Spring List Binding - forms

Question

Thanks in advance for any help.
I have the following object association in my model:
public class Contract {
private Integer id;
private String name;
//getters/setters...
}
public class User {
....
private List<Contract> contracts;
....
}
Controller:
#RequestMapping(....)
public String getUser(#PathVariable Integer userId, Model model) {
....
model.addAttribute(userDao.findUser(userId));
model.addAttribute("contractsList", contractDao.findAllContracts());
....
}
#RequestMapping(....)
public String processUser(#ModelAttribute User user, Model model) {
....
//Create a copy of the user to update...
User userToUpdate = userDao.findUser(user.getId);
....
userToUpdate.setContracts(user.getContracts());
//set other properties...
userDao.updateUser(userToUpdate);
return "someSuccessView";
}
#InitBinder
protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder) throws Exception {
binder.registerCustomEditor(Contract.class, new UserContractsPropertyEditor());
}
My PropertyEditor:
public class UserContractsPropertyEditor extends PropertyEditorSupport {
#Inject ContractDao contractDao;
#Override
public void setAsText(String text) throws IllegalArgumentException {
System.out.println("matching value: " + text);
if (text != "") {
Integer contractId = new Integer(text);
super.setValue(contractDao.findContract(contractId));
}
}
}
My JSP form:
<form:form commandName="user">
<%-- Other fields... --%>
<form:checkboxes items="${contractsList}"
path="contracts"
itemValue="id"
itemLabel="name" />
</form:form>
The form renders correctly. That is, the checkbox list of Contracts is generated and the correct ones are "checked." The problem is when I submit I get:
java.lang.IllegalArgumentException: 'items' must not be null
at org.springframework.util.Assert.notNull(Assert.java:112)
at org.springframework.web.servlet.tags.form.AbstractMultiCheckedElementTag.setItems(AbstractMultiCheckedElementTag.java:83)
at org.apache.jsp.WEB_002dINF.jsp._005fn.forms.user_jsp._jspx_meth_form_005fcheckboxes_005f0(user_jsp.java:1192)
....
The custom property editor seems to be doing its job and there are no null/empty strings being passed.
If the form and controller makes the conversion when viewing the form, why is it having trouble when processing the form? What am I missing here?

Answer 1

You need to ensure that a call to getContract() returns a List instance:
public List<Contract> getContracts() {
if (contracts == null) contracts = new ArrayList<Contract>();
return contracts;
}

Answer 2

Thanks for your response. I guess a fresh set of eyes first thing in the morning does the trick again.
Apparently, my custom property editor had no clue what to do with the id value I was passing in since it couldn't access my DAO/service. So, I had to change the constructor:
public class UserContractsPropertyEditor extends PropertyEditorSupport {
private ContractDao contractDao;
public UserContractsPropertyEditor(ContractDao contractDao) {
this.contractDao = contractDao;
}
#Override
public void setAsText(String text) throws IllegalArgumentException {
Integer contractId = new Integer(text);
Contract contract = contractDao.findContract(contractId);
super.setValue(contract);
}
}
Then, modified the initBinder in my controller:
#Inject ContractDao contractDao;
....
#InitBinder
protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder) throws Exception {
binder.registerCustomEditor(Contract.class, new UserContractsPropertyEditor(this.contractDao));
}
Maybe this will help someone else.