Example code of operating S3 on Outposts with AWS Java SDK v2. Checkout AWS offical document for using v1: https://docs.aws.amazon.com/AmazonS3/latest/userguide/S3OutpostsCreateAccessPoint.html

pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">

    <modelVersion>4.0.0</modelVersion>

    <groupId>com.example</groupId>
    <artifactId>aws-sdk-example</artifactId>
    <version>1.0-SNAPSHOT</version>
    <packaging>jar</packaging>

    <name>AWS SDK Example</name>

    <dependencyManagement>
        <dependencies>
            <dependency>
                <groupId>software.amazon.awssdk</groupId>
                <artifactId>bom</artifactId>
                <version>2.20.28</version>
<!--                <version>2.25.63</version>-->
                <type>pom</type>
                <scope>import</scope>
            </dependency>
        </dependencies>
    </dependencyManagement>

    <dependencies>
        <dependency>
            <groupId>software.amazon.awssdk</groupId>
            <artifactId>s3</artifactId>
        </dependency>
        <dependency>
            <groupId>software.amazon.awssdk</groupId>
            <artifactId>s3control</artifactId>
        </dependency>
        <dependency>
            <groupId>software.amazon.awssdk</groupId>
            <artifactId>apache-client</artifactId>
        </dependency>
        <dependency>
            <groupId>software.amazon.awssdk</groupId>
            <artifactId>netty-nio-client</artifactId>
        </dependency>
        <!-- SLF4J Logging API -->
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-api</artifactId>
            <version>1.7.30</version>
        </dependency>
        <dependency>
            <groupId>org.slf4j</groupId>
            <artifactId>slf4j-simple</artifactId>
            <version>1.7.30</version>
        </dependency>
    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.apache.maven.plugins</groupId>
                <artifactId>maven-compiler-plugin</artifactId>
                <version>3.8.1</version>
                <configuration>
                    <source>1.8</source>
                    <target>1.8</target>
                </configuration>
            </plugin>
        </plugins>
    </build>
</project>

S3OutpostsBucket.java

import software.amazon.awssdk.auth.credentials.ProfileCredentialsProvider;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.s3control.S3ControlClient;
import software.amazon.awssdk.services.s3control.model.*;

import java.util.stream.Collectors;

public class S3OutpostsBucket {
    public static void main(String[] args) {
        // Enable debug-level logging for the AWS Java SDK v2
//        System.setProperty(SimpleLogger.DEFAULT_LOG_LEVEL_KEY, "debug");
//        System.setProperty(SimpleLogger.LOG_FILE_KEY, "System.out");
//        System.setProperty("org.slf4j.simpleLogger.log.software.amazon.awssdk", "debug");

        String accountId = "xxx";
        String vpcId = "vpc-xxx";
        String outpostId = "op-xxx";
        String bucketName = "test-java-create";
        String accessPointName = "poc-java-sdk-ap2";

        // Create an S3ControlClient
        S3ControlClient s3ControlClient = S3ControlClient.builder()
                .credentialsProvider(ProfileCredentialsProvider.create())
//                .region(Region.AP_NORTHEAST_1)
                .build();

        // Create the bucket request
        String bucketArn;
        try {
            CreateBucketRequest createBucketRequest = CreateBucketRequest.builder()
                    .bucket(bucketName)
                    .outpostId(outpostId)
                    .build();

            CreateBucketResponse createBucketResponse = s3ControlClient.createBucket(createBucketRequest);
            bucketArn = createBucketResponse.bucketArn();
        } catch (BucketAlreadyOwnedByYouException e) {
            System.out.println("Bucket already exist");
            ListRegionalBucketsResponse buckets = s3ControlClient.listRegionalBuckets(ListRegionalBucketsRequest.builder().accountId(accountId).outpostId(outpostId).build());
            bucketArn = buckets.regionalBucketList().stream().filter(x -> x.bucket().equals(bucketName)).map(RegionalBucket::bucketArn).collect(Collectors.toList()).get(0);
        }
        System.out.println("Bucket Arn: " + bucketArn);

        // create AP
        CreateAccessPointResponse accessPoint = s3ControlClient.createAccessPoint(CreateAccessPointRequest.builder()
                .name(accessPointName)
                .accountId(accountId)
                .vpcConfiguration(VpcConfiguration.builder()
                        .vpcId(vpcId).build()
                )
                .bucket(bucketArn).build()
        );
        System.out.println("Access point Arn: " + accessPoint.accessPointArn());
        System.out.println("Wait a few minutes for the new access point to become usable.");
    }


}

S3OutpostsObject.java

import software.amazon.awssdk.auth.credentials.ProfileCredentialsProvider;
import software.amazon.awssdk.core.exception.SdkClientException;
import software.amazon.awssdk.regions.Region;
import software.amazon.awssdk.services.s3.S3Client;
import software.amazon.awssdk.services.s3.model.*;

import java.nio.file.Paths;

public class S3OutpostsObject {
    public static void main(String[] args) {
        String accessPointArn = "TBD;
        String filePath = "/tmp/100M";
        String keyName = "test-v2-sdk-obj";

        // Create an S3 client using the default credentials profile
        S3Client s3 = S3Client.builder()
                .credentialsProvider(ProfileCredentialsProvider.create())
                .build();



        ////////
        System.out.println("Create object");

        try {
            // Create a PutObjectRequest
            PutObjectRequest putObjectRequest = PutObjectRequest.builder()
                    .bucket(accessPointArn)
                    .key(keyName)
                    .build();

            // Upload the file
            PutObjectResponse putObjectResponse = s3.putObject(putObjectRequest, Paths.get(filePath));

            System.out.println("File uploaded successfully. ETag: " + putObjectResponse.eTag());
        } catch (S3Exception e) {
            // The call was transmitted successfully, but Amazon S3 couldn't process it, so it returned an error response.
            e.printStackTrace();
        } catch (SdkClientException e) {
            // Amazon S3 couldn't be contacted for a response, or the client couldn't parse the response from Amazon S3.
            e.printStackTrace();
        }

        ////////
        System.out.println("Listing objects");



        // maxKeys is set to 2 to demonstrate the use of
        // ListObjectsV2Response.nextContinuationToken()
        ListObjectsV2Request req = ListObjectsV2Request.builder()
                .bucket(accessPointArn)
                .maxKeys(2)
                .build();

        ListObjectsV2Response result;

        do {
            result = s3.listObjectsV2(req);

            for (S3Object objectSummary : result.contents()) {
                System.out.printf(" - %s (size: %d)\n", objectSummary.key(), objectSummary.size());
            }
            // If there are more than maxKeys keys in the bucket, get a continuation token
            // and list the next objects.
            String token = result.nextContinuationToken();
            System.out.println("Next Continuation Token: " + token);
            req = req.toBuilder().continuationToken(token).build();
        } while (result.isTruncated());


        ////////
        System.out.println("Delete object");
        s3.deleteObject(DeleteObjectRequest.builder().bucket(accessPointArn).key(keyName).build());



        // Close the S3 client
        s3.close();
    }
}