HTTP Status 400 - Required String parameter 'x

I'm trying to make a simple Spring MVC application.

Here's my HelloController

package com.springapp.mvc;
import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RequestParam;


@Controller
@RequestMapping("/")
public class HelloController {
@RequestMapping(method = RequestMethod.GET)
public String printWelcome(ModelMap model,@RequestParam(value = "xx",required
=true)String xx) {

        model.addAttribute("message", "Hello Mahdi");

    return "hello";
}
}

and the JSP file:

<html>
<body>
<h1>${message}</h1>
<form action="/" method="GET">
    <input type="text" name="xx">
    <button type="submit">submit</button>
</form>
</body>
</html>

I'm getting the following error when I try to run the application:

HTTP Status 400 - Required String parameter 'xx' is not present

I'm new to Spring MVC, please help.

Your use case requires two actions:

View and edit the <form>
Submit the <form>

This should be mapped to two handler methods

@RequestMapping(method = RequestMethod.GET)
public String getForm() {

    model.addAttribute("message", "Hello Mahdi");
    return "hello"; // assume hello.jsp
}

@RequestMapping(params={"submit"}, method = RequestMethod.GET)
public String printWelcome(ModelMap model, @RequestParam(value = "xx",required=true) String xx) {

    /*
     Do something with submitted parameter
     and return some view name
    */
}

When you want to access the form, you make a GET to /. When you submit the form, you can also do a GET to /, but you would need something else to distinguish the request. Here, I've used params="submit". So you need to change your submit input to

<input type="submit" name="submit">submit</button>

or just put the parameter you're already using (params={"xx"}).

HTTP Status 400 - Required String parameter 'x

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HTTP Status 400 - Required String parameter 'x

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