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In this quick article, we’re going to explore the AWS support provided in the Spring Cloud platform – focusing on S3.

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:

@Autowired
ResourcePatternResolver resourcePatternResolver;

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.

4. Conclusion

And we’re done – this is a quick and to-the-point introduction to accessing S3 with Spring Cloud AWS.

In the next article of the series, we’ll explore the EC2 support of the framework.

I just announced the new Spring 5 modules in REST With Spring:

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