Question

在S3存储桶中没有密钥时收到消息。我检索该存储桶中的所有对象，并将这些键与给定的搜索关键字匹配。如果可用，则返回URL-String，否则返回消息'指定的密钥不存在'。

是否可以通过其他方式在访问密钥时提高性能，这在S3存储桶中不可用。

这是我的代码：

public class S3Objects {
    static Properties props = new Properties();
    static InputStream resourceAsStream;
    static {
        ClassLoader classLoader = new S3Objects().getClass().getClassLoader();
        resourceAsStream = classLoader.getResourceAsStream("aws.properties");
        try {
            props.load(resourceAsStream);
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

    public static void main(String[] args) throws IOException, AmazonServiceException, AmazonClientException, InterruptedException {
        AWSCredentials awsCreds = new 
                        BasicAWSCredentials(props.getProperty("accessKey"), props.getProperty("secretKey"));
                        // PropertiesCredentials(resourceAsStream);
        AmazonS3 s3Client = new AmazonS3Client( awsCreds );

        String s3_BucketName = props.getProperty("bucketname");
        String folderPath_fileName = props.getProperty("path");

        //uploadObject(s3Client, s3_BucketName, folderPath_fileName);
        //downloadObject(s3Client, s3_BucketName, folderPath_fileName);
        //getSignedURLforS3File(s3Client, s3_BucketName, folderPath_fileName);
        String url = getSingnedURLKey(s3Client, s3_BucketName, folderPath_fileName);
        System.out.println("Received response:"+url);
    }
    //  <MaxKeys>1000</MaxKeys>
    private static String getSingnedURLKey(AmazonS3 s3Client, String s3_BucketName, String folderPath_fileName) {
        String folderPath = folderPath_fileName.substring(0,folderPath_fileName.lastIndexOf("/"));      
        ObjectListing folderPath_Objects = s3Client.listObjects(s3_BucketName, folderPath);

        List<S3ObjectSummary> listObjects = folderPath_Objects.getObjectSummaries();
        for(S3ObjectSummary object : listObjects){
            if(object.getKey().equalsIgnoreCase(folderPath_fileName)){
                return getSignedURLforS3File(s3Client, s3_BucketName, folderPath_fileName);
            }
        }
        return "The specified key does not exist.";
    }

    //  providing pre-signed URL to access an object w/o any AWS security credentials.
   //   Pre-Signed URL = s3_BucketName.s3.amazonaws.com/folderPath_fileName?AWSAccessKeyId=XX&Expires=XX&Signature=XX
    public static String getSignedURLforS3File(AmazonS3 s3Client, String s3_BucketName, String folderPath_fileName){
        GeneratePresignedUrlRequest request = new GeneratePresignedUrlRequest(s3_BucketName, folderPath_fileName, HttpMethod.GET);
        request.setExpiration( new Date(System.currentTimeMillis() + 1000 * 60 * 15) ); // Default 15 min

        String url = s3Client.generatePresignedUrl( request ).toString();
        System.out.println("Pre-Signed URL = " + url);
        return url;
    }

    public static void uploadObject(AmazonS3 s3Client, String s3_BucketName, String folderPath_fileName) 
            throws AmazonServiceException, AmazonClientException, InterruptedException{
        TransferManager tm = new TransferManager(s3Client);

        PutObjectRequest putObjectRequest = 
                new PutObjectRequest(s3_BucketName, folderPath_fileName, new File("newImg.jpg"));
        Upload myUpload = tm.upload( putObjectRequest );
        myUpload.waitForCompletion();//block the current thread and wait for your transfer to complete.
        tm.shutdownNow();            //to release the resources once the transfer is complete.
    }
   //   When accessing a key which is not available in S3, it throws an exception The specified key does not exist.
    public static void downloadObject(AmazonS3 s3Client, String s3_BucketName, String folderPath_fileName) throws IOException{
        GetObjectRequest request = new GetObjectRequest(s3_BucketName,folderPath_fileName);
        try{
            S3Object s3object = s3Client.getObject( request );
            System.out.println("Content-Type: " + s3object.getObjectMetadata().getContentType());
            S3ObjectInputStream objectContent = s3object.getObjectContent();

            FileUtils.copyInputStreamToFile(objectContent, new File("targetFile.jpg"));
        }catch(AmazonS3Exception s3){
            System.out.println("Received error response:"+s3.getMessage());
        }
    }

}

aws.properties

accessKey   =XXXXXXXXX
secretKey   =XXXXXXXXX

bucketname  =examplebucket
path        =/photos/2006/February/sample.jpg

请告诉我天气，他们可以通过任何其他方式减少所有密钥的迭代次数，并获得一些消息“密钥不存在”。

请求密钥生成预签名URL时。如果

Key Present«返回已签名的网址。
Key Not Present«消息为密钥不可用。

Answer 1

在给定密钥的情况下，使用getObjectMetadata快速确定对象是否存在。如果成功，则该对象存在。如果没有，请检查错误以确认它不是需要重试的瞬态错误。如果没有，就没有这样的钥匙。

通过对象进行迭代不仅不会扩展，而且实际上也更加昂贵，因为列表请求每个请求的价格高于获取对象或获取其元数据，这应该非常快。此操作向S3发送HTTP HEAD请求，仅当对象存在时才返回200 OK。

但是，从设计的角度来看，我认为这项服务不应该真正关心对象是否存在。为什么你会收到不存在的对象的请求？谁在要求这个？这应该是调用者的问题 - 如果您为不存在的对象生成签名URL，则当调用者尝试使用URL时，请求将失败并显示错误...但是为一个生成签名的URL不存在的对象是一个完全有效的操作。在实际上传对象之前，可以对进行签名，并且，只要URL未过期，一旦创建了对象，它将仍然有效，如果它是稍后创建的。

Answer 2

Amazon S3：检查密钥存在并生成PresignedUrl

使用 getObjectMetadata()：AmazonS3Client 这对于仅获取对象元数据很有用，并避免在获取对象数据时浪费带宽。

private static String getPreSignedURLAsString_GetMetaData(AmazonS3 s3Client, String s3_BucketName, String folderPath_fileName) {
    GetObjectMetadataRequest request = new GetObjectMetadataRequest(s3_BucketName,folderPath_fileName);
    try{
        ObjectMetadata objectMetadata = s3Client.getObjectMetadata( request );
        System.out.println("Key Exists in S3");
        return getSignedURLforS3File(s3Client, s3_BucketName, folderPath_fileName);
    }catch(AmazonS3Exception s3){
        System.out.println("Received error response:"+s3.getMessage());
    }
    return "Key Not Found.";
}

使用 doesObjectExist（）：AmazonS3Client 在内部，它正在调用getObjectMetadata（bucketName，objectName）; - [aws-java- SDK-68年1月10日]

private static String getPreSignedURLAsString_DoesKeyExists(AmazonS3 s3Client, String s3_BucketName, String folderPath_fileName) {
    try{
        boolean doesObjectExist = s3Client.doesObjectExist(s3_BucketName, folderPath_fileName);
        if (doesObjectExist) {
            System.out.println("Key Exists in S3");
            return getSignedURLforS3File(s3Client, s3_BucketName, folderPath_fileName);
        }
    }catch(AmazonS3Exception s3){
        System.out.println("Received error response:"+s3.getMessage());
    }
    return "Key Not Found.";
}

必需的Jars [aws-java {sdk，sdk-core，sdk-s3}， fasterxml。jackson {databind，core，annotations}， joda - 时间，http {clent，core}]

S3：为给定密钥生成预签名URL。 [钥匙可能/不存在]

2 个答案: