Question

我们如何检查对象是否已完全上传到Amazon s3？我正在从Android应用程序上传图像到s3，然后调用lambda函数。我想确保在调用lambda之前已将对象上传到s3。目前，大型文件上传会产生问题。

Answer 1

不是在将对象上传到Amazon S3后调用AWS Lambda函数，只需配置S3存储桶以触发lambda本身：

S3 to Lambda

这样，只有当对象成功上传到S3时才会触发该功能，并且您的应用程序的工作量会减少。

如果您确实想单独执行此操作，则可以使用ETag（MD5校验和）确认文件已按预期上传。

Answer 2

您可以使用 PutObjectResult 进行检查。响应表明对象已成功存储。 Amazon S3从不存储部分对象：如果您收到成功的响应，那么您可以确信存储了整个对象。所以主要的关键播放器是MD5算法，使用它可以确认你想要上传的对象是否与上传的相同，为了让你知道任何文件的MD5值，让我们说你可以使用它的图像以下找到如此

`    package aws.example.s3;

    import java.io.File;
    import java.io.FileInputStream;
    import java.io.IOException;
    import java.security.MessageDigest;
    import java.security.NoSuchAlgorithmException;

    public class MD5demo {
      public static String MD5check(String path){
        // TODO Auto-generated method stub
        //Create checksum for this file
        File file = new File(path);

        //Get the checksum
        String checksum="null";
        try {
            //Use MD5 algorithm
            MessageDigest md5Digest;
            try {
                md5Digest = MessageDigest.getInstance("MD5");
                checksum = getFileChecksum(md5Digest, file);
                //see checksum
                //System.out.println("Checksum: "+checksum);
            } catch (NoSuchAlgorithmException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
         }catch (IOException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        return checksum;

    }

    private static String getFileChecksum(MessageDigest digest, File file) 
     throws IOException
    {
        //Get file input stream for reading the file content
        FileInputStream fis = new FileInputStream(file);

        //Create byte array to read data in chunks
        byte[] byteArray = new byte[1024];
        int bytesCount = 0;

        //Read file data and update in message digest
        while ((bytesCount = fis.read(byteArray)) != -1) {
            digest.update(byteArray, 0, bytesCount);
        };

        //close the stream; We don't need it now.
        fis.close();

        //Get the hash's bytes
        byte[] bytes = digest.digest();

        //This bytes[] has bytes in decimal format;
        //Convert it to hexadecimal format
        StringBuilder sb = new StringBuilder();
        for(int i=0; i< bytes.length ;i++)
        {
            sb.append(Integer.toString((bytes[i] & 0xff) + 0x100, 
      16).substring(1));
        }

        //return complete hash
       return sb.toString();
      }
}`

所以，您只需要在MD5check（String路径）中传递文件路径，它将返回MD5值

现在，在您编写上传任何文档的代码的课程中，只需使用以下代码

即可

PutObjectResult putObjectResult = null;
    try  {
           putObjectResult = s3.putObject(new PutObjectRequest(<Enter your Bucket name here>, <KeyName> , <pass your file object here>));

           String MD5=MD5check(<pls enter your file path here>);  //you can pass your file also directly, for that please change the method implementation of MD5Demo class accepting a file instead of path

           System.out.println("Etag: "+putObjectResult.getETag()); //getting the Etag which is nothing but same as MD5 value of the file that got uploaded in S3
           System.out.println("MD5:  "+MD5);

           if(MD5==putObjectResult.getETag()) {
               System.out.println("Congrats!! Document Uploaded Successfully");
           }else {
               System.out.println("Sorry! Could not upload the document");
           }

希望它有所帮助，如果您有任何建议，请告诉我们。）

如何知道对象是否已完全上传到亚马逊s3？

2 个答案: