What does the @Valid annotation indicate in Spring?

Question

In the following example, the ScriptFile parameter is marked with an @Valid annotation.

What does @Valid annotation do?

@RequestMapping(value = "/scriptfile", method = RequestMethod.POST)    
public String create(@Valid ScriptFile scriptFile, BindingResult result, ModelMap modelMap) {    
    if (scriptFile == null) throw new IllegalArgumentException("A scriptFile is required");        
    if (result.hasErrors()) {        
        modelMap.addAttribute("scriptFile", scriptFile);            
        modelMap.addAttribute("showcases", ShowCase.findAllShowCases());            
        return "scriptfile/create";            
    }        
    scriptFile.persist();        
    return "redirect:/scriptfile/" + scriptFile.getId();        
}    

Answer 1

It's for validation purposes.

Validation It is common to validate a model after binding user input to it. Spring 3 provides support for declarative validation with JSR-303. This support is enabled automatically if a JSR-303 provider, such as Hibernate Validator, is present on your classpath. When enabled, you can trigger validation simply by annotating a Controller method parameter with the @Valid annotation: After binding incoming POST parameters, the AppointmentForm will be validated; in this case, to verify the date field value is not null and occurs in the future.

Look here for more info:
http://blog.springsource.com/2009/11/17/spring-3-type-conversion-and-validation/