Automatic Parameter Binding in Controller Methods

SpringMVC automatically maps request parameters to method arguments. The parameter names must match the incoming request parameter names.

@Controller
@RequestMapping("/api")
public class UserController {
    
    @RequestMapping("/greet")
    public String greet(Model model, String username, double score) {
        model.addAttribute("result", username + "|" + String.valueOf(score));
        return "result";
    }
}

Restricting Access by HTTP Method

Use the method attribute to limit which HTTP methods can access a specific endpoint. This enforces RESTful API conventions and improves security.

@Controller
@RequestMapping("/api")
public class UserController {
    
    @RequestMapping(method = {RequestMethod.POST, RequestMethod.GET}, value = "/greet")
    public String greet(Model model) {
        model.addAttribute("message", "Welcome");
        return "result";
    }
    
    @RequestMapping(method = RequestMethod.GET, value = "/leave")
    public String leave(Model model) {
        model.addAttribute("message", "Farewell");
        return "result";
    }
}

Traditional Servlet API Support

SpringMVC controllers can accept HttpServletRequest and HttpServletResponse directly, enabling compatibility with legacy code and fine-grained control over the request-response cycle.

@Controller
@RequestMapping("/api")
public class UserController {
    
    @RequestMapping(method = {RequestMethod.POST, RequestMethod.GET}, value = "/process")
    public void processData(HttpServletRequest request, HttpServletResponse response) 
            throws IOException {
        String username = request.getParameter("username");
        String identifier = request.getParameter("identifier");
        System.out.println(username + ":" + identifier);
        
        request.getSession().setAttribute("username", username);
        request.getSession().setAttribute("identifier", identifier);
        
        response.sendRedirect(request.getContextPath() + "/output.jsp");
    }
}

Custom Property Editors and Multiple Domain Objects

SpringMVC cannot automatically convert String to java.util.Date. Use @InitBinder to register custom property editors for type conversion. This mechanism also supports handling multiple domain objects in a single request.

@Controller
@RequestMapping("/api")
public class UserController {
        
    /**
     * Register custom date editor with specified format
     */
    @InitBinder
    protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder)
            throws Exception {
        binder.registerCustomEditor(Date.class, new CustomDateEditor
                (new SimpleDateFormat("yyyy-MM-dd"), true));
    }
    
    @RequestMapping("/person")
    public String handlePerson(Model model, Person person) {
        System.out.println(person.toString());
        model.addAttribute("person", person);
        return "result";
    }
    
    /**
     * Receiving multiple entity objects through wrapper class
     */
    @RequestMapping("/entities")
    public String handleEntities(Model model, Bean wrapper) {
        System.out.println(wrapper.getPerson());
        System.out.println(wrapper.getAnimal());
        model.addAttribute("person", wrapper.getPerson());
        model.addAttribute("animal", wrapper.getAnimal());
        return "result";
    }
}

Collecting Array Parameters

Controllers can directly receive arrays from form submissions. Each checkbox or multi-select value maps to the array element.

<form action="${pageContext.request.contextPath}/api/batch.action" method="post">
    | Item A | <input name="selectedIds" type="checkbox" value="101"></input> |
|---|---|
| Item B | <input name="selectedIds" type="checkbox" value="202"></input> |
| Item C | <input name="selectedIds" type="checkbox" value="303"></input> |
| <input type="submit" value="Submit Selection"></input> |
</form>

@Controller
@RequestMapping("/api")
public class UserController {
    
    @RequestMapping("/batch")
    public String processBatch(Model model, int[] selectedIds) {
        for (int id : selectedIds) {
            System.out.println(id);
        }
        return "success";
    }
}

Collecting List Parameters

For complex form submissions, use indexed notation in input names to populate a list of domain objects.

<form action="${pageContext.request.contextPath}/api/batchPersons.action" method="post">
    | <input name="userList[0].name" type="text" value="Alice"></input> | <input name="userList[0].code" type="text" value="A001"></input> |
|---|---|
| <input name="userList[1].name" type="text" value="Bob"></input> | <input name="userList[1].code" type="text" value="B002"></input> |
| <input type="submit" value="Submit Users"></input> |
</form>

public class BatchWrapper {
    private List<Person> userList = new ArrayList<Person>();

    public List<Person> getUserList() {
        return userList;
    }

    public void setUserList(List<Person> userList) {
        this.userList = userList;
    }
}

@Controller
@RequestMapping("/api")
public class UserController {
    
    @RequestMapping("/batchPersons")
    public String processBatchPersons(Model model, BatchWrapper wrapper) {
        System.out.println(wrapper.getUserList());
        return "success";
    }
}

Forward and Redirect Operations

SpringMVC supports both forward and redirect prefixes for navigation between controllers. Forward preserves request attributes while redirect creates a new request.

@Controller
@RequestMapping("/api")
public class UserController {
    
    @RequestMapping("/start")
    public String start(Model model, String userName) {
        System.out.println("Starting " + userName);
        return "forward:/api/complete";
    }
    
    @RequestMapping("/complete")
    public String complete(Model model, String userName) {
        System.out.println("Completing " + userName);
        return "result";
    }
}

Returning JSON Responses with @ResponseBody

The @ResponseBody annotation enables controllers to return data directly as JSON, elimianting the need for view resolution. This is essential for building RESTful APIs and AJAX-powered interfaces.

<h3>JSON API Tests</h3>
<input type="button" value="Single Object" class="json-btn" data-target="single">
<input type="button" value="Object List" class="json-btn" data-target="list">
<input type="button" value="Map Data" class="json-btn" data-target="map">
<script type="text/javascript">
    $(".json-btn").click(function() {
        var endpoint = "${pageContext.request.contextPath}/api/" + $(this).data("target");
        $.post(endpoint, null, function(response, status, xhr) {
            alert(xhr.responseText);
        });
    });
</script>

@Controller
@RequestMapping("/api")
public class ApiController {
    
    @RequestMapping("/single")
    public @ResponseBody Person getSinglePerson() {
        return new Person("Alice", "Developer", "28");
    }
    
    @RequestMapping("/list")
    public @ResponseBody List<Person> getPersonList() {
        List<Person> users = new ArrayList<Person>();
        users.add(new Person("Dog", "Breed1", "3"));
        users.add(new Person("Cat", "Breed2", "4"));
        return users;
    }
    
    @RequestMapping("/map")
    public @ResponseBody Map<String, Object> getMapData() {
        Map<String, Object> data = new HashMap<String, Object>();
        data.put("count", 1);
        data.put("title", "Sample");
        return data;
    }
}