SpringMVC model attribute returns null in post
I was developing a trivial SpringMVC 3 application but got stuck somewhere. Essentially, the model attribute whose fields are filled in in the GET operation is returned in the POST NULL field (even if I don't). I checked this and other forums and the only answer I came up with was injecting editors for the classes that I had to put in the model, an initializer that could be used to register custom editors and make it available to the application (in the servletname file -servlet.xml). All the operations I did, but definitely no luck. I was wondering if someone out there could give me a hand. Thank.
Next controller:
@Controller
@RequestMapping(value="/nourish")
public class NourishController {
private PetDAO pdao = new PetDAO();
private UserDAO udao = new UserDAO();
private FeedVirtualPet feedvp = new FeedVirtualPet();
@RequestMapping(method = RequestMethod.GET)
public String nourish(Model model, HttpServletRequest request){
NourishPetDTO npdto = new NourishPetDTO();
PetDTO pdto=pdao.findPetByBusinessKey((PetDTO)request.getSession().getAttribute("pet"));
npdto.setPet(pdto);
npdto.setAmt(0);
model.addAttribute("npdto", npdto);
return "nourish";
}
@RequestMapping(method = RequestMethod.POST)
public String nourishPOST(@ModelAttribute("npdto") NourishPetDTO npdto,
//BindingResult result,
HttpServletRequest request){
System.out.println("*****nourishPOST.npdto.amt: "+npdto.getAmt());
System.out.println("*****nourishPOST.npdto.pet.petname: "+npdto.getPet().getPetName());
System.out.println("*****nourishPOST.npdto.pet.hunger: "+npdto.getPet().getHunger());
PetDTO pdto = feedvp.feed(npdto.getPet(), npdto.getAmt());
request.getSession().setAttribute("user", pdto.getOwner());
return "redirect:detailPet";
}
}
has methods for both GET and POST operations and is linked to the following jsp - in this view, all model data is correctly displayed via EL:
<%@ page language="java" contentType="text/html; charset=ISO-8859-1" session="true" pageEncoding="ISO-8859-1"%>
<%@ taglib prefix="c" uri="http://java.sun.com/jsp/jstl/core" %>
<%@ taglib prefix="form" uri="http://www.springframework.org/tags/form" %>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=ISO-8859-1">
<title>Nourish your pet!!</title>
</head>
<body>
Your stats for <h3>${npdto.pet.petName}</h3><br>
Please note that any value you put inside will:
<ol>
<li>Subtract value to your current hunger level</li>
<li>Add (value) to your current health level</li>
</ol>
Please note that any value you'll put will in many manners "resized":
<ol>
<li>It must be even. If not, a default 0 value will be applied</li>
<li>It can't be greater than 4. If it greater, the maxium value of 4 will be anyway considered.</li>
<li>If it ain't a number, a default zero value will be passed</li>
</ol>
<table>
<tr><td>Health</td><td>${npdto.pet.health}</td></tr>
<tr><td>Hunger</td><td>${npdto.pet.hunger}</td></tr>
</table>
<form action="nourish" method="post" >
nourishment: <input type="text" name="amt"/>
<input type="submit" value="Nourish!"/>
</form>
</body>
</html>
(Note that I did not use the model attribute returning NULL to make sure I didn’t do anything with it)
POST operations are completed with the command
System.out.println("*****nourishPOST.npdto.pet.petname:"+npdto.getPet().getPetName());
because Tomcat is returning NullPointerException.
As mentioned, I was looking for a solution to this problem and all I could find was to add Editor classes and register Editors for the binder. The result is still the same.
Anyway, these are classes:
NourishPetEditor.java
public class NourishPetEditor extends PropertyEditorSupport {
private PetEditor pedit;
public PetEditor getPedit() {
return pedit;
}
public NourishPetEditor() {
// TODO Auto-generated constructor stub
pedit = new PetEditor();
}
@Override
public String getAsText(){
NourishPetDTO npdto= (NourishPetDTO)getValue();
return super.getAsText()+","+npdto.getAmt();
}
public NourishPetDTO makeNourishPetDTOInstance(String [] parts){
NourishPetDTO npdto = new NourishPetDTO();
npdto.setPet(pedit.makePetDTOInstance(parts));
npdto.setAmt(Integer.parseInt(parts[9]));
return npdto;
}
public void setAsText(String key){
String []parts = key.split(",");
NourishPetDTO npdto = makeNourishPetDTOInstance(parts);
setValue(npdto);
}
}
PetEditor.java
package com.virtualpet.dtoeditors;
import java.beans.PropertyEditorSupport;
import com.virtualpet.virtualpet_daos.PetDAO;
import com.virtualpet.virtualpet_dtos.PetDTO;
import com.virtualpet.virtualpet_dtos.UserDTO;
public class PetEditor extends PropertyEditorSupport{
private PetDAO pdao;
public PetEditor() {
// TODO Auto-generated constructor stub
}
public PetEditor(PetDAO pdao) {
// TODO Auto-generated constructor stub
this.pdao = pdao;
}
public String getAsText(){
PetDTO pdto = (PetDTO) this.getValue();
return pdto.getClass().getName()+","+ //0
pdto.getPetName()+","+ //1
pdto.getHealth()+","+ //2
pdto.getHunger()+","+ //3
pdto.getMood()+","+","+ //4
pdto.getOwner().getClass().getName()+","+ //5
pdto.getOwner().getUsername()+","+ //6
pdto.getOwner().getEmail()+","+pdto.getOwner().getPassword(); //7,8
}
public void setAsText(String key) throws IllegalArgumentException {
String []parts = key.split(",");
PetDTO pdto = makePetDTOInstance(parts);
setValue(pdto);
}
public UserDTO makeUserDTOInstance(String[] parts)
throws InstantiationException, IllegalAccessException,
ClassNotFoundException {
UserDTO udto = (UserDTO)Class.forName(parts[5]).newInstance();
udto.setUsername(parts[6]);
udto.setEmail(parts[7]);
udto.setPassword(parts[8]);
return udto;
}
public PetDTO makePetDTOInstance(String[]parts){
try{
PetDTO pdto = (PetDTO) Class.forName(parts[0]).newInstance();
pdto.setPetName(parts[1]);
pdto.setHealth(Integer.parseInt(parts[2]));
pdto.setHunger(Integer.parseInt(parts[3]));
pdto.setMood(Integer.parseInt(parts[4]));
UserDTO udto = makeUserDTOInstance(parts);
pdto.setOwner(udto);
return pdto;
}
catch (Exception e){
throw new IllegalArgumentException();
}
}
}
I will spare you UserEditor as it is very similar to PetEditor. Finally, the initializer binds custom editors and model classes.
VirtualPetDTOInitializer.java
package com.virtualpet.dtoeditors;
import org.springframework.web.bind.WebDataBinder;
import org.springframework.web.bind.support.WebBindingInitializer;
import org.springframework.web.context.request.WebRequest;
import com.virtualpet.virtualpet_dtos.NourishPetDTO;
import com.virtualpet.virtualpet_dtos.PetDTO;
import com.virtualpet.virtualpet_dtos.UserDTO;
public class VirtualPetDTOInitializer implements WebBindingInitializer {
public void initBinder(WebDataBinder binder, WebRequest arg1) {
// TODO Auto-generated method stub
binder.registerCustomEditor(UserDTO.class, new UserEditor( ));
binder.registerCustomEditor(PetDTO.class, new PetEditor( ));
binder.registerCustomEditor(NourishPetDTO.class, new NourishPetEditor());
}
}
This class defines the property value in dispatcher-servlet.xml:
<?xml version="1.0" encoding="UTF-8"?>
<beans ...>
<bean id="userDao"
class="com.virtualpet.virtualpet_daos.UserDAO"/>
<bean id="petDao"
class="com.virtualpet.virtualpet_daos.PetDAO" />
<bean class="org.springframwork.web.servlet.web.servlet.mvc.annotation.AnnotationMethodHandlerAdapter">
<property name="webBindingInitializer">
<bean class="com.virtualpet.dtoeditors.VirtualPetDTOInitializer"/>
</property>
</bean>
</beans>
As a complete newbie to Spring MVC, I must tell you that this error is what I got even before I implemented these classes. So it looks like they are not a factor and yet their implementation is all I could find, the aboud model attribute returned null after POST. Can anyone please help? Thank you in advance.
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You need to do one of the following:
-
Save values
npdto
in hidden forms -
Save
npdto
in session -
Reread
npdto
from database in message handler
You probably want # 2, in which case add @SessionAttributes("npdto")
on top of your controller.
You should also add a parameter SessionStatus
to your message handler and call sessionStatus.complete()
to clear the item from the session when you no longer need it.
See Spring MVC: validation, post-redirect-fetch, partial updates, optimistic Concurrency, field guards for a reference answer.
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