How to Calculate S3 Folder Size Using listObjectsV2() in Java

Amazon S3 (Simple Storage Service) is a popular object storage service that is widely used in cloud environments. While it’s easy to store objects in S3, there are times when we need to know the size of a folder that contains these objects, especially when dealing with large amounts of data. In this tutorial, we will explore how to use listObjectsV2() in Java to calculate the size of a folder in Amazon S3.

What is listObjectsV2()?

listObjectsV2() is a method provided by the AWS SDK for Java that allows you to list objects in a specified S3 bucket. However, when it comes to calculating the total size of a folder containing many files, you’ll face challenges. The listObjectsV2() method helps by retrieving object information from S3, and from there, you can calculate the total size of these objects.

Setting Up Your Environment

Before we start writing the code, let's set up the environment.

1. Add AWS SDK Dependency
   If you're using Maven, you can add the following dependency to your pom.xml file:

    <dependency>
        <groupId>com.amazonaws</groupId>
        <artifactId>aws-java-sdk-s3</artifactId>
        <version>1.12.118</version>
    </dependency>
   

2. Configure AWS Credentials
   You need to configure your AWS credentials. You can do this either by using the AWS Management Console or by creating a credentials file at ~/.aws/credentials on your machine. Your credentials file should look like this:

    [default]
    aws_access_key_id = YOUR_ACCESS_KEY
    aws_secret_access_key = YOUR_SECRET_KEY
   

3. Set up your AWS Region
   Make sure you are using the correct region for your S3 bucket. In this example, we’ll use the us-west-2 region.

Java Code to Calculate Folder Size

Now let’s write the Java code to calculate the total size of the folder in an S3 bucket.

Code Example

import com.amazonaws.auth.AWSStaticCredentialsProvider;
import com.amazonaws.auth.BasicAWSCredentials;
import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.AmazonS3ClientBuilder;
import com.amazonaws.services.s3.model.ListObjectsV2Request;
import com.amazonaws.services.s3.model.ListObjectsV2Result;
import com.amazonaws.services.s3.model.S3ObjectSummary;

public class S3FolderSizeCalculator {
    private static final String BUCKET_NAME = "your-bucket-name";  // Replace with your bucket name
    private static final String FOLDER_PREFIX = "your-folder-name/";  // Replace with your folder name

    public static void main(String[] args) {
        // Create an AWS credentials object
        BasicAWSCredentials awsCredentials = new BasicAWSCredentials("YOUR_ACCESS_KEY", "YOUR_SECRET_KEY");

        // Create an AmazonS3 client
        AmazonS3 s3Client = AmazonS3ClientBuilder.standard()
                                                 .withCredentials(new AWSStaticCredentialsProvider(awsCredentials))
                                                 .withRegion("us-west-2")  // Specify your region
                                                 .build();

        // Calculate the total size of the folder
        long totalSize = calculateFolderSize(s3Client, BUCKET_NAME, FOLDER_PREFIX);
        System.out.println("Total size of folder '" + FOLDER_PREFIX + "' is: " + totalSize + " bytes");
    }

    public static long calculateFolderSize(AmazonS3 s3Client, String bucketName, String folderPrefix) {
        long totalSize = 0;

        // Create a ListObjectsV2Request to list objects in the folder
        ListObjectsV2Request request = new ListObjectsV2Request()
                                         .withBucketName(bucketName)
                                         .withPrefix(folderPrefix);

        ListObjectsV2Result result;

        // Loop through the objects in the folder and sum their sizes
        do {
            result = s3Client.listObjectsV2(request);
            for (S3ObjectSummary objectSummary : result.getObjectSummaries()) {
                totalSize += objectSummary.getSize();
            }

            // If there are more objects, set the continuation token for the next request
            request.setContinuationToken(result.getNextContinuationToken());
        } while (result.isTruncated());  // Continue until all objects are listed

        return totalSize;
    }
}

Code Explanation

• AWS Credentials: The BasicAWSCredentials class is used to set up your AWS access key and secret key.

• AmazonS3 Client: The AmazonS3ClientBuilder is used to create a client to interact with S3.

• ListObjectsV2Request: We create a request object to list objects within a specific folder, identified by the prefix.

• Loop Through Objects: The listObjectsV2() method is used to retrieve the objects in the folder. We loop through the objects and sum their sizes to get the total folder size.

• Handling Pagination: If there are more than 1000 objects in the folder, the listObjectsV2() method will paginate the results. We handle this by checking the isTruncated() flag and setting the ContinuationToken for the next set of objects.

Running the Code

Once you have the code set up, you can run it in your local environment or any Java IDE like IntelliJ IDEA or Eclipse. The program will output the total size of the specified folder in bytes.

Conclusion

In this tutorial, we’ve learned how to calculate the size of a folder in Amazon S3 by iterating through its objects and summing their sizes. The approach using listObjectsV2() is efficient for most use cases, but keep in mind that for extremely large datasets, it may take some time to retrieve all the object information, especially if there are many objects or large files involved.

If you are dealing with very large datasets or need this calculation in real-time, you may want to consider using other solutions such as AWS Lambda, S3 Event notifications, or storing the size information in a database for faster retrieval.

Tags

• #Java

• #AWS

• #S3

• #Cloud

• #DevOps