good for him, so I’m expecting him to come in, and he said he’s ready to pitch like he’s capable of pitching.” Though today is the official reporting date for Mets pitchers and catchers, Santana isn’t required at the team’s training complex until tomorrow, when players will undergo physicals. Santana’s first spring training throwing session is scheduled for Wednesday. The last time the Mets saw Santana throwing a baseball was during a bullpen session on Aug. 21, when team officials decided to shut him down for the season with lower back stiffness. In his comeback from September 2010 surgery to repair a torn anterior capsule in his left shoulder, Santana was 3-7 with an 8.27 ERA over his final 10 starts after starting the season strong. Included was a June 1 no-hitter against the Cardinals — in which Santana remained in the game to throw 134 pitches, possibly adding to his second-half woes. He is beginning the final year of the $137.5 million contract he signed with the club before the 2008 season. Including a 2014 buyout, Santana is still owed $31 million. As relieved as Collins is to have Santana back in uniform, the manager said he won’t necessarily be rushing out to watch the lefty throw on Wednesday. “I judge my stuff once they start playing games,” Collins said. “Those kinds of guys, a guy like him if he’s healthy, you’ve got to write off spring training. I’ve seen too many guys get thrashed in spring training and have big seasons. As long as his arm feels good, he will give us the innings.” Collins plans to meet with all his pitchers on Wednesday, but will save his motivational talk until next week, after the position players have reported.