如何计算S3文件内容的SHA-256校验和 [英] How to calculate SHA-256 checksum of S3 file content

问题描述

开箱即用的S3提供S3对象内容的MD5校验和.但是我需要计算文件内容的SHA-256校验和.该文件可能足够大，所以我不想将文件加载到内存中并计算校验和，相反，我需要一种解决方案来计算校验和而不将整个文件加载到内存中.

S3 out of the box provides the MD5 checksum of the S3 object content. But I need to calculate the SHA-256 checksum of the file content. The file could be large enough so I do not want to load the file in memory and calculate the checksum, instead I need a solution to calculate the checksum without loading the whole file in memory.

推荐答案

可以通过Java中的以下步骤来实现:

It can be achieved by following steps in Java:

1. 获取S3对象的InputStream
2. 将MessageDigest和DigestInputStream类用于SHA-256哈希(或SHA-1或MD5)

以下是有关操作方法的摘要:

Following is the snippet on how to do it:

String getS3FileHash(AmazonS3 amazonS3, String s3bucket, String filePath) {
    try {
        InputStream inputStream = amazonS3.getObject(s3bucket, filePath).getObjectContent();
        MessageDigest messageDigest = MessageDigest.getInstance("SHA-256");
        DigestInputStream digestInputStream = new DigestInputStream(inputStream, messageDigest);
        byte[] buffer = new byte[4096];
        int count = 0;
        while (digestInputStream.read(buffer) > -1) {
            count++;
        }
        log.info("total read: " + count);
        MessageDigest digest = digestInputStream.getMessageDigest();
        digestInputStream.close();
        byte[] md5 = digest.digest();
        StringBuilder sb = new StringBuilder();
        for (byte b: md5) {
            sb.append(String.format("%02X", b));
        }
        return sb.toString().toLowerCase();
    } catch (Exception e) {
        log.error(e);
    }
    return null; 
}

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