Create a Model

In the next several pages, we will be making updates to codingevents to demonstrate model creation, how models relate to data, and the practice of model binding. The first of these steps is to move data handling out of our controller classes and into a model class. As we discussed on the previous page, the controller class is not responsible for holding data.

In codingevents, we’ll remove the ArrayList data from EventController and create a proper Java class to deal with event items. We’ll then update our controller methods to take advantage of the new model and its properties, rather than the strings stored in the list. Lastly, because the controller is updating, the template variables it relies upon will also need to change to reflect the model properties.

Create a Model Class - Video

Create a Model Class - Text

Like controllers, model classes are conventionally located in a models package. Structurally, model classes most closely resemble the kinds of classes we practiced making at the start of this course, before introducing Spring Boot. In other words, models are plain old Java objects, or POJOs.

To create a model to shape event data, we include a field for name. Of course, we’ll also like at least one constructor and some getters and setters.

In models/Event.java:

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public class Event {

   private String name;

   public Event(String name) {
      this.name = name;
   }

   public String getName() {
      return name;
   }

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

   @Override
   public String toString() {
      return name;
   }
}

Now that we’re working to move the data handling out from the controller classes and into a class of its own, we’ll need to update the POST handler that creates new events. Update the .add() method inside of processCreateEventForm to add a new Event instance:

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@PostMapping("create")
public String processCreateEventForm(@RequestParam String eventName) {
   events.add(new Event(eventName));
   return "redirect:/events";
}

And you’ll notice, we’re adding a different type of data to the ArrayList, so we’ll have to update that too:

private static List<Event> events = new ArrayList<>();

Back in the events/index.html template, update the HTML to use the Event object’s fields, rather than simply strings.

<td th:text="${event.name}"></td>

Add a Model Property - Video

Add a Model Property - Text

To round out the Event class, we’ll add a description field to showcase what our events are all about.

Updates to models/Event.java:

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public class Event {

   private String name;
   private String description;

   public Event(String name, String description) {
      this.name = name;
      this.description = description;
   }

   public String getName() {
      return name;
   }

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

   public String getDescription() {
      return description;
   }

   public void setDescription(String description) {
      this.description = description;
   }

   @Override
   public String toString() {
      return name;
   }
}

Now that our data is object-oriented, it’s quick and easy to add a new property affiliated with an event. If after this, we decide to add a date or location field, we would simply follow the pattern established. Before, with events stored as name strings, we would have had more changes to make in order to add other information fields to the shape of the data.

Update both the events/create.html and events/index.html templates to create an event object with a description field and to display that description along with the event’s name.

events/create.html:

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<label>
   Description
   <input type="text" name="eventDescription"  class="form-control">
</label>

events/index.html:

<td th:text="${event.description}"></td>

Lastly, add a parameter to the processCreateEventForm to handle the form submission and pass the description value into the creation of the Event object.

EventController:

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@PostMapping("create")
public String processCreateEventForm(@RequestParam String eventName, @RequestParam String eventDescription) {
   events.add(new Event(eventName, eventDescription));
   return "redirect:";
}

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