概要

ローカル開発環境のdockerでS3を起動してJavaからアクセスする。

MinIO https://min.io/ を使用する。dockerhubは https://hub.docker.com/r/minio/minio

サンプルコード

docker run

とりあえず最低限の動作確認を行うためのコマンド。

docker run -p 9000:9000 -p 9001:9001 minio/minio:RELEASE.2024-12-18T13-15-44Z.fips server /data --console-address ":9001"

実行時のログ例は以下の通り。

INFO: Formatting 1st pool, 1 set(s), 1 drives per set.
INFO: WARNING: Host local has more than 0 drives of set. A host failure will result in data becoming unavailable.
MinIO Object Storage Server
Copyright: 2015-2025 MinIO, Inc.
License: GNU AGPLv3 - https://www.gnu.org/licenses/agpl-3.0.html
Version: RELEASE.2024-12-18T13-15-44Z (go1.23.4 X:boringcrypto linux/amd64)

API: http://172.17.0.2:9000  http://127.0.0.1:9000
WebUI: http://172.17.0.2:9001 http://127.0.0.1:9001

Docs: https://docs.min.io
WARN: Detected default credentials 'minioadmin:minioadmin', we recommend that you change these values with 'MINIO_ROOT_USER' and 'MINIO_ROOT_PASSWORD' environment variables

https://hub.docker.com/r/minio/minio - imageのversionは左記から適宜参照。
--console-address ":9001" によりWeb UIのportがこれになる。URLはログにある通り http://127.0.0.1:9001
Web UIのデフォルトのcredentialはログにある通り minioadmin:minioadmin で基本的には変更するものだろう。

Web UI

http://localhost:9001/ でWeb UIにアクセスして適当なオブジェクトを作成しておく。

Access Keys -> Create access key

適当なAccess Keyを作成。

適当なbucketを作成。ここではsample1という名前にしている。

Object Browser -> さっき作ったsample1のBucket -> Uploadで適当なファイルをUploadする。

Java

https://mvnrepository.com/artifact/software.amazon.awssdk/s3 の依存性を追加。

implementation 'software.amazon.awssdk:s3:2.29.50'

さっき作ったbucketにアクセスしてオブジェクトを取得する。

import java.net.URI;
import software.amazon.awssdk.auth.credentials.AwsBasicCredentials;
import software.amazon.awssdk.auth.credentials.AwsCredentials;
import software.amazon.awssdk.auth.credentials.StaticCredentialsProvider;
import software.amazon.awssdk.core.ResponseBytes;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.s3.S3Client;
import software.amazon.awssdk.services.s3.model.GetObjectRequest;
import software.amazon.awssdk.services.s3.model.GetObjectResponse;

public class S3SampleMain {

  public static void main(String[] args) {
    AwsCredentials credentials = AwsBasicCredentials.create("xxx", "xxx");

    S3Client client = S3Client.builder()
        .region(Region.US_EAST_1)
        .credentialsProvider(StaticCredentialsProvider.create(credentials))
        .endpointOverride(URI.create("http://localhost:9000"))
        .forcePathStyle(true) 
        .build();

    GetObjectRequest request = GetObjectRequest
        .builder()
        .key("hogehoge.txt")
        .bucket("sample1")
        .build();

    ResponseBytes<GetObjectResponse> response = client.getObjectAsBytes(request);
    String message = response.asUtf8String();
    System.out.println(message);

  }
}

credentialsにはWeb UIで作成したAccesss Keyを指定する。
endpointOverride にはdocker run時のログAPI: (略) http://127.0.0.1:9000に従ったURLを指定する。
forcePathStyle(true)はローカルで試す分には必要。
GetObjectRequestにあらかじめ作成しておいたオブジェクトを指定する。

ハマったところ

region(Region.US_EAST_1)は必要

未指定だと以下のような例外になる。

Exception in thread "main" software.amazon.awssdk.core.exception.SdkClientException: Unable to load region from any of the providers in the chain software.amazon.awssdk.regions.providers.DefaultAwsRegionProviderChain@732c2a62: [software.amazon.awssdk.regions.providers.SystemSettingsRegionProvider@1ff4931d: Unable to load region from system settings. Region must be specified either via environment variable (AWS_REGION) or  system property (aws.region)., software.amazon.awssdk.regions.providers.AwsProfileRegionProvider@510f3d34: No region provided in profile: default, software.amazon.awssdk.regions.providers.InstanceProfileRegionProvider@1ba9117e: Unable to contact EC2 metadata service.]

Received an UnknownHostException when attempting to interact with a service.

https://dev.classmethod.jp/articles/access-minio-using-aws-sdk-for-go/ にある通り S3Client#forcePathStyle(true) が必要となる。

Exception in thread "main" software.amazon.awssdk.core.exception.SdkClientException: Received an UnknownHostException when attempting to interact with a service. See cause for the exact endpoint that is failing to resolve. If this is happening on an endpoint that previously worked, there may be a network connectivity issue or your DNS cache could be storing endpoints for too long.
    ...
at org.example.app.S3SampleMain.main(S3SampleMain.java:47)
Caused by: software.amazon.awssdk.core.exception.SdkClientException: Unable to execute HTTP request: sample0001.localhost
        ...
Suppressed: software.amazon.awssdk.core.exception.SdkClientException: Request attempt 1 failure: Unable to execute HTTP request: ���̂悤�ȃz�X�g�͕s���ł��B (sample0001.localhost)
Suppressed: software.amazon.awssdk.core.exception.SdkClientException: Request attempt 2 failure: Unable to execute HTTP request: sample0001.localhost
Suppressed: software.amazon.awssdk.core.exception.SdkClientException: Request attempt 3 failure: Unable to execute HTTP request: sample0001.localhost
Caused by: java.net.UnknownHostException: sample0001.localhost
        ...