check existance of object after uploading it to S3

I want to check if an object us successfuly uploaded to S3 just after uploading it.

PutObjectRequest putObjReq = new PutObjectRequest(bucketName, s3Key, tmpArchivePath.toFile());
Upload upload = transferManager.upload(putObjReq);
upload.waitForCompletion();
boolean fileExistsAfter = s3Client.doesObjectExist(bucketName, s3Key);

that returns always true ,even if the object is not successfully uploaded. I think that is because of the Eventual Consistency,
example:
when the s3Key starts with / , it is not a valid key ,so the object will not be uploaded however it returns true

Your code is working correctly.

When you upload to a key such as /dog.png, you do indeed get an S3 object with the key /dog.png. You can see this if you run aws s3 ls s3://mybucket// (with extra trailing slash) instead of aws s3 ls s3://mybucket/. You can also verify this by issuing a HeadObject request for the key /dog.png, which is effectively what the doesObjectExist() method does.

To verify the object exists using the awscli, run:

aws s3api head-object --bucket mybucket --key /dog.png

So the upload succeeds and doesObjectExist() correctly returns true.

As a general rule, you probably want to avoid leading slash because it is confusing for people.