Spring WebFlux Reactive Repository using R2DBC - PART-3

Continuing the Spring WeFlux series , here now we will cover the Reactive Repository. Here is the link for Part-2 where we have covered the controller part.

Why we need Reactive Repository

All the database calls using JDBC drivers are blocking in nature. That means a thread that calls the database wait until the database return any result or timeouts. So this is huge waste of the resource , thread which is just waiting ideally can be used for better purpose . So what are the different solutions for this problem ? There can be number of solutions but we will discuss below two and implement only one .

Using CompletableFuture and ThreadPool
Using Reactive Relational Database Connectivity (R2DBC) .

CompletableFuture and ThreadPool

This way of executing database query is not a non-blocking way but it separates the blocking query into different execution context. Here we can create a Thread Pool and use that pool with CompletableFuture to execute database query something like this.

Executor executor = Executors.newFixedThreadPool(10);
CompletableFuture future = CompletableFuture.supplyAsync(() -> {
    String sql = "SELECT * FROM users";
    ResultSet rs = stmt.executeQuery(sql);
    //iterate over result set and return result
    User user = new User();
    while(rs.next()){
      user.setName(rs.getString("name"));
      user.setId(rs.getInt("id"));
    }
     return user;
}, executor);

Using Reactive Relational Database Connectivity (R2DBC)

R2DBC is a project that enables us to use the reactive programming API to connect to Relational Database. Until now it is not possible to use JDBC as those are blocking API’s. We can use the R2DBC project along with Spring data to talk to Relational Database. We are continuing example for last post and now we will add this R2DBC project , but for that we will have to add the following dependencies.

Spring Boot Data R2DBC

<dependency>
    <groupId>org.springframework.boot</groupId>
    <artifactId>spring-boot-starter-data-r2dbc</artifactId>
</dependency>

R2DBC MySql Driver

<dependency>
    <groupId>dev.miku</groupId>
    <artifactId>r2dbc-mysql</artifactId>
    <version>0.8.2.RELEASE</version>
</dependency>

By adding above dependency we have all that we need to use the reactive API to access the relational database . In this case we are using R2DBC and Spring Data R2DBC

Data Base Configuration

For R2DBC to work we will have to add certain configuration , fo this we will add a DataBaseConfiguration class that creates a Spring Bean of ConnectionFactory this bean will have r2dbc connection url , data base name etc. We will create this Configuration class by extending AbstractR2dbcConfiguration. Below is the code for the same.

@org.springframework.context.annotation.Configuration
@ComponentScan("dev.tgarde.webflux")
@EnableWebFlux
@EnableR2dbcRepositories
public class DataBaseConfiguration extends AbstractR2dbcConfiguration {

  @Bean
  public ConnectionFactory connectionFactory() {
    ConnectionFactory connectionFactory = ConnectionFactories.get(
        "r2dbcs:mysql://localhost:3306/ExampleDB?"+
            "zeroDate=use_round&"+
            "sslMode=disabled");

    return connectionFactory;
  }
}

@EnableR2dbcRepositories Annotation is used activate reactive relational repositories using R2DBC.

Reactive Repository

ReactiveRepository are similar to JPA repository, it can be created by simple interface and extending ReactiveCrudRepository interface with Entity class name and primary key type.

public interface UserRepository extends ReactiveCrudRepository<User, Long> {

  @Query("SELECT * FROM user WHERE firstname = :firstname")
  Flux<User> findByFirstName(String firstname);
}

Now with above repository implementation we the only difference in it compared to JpaRepository is that the return type of the Interface is of type Reactive in this case Flux or Mono.

We can call above repository from our UserService and just use it the way we use JpaRepository.

@Autowired
private UserRepository userRepository;

@Override
public Flux<User> findUserByFirstName(String firstName) {
  return userRepository.findByFirstName(firstName);
}

So now we have completed the implementation of Non-Blocking Connection using R2DBC with data base with Service and Repository layer to use it.

You can find the latest code at Github . The link will open the commits for above code so that you can see what exact changes are done.

Spring WebFlux Reactive Repository using R2DBC – PART-3