Spring JPA

The Java Persistence API (JPA) is a specification for the set of interfaces to store, query, and update data stored in a database. JPA can be implemented by an Object Relational Mapping (ORM) which maps classes to a database table. JPA’s use of ORM allows developers to interact with the database without having to write database queries.

JPA Repository Injection

With Spring Data JPA, listing repositories as properties allows them to be made available to other classes. This functionality is facilitated by the repository instance being injected into the class at runtime.

@RestController
public class PersonController {
  private final PersonRepository personRepository;
 
  public PersonController(final PersonRepository personRepository) {
    this.personRepository = personRepository;
}

Spring H2 Database

H2 is a type of database engine in Java. It is embedded into the application and supports in-memory or disk-based persistence.

JPA H2 Console

Spring Boot configures an H2 console that allows developers to inspect the application’s database. The console can be accessed via the browser at the URI /h2-console.

JdbcTemplate class

The Spring JDBC template is the primary API through which we can access database operations logic that we’re interested in:

• Creation and closing of connections
• Executing statements and stored procedure calls
• Iterating over the ResultSet and returning results

In order to use it, we’ll need to define the simple configuration of DataSource:

@Configuration
@ComponentScan("org.baeldung.jdbc")
publicclassSpringJdbcConfig {
    @Bean
		public DataSourcemysqlDataSource() {
				DriverManagerDataSource dataSource = newDriverManagerDataSource();
        dataSource.setDriverClassName("com.mysql.jdbc.Driver");
        dataSource.setUrl("jdbc:mysql://localhost:3306/springjdbc");
        dataSource.setUsername("guest_user");
        dataSource.setPassword("guest_password");

				return dataSource;
    }
}