Spring MVC: Validation, Post-Redirect-Get, Partial Updates, Optimistic Concurrency, Field Security

Question

[This is a list of common questions I see about Spring MVC, which are solved in similar ways. I've posted them here, so I can easily refer to them from other questions]

How do I update only a few fields of a model entity with forms?

How do I use the Post-Redirect-Get pattern with Spring MVC, especially with form validation?

How do I secure certain fields in my entities?

How do I implement Optimistic Concurrency Control?

Answer 1

1. To partially update an entity, you should use @SessionAttributes to store the model in session between requests. You could use hidden form fields, but session is more secure.

2. To use P/R/G with validation, use flashAttributes

3. To secure fields use webDataBinder.setAllowedFields("field1","field2",...) or create a class specific to the form then copy values to your entity. Entities don't require setters for id and version (if using Hibernate).

4. To use Optimistic Concurrency Control use the @Version annotation in your Entity and use @SessionAttributes on your controller.

Example code:

@Controller
@RequestMapping("/foo/edit/{id}")
@SessionAttributes({FooEditController.ATTRIBUTE_NAME})
public class FooEditController {

    static final String ATTRIBUTE_NAME = "foo";
    static final String BINDING_RESULT_NAME = "org.springframework.validation.BindingResult." + ATTRIBUTE_NAME;

    @Autowired
    private FooRepository fooRepository;

    /*
     Without this, user can set any Foo fields they want with a custom HTTP POST
     setAllowedFields disallows all other fields. 
     You don't even need setters for id and version, as Hibernate sets them using reflection
    */
    @InitBinder
    void allowFields(WebDataBinder webDataBinder){
        webDataBinder.setAllowedFields("name"); 
    }

    /*
     Get the edit form, or get the edit form with validation errors
    */
    @RequestMapping(method = RequestMethod.GET)
    String getForm(@PathVariable("id") long id, Model model) {

        /* if "fresh" GET (ie, not redirect w validation errors): */
        if(!model.containsAttribute(BINDING_RESULT_NAME)) {
            Foo foo = fooRepository.findOne(id);
            if(foo == null) throw new ResourceNotFoundException();
            model.addAttribute(ATTRIBUTE_NAME, foo);
        }

        return "foo/edit-form";
    }

    /*
     @Validated is better than @Valid as it can handle http://docs.jboss.org/hibernate/validator/5.1/reference/en-US/html/chapter-groups.html
     @ModelAttribute will load Foo from session but also set values from the form post
     BindingResult contains validation errors
     RedirectAttribute.addFlashAttribute() lets you put stuff in session for ONE request
     SessionStatus lets you clear your SessionAttributes
    */
    @RequestMapping(method = RequestMethod.POST)
    String saveForm(
       @Validated @ModelAttribute(ATTRIBUTE_NAME) Foo foo,
       BindingResult bindingResult, 
       RedirectAttributes redirectAttributes, 
       HttpServletRequest request, 
       SessionStatus sessionStatus
    ) {

        if(!bindingResult.hasErrors()) {
            try {
                fooRepository.save(foo);
            } catch (JpaOptimisticLockingFailureException exp){
                bindingResult.reject("", "This record was modified by another user. Try refreshing the page.");
            }
        }

        if(bindingResult.hasErrors()) {

            //put the validation errors in Flash session and redirect to self
            redirectAttributes.addFlashAttribute(BINDING_RESULT_NAME, bindingResult);
            return "redirect:" + request.getRequestURI();
        }

        sessionStatus.setComplete(); //remove Foo from session

        redirectAttributes.addFlashAttribute("message", "Success. The record was saved");
        return "redirect:" + request.getRequestURI();
    }
}

Foo.java:

@Entity
public class Foo {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Version //for optimistic concurrency control
    private int version;

    @NotBlank
    private String name;

    public Long getId() {
        return id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

edit-form.jsp (Twitter Bootstrap compatible):

<%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c" %>
<%@ taglib uri="http://www.springframework.org/tags" prefix="spring" %>
<%@ taglib uri="http://www.springframework.org/tags/form" prefix="form" %>

<form:form modelAttribute="foo">

    <spring:hasBindErrors name="foo">
        <c:if test="${errors.globalErrorCount > 0}">
            <div class="alert alert-danger" role="alert"><form:errors/></div>
        </c:if>
    </spring:hasBindErrors>

    <c:if test="${not empty message}">
      <div class="alert alert-success"><c:out value="${message}"/></div>
    </c:if>

    <div class="panel panel-default">
        <div class="panel-heading">
            <button class="btn btn-primary" name="btnSave">Save</button>
        </div>

        <div class="panel-body">

            <spring:bind path="name">
                <div class="form-group${status.error?' has-error':''}">
                    <form:label path="name" class="control-label">Name <form:errors path="name"/></form:label>
                    <form:input path="name" class="form-control" />
                </div>
            </spring:bind>

        </div>
    </div>

</form:form>

ResourceNotFoundException.java:

@ResponseStatus(HttpStatus.NOT_FOUND)
public class ResourceNotFoundException extends RuntimeException {
}