将对象下载到内存中

本页面介绍如何使用 Cloud Storage 客户端库将对象从 Cloud Storage 存储桶下载到内存中。如果您想避免对永久性存储的不必要写入，下载到内存就非常有用。如需了解如何直接将对象下载到永久性内存，请参阅将对象下载到永久性内存。若要大致了解在 Cloud Storage 中下载内容的工作原理，请参阅上传和下载。

所需的角色

为了获得将对象下载到内存中所需的权限，请让您的管理员向您授予存储桶的 Storage Object Viewer (roles/storage.objectViewer) 角色。

此角色包含下载对象所需的权限。如需查看所需的确切权限，请展开所需权限部分：

所需权限

  • storage.objects.get

您也可以使用其他预定义角色或自定义角色来获取这些权限。

如需了解如何授予存储桶的角色，请参阅将 IAM 与存储桶搭配使用。

将对象下载到内存中

客户端库

C++

如需了解详情，请参阅 Cloud Storage C++ API 参考文档。

如需向 Cloud Storage 进行身份验证，请设置应用默认凭据。 如需了解详情，请参阅为本地开发环境设置身份验证。 

namespace gcs = ::google::cloud::storage;
[](gcs::Client client, std::string const& bucket_name,
   std::string const& object_name) {
  gcs::ObjectReadStream stream = client.ReadObject(bucket_name, object_name);
  std::string buffer{std::istream_iterator<char>(stream),
                     std::istream_iterator<char>()};
  if (stream.bad()) throw google::cloud::Status(stream.status());

  std::cout << "The object has " << buffer.size() << " characters\n";
}

C#

如需了解详情，请参阅 Cloud Storage C# API 参考文档。

如需向 Cloud Storage 进行身份验证，请设置应用默认凭据。 如需了解详情，请参阅为本地开发环境设置身份验证。 


using Google.Cloud.Storage.V1;
using System;
using System.IO;

public class DownloadObjectIntoMemorySample
{
    public Stream DownloadObjectIntoMemory(
        string bucketName = "unique-bucket-name",
        string objectName = "file-name")
    {
        var storage = StorageClient.Create();
        Stream stream = new MemoryStream();
        storage.DownloadObject(bucketName, objectName, stream);

        Console.WriteLine($"The contents of {objectName} from bucket {bucketName} are downloaded");
        return stream;
    }
}

Go

如需了解详情，请参阅 Cloud Storage Go API 参考文档。

如需向 Cloud Storage 进行身份验证，请设置应用默认凭据。 如需了解详情，请参阅为本地开发环境设置身份验证。 


import (
	"context"
	"fmt"
	"io"
	"io/ioutil"
	"time"

	"cloud.google.com/go/storage"
)

// downloadFileIntoMemory downloads an object.
func downloadFileIntoMemory(w io.Writer, bucket, object string) ([]byte, error) {
	// bucket := "bucket-name"
	// object := "object-name"
	ctx := context.Background()
	client, err := storage.NewClient(ctx)
	if err != nil {
		return nil, fmt.Errorf("storage.NewClient: %w", err)
	}
	defer client.Close()

	ctx, cancel := context.WithTimeout(ctx, time.Second*50)
	defer cancel()

	rc, err := client.Bucket(bucket).Object(object).NewReader(ctx)
	if err != nil {
		return nil, fmt.Errorf("Object(%q).NewReader: %w", object, err)
	}
	defer rc.Close()

	data, err := ioutil.ReadAll(rc)
	if err != nil {
		return nil, fmt.Errorf("ioutil.ReadAll: %w", err)
	}
	fmt.Fprintf(w, "Blob %v downloaded.\n", object)
	return data, nil
}

Java

如需了解详情，请参阅 Cloud Storage Java API 参考文档。

如需向 Cloud Storage 进行身份验证，请设置应用默认凭据。 如需了解详情，请参阅为本地开发环境设置身份验证。 


import com.google.cloud.storage.Storage;
import com.google.cloud.storage.StorageOptions;
import java.nio.charset.StandardCharsets;

public class DownloadObjectIntoMemory {
  public static void downloadObjectIntoMemory(
      String projectId, String bucketName, String objectName) {
    // The ID of your GCP project
    // String projectId = "your-project-id";

    // The ID of your GCS bucket
    // String bucketName = "your-unique-bucket-name";

    // The ID of your GCS object
    // String objectName = "your-object-name";

    Storage storage = StorageOptions.newBuilder().setProjectId(projectId).build().getService();
    byte[] content = storage.readAllBytes(bucketName, objectName);
    System.out.println(
        "The contents of "
            + objectName
            + " from bucket name "
            + bucketName
            + " are: "
            + new String(content, StandardCharsets.UTF_8));
  }
}

Node.js

如需了解详情，请参阅 Cloud Storage Node.js API 参考文档。

如需向 Cloud Storage 进行身份验证，请设置应用默认凭据。 如需了解详情，请参阅为本地开发环境设置身份验证。 

/**
 * TODO(developer): Uncomment the following lines before running the sample.
 */
// The ID of your GCS bucket
// const bucketName = 'your-unique-bucket-name';

// The ID of your GCS file
// const fileName = 'your-file-name';

// Imports the Google Cloud client library
const {Storage} = require('@google-cloud/storage');

// Creates a client
const storage = new Storage();

async function downloadIntoMemory() {
  // Downloads the file into a buffer in memory.
  const contents = await storage.bucket(bucketName).file(fileName).download();

  console.log(
    `Contents of gs://${bucketName}/${fileName} are ${contents.toString()}.`
  );
}

downloadIntoMemory().catch(console.error);

PHP

如需了解详情，请参阅 Cloud Storage PHP API 参考文档。

如需向 Cloud Storage 进行身份验证，请设置应用默认凭据。 如需了解详情，请参阅为本地开发环境设置身份验证。 

use Google\Cloud\Storage\StorageClient;

/**
 * Download an object from Cloud Storage and save into a buffer in memory.
 *
 * @param string $bucketName The name of your Cloud Storage bucket.
 *        (e.g. 'my-bucket')
 * @param string $objectName The name of your Cloud Storage object.
 *        (e.g. 'my-object')
 */
function download_object_into_memory(
    string $bucketName,
    string $objectName
): void {
    $storage = new StorageClient();
    $bucket = $storage->bucket($bucketName);
    $object = $bucket->object($objectName);
    $contents = $object->downloadAsString();
    printf(
        'Downloaded %s from gs://%s/%s' . PHP_EOL,
        $contents,
        $bucketName,
        $objectName
    );
}

Python

如需了解详情，请参阅 Cloud Storage Python API 参考文档。

如需向 Cloud Storage 进行身份验证，请设置应用默认凭据。 如需了解详情，请参阅为本地开发环境设置身份验证。 

from google.cloud import storage


def download_blob_into_memory(bucket_name, blob_name):
    """Downloads a blob into memory."""
    # The ID of your GCS bucket
    # bucket_name = "your-bucket-name"

    # The ID of your GCS object
    # blob_name = "storage-object-name"

    storage_client = storage.Client()

    bucket = storage_client.bucket(bucket_name)

    # Construct a client side representation of a blob.
    # Note `Bucket.blob` differs from `Bucket.get_blob` as it doesn't retrieve
    # any content from Google Cloud Storage. As we don't need additional data,
    # using `Bucket.blob` is preferred here.
    blob = bucket.blob(blob_name)
    contents = blob.download_as_bytes()

    print(
        "Downloaded storage object {} from bucket {} as the following bytes object: {}.".format(
            blob_name, bucket_name, contents.decode("utf-8")
        )
    )

Ruby

如需了解详情，请参阅 Cloud Storage Ruby API 参考文档。

如需向 Cloud Storage 进行身份验证，请设置应用默认凭据。 如需了解详情，请参阅为本地开发环境设置身份验证。 

# The name of the bucket to access
# bucket_name = "my-bucket"

# The name of the remote file to download
# file_name = "file.txt"

require "google/cloud/storage"

storage = Google::Cloud::Storage.new
bucket  = storage.bucket bucket_name, skip_lookup: true
file    = bucket.file file_name

downloaded = file.download
downloaded.rewind # Optional - not needed on first read
contents = downloaded.read

puts "Contents of storage object #{file.name} in bucket #{bucket_name} are: #{contents}"

后续步骤