Required String parameter is not present error in Spring MVC

Question

I try to make an AJAX query to my controller in Spring MVC.

My action code is:

@RequestMapping(value = "events/add", method = RequestMethod.POST)
public void addEvent(@RequestParam(value = "start_date") String start_date, @RequestParam(value = "end_date") String end_date, @RequestParam(value = "text") String text, @RequestParam(value = "userId") String userId){
    //some code    
}

My Ajax query is:

$.ajax({
        type: "POST",
        url:url,
        contentType: "application/json",
        data:     {
                start_date:   scheduler.getEvent(id).start_date,
                end_date:  scheduler.getEvent(id).end_date,
                text: scheduler.getEvent(id).text,
                userId: userId
        },
        success:function(result){
         //here some code
        }
    });

But I got an error:

Required String parameter ''start_date is not present

Why? As I know I presented it like (@RequestParam(value = "start_date") String start_date

UDP
Now I give 404 My class to take data

public class EventData {
    public String end_date;
    public String start_date;
    public String text;
    public String userId;
    //Getters and setters
}

My js AJAX call is:

$.ajax({
    type: "POST",
    url:url,
    contentType: "application/json",
    // data: eventData,
    processData: false,
    data:    JSON.stringify({
        "start_date":   scheduler.getEventStartDate(id),
        "end_date":  scheduler.getEventEndDate(id),
        "text": scheduler.getEventText(id),
        "userId": "1"
    }),

And controller action:

@RequestMapping(value = "events/add", method = RequestMethod.POST)
public void addEvent(@RequestBody EventData eventData){    
}

And JSON data is:

end_date: "2013-10-03T20:05:00.000Z"
start_date: "2013-10-03T20:00:00.000Z"
text: "gfsgsdgs"
userId: "1"

Solution

On the server side you expect your request parameters as query strings but on client side you send a json object. To bind a json you will need to create a single class holding all your parameters and use the @RequestBody annotation instead of @RequestParam.

@RequestMapping(value = "events/add", method = RequestMethod.POST)
public void addEvent(@RequestBody CommandBean commandBean){
    //some code
}

Here is a more detailed explanation.