Server Sent Event with SQL Database connection using Spring Boot - spring-boot

Question

I want to implement Server Sent Events in Spring Boot. The data is there in SQL database, It is resulting in blocking connection. Web Flux is an option but it is supported only for some NoSQL database.

Answer 1

Yes, you right WebFlux framework doesn't SQL databases in the non blocking mode because reactive drivers does not exist.
But WebFlux provides some instruments to avoid blocking our main threads while we are making blocking long queries to a database.
1) Create configuration with Scheduler where count of threads equals to pool size:
#Configuration
public class SchedulerConfiguration {
#Value("${spring.datasource.maximum-pool-size}
private final Integer connectionPoolSize;
#Bean
#Qualifier("jdbcScheduler")
public Scheduler jdbcScheduler() {
return Schedulers.fromExecutor(Executors.newFixedThreadPool(connectionPoolSize));
}
}
2) Inject your "jdbcScheduler" to the service class:
#Service
public class DataService {
#Autowired
private final DataRepository jdbcRepository;
#Autowired #Qualifier("jdbcScheduler")
private final Scheduler scheduler;
public Mono<String> findById(long id) {
return async(() -> repository.findById(id));
}
private <T> Mono<T> async(Callable<T> callable) {
return Mono.fromCallable(callable).publishOn(scheduler);
}
}
Wrap your blocking method by Mono.fromCallable and delegate from main thread to your "scheduler" via Mono.publishOn
More about schedulers you can read here: Threading and Schedulers

Answer 2

Yes you can achieve asynchronous processing in spring without flux by using their inbuilt #Async processing, here how you can achieve it.
Step1: Enable Aysnc and define a bean for Executor. You can define separate configuration or directly under Main application class.
#SpringBootApplication
#EnableAsync
public class Application {
public static void main(String[] args) {
// close the application context to shut down the custom ExecutorService
SpringApplication.run(Application.class, args).close();
}
#Bean
public Executor asyncExecutor() {
ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
executor.setCorePoolSize(2);
executor.setMaxPoolSize(2);
executor.setQueueCapacity(500);
executor.setThreadNamePrefix("GithubLookup-");
executor.initialize();
return executor;
}
STEP2:
Following is the simple way to configure a method with void return type to run asynchronously, You can also invoke method by retrieve the result of the asynchronous process using the Future object.
#Async
public void asyncMethodWithVoidReturnType() {
System.out.println("Execute method asynchronously. "
+ Thread.currentThread().getName());
}
For more information, You can visit Spring official guide Spring Async