Spring Cloud AWS – S3 - VietMX's Blog

Table of Contents

1. Simple S3 Download
2. Simple S3 Upload
3. S3 URL Structure
4. Conclusion

1. Simple S3 Download

Let’s start by easily accessing files stored on S3:

@Autowired
ResourceLoader resourceLoader;

public void downloadS3Object(String s3Url) throws IOException {
    Resource resource = resourceLoader.getResource(s3Url);
    File downloadedS3Object = new File(resource.getFilename());
 
    try (InputStream inputStream = resource.getInputStream()) {
        Files.copy(inputStream, downloadedS3Object.toPath(), 
          StandardCopyOption.REPLACE_EXISTING);
    }
}

2. Simple S3 Upload

We can also upload files:

public void uploadFileToS3(File file, String s3Url) throws IOException {
    WritableResource resource = (WritableResource) resourceLoader
      .getResource(s3Url);
 
    try (OutputStream outputStream = resource.getOutputStream()) {
        Files.copy(file.toPath(), outputStream);
    }
}

3. S3 URL Structure

The s3Url is represented using the format:

s3://<bucket>/<object>

For example, if a file bar.zip is in the folder foo on a my-s3-bucket bucket, then the URL will be:

s3://my-s3-bucket/foo/bar.zip

And, we can also download multiple objects at once using ResourcePatternResolver and the Ant-style pattern matching:

private ResourcePatternResolver resourcePatternResolver;
 
@Autowired
public void setupResolver(ApplicationContext applicationContext, AmazonS3 amazonS3) {
    this.resourcePatternResolver = 
      new PathMatchingSimpleStorageResourcePatternResolver(amazonS3, applicationContext);
 }

public void downloadMultipleS3Objects(String s3Url) throws IOException {
    Resource[] allFileMatchingPatten = this.resourcePatternResolver
      .getResources(s3Url);
        // ...
    }
}

URLs can contain wildcards instead of exact names.

For example the s3://my-s3-bucket/**/a*.txt URL will recursively look for all text files whose name starts with ‘a‘ in any folder of the my-s3-bucket.

Note that the beans ResourceLoader and ResourcePatternResolver are created at application startup using Spring Boot’s auto-configuration feature.