How to create partly async post request in Spring boot?

Question

I'm new to Spring Boot and I would like to create a kind of async request. It should allow user to upload a file. Then Spring application should save it and answer the user that the file was properly saved.

Then the whole async part happens. Server should start processing the file (in background) right after having it saved. Currently, it does not run in background (user needs to wait until processFileInBackground finishes):

Controller:

@CrossOrigin
@RestController
public class ProcessFileController {
    @Autowired
    ProcessFileService processFileService;

    @CrossOrigin
    @PostMapping("/files/upload")
    public ResponseEntity<String> singleFileUpload(@RequestParam("file") MultipartFile file) {
        System.out.println("singleFileUpload tid: " + Thread.currentThread().getId());
        bytes = file.getBytes();
        // Save file...
        String plainText = new String(bytes, StandardCharsets.UTF_8);
        processFileInBackground(plainText);
        return new ResponseEntity<>("File successfully uploaded!", HttpStatus.OK);
    }


    private void processFileInBackground(String plainText) {
        processFileService = new ProcessFileService(plainText);
        String result = processFileService.getResult();
    }
}

Service:

@Service
public class ProcessFileService {

    private FileProcessor fileProcessor;

    public CompilerApiService(String plainText){
        fileProcessor = new FileProcessor(code);
    }

    @Async
    public String getResult(){
        System.out.println("getResult tid: " + Thread.currentThread().getId());
        // The call below takes a long time to finish
       return fileProcessor.getResult();
    }

}

Configuration:

@EnableAsync
@Configuration
public class AsyncConfig {
    @Bean
    public Executor threadPoolTaskExecutor() {
        return new ConcurrentTaskExecutor(Executors.newCachedThreadPool());
    }
}

Answer 1

Spring offers @Async annotation to you, you need to separate your async logic in a separate class and annotate your method with this async, this will execute your logic in a separate thread. Check this https://spring.io/guides/gs/async-method/

Be ware that you must call the async method from outside the caller class in order to execute in async mode, something like this

@CrossOrigin
@RestController
public class ProcessFileController {
    @Autowired
    ProcessFileService processFileService;

    @CrossOrigin
    @PostMapping("/files/upload")
    public ResponseEntity<String> singleFileUpload(@RequestParam("file") MultipartFile file) {
        bytes = file.getBytes();
        // Save file...
        String plainText = new String(bytes, StandardCharsets.UTF_8);
        processFileInBackground(plainText);
        return new ResponseEntity<>("File successfully uploaded!", HttpStatus.OK);
    }


    private void processFileInBackground(String plainText) {
        processFileService = new ProcessFileService(plainText);
        String result = processFileService.getResult();
    }
}

Service

@Service
public class ProcessFileService {

    private FileProcessor fileProcessor;

    public CompilerApiService(String plainText){
        fileProcessor = new FileProcessor(code);
    }

    @Async
    public String getResult(){
       return fileProcessor.getResult();
    }

}

Configuration

@EnableAsync
@Configuration
public class AsyncConfig {
    @Bean(name = "threadPoolExecutor")
    public Executor getAsyncExecutor() {
      ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
      executor.setCorePoolSize(7);
      executor.setMaxPoolSize(42);
      executor.setQueueCapacity(11);
      executor.setThreadNamePrefix("threadPoolExecutor-");
      executor.initialize();
      return executor;
    }
}