@RequestParam in Spring MVC handling optional parameters

Question

Is it possible for a Spring controller to handle both kind of requests?

1) http://localhost:8080/submit/id/ID123432?logout=true

2) http://localhost:8080/submit/id/ID123432?name=sam&password=543432

If I define a single controller of the kind:

 @RequestMapping (value = "/submit/id/{id}", method = RequestMethod.GET,   
 produces="text/xml")
public String showLoginWindow(@PathVariable("id") String id,
                              @RequestParam(value = "logout", required = false) String logout,
                              @RequestParam("name") String username,
                              @RequestParam("password") String password,
                              @ModelAttribute("submitModel") SubmitModel model,
                              BindingResult errors) throws LoginException {...}

the HTTP request with "logout" is not accepted.

If I define two controllers to handle each request separately, Spring complains with the exception "There is already 'Controller' bean method ... mapped".

Answer 1

Before Java 8 and Spring 5 (but works with Java 8+ and Spring 5+ too)

You need to give required = false for name and password request parameters as well. That's because, when you provide just the logout parameter, it actually expects for name and password because they are still "implicitly" mandatory.

It worked when you just gave name and password because logout wasn't a mandatory parameter thanks to required = false already given for logout.

Update for Java 8 and Spring 5 (and above)

You can now use the Optional class from Java 8 onwards to make the parameters optional.

@RequestMapping (value = "/path", method = RequestMethod.GET)
public String handleRequest(@RequestParam("paramName") Optional<String> variableName) {
    String paramValue = variableName.orElse("");
    // use the paramValue
}

Answer 2

As part of Spring 4.1.1 onwards you now have full support of Java 8 Optional (original ticket) therefore in your example both requests will go via your single mapping endpoint as long as you replace required=false with Optional for your 3 params logout, name, password:

@RequestMapping (value = "/submit/id/{id}", method = RequestMethod.GET,   
 produces="text/xml")
public String showLoginWindow(@PathVariable("id") String id,
                              @RequestParam(value = "logout") Optional<String> logout,
                              @RequestParam("name") Optional<String> username,
                              @RequestParam("password") Optional<String> password,
                              @ModelAttribute("submitModel") SubmitModel model,
                              BindingResult errors) throws LoginException {...}

Answer 3

Create 2 methods which handle the cases. You can instruct the @RequestMapping annotation to take into account certain parameters whilst mapping the request. That way you can nicely split this into 2 methods.

@RequestMapping (value="/submit/id/{id}", method=RequestMethod.GET, 
                 produces="text/xml", params={"logout"})
public String handleLogout(@PathVariable("id") String id, 
        @RequestParam("logout") String logout) { ... }

@RequestMapping (value="/submit/id/{id}", method=RequestMethod.GET, 
                 produces="text/xml", params={"name", "password"})
public String handleLogin(@PathVariable("id") String id, @RequestParam("name") 
        String username, @RequestParam("password") String password, 
        @ModelAttribute("submitModel") SubmitModel model, BindingResult errors) 
        throws LoginException {...}

Answer 4

In case someone is looking for mapping Optional parameters with Pojo, same can be done like below.

@RequestMapping (value = "/submit/id/{id}", method = RequestMethod.GET,   
 produces="text/xml")
public String showLoginWindow(@PathVariable("id") String id,
                              LoginRequest loginRequest,
                              @ModelAttribute("submitModel") SubmitModel model,
                              BindingResult errors) throws LoginException {...}

@Data
@NoArgsConstructor
//@AllArgsConstructor - Don't use this
public class LoginRequest {
    private Optional<String> logout = Optional.empty();
    private Optional<String> username = Optional.empty();
    private Optional<String> password = Optional.empty();
}

Note: Do not use @AllArgsConstructor on POJO else it will initialize the fields as null.