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 an 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): <a href="https://github.com/marco76/SpringAngular2TypeScript/tree/feature/database/server/src" target="_blank">SpringAngular2TypeScript</a>

Here the example of the <a href="https://github.com/marco76/SpringAngular2TypeScript/blob/feature/database/server/src/main/java/ch/javaee/demo/angular2/service/blog/BlogServiceImpl.java" target="_blank">Service</a>:

``` java @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</a> ::add

To test the code <a href="https://github.com/marco76/SpringAngular2TypeScript/blob/feature/database/server/src/test/java/ch/javaee/demo/angular2/service/blog/BlogServiceTest.java" target="_blank">BlogServiceTest.java</a>:

To fill the database for the test, it's enough to create two files in your resources (_src/test/resources_) directory.
  
Spring looks for those files when it starts.
  
With <a href="https://github.com/marco76/SpringAngular2TypeScript/blob/feature/database/server/src/test/resources/schema.sql" target="_blank">schema.sql</a> Spring creates the database:

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

And with <a href="https://github.com/marco76/SpringAngular2TypeScript/blob/feature/database/server/src/test/resources/schema.sql" target="_blank">import.sql</a> Spring inserts the data:

``` sql

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"); } }