Configuring the AWS S3 Java Client

The AWS SDK for Java v2 makes S3 access straightforward once you’ve seen the right shape for it. This post walks through a minimal Spring Boot configuration, the YAML settings that drive it, a small service with the S3 operations you’ll use most, and an integration test that runs against a real S3 API — without touching AWS — using Testcontainers and LocalStack.

Dependencies

xml

			
<dependency>
    <groupId>software.amazon.awssdk</groupId>
    <artifactId>s3</artifactId>
    <version>2.x.x</version>
</dependency>

		

`application.yml`

Keep credentials out of the YAML in real deployments — use environment variables, an instance profile, or a secrets manager. The block below shows the settings worth externalizing either way.

yaml

			
aws:
  s3:
    region: eu-central-1
    bucket: my-app-bucket
    endpoint: ${AWS_S3_ENDPOINT:}     # only set for LocalStack/MinIO; blank for real AWS
    path-style-access: false          # true for LocalStack/MinIO

		

A matching @ConfigurationProperties class:

java

			
@ConfigurationProperties(prefix = "aws.s3")
public record S3Properties(
        String region,
        String bucket,
        String endpoint,
        boolean pathStyleAccess) {}

		

The `S3Client` bean

java

			
@Configuration
@EnableConfigurationProperties(S3Properties.class)
public class S3Config {
    @Bean
    public S3Client s3Client(S3Properties props) {
        S3ClientBuilder builder = S3Client.builder()
                .region(Region.of(props.region()))
                .credentialsProvider(DefaultCredentialsProvider.create())
                .serviceConfiguration(b -> b.pathStyleAccessEnabled(props.pathStyleAccess()));
        if (props.endpoint() != null && !props.endpoint().isBlank()) {
            builder.endpointOverride(URI.create(props.endpoint()));
        }
        return builder.build();
    }
}

		

DefaultCredentialsProvider checks environment variables, system properties, the shared ~/.aws/credentials file, and the EC2/ECS instance role, in that order — so the same code works locally and in production without changes.

A minimal S3 service

java

			
@Service
public class S3StorageService {
    private final S3Client s3Client;
    private final String bucket;
    public S3StorageService(S3Client s3Client, S3Properties props) {
        this.s3Client = s3Client;
        this.bucket = props.bucket();
    }
    public void upload(String key, byte[] content, String contentType) {
        s3Client.putObject(
                PutObjectRequest.builder()
                        .bucket(bucket)
                        .key(key)
                        .contentType(contentType)
                        .build(),
                RequestBody.fromBytes(content));
    }
    public byte[] download(String key) {
        return s3Client.getObject(
                GetObjectRequest.builder().bucket(bucket).key(key).build(),
                ResponseTransformer.toBytes()).asByteArray();
    }
    public List<String> listKeys(String prefix) {
        return s3Client.listObjectsV2(
                        ListObjectsV2Request.builder()
                                .bucket(bucket)
                                .prefix(prefix)
                                .build())
                .contents()
                .stream()
                .map(S3Object::key)
                .toList();
    }
    public void delete(String key) {
        s3Client.deleteObject(
                DeleteObjectRequest.builder().bucket(bucket).key(key).build());
    }
}

		

Four methods cover most day-to-day usage: putObject, getObject, listObjectsV2, and deleteObject. Everything else in the SDK is a variation on this same request/response builder pattern.

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