H2 with Spring Boot and JPA - Tutorial

I want to add a blog feature to my reference Angular / Java application. For this I need to write and read the database.

I decided to use H2 database and access it with the Spring Repositories and JPA. Spring Boot has a lot of features to easy manage our data.

The call hierarchy for the data is the following: Web controller -> Service -> Repository

You find the complete code here (Database branch): SpringAngular2TypeScript

Here the example of the Service:

@Service 
public class BlogServiceImpl implements BlogService { 
 
    @Autowired 
    ArticleRepository articleRepository; 
 
    @Override 
    @Transactional(readOnly = true) 
    public List<Article> getArticles() { 
 
        List<Article> articleList = new ArrayList<>(); 
 
        // lambda expression 
        // findAll() retrieve an Iterator 
 
        // method reference ... 
        articleRepository.findAll().forEach(articleList::add); 
        // ... it is equivalent to 
        // articleRepository.findAll().forEach(article -&gt; articleList.add(article)); 
 
        return articleList; 
 
    } 

Interesting is the Iterable object returned by the CrudRepository for the findAll() method.

It could create a surprise to who has the habit to receive a List of objects.

The iterator can easily be transformed in a list using the lambda expression forEach combined with the <a href="https://docs.oracle.com/javase/tutorial/java/javaOO/methodreferences.html" rel=“nofollow" target="_blank">method reference ::add

To test the code BlogServiceTest.java:

To fill the database for the test it’s enough to create 2 files in your resources (src/test/resources) directory.

Spring looks for those files when it starts.

With schema.sql Spring creates the database:

CREATE TABLE ARTICLE (ID INT PRIMARY KEY auto_increment, TITLE VARCHAR2(100), CONTENT TEXT) 

And with import.sql Spring inserts the data:

 
INSERT INTO ARTICLE(TITLE, CONTENT) VALUES ('Article Example', 'Hello World from Java and H2'); 
INSERT INTO ARTICLE(TITLE, CONTENT) VALUES ('Blog in Angular ?', 'Maybe for fun'); 
 

 
@RunWith(SpringRunner.class) 
@SpringBootApplication 
@EnableJpaRepositories(basePackages = ("ch.javaee.demo.angular2")) 
@EntityScan(basePackages = "ch.javaee.demo.angular2") 
public class BlogServiceTest { 
 
    @Autowired 
    BlogService blogService; 
 
    @Test 
    public void getAllArticlesTest() { 
 
        List<Article> articleList = blogService.getArticles(); 
        assertThat(articleList).isNotNull(); 
 
        Article article = articleList.get(0); 
        assertThat(article).hasNoNullFieldsOrProperties(); 
        assertThat(article.getId().equals(1L)); 
        assertThat(article.getTitle()).isEqualTo("Article Example"); 
 
        Article articleTwo = articleList.get(1); 
        assertThat(articleTwo).hasNoNullFieldsOrProperties(); 
        assertThat(articleTwo.getId().equals(2L)); 
        assertThat(articleTwo.getContent()).isEqualTo("Maybe for fun"); 
    } 
} 

I had few problems to find the correct annotations combination. @SpringBootTest tried to load the WebController ending in error.

In conclusion with:

• 1 Service
• 1 'Empty' Repository
• 1 Entity
• 2 SQL files

You have your database. No configuration is needed because Spring Boot automatically recognise and configure H2.