java 如何从 Amazon S3 下载文件？
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How to download files from Amazon S3?
提问by kylas
I have a folder named outputinside a bucket named BucketA. I have a list of files in outputfolder. How do I download them to my local machine using AWS Java SDK ?
我有一个output名为BucketA. 我有文件output夹中的文件列表。如何使用 AWS Java SDK 将它们下载到我的本地机器？
Below is my code:
下面是我的代码：
AmazonS3Client s3Client = new AmazonS3Client(credentials);
File localFile = new File("/home/abc/Desktop/AmazonS3/");
s3Client.getObject(new GetObjectRequest("bucketA", "/bucketA/output/"), localFile);
And I got the error:
我得到了错误：
AmazonS3Exception: The specified key does not exist.
回答by Bruce P
Keep in mind that S3 is not a filesystem, but it is an object store. There's a huge difference between the two, one being that directory-style activities simply won't work.
请记住，S3 不是文件系统，而是一个对象存储。两者之间存在巨大差异，其一是目录样式的活动根本行不通。
Suppose you have an S3 bucket with two objects in it:
假设您有一个包含两个对象的 S3 存储桶：
/path/to/file1.txt
/path/to/file2.txt
When working with these objects you can't simply refer to /path/to/like you can when working with files in a filesystem directory. That's because /path/to/is not a directory but just part of a key in a very large hash table. This is why the error message indicates an issue with a key. These are not filename paths but keys to objects within the object store.
处理这些对象时，您不能/path/to/像处理文件系统目录中的文件那样简单地引用。那是因为/path/to/它不是目录，而是非常大的哈希表中键的一部分。这就是错误消息表明密钥存在问题的原因。这些不是文件名路径，而是对象存储中对象的键。
In order to copy all the files in a location like /path/to/you need to perform it in multiple steps. First, you need to get a listing of all the objects whose keys begin with /path/to, then you need to loop through each individual object and copy them one by one.
为了复制一个位置中的所有文件，/path/to/您需要分多个步骤执行。首先，您需要获取键以 开头的所有对象的列表/path/to，然后您需要循环遍历每个单独的对象并逐个复制它们。
Here is a similar questionwith an answer that shows how to download multiple files from S3 using Java.
这是一个类似的问题，其答案显示了如何使用 Java 从 S3 下载多个文件。
回答by Pramesh
I know this question was asked longtime ago, but still this answer might help some one.
我知道这个问题很久以前就有人问过了，但这个答案仍然可能对某些人有所帮助。
你可能想使用这样的东西从 S3 下载对象 new ListObjectsV2Request().withBucketName("bucketName").withDelimiter("delimiter").withPrefix("path/to/image/");
as mentioned in the S3 doc
delimiterbe "/"and prefixbe your "folder like structure".
分隔符是“/”，前缀是你的“类似结构的文件夹”。
回答by janardhan randhi
You can use the predefined classes for upload directory and download directory
您可以使用预定义的类作为上传目录和下载目录
For Download
下载
MultipleFileDownload xfer = xfer_mgr.downloadDirectory(
bucketName, key, new File("C:\Users\miracle\Deskto\Downloads"));
For Upload
上传
MultipleFileUpload xfer = xfer_mgr.uploadDirectory(bucketName, key,Dir,true);
回答by Rob
The error message means that the bucket (in this case "bucketA") does not contain a file with the name you specified (in this case "/bucketA/output/").
错误消息意味着存储桶（在本例中为“bucketA”）不包含具有您指定名称的文件（在本例中为“/bucketA/output/”）。
When you specify the key, do not include the bucket name in the key. S3 supports "folders" in the key, which are delimited with "/", so you probably do not want to try to use keys that end with "/".
指定key时，key中不要包含bucket名称。 S3 支持键中的“文件夹”，它们以“/”分隔，因此您可能不想尝试使用以“/”结尾的键。
If your bucket "bucketA" contains a file called "output", you probably want to say
如果您的存储桶“bucketA”包含一个名为“output”的文件，您可能想说
new GetObjectRequest("bucketA", "output")
If this doesn't work, other things to check:
如果这不起作用，请检查其他事项：
- Do the credentials you are using have permission to read from the bucket?
- Did you spell all the names correctly?
- 您使用的凭据是否有权从存储桶中读取？
- 您是否正确拼写了所有名称？
You might want to use listObjects("bucketA")to verify what the bucket actually contains (as seen with the credentials you are using).
您可能想使用它listObjects("bucketA")来验证存储桶实际包含的内容（如您使用的凭证所示）。
