Some doubts about @Valid annotation in Spring MVC validation form

Question

I have the following situation, in my view I have the following form:

<form id="readJson" class="readJsonForm" action="<c:url value="/messageconverters/json" />" method="post">
    <input id="readJsonSubmit" type="submit" value="Read JSON" />   
</form>

Related to the submit event of this form form (having class="readJsonForm) I have the following Jquery callback function:

$("form.readJsonForm").submit(function() {          

    // Riferimento all'elemento che ha scatenato l'evento submit (il form) 
    var form = $(this);                  
    var button = form.children(":first");// Seleziona il bottone submit 

    // OPERATORE CONDIZIONALE: il form ha classe "invalid" ? 
    var data = form.hasClass("invalid") ?       
            "{ \"foo\": \"bar\" }" :            // SI: foo = bar 
            // NO: foo= bar ; fruit = apple 
            "{ \"foo\": \"bar\", \"fruit\": \"apple\" }";    


    /* AJAX CALL PARAMETER:
       type: Say to the servlet tath the request is a POST HTTP Request
       url: The address to which to send the call   
       data: the content of my data variable
       contentType: an object having JSON format
       dataType: the type of content returned by the server
    */
    $.ajax({ 
        type: "POST", 
        url: form.attr("action"), 
        data: data, contentType: "application/json", 
        dataType: "text", 

        success: function(text) {       // CASO DI SUCCESSO:
            /* Passa al metodo il testo ritornato dalla chiamata AJAX ed il 
               riferimento nel DOM al bottone accanto ala quale mostrare
               tale output */
            MvcUtil.showSuccessResponse(text, button);
        }, 

        error: function(xhr) {        // CASO DI ERRORE
            MvcUtil.showErrorResponse(xhr.responseText, button); 
        }
    });

    return false;
});

So this Jquery function create a new JSON object having the two properties (foo and fruit) valorized in this way:

foo = bar

fruit = apple

The HTTP request is handled by the following method of my controller class:

/* Metodo che gestisce HTTP Request di tipo POST dirette verso
 * l'URL: "/messageconverters/json"
 * @param L'oggetto JSON inserito all'interno del campo body dell'HTTP
 *        su cui viene eseguita una validazione
 *        
 */
@RequestMapping(value="/json", method=RequestMethod.POST)
public @ResponseBody String readJson(@Valid @RequestBody JavaBean bean) {
    return "Read from JSON: " + bean;
}

this method simply take the JSON object from the body field of the HTTP Request and, using Jaxb2RootElementHttpMessageConverter transport it in a new JavaBean object

In my case JavaBean object is an object having only two properties: foo and fruit and getter, setter and toString() methods, something like this:

@XmlRootElement public class JavaBean {

@NotNull
private String foo;

@NotNull
private String fruit;

public JavaBean() {
}

public JavaBean(String foo, String fruit) {
    this.foo = foo;
    this.fruit = fruit;
}
    // GETTER, SETTER & toString() methods

Ok, so the value inside the JSON object are put inside the JavaBean object variables having the same name...this thing is pretty clear for me.

I have some problem about the rule of @Valid annotation.

My JavaBean parameter is annoted using the @Valid annotation, reading the documentation I have understand that this is not a Spring annotation but this is related to the Validation Framework JSR-303 Validation API

I know only a litle bit about this API and I remember that @Valid triggered the validation on the object fields

But I remember that my object fields (my variables inside JavaBeans object) have to be annothed using some validation annotation, for example like @NotNull or using a personal validation Java class that implement my personal validator.

In this case I have nothing about it, I only have the @Valid annotation on my method parameter...

What exactly do in this case?

The only thing that I can think is that check if my JSON object is correctly mapped with the JavaBean object (if have the same valorized properties), and for example...if the JSON object have only one properties valorized go into error...

Someone can help me?

Tnx Andrea

Martin Frey Martin Frey · Accepted Answer · 2013-01-16T19:06:17

First: if you are sendig down Json you need to add consumes="application/json" to your @requestmapping annotation and viceversa for produces if you like to send a json responsebody.

Second: @Valid is used to call the validation api to check all the constraints durig mappig of your command object. So you need to have an implementation in your classpath like hibernate-validator. I'm not sure what happens if its not there at runtime. Probably its just ignored?

To get all the validation errors in your controller you add a parameter of type BindingResult. This class holds all the validation errors. Nothing is preventing the controller to handle your object. You are responsible for calling "hasError" on the bindingresult and act accordingly.

Third: Since you mention foo and bar together with JavaBean, it looks like you are using the showcase application. This example is in general very well written and welll explained. Try to deploy the application as is and play around directly. I have learned most of spring mvc through this.

Some doubts about @Valid annotation in Spring MVC validation form

1 Answers