In this post, we'll take a look at how to work with Spring Boot and Spring Data JPA.
We'll start by looking at what JPA is and why we would want to use it. Then, we'll take a look at how to configure Spring Boot to work with JPA. Finally, we'll write a few simple example programs to show how to use JPA in a Spring Boot application.
JPA is the Java Persistence API. It's a specification for how to map Java objects to a relational database.
There are many implementations of JPA, the most popular being Hibernate. When you use JPA, you can write your code against the JPA API and let the JPA implementation (like Hibernate) handle the details of mapping your objects to the database.
There are a few reasons you might want to use JPA in your applications:
JPA is a standard. This means that there are many JPA implementations to choose from, and you can switch implementations if you need to.
JPA is flexible. You can use JPA with different types of databases, and you can map your Java objects to the database in different ways.
JPA is easy to use. The JPA API is designed to be easy to use, so you can get started with JPA quickly.
Spring Boot makes it easy to configure Spring for use with JPA. All you need to do is add the spring-boot-starter-data-jpa dependency to your project.
This dependency will pull in all of the necessary JPA dependencies, and it will also configure Spring Boot to use a JPA implementation (Hibernate, by default).
Now that we have Spring Boot configured to use JPA, let's write a few example programs to show how to use JPA in a Spring Boot application.
To use JPA in your application, you need to create a JPA entity. A JPA entity is a Java class that is mapped to a database table.
Let's create a simple JPA entity:
@Entity
public class Person {
@Id
@GeneratedValue
private Long id;
private String name;
// ... getters and setters
}
This class is mapped to the person
table in the database. The @Entity
annotation indicates that this is a JPA entity. The @Id
annotation indicates that the id
field is the primary key for the entity. The @GeneratedValue
annotation tells JPA to generate a unique id for each entity.
Now that we have our JPA entity, we need a way to access it. We can do this by creating a JPA repository.
A JPA repository is a Spring Data repository that is used to access JPA entities. To create a JPA repository, we need to create an interface that extends the JpaRepository
interface:
public interface PersonRepository extends JpaRepository<Person, Long> {
}
This interface is used to access the Person
entity. The JpaRepository
interface provides many methods for working with JPA entities, so we don't need to write any code to implement this interface.
Now that we have our JPA entity and repository, let's write a program that uses the repository to create, read, update, and delete entities.
First, we'll inject the PersonRepository
into our program:
@Autowired
private PersonRepository personRepository;
Next, we'll use the repository to create a Person
entity:
Person person = new Person();
person.setName("John Doe");
personRepository.save(person);
This will insert a new row into the person
table. The save
method will generate a unique id for the entity and set it on the entity.
We can use the findById
method to retrieve an entity by its id:
Person person = personRepository.findById(1L);
We can use the findAll
method to retrieve all entities:
List<Person> people = personRepository.findAll();
We can use the deleteById
method to delete an entity:
personRepository.deleteById(1L);
And we can use the delete
method to delete an entity:
personRepository.delete(person);
These are just a few of the methods that are available on the JpaRepository
interface. For a complete list of methods, see the JpaRepository documentation.
In this post, we've looked at how to work with Spring Boot and Spring Data JPA. We've seen how to configure Spring Boot to use JPA, and we've written a few simple example programs to show how to use JPA in a Spring Boot application.