This guide walks you through the process of building an application that uses Spring Data JPA to store and retrieve data in a relational database.

What you’ll build

You’ll build an application that stores Customer POJOs in a memory-based database.

What you’ll need

  • About 15 minutes

  • A favorite text editor or IDE

  • JDK 1.8 or later

  • Gradle 2.3+ or Maven 3.0+

  • You can also import the code straight into your IDE:

    • Spring Tool Suite (STS)

    • IntelliJ IDEA

How to complete this guide

Like most Spring Getting Started guides, you can start from scratch and complete each step, or you can bypass basic setup steps that are already familiar to you. Either way, you end up with working code.

To start from scratch, move on to Build with Gradle.

To skip the basics, do the following:

  • Download and unzip the source repository for this guide, or clone it using Git: git clone https://github.com/spring-guides/gs-accessing-data-jpa.git

  • cd into gs-accessing-data-jpa/initial

  • Jump ahead to Define a simple entity.

When you’re finished, you can check your results against the code in gs-accessing-data-jpa/complete.

Build with Gradle

Build with Maven

Build with your IDE

Define a simple entity

In this example, you store Customer objects, annotated as a JPA entity.

src/main/java/hello/Customer.java

package hello;

import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;

@Entity
public class Customer {

    @Id
    @GeneratedValue(strategy=GenerationType.AUTO)
    private Long id;
    private String firstName;
    private String lastName;

    protected Customer() {}

    public Customer(String firstName, String lastName) {
        this.firstName = firstName;
        this.lastName = lastName;
    }

    @Override
    public String toString() {
        return String.format(
                "Customer[id=%d, firstName='%s', lastName='%s']",
                id, firstName, lastName);
    }

}

Here you have a Customer class with three attributes, the id, the firstName, and the lastName. You also have two constructors. The default constructor only exists for the sake of JPA. You won’t use it directly, so it is designated as protected. The other constructor is the one you’ll use to create instances of Customer to be saved to the database.

In this guide, the typical getters and setters have been left out for brevity.

The Customer class is annotated with @Entity, indicating that it is a JPA entity. For lack of a @Table annotation, it is assumed that this entity will be mapped to a table named Customer.

The Customer’s id property is annotated with @Id so that JPA will recognize it as the object’s ID. The id property is also annotated with @GeneratedValue to indicate that the ID should be generated automatically.

The other two properties, firstName and lastName are left unannotated. It is assumed that they’ll be mapped to columns that share the same name as the properties themselves.

The convenient toString() method will print out the customer’s properties.

Create simple queries

Spring Data JPA focuses on using JPA to store data in a relational database. Its most compelling feature is the ability to create repository implementations automatically, at runtime, from a repository interface.

To see how this works, create a repository interface that works with Customer entities:

src/main/java/hello/CustomerRepository.java

package hello;

import java.util.List;

import org.springframework.data.repository.CrudRepository;

public interface CustomerRepository extends CrudRepository<Customer, Long> {

    List<Customer> findByLastName(String lastName);
}

CustomerRepository extends the CrudRepository interface. The type of entity and ID that it works with,Customer and Long, are specified in the generic parameters on CrudRepository. By extending CrudRepository, CustomerRepository inherits several methods for working with Customer persistence, including methods for saving, deleting, and finding Customerentities.

Spring Data JPA also allows you to define other query methods by simply declaring their method signature. In the case of CustomerRepository, this is shown with a findByLastName()method.

In a typical Java application, you’d expect to write a class that implements CustomerRepository. But that’s what makes Spring Data JPA so powerful: You don’t have to write an implementation of the repository interface. Spring Data JPA creates an implementation on the fly when you run the application.

Let’s wire this up and see what it looks like!

Create an Application class

Here you create an Application class with all the components.

src/main/java/hello/Application.java

package hello;

import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.springframework.boot.CommandLineRunner;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.annotation.Bean;

@SpringBootApplication
public class Application {

	private static final Logger log = LoggerFactory.getLogger(Application.class);

	public static void main(String[] args) {
		SpringApplication.run(Application.class);
	}

	@Bean
	public CommandLineRunner demo(CustomerRepository repository) {
		return (args) -> {
			// save a couple of customers
			repository.save(new Customer("Jack", "Bauer"));
			repository.save(new Customer("Chloe", "O'Brian"));
			repository.save(new Customer("Kim", "Bauer"));
			repository.save(new Customer("David", "Palmer"));
			repository.save(new Customer("Michelle", "Dessler"));

			// fetch all customers
			log.info("Customers found with findAll():");
			log.info("-------------------------------");
			for (Customer customer : repository.findAll()) {
				log.info(customer.toString());
			}
			log.info("");

			// fetch an individual customer by ID
			Customer customer = repository.findOne(1L);
			log.info("Customer found with findOne(1L):");
			log.info("--------------------------------");
			log.info(customer.toString());
			log.info("");

			// fetch customers by last name
			log.info("Customer found with findByLastName('Bauer'):");
			log.info("--------------------------------------------");
			for (Customer bauer : repository.findByLastName("Bauer")) {
				log.info(bauer.toString());
			}
			log.info("");
		};
	}

}

@SpringBootApplication is a convenience annotation that adds all of the following:

  • @Configuration tags the class as a source of bean definitions for the application context.

  • @EnableAutoConfiguration tells Spring Boot to start adding beans based on classpath settings, other beans, and various property settings.

  • Normally you would add @EnableWebMvc for a Spring MVC app, but Spring Boot adds it automatically when it sees spring-webmvc on the classpath. This flags the application as a web application and activates key behaviors such as setting up a DispatcherServlet.

  • @ComponentScan tells Spring to look for other components, configurations, and services in the hello package, allowing it to find the controllers.

The main() method uses Spring Boot’s SpringApplication.run() method to launch an application. Did you notice that there wasn’t a single line of XML? No web.xml file either. This web application is 100% pure Java and you didn’t have to deal with configuring any plumbing or infrastructure.

Application includes a main() method that puts the CustomerRepository through a few tests. First, it fetches the CustomerRepository from the Spring application context. Then it saves a handful of Customer objects, demonstrating the save() method and setting up some data to work with. Next, it calls findAll() to fetch all Customer objects from the database. Then it calls findOne() to fetch a single Customer by its ID. Finally, it calls findByLastName() to find all customers whose last name is "Bauer".

By default, Spring Boot will enable JPA repository support and look in the package (and its subpackages) where @SpringBootApplication is located. If your configuration has JPA repository interface definitions located in a package not visible, you can point out alternate packages using @EnableJpaRepositories and its type-safe basePackageClasses=MyRepository.class parameter.

Build an executable JAR

You can run the application from the command line with Gradle or Maven. Or you can build a single executable JAR file that contains all the necessary dependencies, classes, and resources, and run that. This makes it easy to ship, version, and deploy the service as an application throughout the development lifecycle, across different environments, and so forth.

If you are using Gradle, you can run the application using ./gradlew bootRun. Or you can build the JAR file using ./gradlew build. Then you can run the JAR file:

java -jar build/libs/gs-accessing-data-jpa-0.1.0.jar

If you are using Maven, you can run the application using ./mvnw spring-boot:run. Or you can build the JAR file with ./mvnw clean package. Then you can run the JAR file:

java -jar target/gs-accessing-data-jpa-0.1.0.jar
The procedure above will create a runnable JAR. You can also opt to build a classic WAR file instead.

You should see something like this:

== Customers found with findAll():
Customer[id=1, firstName='Jack', lastName='Bauer']
Customer[id=2, firstName='Chloe', lastName='O'Brian']
Customer[id=3, firstName='Kim', lastName='Bauer']
Customer[id=4, firstName='David', lastName='Palmer']
Customer[id=5, firstName='Michelle', lastName='Dessler']

== Customer found with findOne(1L):
Customer[id=1, firstName='Jack', lastName='Bauer']

== Customer found with findByLastName('Bauer'):
Customer[id=1, firstName='Jack', lastName='Bauer']
Customer[id=3, firstName='Kim', lastName='Bauer']

Summary

Congratulations! You’ve written a simple application that uses Spring Data JPA to save objects to a database and to fetch them — all without writing a concrete repository implementation.

If you’re interesting in exposing JPA repositories with a hypermedia-based RESTful front end with little effort, you might want to read Accessing JPA Data with REST.

Want to write a new guide or contribute to an existing one? Check out our contribution guidelines.

All guides are released with an ASLv2 license for the code, and an Attribution, NoDerivatives creative commons license for the writing.