Java Awssdk S3 List objects

Library
List objects with nextContinuationToken
List objects with ListObjectsV2Iterable
List objects by prefix
Get basic information about the object

In this article, I will show you how to use Java S3Client to list objects on an S3 Bucket. Specifically we will focus on using the listObjectsV2 and listObjectsV2Paginator methods, which are new and better than using the listObject method.

In addition, you can also get basic information on each object you have listed, they include:

File size
The owner of the object
Date of last modification.
...

First, we create the MyUtils class with a utility method to create the S3Client object, which is used in the examples of this article.

MyUtils.java

import software.amazon.awssdk.auth.credentials.AwsBasicCredentials;
import software.amazon.awssdk.auth.credentials.AwsCredentials;
import software.amazon.awssdk.auth.credentials.AwsCredentialsProvider;
import software.amazon.awssdk.auth.credentials.StaticCredentialsProvider;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.s3.S3Client;

public class MyUtils {  

	public static S3Client createS3Client(Region region) {
		AwsCredentials credentials = AwsBasicCredentials.create("accessKeyId", "secretAccessKey");
		AwsCredentialsProvider credentialsProvider = StaticCredentialsProvider.create(credentials);

		S3Client client = S3Client.builder() //
				.credentialsProvider(credentialsProvider) //
				.region(region) //
				.build();

		return client;
	} 
}

To create an S3Client object you need to create an AwsCredentialsProvider object, this object provides credentials that allow you to interact with AWS. See the article below to create an AwsCredentialsProvider suitable for your purposes.
Java Awssdk Common Credentials Providers

1. Library

<!-- https://mvnrepository.com/artifact/software.amazon.awssdk/s3 -->
<dependency>
	<groupId>software.amazon.awssdk</groupId>
	<artifactId>s3</artifactId>
	<version>2.21.10</version>
</dependency>

<!-- https://mvnrepository.com/artifact/software.amazon.awssdk/s3-transfer-manager -->
<dependency>
    <groupId>software.amazon.awssdk</groupId>
    <artifactId>s3-transfer-manager</artifactId>
    <version>2.21.10</version>
</dependency>

<!-- https://mvnrepository.com/artifact/software.amazon.awssdk.crt/aws-crt -->
<dependency>
    <groupId>software.amazon.awssdk.crt</groupId>
    <artifactId>aws-crt</artifactId>
    <version>0.28.0</version>
</dependency>

<!-- Log Library -->
<!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-api -->
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-api</artifactId>
    <version>2.0.9</version>
</dependency>

<!-- Log Library -->
<!-- https://mvnrepository.com/artifact/org.slf4j/slf4j-simple -->
<dependency>
    <groupId>org.slf4j</groupId>
    <artifactId>slf4j-simple</artifactId>
    <version>2.0.9</version> 
</dependency>

2. List objects with nextContinuationToken

By design, each user request sent to S3 Service only receives a maximum of 1000 objects. So if you want to get a list of all objects on a Bucket you have to send multiple requests. For each request you will receive a response consisting of a sublist of objects and a nextContinuationToken that creates a follow-up request for the next sublist. This seems a bit manual, see the full example:

ListObjectV2TokenExample.java

package org.o7planning.java_14211_awssdk_s3;

import java.util.List;

import org.o7planning.awssdks3.utils.MyUtils;

import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.s3.S3Client;
import software.amazon.awssdk.services.s3.model.ListObjectsV2Request;
import software.amazon.awssdk.services.s3.model.ListObjectsV2Response;
import software.amazon.awssdk.services.s3.model.S3Exception;
import software.amazon.awssdk.services.s3.model.S3Object;

public class ListObjectV2TokenExample {
	private static Region myRegion = Region.EU_CENTRAL_1;
	private static String myBucket = "test1.o7planning.org"; // Change to your bucket name

	private static final int MAX_KEYS_PER_REQUEST = 10;

	private static void listAllObjectsInBucket(S3Client s3Client, String bucketName) {
		String nextContinuationToken = null;

		int requestNo = 0;
		do {
			requestNo++;
			ListObjectsV2Request.Builder requestBuilder = ListObjectsV2Request.builder() //
					.bucket(bucketName) //
					.maxKeys(MAX_KEYS_PER_REQUEST) // Optional (Default 1000).
					.continuationToken(nextContinuationToken);

			ListObjectsV2Response response = s3Client.listObjectsV2(requestBuilder.build());
			List<S3Object> s3Objects = response.contents();

			nextContinuationToken = response.nextContinuationToken();

			System.out.println("Request " + requestNo + " returns " + s3Objects.size() + " keys");
			System.out.println(" - nextContinuationToken: " + nextContinuationToken);
		} while (nextContinuationToken != null);
	}

	public static void main(String[] args) {
		S3Client s3Client = MyUtils.createS3Client(myRegion);

		try {
			listAllObjectsInBucket(s3Client, myBucket);
		} catch (S3Exception e) {
			System.err.println(e.awsErrorDetails().errorMessage());
			e.printStackTrace();
			System.exit(1);
		}
	}
}

Output:

Request 1 returns 10 keys
 - nextContinuationToken: 1qVzSfeqc5jfInTSOGJoqaWoKqXcwgEdI2u+SuejyNNhjqg38Wf8Xhz/edWke6K2N8r21lARSBC0d1FTHzhN88CBU34f/cG2RtN6iPW4Y218=
Request 2 returns 10 keys
 - nextContinuationToken: 1uWdHKsz+nTpAXihAPDJJRvXc5lXavGBdd71iEvJVwzQLtcJxu9A/Gh4eWwzbW+/ZphmE6xnNDRSkJPbJpSR1LSWYxR6k2QBe
Request 3 returns 10 keys
 - nextContinuationToken: 1s2ypTkPxF9QpwD5t6815Nj+SNJanjsmMBGmQVTvb0thQ4n7+LsmGBAy79tajYSI4YspaQGlbNnlwySwuWxE1ZFRgeWK13vVf
Request 4 returns 10 keys
 - nextContinuationToken: 1lX92l0uLSnJs2hed1U35Rf25oorI8qrgyunlUqdDdjnDIzqC1L4EWJbLNrV1aE5FVdyey7CA/Q6O1H3YqQLLT+OPkHO6CRxAkswi7/a+opg=
Request 5 returns 10 keys
 - nextContinuationToken: 11pD2mJjgIwgOe1vDSbyitV4soW789+XL90xIr/grScGh3GxE9iSD/UlzXakWgtA2+l67g1WscfcN1WHM6kHoU5LuMAAU42aIjCvr+pJHWcs=
Request 6 returns 10 keys
 - nextContinuationToken: 1sqhUsdzV5B4yizBd2SEIdOpnY5NtX+78a5ZRemPMa8gtR6yu1JZhzsIrt0ARsdMY6HzGgoAM4tA=
Request 7 returns 5 keys
 - nextContinuationToken: null

3. List objects with ListObjectsV2Iterable

Instead of using s3Client.listObjectsV2(request) and nextContinuationToken as in the above example, in this example we use the s3Client.listObjectsV2Paginator(request) method, which is much shorter and easier to understand.

ListObjectsV2Example1.java

package org.o7planning.java_14211_awssdk_s3;

import java.util.Iterator;
import java.util.List;

import org.o7planning.awssdks3.utils.MyUtils;

import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.s3.S3Client;
import software.amazon.awssdk.services.s3.model.ListObjectsV2Request;
import software.amazon.awssdk.services.s3.model.ListObjectsV2Response;
import software.amazon.awssdk.services.s3.model.S3Exception;
import software.amazon.awssdk.services.s3.model.S3Object;
import software.amazon.awssdk.services.s3.paginators.ListObjectsV2Iterable;

public class ListObjectsV2Example1 {
	private static Region myRegion = Region.EU_CENTRAL_1;
	private static String myBucket = "test1.o7planning.org"; // Change to your bucket name

	private static final int MAX_KEYS_PER_REQUEST = 10;

	private static void listBucketObjects(S3Client s3Client, String bucketName) { 
		ListObjectsV2Request listV2Request = ListObjectsV2Request.builder() //
				.bucket(bucketName) //
				.maxKeys(MAX_KEYS_PER_REQUEST) //
				.build();

		ListObjectsV2Iterable listResponse = s3Client.listObjectsV2Paginator(listV2Request);
		Iterator<ListObjectsV2Response> responseIterator = listResponse.iterator();

		int requestNo = 0;
		while (responseIterator.hasNext()) {
			requestNo++;
			ListObjectsV2Response response = responseIterator.next();
			List<S3Object> s3Objects = response.contents();
			System.out.println("Request " + requestNo + " returns " + s3Objects.size() + " keys");
		} 
	}

	public static void main(String[] args) {
		S3Client s3Client = MyUtils.createS3Client(myRegion);

		try {
			listBucketObjects(s3Client, myBucket);
		} catch (S3Exception e) {
			System.err.println(e.awsErrorDetails().errorMessage());
			e.printStackTrace();
			System.exit(1);
		}
	}
}

Output:

Request 1 returns 10 keys
Request 2 returns 10 keys
Request 3 returns 10 keys
Request 4 returns 10 keys
Request 5 returns 10 keys
Request 6 returns 10 keys
Request 7 returns 5 keys

4. List objects by prefix

In some cases you may only want to list objects with a specified prefix such as "static/images/".

ListObjectsV2Request listReq = ListObjectsV2Request.builder() //
		.bucket(bucketName) //
		.maxKeys(MAX_KEYS_PER_REQUEST) //
		.prefix("static/images/") // Key Prefix
		.build();

5. Get basic information about the object

Example: List objects in an S3 Bucket and print out the basic information of each object.

File size
The owner of the object
Date of last modification.
...

ListObjectsV2Example2.java

package org.o7planning.java_14211_awssdk_s3;

import java.time.Instant;
import java.time.LocalDateTime;
import java.time.ZoneOffset;
import java.util.Iterator;
import java.util.List;
import java.util.Map;

import org.o7planning.awssdks3.utils.MyUtils;

import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.s3.S3Client;
import software.amazon.awssdk.services.s3.model.HeadObjectRequest;
import software.amazon.awssdk.services.s3.model.HeadObjectResponse;
import software.amazon.awssdk.services.s3.model.ListObjectsV2Request;
import software.amazon.awssdk.services.s3.model.ListObjectsV2Response;
import software.amazon.awssdk.services.s3.model.S3Exception;
import software.amazon.awssdk.services.s3.model.S3Object;
import software.amazon.awssdk.services.s3.paginators.ListObjectsV2Iterable;

public class ListObjectsV2Example2 {
	private static Region myRegion = Region.EU_CENTRAL_1;
	private static String myBucket = "test1.o7planning.org"; // Change to your bucket name

	private static final int MAX_KEYS_PER_REQUEST = 10;

	private static void listBucketObjects(S3Client s3Client, String bucketName) {
		ListObjectsV2Request listV2Request = ListObjectsV2Request.builder() //
				.bucket(bucketName) //
				.maxKeys(MAX_KEYS_PER_REQUEST) //
				.build();

		ListObjectsV2Iterable listResponse = s3Client.listObjectsV2Paginator(listV2Request);
		Iterator<ListObjectsV2Response> responseIterator = listResponse.iterator();

		while (responseIterator.hasNext()) {
			ListObjectsV2Response response = responseIterator.next();
			List<S3Object> s3Objects = response.contents();
			//
			for (S3Object s3Object : s3Objects) {
				System.out.println("\n\nObject Key: " + s3Object.key());
				System.out.println("Size: " + toKB(s3Object.size()) + " KB");
				System.out.println("Owner: " + s3Object.owner());
				//
				Instant instant = s3Object.lastModified();
				LocalDateTime lastModified = LocalDateTime.ofInstant(instant, ZoneOffset.UTC);
				System.out.println("Last Modified: " + lastModified);
				//
				moreInfo(s3Client, bucketName, s3Object.key());
			}
		}
	}

	private static void moreInfo(S3Client s3Client, String bucketName, String objectKey) {
		HeadObjectRequest headObjectRequest = HeadObjectRequest.builder() //
				.bucket(bucketName) //
				.key(objectKey) //
				.build();
		HeadObjectResponse headObjectResponse = s3Client.headObject(headObjectRequest);
		//
		System.out.println(" - contentType: " + headObjectResponse.contentType());
		System.out.println(" - cacheControl: " + headObjectResponse.cacheControl());
		System.out.println(" - websiteRedirectLocation: " + headObjectResponse.websiteRedirectLocation());
		//
		Map<String, String> metadata = headObjectResponse.metadata();
		System.out.println(" User Defined Metadata: " + metadata);
		for (String metaKey : metadata.keySet()) {
			System.out.println(" Metadata " + metaKey + " : " + metadata.get(metaKey));
		}
	}

	// Convert bytes to KB.
	private static long toKB(long bytes) {
		return bytes / 1024;
	}

	public static void main(String[] args) {
		S3Client s3Client = MyUtils.createS3Client(myRegion);

		try {
			listBucketObjects(s3Client, myBucket);
		} catch (S3Exception e) {
			System.err.println(e.awsErrorDetails().errorMessage());
			e.printStackTrace();
			System.exit(1);
		}
	}
}

Output:

Object Key: icons/
Size: 0 KB
Owner: Owner(ID=d3c6d6ab076f6bfb589d38b23110f1890de07fbd613da51c075cc37800fd59d3)
Last Modified: 2023-11-09T17:04:35
 - contentType: application/x-directory; charset=UTF-8
 - cacheControl: null
 - websiteRedirectLocation: null
 User Defined Metadata: {}


Object Key: sample.png
Size: 2 KB
Owner: Owner(ID=d3c6d6ab076f6bfb589d38b23110f1890de07fbd613da51c075cc37800fd59d3)
Last Modified: 2023-11-09T18:06:27
 - contentType: image/png
 - cacheControl: null
 - websiteRedirectLocation: null
 User Defined Metadata: {my-meta=Some Value}
 Metadata my-meta : Some Value


Object Key: static/
Size: 0 KB
Owner: Owner(ID=d3c6d6ab076f6bfb589d38b23110f1890de07fbd613da51c075cc37800fd59d3)
Last Modified: 2023-11-09T17:05:01
 - contentType: application/x-directory; charset=UTF-8
 - cacheControl: null
 - websiteRedirectLocation: null
 User Defined Metadata: {} 


Object Key: static/icons/close.png
Size: 1 KB
Owner: Owner(ID=d3c6d6ab076f6bfb589d38b23110f1890de07fbd613da51c075cc37800fd59d3)
Last Modified: 2023-11-09T17:05:43
 - contentType: image/png
 - cacheControl: null
 - websiteRedirectLocation: null
 User Defined Metadata: {}

Java Awssdk S3 Object Info

Java Awssdk S3 List objects

1. Library

2. List objects with nextContinuationToken

3. List objects with ListObjectsV2Iterable

4. List objects by prefix

5. Get basic information about the object

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