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

Question!

I would like to check if a key exists in a given bucket using Java. I looked at the API but there aren't any methods that are useful. I tried to use getObject but it threw an exception.



Answers
Use the jets3t library. Its a lot more easier and robust than the AWS sdk. Using this library you can call, s3service.getObjectDetails(). This will check and retrieve only the details of the object (not the contents) of the object. It will throw a 404 if the object is missing. So you can catch that exception and deal with it in your app.

But in order for this to work, you will need to have ListBucket access for the user on that bucket. Just GetObject access will not work. The reason being, Amazon will prevent you from checking for the presence of the key if you dont have ListBucket access. Just knowing whether a key is present or not, will also suffice for malicious users in some cases. Hence unless they have ListBucket access they will not be able to do so.

By : sethu


Congratulations, you've scrolled all the way down and found the simplest answer!

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

Enjoy!



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.



This video can help you solving your question :)
By: admin