Error handling with Spring CommandName - spring

Question

when using Spring framework and binding a form on a commandName object to add let's say a person with the following fields.
<form method="POST" action="addPerson.htm" commandName="person">
<input id="firstname" name="firstname"value="${person.firstname}"/>
<br>
<input id="name" name="name" value="${person.name}"/>
<br>
<input id="age" name="age" value="${person.age}"/>
</form>
On the server I've got the following code
#RequestMapping(value="/addPerson", method={RequestMethod.POST})
public String addPerson(#ModelAttribute(value="person") Person p){
service.addPerson(p);
return "redirect:/overview.htm";
}
How do I do error handling with this, so let's say for example the age must be a positive number and firstname can be left empty.

Answer 1

You need to create a new Validator class, implementing Validator interface.
Your validator can be something like this:
public class PersonValidator implements Validator {
public boolean supports(Class<?> clazz) {
return Person.class.equals(clazz);
}
public void validate(Object target, Errors errors) {
Person person=(Person)target;
if ( person.getAge() < 0 ) {
errors.rejectValue("age", "age_positive");
// Or you can use this approach as well to parametrize the error message:
//errors.rejectValue("age", "age_positive", ArrayParametersIfNeeded, "DefaultMessage");
}
}
}
You also need to have a error.properties file to hold the errors messages allowing i18n.
You can have all needed information about validators here: Validators
When you have it, you need to create the initBinder method in the controller:
#InitBinder
public void initBinder(WebDataBinder binder) {
binder.addValidators(yourValidator);
}
Then, in the controller method, you can pass this additional parameter: BindingResult result and there you will have the information of the errors if you need it.
Also, you need to add this bit to the form:
<form:errors path="age"/></c:set>
Below your <input id="age" name="age" value="${person.age}"/>
I suggest you to change your <input> elements for the <form:input> tag.