need clarification on @ModelAttribute

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posted 9 years ago

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Hi,

I am implementing form handling. I have a form page student.jsp where the user is required to fill in the details.
I have a POJO class for that. Then I have a formOutput.jsp which displays the user details.

Here is the code for my controller

import model.Student;

import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.servlet.ModelAndView;

@Controller
public class StudentController {

@RequestMapping(value = "/Student", method = RequestMethod.GET)
   public ModelAndView student() {
	   System.out.println("Inside student");
	   return new ModelAndView("Student", "command", new Student());
   }
   
   @RequestMapping(value = "/addStudent", method = RequestMethod.POST)
   public String addStudent(@ModelAttribute("SpringWeb")Student student, ModelMap model) {
      
	   System.out.println("Inside addStudent");
	  model.addAttribute("name", student.getName());
      model.addAttribute("age", student.getAge());
      model.addAttribute("id", student.getId());
      
      return "FormOutput";
   }
}

My code is working fine. Can anyone please tell me what is the role of "@ModelAttribute("SpringWeb")Student student" parameter in addStudent method.
Thanks.

My POJO class

My form jsp

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
	pageEncoding="ISO-8859-1"%>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<%-- <%@ taglib prefix="spring" uri="http://www.springframework.org/tags"%> --%>
<%@taglib uri="http://www.springframework.org/tags/form" prefix="form"%>
<html>
<head>
    <title>Spring MVC Form Handling</title>
</head>
<body>

<h2>Student Information</h2>
<form:form method="POST" action="addStudent">
   <table>
     <tr>
         <td><form:label path="name">Name</form:label></td>
         <td><form:input path="name" /></td>
     </tr>
     <tr>
         <td><form:label path="age">Age</form:label></td>
         <td><form:input path="age" /></td>
     </tr>
     <tr>
         <td><form:label path="id">id</form:label></td>
         <td><form:input path="id" /></td>
     </tr>
     <tr>
         <td >
             <input type="submit" value="Submit"/>
         </td>
     </tr>
 </table>  
</form:form>
</body>
</html>

Himanshu bisht bebo

Greenhorn

Posts: 16

posted 9 years ago

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@ModelAttribute is used to direclty set the values in the Student object from the jsp, other wise in the servlet you have to get the properties using request.getattribute() and than call student setter method.

Bill Gorder

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Posts: 1682

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posted 9 years ago

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There is an implicit model even if you do not pass one in. This Model is used by spring to store information needed to render the view. A model is just a glorified Map. A ModelAttribute is stored in the model under the name you give or using convention if a name is not provided. In your case you have a Person, that means that if a Person object exists in the Model under the key "SpringWeb" (would make more sense to name it "person" here. It will be retrieved and passed into your method. If it does not exist a new Person object will be created automatically and put in the model. You can than access it directly in your jsp (you would get rid of command)

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