public void setMatchingETagConstraints(List<String> etagList) {
        this.matchingETagConstraints = etagList;
    }
Sets the optional list of ETag constraints for this request.
If the ETag of the object stored in Amazon S3 matches any of the specified
ETags, the request will be executed normally. Otherwise, the request will
fail with a precondition failed exception.

@param etagList
           The list of ETags to constrain this request.

@see PresignedUrlDownloadRequest#getMatchingETagConstraints()
@see PresignedUrlDownloadRequest#withMatchingETagConstraint(String)
aws-java-sdk-s3/src/main/java/com/amazonaws/services/s3/model/PresignedUrlDownloadRequest.java