# 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`.

   ```java
    @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`.

   ```java
    @NotNull
    @FormParam("duedate")
    private LocalDate dueDate;
   ```
3. In the view, add a new form field named `duedate`.

   ```markup
    <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`.

   ```java
    @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.

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

The result looks like:

![date formatting result](https://1346068621-files.gitbook.io/~/files/v0/b/gitbook-legacy-files/o/assets%2F-LmZrxBGc7qpcVDunhVV%2Fsync%2Fa876a11259634e282b3e304f735f12a4290ac87e.png?generation=1615114443675672\&alt=media)

## 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.