How to check if a specified key exists in a given S3 bucket using Java

Solution 1:

There's now a doesObjectExist method in the official Java API.

Enjoy!

Solution 2:

Update:

It seems there's a new API to check just that. See another answer in this page: https://stackoverflow.com/a/36653034/435605

Original post:

Use errorCode.equals("NoSuchKey")

try {
    AmazonS3 s3 = new AmazonS3Client(new ClasspathPropertiesFileCredentialsProvider());
    String bucketName = getBucketName();
    s3.createBucket(bucketName);
    S3Object object = s3.getObject(bucketName, getKey());
} catch (AmazonServiceException e) {
    String errorCode = e.getErrorCode();
    if (!errorCode.equals("NoSuchKey")) {
        throw e;
    }
    Logger.getLogger(getClass()).debug("No such key!!!", e);
}

Note about the exception: I know exceptions should not be used for flow control. The problem is that Amazon didn't provide any api to check this flow - just documentation about the exception.

Solution 3:

Using the AWS SDK use the getObjectMetadata method. The method will throw an AmazonServiceException if the key doesn't exist.

private AmazonS3 s3;
...
public boolean exists(String path, String name) {
    try {
        s3.getObjectMetadata(bucket, getS3Path(path) + name); 
    } catch(AmazonServiceException e) {
        return false;
    }
    return true;
}

Solution 4:

In Amazon Java SDK 1.10+, you can use getStatusCode() to get the status code of the HTTP response, which will be 404 if the object does not exist.

import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.model.AmazonS3Exception;
import org.apache.http.HttpStatus;

try {
    AmazonS3 s3 = new AmazonS3Client();
    ObjectMetadata object = s3.getObjectMetadata("my-bucket", "my-client");
} catch (AmazonS3Exception e) {
    if (e.getStatusCode() == HttpStatus.SC_NOT_FOUND) {
        // bucket/key does not exist 
    } else {
        throw e;
    }
}

getObjectMetadata() consumes fewer resources, and the response doesn't need to be closed like getObject().

In previous versions, you can use getErrorCode() and check for the appropriate string (depends on the version).