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 Person POJOs in a memory-based database.

What you'll need

• About 15 minutes
• A favorite text editor or IDE
• JDK 6 or later
• Gradle 1.8+ or Maven 3.0+
• You can also import the code from this guide as well as view the web page directly into Spring Tool Suite (STS) and work your way through it from there.

How to complete this guide

Like all Spring's 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 Set up the project.

To skip the basics, do the following:

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

Set up the project

First you set up a basic build script. You can use any build system you like when building apps with Spring, but the code you need to work with Gradle and Maven is included here. If you're not familiar with either, refer to Building Java Projects with Gradle or Building Java Projects with Maven.

Create the directory structure

In a project directory of your choosing, create the following subdirectory structure; for example, with mkdir -p src/main/java/hello on *nix systems:

└── src
    └── main
        └── java
            └── hello

Create a Gradle build file

Below is the initial Gradle build file. But you can also use Maven. The pom.xml file is included right here. If you are using Spring Tool Suite (STS), you can import the guide directly.

build.gradle

buildscript {
    repositories {
        maven { url "http://repo.spring.io/libs-snapshot" }
        mavenLocal()
    }
}

apply plugin: 'java'
apply plugin: 'eclipse'
apply plugin: 'idea'

jar {
    baseName = 'gs-accessing-data-jpa'
    version =  '0.1.0'
}

repositories {
    mavenCentral()
    maven { url "http://repo.spring.io/libs-snapshot" }
    maven { url "https://repository.jboss.org/nexus/content/repositories/releases" }
}

dependencies {
    compile("org.springframework.boot:spring-boot-starter-web:0.5.0.M4")
    compile("org.springframework:spring-orm:4.0.0.M3")
    compile("org.springframework.data:spring-data-jpa:1.3.2.RELEASE")
    compile("org.hibernate:hibernate-entitymanager:4.2.1.Final")
    compile("com.h2database:h2:1.3.172")
    testCompile("junit:junit:4.11")
}

task wrapper(type: Wrapper) {
    gradleVersion = '1.8'
}

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;

    private 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 private. The other constructor is the one you'll use to create instances of Customer to be saved to the database.

Note: 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.jpa.repository.JpaRepository;

public interface CustomerRepository extends JpaRepository<Customer, Long> {

    List<Customer> findByLastName(String lastName);

}

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

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 static org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseType.H2;

import java.util.List;

import javax.persistence.EntityManagerFactory;
import javax.sql.DataSource;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.context.support.AbstractApplicationContext;
import org.springframework.data.jpa.repository.config.EnableJpaRepositories;
import org.springframework.jdbc.datasource.embedded.EmbeddedDatabaseBuilder;
import org.springframework.orm.jpa.JpaTransactionManager;
import org.springframework.orm.jpa.JpaVendorAdapter;
import org.springframework.orm.jpa.LocalContainerEntityManagerFactoryBean;
import org.springframework.orm.jpa.vendor.Database;
import org.springframework.orm.jpa.vendor.HibernateJpaVendorAdapter;
import org.springframework.transaction.PlatformTransactionManager;

@Configuration
@EnableJpaRepositories
public class Application {
    
    @Bean
    public DataSource dataSource() {
        return new EmbeddedDatabaseBuilder().setType(H2).build();
    }

    @Bean
    public LocalContainerEntityManagerFactoryBean entityManagerFactory(DataSource dataSource, JpaVendorAdapter jpaVendorAdapter) {
        LocalContainerEntityManagerFactoryBean lef = new LocalContainerEntityManagerFactoryBean();
        lef.setDataSource(dataSource);
        lef.setJpaVendorAdapter(jpaVendorAdapter);
        lef.setPackagesToScan("hello");
        return lef;
    }

    @Bean
    public JpaVendorAdapter jpaVendorAdapter() {
        HibernateJpaVendorAdapter hibernateJpaVendorAdapter = new HibernateJpaVendorAdapter();
        hibernateJpaVendorAdapter.setShowSql(false);
        hibernateJpaVendorAdapter.setGenerateDdl(true);
        hibernateJpaVendorAdapter.setDatabase(Database.H2);
        return hibernateJpaVendorAdapter;
    }

    @Bean
    public PlatformTransactionManager transactionManager(EntityManagerFactory entityManagerFactory) {
        return new JpaTransactionManager(entityManagerFactory);
    }


    public static void main(String[] args) {
        AbstractApplicationContext context = new AnnotationConfigApplicationContext(Application.class);
        CustomerRepository repository = context.getBean(CustomerRepository.class);

        // 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
        List<Customer> customers = repository.findAll();
        System.out.println("Customers found with findAll():");
        System.out.println("-------------------------------");
        for (Customer customer : customers) {
            System.out.println(customer);
        }
        System.out.println();

        // fetch an individual customer by ID
        Customer customer = repository.findOne(1L);
        System.out.println("Customer found with findOne(1L):");
        System.out.println("--------------------------------");
        System.out.println(customer);
        System.out.println();

        // fetch customers by last name
        List<Customer> bauers = repository.findByLastName("Bauer");
        System.out.println("Customer found with findByLastName('Bauer'):");
        System.out.println("--------------------------------------------");
        for (Customer bauer : bauers) {
            System.out.println(bauer);
        }

        context.close();
    }

}

In the configuration, you need to add the @EnableJpaRepositories annotation. This annotation tells Spring Data JPA that it should seek out any interface that extends org.springframework.data.repository.Repository and automatically generate an implementation. By extending JpaRepository, your CustomerRepository interface transitively extends Repository. Therefore, Spring Data JPA will find it and create an implementation for you.

Most of the content in Application sets up several beans to support Spring Data JPA and the sample:

• The dataSource() method defines a DataSource bean, as an embedded database to which the objects are persisted.
• The entityManagerFactory() method defines a LocalContainerEntityManagerFactoryBean that is ultimately used to create LocalContainerEntityManagerFactory a bean that implements the EntityManagerFactory interface. It is the bean through which JPA operations will be performed. Note that this factory bean's packagesToScan property is set to look for entities in the package named "hello". This makes it possible to work with JPA without defining a "persistence.xml" file.
• The jpaVendorAdapter() method defines a Hibernate-based JPA vendor adapter bean for use by the EntityManagerFactory bean.
• The transactionManager() method defines a JpaTransactionManager bean for transactional persistence.

Finally, 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".

Build an executable JAR

Now that your Application class is ready, you simply instruct the build system to create a single, executable jar containing everything. This makes it easy to ship, version, and deploy the service as an application throughout the development lifecycle, across different environments, and so forth.

Below are the Gradle steps, but if you are using Maven, you can find the updated pom.xml right here and build it by typing mvn clean package.

Update your Gradle build.gradle file's buildscript section, so that it looks like this:

buildscript {
    repositories {
        maven { url "http://repo.spring.io/libs-snapshot" }
        mavenLocal()
    }
    dependencies {
        classpath("org.springframework.boot:spring-boot-gradle-plugin:0.5.0.M4")
    }
}

Further down inside build.gradle, add the following to the list of applied plugins:

apply plugin: 'spring-boot'

You can see the final version of build.gradle [right here]((https://github.com/spring-guides/gs-accessing-data-jpa/blob/master/complete/build.gradle).

The Spring Boot gradle plugin collects all the jars on the classpath and builds a single "über-jar", which makes it more convenient to execute and transport your service. It also searches for the public static void main() method to flag as a runnable class.

Now run the following command to produce a single executable JAR file containing all necessary dependency classes and resources:

$ ./gradlew build

If you are using Gradle, you can run the JAR by typing:

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

If you are using Maven, you can run the JAR by typing:

$ java -jar target/gs-accessing-data-jpa-0.1.0.jar

Note: The procedure above will create a runnable JAR. You can also opt to build a classic WAR file instead.

Run the service

If you are using Gradle, you can run your service at the command line this way:

$ ./gradlew clean build && java -jar build/libs/gs-accessing-data-jpa-0.1.0.jar

Note: If you are using Maven, you can run your service by typing mvn clean package && java -jar target/gs-accessing-data-jpa-0.1.0.jar.

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.