为什么Amazon S3存储桶策略访问被拒绝

Question

{
    "Version":"2012-10-17",
    "Statement":[
        {
        "Sid":"PublicReadGetObject",
        "Effect":"Allow",
        "Principal":"*",
        "Action":["s3:GetObject"],
        "Resource":[
         "arn:aws:s3:::mybucketname/*"
           ]
       }
    ]
}