1. Overview
The implementation of DAO layers that provide CRUD functionality on JPA entities can be a repetitive, time-consuming task that we want to avoid in most cases. Luckily, Spring Boot makes it easy to create CRUD applications through a layer of standard JPA-based CRUD repositories.
In this tutorial, we’ll learn how to develop a CRUD web application with Spring Boot and Thymeleaf.
2. The Maven Dependencies
In this case, we’ll rely on spring-boot-starter-parent for simple dependency management, versioning, and plug-in configuration. As a result, we won’t need to specify the versions of the project dependencies in our pom.xml file, excepting for overriding the Java version:
<parent>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-parent</artifactId>
<version>2.0.6.RELEASE</version>
</parent>
<dependencies>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-web</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-thymeleaf</artifactId>
</dependency>
<dependency>
<groupId>org.springframework.boot</groupId>
<artifactId>spring-boot-starter-data-jpa</artifactId>
</dependency>
<dependency>
<groupId>com.h2database</groupId>
<artifactId>h2</artifactId>
</dependency>
</dependencies>
<properties>
<java.version>1.8</java.version>
</properties>
We need to override the <java.version> property because the default Java version that spring-boot-starter-parent defines is 1.6.
3. The Domain Layer
With all the project dependencies already in place, let’s now implement a naive domain layer.
For simplicity’s sake, this layer will include one single class which will be responsible for modeling User entities:
@Entity
public class User {
@Id
@GeneratedValue(strategy = GenerationType.AUTO)
private long id;
@NotBlank(message = "Name is mandatory")
private String name;
@NotBlank(message = "Email is mandatory")
private String email;
// standard constructors / setters / getters / toString
}
Let’s keep in mind that we’ve annotated the class with the @Entity annotation. Therefore, the JPA implementation, which is Hibernate, in this case, will be able to perform CRUD operations on the domain entities. For an introductory guide to Hibernate, visit our tutorial on Hibernate 5 with Spring.
In addition, we’ve constrained the name and email fields with the @NotBlank constraint. This implies that we can use Hibernate Validator for validating the constrained fields before persisting or updating an entity in the database.
For the basics on this, check out our associated tutorial on Bean Validation.
4. The Repository Layer
At this point, our sample web application does nothing. But that’s about to change.
Spring Data JPA allows us to implement JPA-based repositories (a fancy name for the DAO pattern implementation) with minimal fuss.
Spring Data JPA is a key component of Spring Boot’s spring-boot-starter-data-jpa that makes it easy to add CRUD functionality through a powerful layer of abstraction placed on top of a JPA implementation. This abstraction layer allows us to access the persistence layer without having to provide our own DAO implementations from scratch.
To provide our application with basic CRUD functionality on User objects all that we need to do is to extend the CrudRepository interface:
@Repository
public interface UserRepository extends CrudRepository<User, Long> {}
And that’s it! By just extending the CrudRepository interface, Spring Data JPA will provide implementations for the repository’s CRUD methods for us.
5. The Controller Layer
Thanks to the layer of abstraction that spring-boot-starter-data-jpa places on top of the underlying JPA implementation, we can easily add some CRUD functionality to our web application through a basic web tier.
In our case, a single controller class will suffice for handling GET and POST HTTP requests and then map them to calls to our UserRepository implementation.
The controller class relies on some of Spring MVC’s key features. For a detailed guide on Spring MVC, check out our Spring MVC tutorial.
Let’s start with the controller’s showSignUpForm() and addUser() methods.
The former will display the user signup form, while the latter will persist a new entity in the database after validating the constrained fields.
If the entity doesn’t pass the validation, the signup form will be redisplayed. Otherwise, once the entity has been saved, the list of persisted entities will be updated in the corresponding view:
@Controller
public class UserController {
@GetMapping("/signup")
public String showSignUpForm(User user) {
return "add-user";
}
@PostMapping("/adduser")
public String addUser(@Valid User user, BindingResult result, Model model) {
if (result.hasErrors()) {
return "add-user";
}
userRepository.save(user);
model.addAttribute("users", userRepository.findAll());
return "index";
}
// additional CRUD methods
}
Within the UserController we will also have the showUpdateForm() method which is responsible for fetching the User entity that matches the supplied id from the database.
If the entity exists it will be passed on as a model attribute to the update form view, hence the form can be populated with the values of the name and email fields:
@GetMapping("/edit/{id}")
public String showUpdateForm(@PathVariable("id") long id, Model model) {
User user = userRepository.findById(id)
.orElseThrow(() -> new IllegalArgumentException("Invalid user Id:" + id));
model.addAttribute("user", user);
return "update-user";
}
Finally, we have the updateUser() and deleteUser() methods within the UserController class.
The first one will persist the updated entity in the database, while the last one will remove the given entity.
In either case, the list of persisted entities will be updated accordingly:
@PostMapping("/update/{id}")
public String updateUser(@PathVariable("id") long id, @Valid User user,
BindingResult result, Model model) {
if (result.hasErrors()) {
user.setId(id);
return "update-user";
}
userRepository.save(user);
model.addAttribute("users", userRepository.findAll());
return "index";
}
@GetMapping("/delete/{id}")
public String deleteUser(@PathVariable("id") long id, Model model) {
User user = userRepository.findById(id)
.orElseThrow(() -> new IllegalArgumentException("Invalid user Id:" + id));
userRepository.delete(user);
model.addAttribute("users", userRepository.findAll());
return "index";
}
6. The View Layer
At this point, we’ve implemented a functional controller class which performs CRUD operations on User entities. Even so, there’s still a missing component in this schema: the view layer.
Under the src/main/resources/templates folder we need to create the HTML templates required for displaying the signup form, the update form, and rendering the list of persisted User entities,
As stated in the introduction, we’ll use Thymeleaf as the underlying template engine for parsing the template files.
Here’s the relevant section of the add-user.html file:
<form action="#" th:action="@{/adduser}" th:object="${user}" method="post">
<label for="name">Name</label>
<input type="text" th:field="*{name}" id="name" placeholder="Name">
<span th:if="${#fields.hasErrors('name')}" th:errors="*{name}"></span>
<label for="email">Email</label>
<input type="text" th:field="*{email}" id="email" placeholder="Email">
<span th:if="${#fields.hasErrors('email')}" th:errors="*{email}"></span>
<input type="submit" value="Add User">
</form>
Notice how we’ve used the @{/adduser} URL expression to specify the form’s action attribute and the ${} variable expressions for embedding dynamic content in the template, such as the values of the name and email fields and the post-validation errors.
Similar to add-user.html, here’s how the update-user.html template looks:
<form action="#" th:action="@{/update/{id}(id=${user.id})}" th:object="${user}" method="post">
<label for="name">Name</label>
<input type="text" th:field="*{name}" id="name" placeholder="Name">
<span th:if="${#fields.hasErrors('name')}" th:errors="*{name}"></span>
<label for="email">Email</label>
<input type="text" th:field="*{email}" id="email" placeholder="Email">
<span th:if="${#fields.hasErrors('email')}" th:errors="*{email}"></span>
<input type="submit" value="Update User">
</form>
Finally, we have the index.html file which displays the list of persisted entities along with the links for editing and removing existing ones:
<div th:switch="${users}">
<h2 th:case="null">No users yet!</h2>
<div th:case="*">
<h2>Users</h2>
<table>
<thead>
<tr>
<th>Name</th>
<th>Email</th>
<th>Edit</th>
<th>Delete</th>
</tr>
</thead>
<tbody>
<tr th:each="user : ${users}">
<td th:text="${user.name}"></td>
<td th:text="${user.email}"></td>
<td><a th:href="@{/edit/{id}(id=${user.id})}">Edit</a></td>
<td><a th:href="@{/delete/{id}(id=${user.id})}">Delete</a></td>
</tr>
</tbody>
</table>
</div>
<p><a href="/signup">Add a new user</a></p>
</div>
For simplicity’s sake, the templates look rather skeletal and only provide the required functionality without adding unnecessary cosmetics.
To give the templates an improved, eye-catching look without spending too much time on HTML/CSS we can easily use a free Twitter Bootstrap UI kit, like Shards.
7. Running the Application
Finally, let’s define the application’s entry point. Like most Spring Boot applications, we can do this with a plain old main() method:
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
Now, let’s hit “Run” in our IDE, then open up our browser and point it to http://localhost:8080.
If the build has successfully compiled we should see a basic CRUD user dashboard with links for adding new entities and for editing and removing existing ones.
8. Conclusion
In this tutorial, we learned how to build a basic CRUD web application with Spring Boot and Thymeleaf.
As usual, all the code samples shown in the article are available over on GitHub.