下载对象

当您通过 Amazon SDK for Java 下载对象时，Amazon S3 将返回该对象的所有元数据以及从中读取该对象内容的输入流。

要检索对象，请执行以下操作：

下面是您可能使用的一些变体：

下面的例子通过三种方式从 Amazon S3 存储桶中检索对象：作为完整的对象、作为来自该对象的一系列字节以及作为包含被覆盖的响应标头值的完整对象。有关从 Amazon S3 中获取对象的更多信息，请参阅 GET Object。有关创建和测试有效示例的说明，请参阅测试 Amazon S3 Java 代码示例。

import com.amazonaws.AmazonServiceException;
import com.amazonaws.SdkClientException;
import com.amazonaws.auth.profile.ProfileCredentialsProvider;
import com.amazonaws.regions.Regions;
import com.amazonaws.services.s3.AmazonS3;
import com.amazonaws.services.s3.AmazonS3ClientBuilder;
import com.amazonaws.services.s3.model.GetObjectRequest;
import com.amazonaws.services.s3.model.ResponseHeaderOverrides;
import com.amazonaws.services.s3.model.S3Object;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStream;
import java.io.InputStreamReader;

public class GetObject2 {

    public static void main(String[] args) throws IOException {
        Regions clientRegion = Regions.DEFAULT_REGION;
        String bucketName = "*** Bucket name ***";
        String key = "*** Object key ***";

        S3Object fullObject = null, objectPortion = null, headerOverrideObject = null;
        try {
            AmazonS3 s3Client = AmazonS3ClientBuilder.standard()
                    .withRegion(clientRegion)
                    .withCredentials(new ProfileCredentialsProvider())
                    .build();

            // Get an object and print its contents.
            System.out.println("Downloading an object");
            fullObject = s3Client.getObject(new GetObjectRequest(bucketName, key));
            System.out.println("Content-Type: " + fullObject.getObjectMetadata().getContentType());
            System.out.println("Content: ");
            displayTextInputStream(fullObject.getObjectContent());

            // Get a range of bytes from an object and print the bytes.
            GetObjectRequest rangeObjectRequest = new GetObjectRequest(bucketName, key)
                    .withRange(0, 9);
            objectPortion = s3Client.getObject(rangeObjectRequest);
            System.out.println("Printing bytes retrieved.");
            displayTextInputStream(objectPortion.getObjectContent());

            // Get an entire object, overriding the specified response headers, and print the object's content.
            ResponseHeaderOverrides headerOverrides = new ResponseHeaderOverrides()
                    .withCacheControl("No-cache")
                    .withContentDisposition("attachment; filename=example.txt");
            GetObjectRequest getObjectRequestHeaderOverride = new GetObjectRequest(bucketName, key)
                    .withResponseHeaders(headerOverrides);
            headerOverrideObject = s3Client.getObject(getObjectRequestHeaderOverride);
            displayTextInputStream(headerOverrideObject.getObjectContent());
        } catch (AmazonServiceException e) {
            // The call was transmitted successfully, but Amazon S3 couldn't process 
            // it, so it returned an error response.
            e.printStackTrace();
        } catch (SdkClientException e) {
            // Amazon S3 couldn't be contacted for a response, or the client
            // couldn't parse the response from Amazon S3.
            e.printStackTrace();
        } finally {
            // To ensure that the network connection doesn't remain open, close any open input streams.
            if (fullObject != null) {
                fullObject.close();
            }
            if (objectPortion != null) {
                objectPortion.close();
            }
            if (headerOverrideObject != null) {
                headerOverrideObject.close();
            }
        }
    }

    private static void displayTextInputStream(InputStream input) throws IOException {
        // Read the text input stream one line at a time and display each line.
        BufferedReader reader = new BufferedReader(new InputStreamReader(input));
        String line = null;
        while ((line = reader.readLine()) != null) {
            System.out.println(line);
        }
        System.out.println();
    }
}

当下载某个对象时，您将获得该对象的所有元数据以及从中读取内容的流。您应该尽快读取流的内容，因为数据直接源自 Amazon S3，在您读取所有数据或关闭输入流之前，您的网络连接将保持打开状态。您通过执行以下操作来获取对象：

下面是您可能使用的一些变体：

using Amazon;
using Amazon.S3;
using Amazon.S3.Model;
using System;
using System.IO;
using System.Threading.Tasks;

namespace Amazon.DocSamples.S3
{
    class GetObjectTest
    {
        private const string bucketName = "*** bucket name ***";
        private const string keyName = "*** object key ***";
        // Specify your bucket region (an example region is shown).
        private static readonly RegionEndpoint bucketRegion = RegionEndpoint.USWest2;
        private static IAmazonS3 client;

        public static void Main()
        {
            client = new AmazonS3Client(bucketRegion);
            ReadObjectDataAsync().Wait();
        }

        static async Task ReadObjectDataAsync()
        {
            string responseBody = "";
            try
            {
                GetObjectRequest request = new GetObjectRequest
                {
                    BucketName = bucketName,
                    Key = keyName
                };
                using (GetObjectResponse response = await client.GetObjectAsync(request))
                using (Stream responseStream = response.ResponseStream)
                using (StreamReader reader = new StreamReader(responseStream))
                {
                    string title = response.Metadata["x-amz-meta-title"]; // Assume you have "title" as medata added to the object.
                    string contentType = response.Headers["Content-Type"];
                    Console.WriteLine("Object metadata, Title: {0}", title);
                    Console.WriteLine("Content type: {0}", contentType);

                    responseBody = reader.ReadToEnd(); // Now you process the response body.
                }
            }
            catch (AmazonS3Exception e)
            {
                // If bucket or object does not exist
                Console.WriteLine("Error encountered ***. Message:'{0}' when reading object", e.Message);
            }
            catch (Exception e)
            {
                Console.WriteLine("Unknown encountered on server. Message:'{0}' when reading object", e.Message);
            }
        }
    }
}

本主题介绍如何使用 Amazon SDK for PHP 中的类检索 Amazon S3 对象。您可以检索整个对象或对象中的字节范围。我们假定您已按照 使用Amazon SDK for PHP和运行 PHP 示例 的说明执行操作，并且正确安装了 Amazon SDK for PHP。

在检索对象时，您可以选择覆盖响应标头值，方法是将响应键、ResponseContentType、ResponseContentLanguage、ResponseContentDisposition、ResponseCacheControl 和 ResponseExpires 添加到 getObject() 方法，如以下 PHP 代码示例所示：

$result = $s3->getObject([
    'Bucket'                     => $bucket,
    'Key'                        => $keyname,
    'ResponseContentType'        => 'text/plain',
    'ResponseContentLanguage'    => 'en-US',
    'ResponseContentDisposition' => 'attachment; filename=testing.txt',
    'ResponseCacheControl'       => 'No-cache',
    'ResponseExpires'            => gmdate(DATE_RFC2822, time() + 3600),
]);

有关检索对象的更多信息，请参阅 下载对象。

以下 PHP 示例将检索对象，并在浏览器中显示对象的内容。该示例演示如何使用 getObject() 方法。有关运行本指南中的 PHP 示例的信息，请参阅 运行 PHP 示例。

 require 'vendor/autoload.php';

use Aws\S3\S3Client;
use Aws\S3\Exception\S3Exception;

$bucket = '*** Your Bucket Name ***';
$keyname = '*** Your Object Key ***';

$s3 = new S3Client([
    'version' => 'latest',
    'region'  => 'us-east-1'
]);

try {
    // Get the object.
    $result = $s3->getObject([
        'Bucket' => $bucket,
        'Key'    => $keyname
    ]);

    // Display the object in the browser.
    header("Content-Type: {$result['ContentType']}");
    echo $result['Body'];
} catch (S3Exception $e) {
    echo $e->getMessage() . PHP_EOL;
}