如何在Java中检查Azure Blob容器中是否存在文件

Question

我要检查文件是否在Azure Blob存储的容器中。如果文件存在，那么我将下载文件。

Answer 1

由于没有任何REST API或SDK API来检查blob是否存在，因此您无法直接对其进行检查。如我所知，检查blob是否存在的唯一方法是在获取blob时检查错误信息，请参阅Common REST API Error Codes，如下所示。

这是我使用Microsoft Azure Storage SDK v10 for Java检查斑点是否存在的步骤和示例代码。

适用于Java的Azure存储SDK v10的maven dependency如下。

<!-- https://mvnrepository.com/artifact/com.microsoft.azure/azure-storage-blob -->
<dependency>
    <groupId>com.microsoft.azure</groupId>
    <artifactId>azure-storage-blob</artifactId>
    <version>10.4.0</version>
</dependency>

1. 生成具有SAS签名的Blob网址。

   String accountName = "<your storage account name>";
   String accountKey = "<your storage account key>";
   
   public String generateUrlWithSAS(String containerName, String blobName) throws InvalidKeyException {
       SharedKeyCredentials credentials = new SharedKeyCredentials(accountName, accountKey);
       ServiceSASSignatureValues values = new ServiceSASSignatureValues()
               .withProtocol(SASProtocol.HTTPS_ONLY) // Users MUST use HTTPS (not HTTP).
               .withExpiryTime(OffsetDateTime.now().plusDays(2)) // 2 days before expiration.
               .withContainerName(containerName)
               .withBlobName(blobName);
       BlobSASPermission permission = new BlobSASPermission()
               .withRead(true)
               .withAdd(true)
               .withWrite(true);
       values.withPermissions(permission.toString());
       SASQueryParameters serviceParams = values.generateSASQueryParameters(credentials);
       String sasSign = serviceParams.encode();
       return String.format(Locale.ROOT, "https://%s.blob.core.windows.net/%s/%s%s", accountName, containerName, blobName, sasSign);
   }
   

2. 对具有SAS签名的URL发出Http Head请求，以检查响应状态代码

   public static boolean exists(String urlWithSAS) throws MalformedURLException, IOException {
       HttpURLConnection conn = (HttpURLConnection) new URL(urlWithSAS).openConnection();
       conn.setRequestMethod("HEAD");
       return conn.getResponseCode() == 200;
   }
   

另外，您可以在下载blob时通过捕获相关异常直接检查是否存在。

Answer 2

在@Peter Pan的答案的启发下，如果您是Blob所有者，那么更简单（对我来说也不太混乱）。

boolean blobExists(String containerName, String blobName) {
    ServiceURL serviceUrl = getServiceUrl();
    HttpURLConnection httpUrlConnection = (HttpURLConnection)
        serviceUrl.createContainerURL(containerName)
            .createBlockBlobURL(blobName)
            .toURL().openConnection();
    httpUrlConnection.setRequestMethod("HEAD");
    return httpUrlConnection.getResponseCode() / 100 == 2;
}

ServiceURL getServiceUrl() {
    SharedKeyCredentials credentials = new SharedKeyCredentials(accountName, accountKey);
    return new ServiceURL(new URL(azureUrl), StorageURL.createPipeline(credentials, new PipelineOptions()));
}

经过库com.microsoft.azure:azure-storage-blob:10.5.0的测试。