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Listing 6-45 contains the entire PersonFormController code, highlighting the referenceData() method. Listing 6-45. PersonFormController with Reference Data public class PersonFormController extends SimpleFormController { private String[] languages = new String[]{"Java", "Ruby", "Python"}; public PersonFormController() { setCommandName("person"); setCommandClass(Person.class); setFormView("newPerson"); setSuccessView("newPersonSuccess"); } @Override protected Map referenceData(HttpServletRequest req) throws Exception { Map data = new HashMap(); data.put("languages", languages); return data; } @Override protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder) throws Exception { binder.registerCustomEditor(Date.class, new CustomDateEditor(new SimpleDateFormat("yyyy-MM-dd"), false)); } @Override protected void doSubmitAction(Object command) throws Exception { Person person = (Person) command; } } Now that we are providing a list of favorite languages, we can modify our form XHTML to loop through them to build the <select> and <option> tags, as shown in Listing 6-46. Listing 6-46. XHTML Snippet of Favorite Programming Languages <tr> <td>Favorite Programming Language:</td> <td> <select name="favoriteProgrammingLanguage"> <c:forEach items="${languages}" var="language">
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<option>${language}</option> </c:forEach> </select> </td> </tr> Of course, it s common to return extra information to the View after a form submission. You may, for example, want to provide a confirmation message after the submission completes. In our example so far, we have implemented the doSubmitAction() method, which does not allow for any model to be returned. Again, the doSubmitAction() method is useful when the default success view is sufficient. When you need to return objects required by the success view, you will need to implement an onSubmit() method. For example, we will extend our PersonFormController to persist the person instance into the database, and we will recommend a book to read based on their favorite programming language. We will remove our doSubmitAction() method and override onSubmit() so that we may return a model with the book recommendation, as shown in Listing 6-47. Listing 6-47. PersonFormController with onSubmit() public class PersonFormController extends SimpleFormController { private String[] languages = new String[]{"Java", "Ruby", "Python"}; private PersonDao personDao; public PersonFormController() { setCommandName("person"); setCommandClass(Person.class); setFormView("newPerson"); setSuccessView("newPersonSuccess"); } public void setPersonDao(PersonDao personDao) { this.personDao = personDao; } @Override protected Map<String, String[]> referenceData(HttpServletRequest req) throws Exception { Map<String, String[]> data = new HashMap<String, String[]>(); data.put("languages", languages); return data; }
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@Override protected void initBinder(HttpServletRequest request, ServletRequestDataBinder binder) throws Exception { binder.registerCustomEditor(Date.class, new CustomDateEditor(new SimpleDateFormat("yyyy-MM-dd"), false)); } @Override protected ModelAndView onSubmit(Object command) throws Exception { Person person = (Person) command; personDao.persist(person); Map<String, String> model = new HashMap<String, String>(); model.put("suggestedBook", suggestBook(person.getFavoriteProgrammingLanguage())); model.put(getCommandName(), person); return new ModelAndView(getSuccessView(), model); } private String suggestBook(String favoriteProgrammingLanguage) { Language language = Language.create(favoriteProgrammingLanguage); return language.recommendBookTitle(); } } As you may have noticed, the controller now delegates persistence to a PersonDao class. Thus, a setter method is provided, setPersonDao(), so that the ApplicationContext can easily inject an instance. The old doSubmitAction() is now replaced with the more flexible onSubmit() method, allowing us to return a ModelAndView object. Notice how we simply call getSuccessView() to return the configured success view. We are also now required to manually add the person object into the model, which was previously automatically added.
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If you return null from onSubmit(), a default ModelAndView will be created with getSuccessView() Tip
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and errors.getModel().
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The business logic of choosing a recommended book title is delegated to a Language object. This follows the recommendations of delegating any business logic to the service layer or other POJOs in the system.
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All objects in the model are exposed to the View instance, so the success view XHTML page can now easily display the recommended book, as shown in Listing 6-48. Listing 6-48. XHTML for Recommended Book Title <body> Welcome, ${person.name}! You chose ${person.favoriteProgrammingLanguage} as your favorite programming language. Therefore, we can recommend you check out ${suggestedBook}. </body>
Redirect After Submit Pattern
There is a common problem with the way we are handling the display of the confirmation page, which needs to be fixed. The success view is rendered in the same request as the initial POST, leaving the browser in a state with the ability to replay the form submit. In other words, after the success view is shown, the user can simply reload the page, resubmitting the form. This can lead to inconsistencies, with the best-case scenario of a confused user and a worstcase scenario of multiple identical Person instances being saved into the database. Any form that alters data in persistence, or performs any type of potentially destructive operation, is at risk of being resubmitted. Multiple solutions exist that can ensure that the user must view the form before submitting, thus preventing double submissions. We will cover one of the most common solutions, the Redirect After Submit pattern, in the next example. This pattern simply redirects the user to the success view instead of internally forwarding the request. The redirect forces the browser to obtain a new page, and any reloads will now safely reload the new page instead of the form page.
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