ControllerMain.java在@Controller之后需要一个@RequestMapping（ /）语句。

ControllerMain.java requires a @RequestMapping("/") statement after the @Controller.

更改：

@Controller
public class ControllerMain {

@RequestMapping(value = "/hello", method = RequestMethod.GET)
....
....

收件人：

@Controller
@RequestMapping("/")
public class ControllerMain {

@RequestMapping(value = "/hello", method = RequestMethod.GET)
....
....
....