How to Download Large Files from Amazon S3 Bucket in Spring Boot

Follow these steps to download large files from an Amazon S3 bucket in Spring Boot:

1. Create a Spring Boot Project:

We assume you have a Spring Boot project set up and ready. If not, you can create one using Spring Initializr or your preferred approach.

2. Add Amazon SDK Dependencies:

Add the AWS Java SDK For Amazon S3 dependency to your Spring Boot project:

For Maven:

<dependency>
    <groupid>com.amazonaws</groupid>
    <artifactid>aws-java-sdk-s3</artifactid>
    <version>1.12.556</version>
</dependency>

For Gradle:

implementation group: 'com.amazonaws', name: 'aws-java-sdk-s3', version: '1.12.556'

3. Add Configurations:

To access S3 bucket from a Spring Boot project, you'll need to configure your project with AWS credentials. You can do this by providing your AWS access key and secret key, which can be set in your application.properties or application.yml file or loaded from environment variables. For example, in your application.properties file:

server.port=8080

aws.access-key = your-access-key
aws.access-secret-key = your-access-secret-key
aws.region = us-east-1

4. Create an AmazonS3Client:

Create a bean for the AmazonS3 client in your Spring Boot application configuration class. You can use the @Configuration annotation to create a configuration class:

package com.example.app.config;

import org.springframework.beans.factory.annotation.Value;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import com.amazonaws.auth.AWSStaticCredentialsProvider;
import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.AmazonS3ClientBuilder;

@Configuration
public class AmazonS3Config {

  private String awsAccessKey;
  private String awsAccessSecretKey;
  private String awsRegion;

  public AmazonS3Config(@Value(value = "${aws.access-key}") String awsAccessKey,
      @Value(value = "${aws.access-secret-key}") String awsAccessSecretKey,
      @Value(value = "${aws.region}") String awsRegion) {
    this.awsAccessKey = awsAccessKey;
    this.awsAccessSecretKey = awsAccessSecretKey;
    this.awsRegion = awsRegion;
  }

  public AWSStaticCredentialsProvider getAwsCredentialsProvider() {
    BasicAWSCredentials awsCred =
        new BasicAWSCredentials(this.awsAccessKey, this.awsAccessSecretKey);
    return new AWSStaticCredentialsProvider(awsCred);
  }

  @Bean
  public AmazonS3 getAmazonS3Client() {
    return AmazonS3ClientBuilder.standard().withRegion(this.awsRegion)
        .withCredentials(getAwsCredentialsProvider()).build();
  }

}

5. Configure Asynchronous Processing:

It is recommended that you explicitly configure the TaskExecutor if the file to be downloaded is large and will take more than a minute to download. Here is the complete code for configuring the TaskExecutor with a request timeout of 3600000 milliseconds (60 minutes):

package com.example.app.config;

import java.util.concurrent.Callable;
import org.springframework.aop.interceptor.AsyncUncaughtExceptionHandler;
import org.springframework.aop.interceptor.SimpleAsyncUncaughtExceptionHandler;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.task.AsyncTaskExecutor;
import org.springframework.scheduling.annotation.AsyncConfigurer;
import org.springframework.scheduling.annotation.EnableAsync;
import org.springframework.scheduling.annotation.EnableScheduling;
import org.springframework.scheduling.concurrent.ThreadPoolTaskExecutor;
import org.springframework.web.context.request.NativeWebRequest;
import org.springframework.web.context.request.async.CallableProcessingInterceptor;
import org.springframework.web.context.request.async.TimeoutCallableProcessingInterceptor;
import org.springframework.web.servlet.config.annotation.AsyncSupportConfigurer;
import org.springframework.web.servlet.config.annotation.WebMvcConfigurer;

@Configuration
@EnableAsync
@EnableScheduling
public class AsyncConfig implements AsyncConfigurer {

  @Override
  @Bean(name = "taskExecutor")
  public AsyncTaskExecutor getAsyncExecutor() {
    ThreadPoolTaskExecutor executor = new ThreadPoolTaskExecutor();
    executor.setCorePoolSize(10);
    executor.setMaxPoolSize(15);
    executor.setQueueCapacity(50);
    return executor;
  }

  @Override
  public AsyncUncaughtExceptionHandler getAsyncUncaughtExceptionHandler() {
    return new SimpleAsyncUncaughtExceptionHandler();
  }

  @Bean
  public WebMvcConfigurer webMvcConfigurerConfigurer(AsyncTaskExecutor taskExecutor,
      CallableProcessingInterceptor callableProcessingInterceptor) {
    return new WebMvcConfigurer() {
      @Override
      public void configureAsyncSupport(AsyncSupportConfigurer configurer) {
        configurer.setDefaultTimeout(3600000).setTaskExecutor(taskExecutor);
        configurer.registerCallableInterceptors(callableProcessingInterceptor);
        WebMvcConfigurer.super.configureAsyncSupport(configurer);
      }
    };
  }

  @Bean
  public CallableProcessingInterceptor callableProcessingInterceptor() {
    return new TimeoutCallableProcessingInterceptor() {
      @Override
      public <T> Object handleTimeout(NativeWebRequest request, Callable<T> task) throws Exception {
        return super.handleTimeout(request, task);
      }
    };
  }

}

This configuration class is used to enable and configure asynchronous processing in a Spring Boot application. It defines an AsyncTaskExecutor, sets up default timeouts, and provides exception handling for asynchronous tasks. Additionally, it configures Spring MVC to support asynchronous requests and handles timeouts for callable tasks.

6. Create a Service:

Create a service interface named S3FileDownloadService with a method for downloading files from your S3 bucket:

package com.example.app.service;

import org.springframework.web.servlet.mvc.method.annotation.StreamingResponseBody;
import jakarta.servlet.http.HttpServletResponse;

public interface S3FileDownloadService {

  StreamingResponseBody downloadFileFromS3(HttpServletResponse response, String fileId);

}

7. Create a Service Implementation:

Create an implementation class that implements the S3FileDownloadService interface and handles the business logic. Let's create a class called S3FileDownloadServiceImpl:

package com.example.app.service.impl;

import java.io.InputStream;
import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;
import org.springframework.web.servlet.mvc.method.annotation.StreamingResponseBody;
import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.model.GetObjectRequest;
import com.amazonaws.services.s3.model.S3Object;
import com.example.app.service.S3FileDownloadService;
import jakarta.servlet.http.HttpServletResponse;

@Service
public class S3FileDownloadServiceImpl implements S3FileDownloadService {

  private String bucketName = "my-test-bucket";

  private String s3FolderName = "/myfolder/images/";

  @Autowired
  private AmazonS3 s3Client;

  @Override
  public StreamingResponseBody downloadFileFromS3(HttpServletResponse response, String fileId) {
    // get filename from database by fileId
    String filename = "admission.pdf";
    // file location in S3
    String fileLocationKey = s3FolderName + filename;

    return outputStream -> {
      S3Object s3Object = null;
      InputStream inputStream = null;

      /* Retrieve file as object from S3 */
      s3Object = s3Client.getObject(new GetObjectRequest(bucketName, fileLocationKey));

      inputStream = s3Object.getObjectContent();

      long fileLength = s3Object.getObjectMetadata().getContentLength();

      response.setContentLength((int) fileLength);
      response.setHeader("Content-Disposition", "attachment; filename=" + filename);

      int BUFFER_SIZE = 1024;
      int bytesRead;
      byte[] buffer = new byte[BUFFER_SIZE];

      // Writing to output stream
      while ((bytesRead = inputStream.read(buffer)) != -1) {
        outputStream.write(buffer, 0, bytesRead);
      }

      // Closing all streams
      if (inputStream != null) {
        inputStream.close();
      }
      if (s3Object != null) {
        s3Object.close();
      }
      if (response != null) {
        response.getOutputStream().close();
      }
    };
  }

}

8. Create a Web Controller:

Create a controller class named S3FileDownloadController. It will handle HTTP requests and interact with the S3FileDownloadService to download files from your S3 bucket:

package com.example.app.controller;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.http.ResponseEntity;
import org.springframework.web.bind.annotation.GetMapping;
import org.springframework.web.bind.annotation.PathVariable;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RestController;
import org.springframework.web.servlet.mvc.method.annotation.StreamingResponseBody;
import com.example.app.service.S3FileDownloadService;
import jakarta.servlet.http.HttpServletResponse;

@RestController
@RequestMapping(path = "/files")
public class S3FileDownloadController {

  @Autowired
  private S3FileDownloadService s3FileDownloadService;

  @GetMapping(value = "/{fileId}/download")
  public ResponseEntity<StreamingResponseBody> downloadFile(HttpServletResponse response,
      @PathVariable(name = "fileId", required = true) String fileId) {

    return ResponseEntity.ok(s3FileDownloadService.downloadFileFromS3(response, fileId));
  }

}