如何让Spring Rest 接口中路径参数可选

@RequestMapping(value = "/path/{id}")
public String getResource(@PathVariable String id) {
  return service.processResource(id);
} 
@RequestMapping(value = "/path")
public String getResource() {
  return service.processResource();
}

@RequestMapping(value = {"/path", "/path/{id}")
public String getResource(@PathVariable Optional<String> id) {
  if (id.isPresent()) {
    return service.processResource(id.get());
  } else {
    return service.processResource();
  }
}

package controller;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
@Controller
public class RestfulController {
@RequestMapping("/add")
public String test(int a,int b, Model model){
int res = a+b;
model.addAttribute("msg","结果为"+res);
return "test";
}
}

package controller;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
@Controller
public class RestfulController {
@RequestMapping(value = "/add/{a}/{b}",method = RequestMethod.GET)
public String test(@PathVariable int a,@PathVariable int b, Model model){
int res = a+b;
model.addAttribute("msg","结果为"+res);
return "test";
}
}