Often when working with files in S3, you need information about all the items in a particular S3 bucket. Below is an example class that extends the AmazonS3Client class to provide this functionality. For the most part this class has been adapted from the sample in this AWS post. Aside from some additional methods, one major difference is that the default constructor for this class uses EnvironmentVariableCredentialsProvider instead of ProfileCredentialsProvider. The main() method in the class is doing several things:

• Creates a new BdS3Client object
• Creates a new S3 bucket
• Adds empty files to the new S3 bucket
• Creates a list of object names contained in the bucket
• Prints the object names contained in the bucket

You can view the complete implementation here: Big Datums GitHub

package com.bigdatums.aws;

import java.io.File;
import java.io.IOException;
import java.util.ArrayList;
import java.util.List;

import com.amazonaws.AmazonClientException;
import com.amazonaws.AmazonServiceException;
import com.amazonaws.auth.AWSCredentialsProvider;
import com.amazonaws.auth.EnvironmentVariableCredentialsProvider;
import com.amazonaws.services.s3.AmazonS3Client;
import com.amazonaws.services.s3.model.DeleteObjectsRequest;
import com.amazonaws.services.s3.model.ListObjectsRequest;
import com.amazonaws.services.s3.model.ObjectListing;
import com.amazonaws.services.s3.model.S3ObjectSummary;


public class BdS3Client extends AmazonS3Client{

    public BdS3Client(){
        super(new EnvironmentVariableCredentialsProvider());
    }

    public BdS3Client(AWSCredentialsProvider awsCredentialsProvider){
        super(awsCredentialsProvider);
    }


    public List<S3ObjectSummary> getBucketObjectSummaries(String bucketName){

        List<S3ObjectSummary> s3ObjectSummaries = new ArrayList<S3ObjectSummary>();

        try {
            ListObjectsRequest listObjectsRequest = new ListObjectsRequest().withBucketName(bucketName);
            ObjectListing objectListing;

            do {
                objectListing = this.listObjects(listObjectsRequest);
                for (S3ObjectSummary objectSummary : objectListing.getObjectSummaries()) {
                    s3ObjectSummaries.add(objectSummary);
                }
                listObjectsRequest.setMarker(objectListing.getNextMarker());
            } while (objectListing.isTruncated());
        } catch (AmazonServiceException ase) {
            System.out.println("Caught an AmazonServiceException, " +
                    "which means your request made it " +
                    "to Amazon BdS3Client, but was rejected with an error response " +
                    "for some reason.");
            System.out.println("Error Message:    " + ase.getMessage());
            System.out.println("HTTP Status Code: " + ase.getStatusCode());
            System.out.println("AWS Error Code:   " + ase.getErrorCode());
            System.out.println("Error Type:       " + ase.getErrorType());
            System.out.println("Request ID:       " + ase.getRequestId());
        } catch (AmazonClientException ace) {
            System.out.println("Caught an AmazonClientException, " +
                    "which means the client encountered " +
                    "an internal error while trying to communicate" +
                    " with BdS3Client, " +
                    "such as not being able to access the network.");
            System.out.println("Error Message: " + ace.getMessage());
        }
        return s3ObjectSummaries;
    }

    public List<String> getBucketObjectNames(String bucketName){
        List<String> s3ObjectNames = new ArrayList<String>();
        List<S3ObjectSummary> s3ObjectSummaries = getBucketObjectSummaries(bucketName);

        for(S3ObjectSummary s3ObjectSummary : s3ObjectSummaries){
            s3ObjectNames.add(s3ObjectSummary.getKey());
        }
        return s3ObjectNames;
    }

    public void printBucketObjectNames(String bucketName){
        List<String> s3ObjectNames = getBucketObjectNames(bucketName);
        for (String s3ObjectName : s3ObjectNames){
            System.out.println(s3ObjectName);
        }
    }

    public void putEmptyFiles(String bucketName, String prefix, String extension, int numFiles) throws IOException {

        for (int i = 0; i<numFiles; i++) {
            String filename = prefix + i + "." + extension;
            File file = new File(filename);
            file.createNewFile();
            this.putObject(bucketName, filename, file);
            file.delete();
        }

    }

    public static void main(String[] args){
        BdS3Client s3Client = new BdS3Client();
        String bucketName = "big-datums-tmp";
        s3Client.createBucket(bucketName);

        try {
            s3Client.putEmptyFiles(bucketName, "myTempFiles", "txt", 25);
        } catch (IOException e){
            System.out.println(e);
        }

        List<String> objectList = s3Client.getBucketObjectNames(bucketName);
        s3Client.printBucketObjectNames(bucketName);

    }


}