Bean parameter conversion

Spring MVC provides ConversionService to convert data to bean target type from from data.

In MVC, we can use custom ParamConverter to convert form data to the target type.

Parameter conversion

As an example, add a dueDate to Task entity. We need to convert the form field value(it is a String) to LocalDate type.

1. Create a custom ParamConverterProvider for LocalDate.

    @Provider
    public class CustomConverterProvider implements ParamConverterProvider {
   
        final DateTimeFormatter DATE_FORMAT = DateTimeFormatter.ISO_DATE;
   
        @Override
        public <T> ParamConverter<T> getConverter(Class<T> rawType, Type genericType, Annotation[] annotations) {
   
            if (rawType.getName().equals(LocalDate.class.getName())) {
   
                return new ParamConverter<T>() {
                    @Override
                    public T fromString(String value) {
                        return value != null ? (T) LocalDate.parse(value, DATE_FORMAT) : null;
                    }
   
                    @Override
                    public String toString(T value) {
                        return value != null ? ((LocalDate) value).format(DATE_FORMAT) : "";
                    }
                };
            } 
            ....
    }

2. Add a new field dueDate to TaskForm, which type is LocalDate.

    @NotNull
    @FormParam("duedate")
    private LocalDate dueDate;

3. In the view, add a new form field named duedate.

    <input type="text" id="duedate" name="duedate" class="form-control" placeholder="Due date"/>

When the form is submitted, the duedate will be converted to LocalDate type and bind to dueDate property of TaskForm.

Format

Spring provides Formatting service in the display view. eg. @DateFormat and custom Formatters.

Unfortunately, MVC does not support such features. And JSTL fmt:formatDate does not accept Java 8 DateTime APIs.

We can define a custom CDI beans for date formatting, and call it via expression language.

1. Create RequestScoped bean Formatters.

    @RequestScoped
    @Named("formatters")
    public class Formatters {
   
        static DateTimeFormatter DATE_FORMATTER = DateTimeFormatter.ISO_DATE;
   
        public String formatDate(LocalDate data) {
            return DATE_FORMATTER.format(data);
        }
   
    }

2. Apply it on the dueDate in the details.jspx page.

    <dt>Due date:</dt>
    <dd>${formatters.formatDate(details.dueDate)}</dd>

The result looks like:

date formatting result

Source Codes

1. Clone the codes from my GitHub account.

   https://github.com/hantsy/ee8-sandbox/

2. Open the mvc project in NetBeans IDE.

3. Run it on Glassfish.

4. After it is deployed and running on Glassfish application server, navigate http://localhost:8080/ee8-mvc/mvc/tasks in browser.