对象存储 OSS：使用签名URL下载

注意事项

• 本文以华东1（杭州）外网Endpoint为例。如果您希望通过与OSS同地域的其他阿里云产品访问OSS，请使用内网Endpoint。关于OSS支持的Region与Endpoint的对应关系，请参见OSS地域和访问域名。

• 本文以从环境变量读取访问凭证为例。如何配置访问凭证，请参见Java配置访问凭证。

• 本文以OSS域名新建OSSClient为例。如果您希望通过自定义域名、STS等方式新建OSSClient，请参见新建OSSClient。

• 生成GET方法的签名URL时，您必须具有oss:GetObject权限。具体操作，请参见为RAM用户授权自定义的权限策略。

  说明

  生成签名URL过程中，SDK利用本地存储的密钥信息，根据特定算法计算出签名（signature），然后将其附加到URL上，以确保URL的有效性和安全性。这一系列计算和构造URL的操作都是在客户端完成，不涉及网络请求到服务端。因此，生成签名URL时不需要授予调用者特定权限。但是，为避免第三方用户无法对签名URL授权的资源执行相关操作，需要确保调用生成签名URL接口的身份主体被授予对应的权限。

• 本文以V4签名URL为例，有效期最大为7天。更多信息，请参见签名版本4（推荐）。

使用过程

使用签名URL下载文件的过程如下：

代码示例

1. 文件拥有者生成GET方法的签名URL。

   import com.aliyun.oss.*;
   import com.aliyun.oss.common.auth.*;
   import com.aliyun.oss.common.comm.SignVersion;
   
   import java.net.URL;
   import java.util.Date;
   
   public class Demo {
       public static void main(String[] args) throws Throwable {
           // 以华东1（杭州）的外网Endpoint为例，其它Region请按实际情况填写。
           String endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
           // 从环境变量中获取访问凭证。运行本代码示例之前，请确保已设置环境变量OSS_ACCESS_KEY_ID和OSS_ACCESS_KEY_SECRET。
           EnvironmentVariableCredentialsProvider credentialsProvider = CredentialsProviderFactory.newEnvironmentVariableCredentialsProvider();
           // 填写Bucket名称，例如examplebucket。
           String bucketName = "examplebucket";
           // 填写Object完整路径，例如exampleobject.txt。Object完整路径中不能包含Bucket名称。
           String objectName = "exampleobject.txt";
           // 填写Bucket所在地域。以华东1（杭州）为例，Region填写为cn-hangzhou。
           String region = "cn-hangzhou";
   
           // 创建OSSClient实例。
           ClientBuilderConfiguration clientBuilderConfiguration = new ClientBuilderConfiguration();
           clientBuilderConfiguration.setSignatureVersion(SignVersion.V4);
           OSS ossClient = OSSClientBuilder.create()
                   .endpoint(endpoint)
                   .credentialsProvider(credentialsProvider)
                   .clientConfiguration(clientBuilderConfiguration)
                   .region(region)
                   .build();
   
           try {
               // 设置签名URL过期时间，单位为毫秒。本示例以设置过期时间为1小时为例。
               Date expiration = new Date(new Date().getTime() + 3600 * 1000L);
               // 生成以GET方法访问的签名URL。本示例没有额外请求头，其他人可以直接通过浏览器访问相关内容。
               URL url = ossClient.generatePresignedUrl(bucketName, objectName, expiration);
               System.out.println(url);
           } catch (OSSException oe) {
               System.out.println("Caught an OSSException, which means your request made it to OSS, "
                       + "but was rejected with an error response for some reason.");
               System.out.println("Error Message:" + oe.getErrorMessage());
               System.out.println("Error Code:" + oe.getErrorCode());
               System.out.println("Request ID:" + oe.getRequestId());
               System.out.println("Host ID:" + oe.getHostId());
           } catch (ClientException ce) {
               System.out.println("Caught an ClientException, which means the client encountered "
                       + "a serious internal problem while trying to communicate with OSS, "
                       + "such as not being able to access the network.");
               System.out.println("Error Message:" + ce.getMessage());
           } finally {
               if (ossClient != null) {
                   ossClient.shutdown();
               }
           }
       }
   }

2. 其他人使用GET方法的签名URL下载文件。

   curl

   curl -SO "https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject.txt?x-oss-date=20241112T092756Z&x-oss-expires=3599&x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=LTAI5************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a939feb8d79a389572719f7e2939939936d0**********"

   Java

   import java.io.BufferedInputStream;
   import java.io.FileOutputStream;
   import java.io.IOException;
   import java.io.InputStream;
   import java.net.HttpURLConnection;
   import java.net.URL;
   
   public class Demo {
       public static void main(String[] args) {
           // 替换为生成的GET方法的签名URL。
           String fileURL = "https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject.txt?x-oss-date=20241112T092756Z&x-oss-expires=3599&x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=LTAI5************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a939feb8d79a389572719f7e2939939936d0**********";
           // 填写文件保存的目标路径，包括文件名和扩展名。
           String savePath = "C:/downloads/myfile.txt";
   
           try {
               downloadFile(fileURL, savePath);
               System.out.println("Download completed!");
           } catch (IOException e) {
               System.err.println("Error during download: " + e.getMessage());
           }
       }
   
       private static void downloadFile(String fileURL, String savePath) throws IOException {
           URL url = new URL(fileURL);
           HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
           httpConn.setRequestMethod("GET");
   
           // 检查响应代码
           int responseCode = httpConn.getResponseCode();
           if (responseCode == HttpURLConnection.HTTP_OK) {
               // 输入流
               InputStream inputStream = new BufferedInputStream(httpConn.getInputStream());
               // 输出流
               FileOutputStream outputStream = new FileOutputStream(savePath);
   
               byte[] buffer = new byte[4096]; // 缓冲区
               int bytesRead;
               while ((bytesRead = inputStream.read(buffer)) != -1) {
                   outputStream.write(buffer, 0, bytesRead);
               }
   
               outputStream.close();
               inputStream.close();
           } else {
               System.out.println("No file to download. Server replied HTTP code: " + responseCode);
           }
           httpConn.disconnect();
       }
   }

   Node.js

   const https = require('https');
   const fs = require('fs');
   
   const fileURL = "https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject.txt?x-oss-date=20241112T092756Z&x-oss-expires=3599&x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=LTAI5************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a939feb8d79a389572719f7e2939939936d0**********";
   const savePath = "C:/downloads/myfile.txt";
   
   https.get(fileURL, (response) => {
       if (response.statusCode === 200) {
           const fileStream = fs.createWriteStream(savePath);
           response.pipe(fileStream);
           
           fileStream.on('finish', () => {
               fileStream.close();
               console.log("Download completed!");
           });
       } else {
           console.error(`Download failed. Server responded with code: ${response.statusCode}`);
       }
   }).on('error', (err) => {
       console.error("Error during download:", err.message);
   });

   Python

   import requests
   
   file_url = "https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject.txt?x-oss-date=20241112T092756Z&x-oss-expires=3599&x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=LTAI5************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a939feb8d79a389572719f7e2939939936d0**********"
   save_path = "C:/downloads/myfile.txt"
   
   try:
       response = requests.get(file_url, stream=True)
       if response.status_code == 200:
           with open(save_path, 'wb') as f:
               for chunk in response.iter_content(4096):
                   f.write(chunk)
           print("Download completed!")
       else:
           print(f"No file to download. Server replied HTTP code: {response.status_code}")
   except Exception as e:
       print("Error during download:", e)

   Go

   package main
   
   import (
       "io"
       "net/http"
       "os"
   )
   
   func main() {
       fileURL := "https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject.txt?x-oss-date=20241112T092756Z&x-oss-expires=3599&x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=LTAI5************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a939feb8d79a389572719f7e2939939936d0**********"
       savePath := "C:/downloads/myfile.txt"
   
       response, err := http.Get(fileURL)
       if err != nil {
           panic(err)
       }
       defer response.Body.Close()
   
       if response.StatusCode == http.StatusOK {
           outFile, err := os.Create(savePath)
           if err != nil {
               panic(err)
           }
           defer outFile.Close()
   
           _, err = io.Copy(outFile, response.Body)
           if err != nil {
               panic(err)
           }
           println("Download completed!")
       } else {
           println("No file to download. Server replied HTTP code:", response.StatusCode)
       }
   }

   JavaScript

   const fileURL = "https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject.txt?x-oss-date=20241112T092756Z&x-oss-expires=3599&x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=LTAI5************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a939feb8d79a389572719f7e2939939936d0**********";
   const savePath = "C:/downloads/myfile.txt"; // 文件将在下载时使用的文件名
   
   fetch(fileURL)
       .then(response => {
           if (!response.ok) {
               throw new Error(`Server replied HTTP code: ${response.status}`);
           }
           return response.blob(); // 将响应转换为 blob
       })
       .then(blob => {
           const link = document.createElement('a');
           link.href = window.URL.createObjectURL(blob);
           link.download = savePath; // 设置下载文件的名字
           document.body.appendChild(link); // 此步骤确保链接存在于文档中
           link.click(); // 模拟点击下载链接
           link.remove(); // 完成后移除链接
           console.log("Download completed!");
       })
       .catch(error => {
           console.error("Error during download:", error);
       });

   Android-Java

   import android.os.AsyncTask;
   import android.os.Environment;
   import java.io.BufferedInputStream;
   import java.io.FileOutputStream;
   import java.io.InputStream;
   import java.net.HttpURLConnection;
   import java.net.URL;
   
   public class DownloadTask extends AsyncTask<String, String, String> {
       @Override
       protected String doInBackground(String... params) {
           String fileURL = params[0];
           String savePath = Environment.getExternalStoragePublicDirectory(Environment.DIRECTORY_DOWNLOADS) + "/myfile.txt"; // 修改后的保存路径
           try {
               URL url = new URL(fileURL);
               HttpURLConnection httpConn = (HttpURLConnection) url.openConnection();
               httpConn.setRequestMethod("GET");
               int responseCode = httpConn.getResponseCode();
               if (responseCode == HttpURLConnection.HTTP_OK) {
                   InputStream inputStream = new BufferedInputStream(httpConn.getInputStream());
                   FileOutputStream outputStream = new FileOutputStream(savePath);
                   byte[] buffer = new byte[4096];
                   int bytesRead;
                   while ((bytesRead = inputStream.read(buffer)) != -1) {
                       outputStream.write(buffer, 0, bytesRead);
                   }
                   outputStream.close();
                   inputStream.close();
                   return "Download completed!";
               } else {
                   return "No file to download. Server replied HTTP code: " + responseCode;
               }
           } catch (Exception e) {
               return "Error during download: " + e.getMessage();
           }
       }
   }

   Objective-C

   #import <Foundation/Foundation.h>
   
   int main(int argc, const char * argv[]) {
       @autoreleasepool {
           // 定义文件 URL 和保存路径（修改为有效的路径）
           NSString *fileURL = @"https://examplebucket.oss-cn-hangzhou.aliyuncs.com/exampleobject.txt?x-oss-date=20241112T092756Z&x-oss-expires=3599&x-oss-signature-version=OSS4-HMAC-SHA256&x-oss-credential=LTAI5************/20241112/cn-hangzhou/oss/aliyun_v4_request&x-oss-signature=ed5a939feb8d79a389572719f7e2939939936d0**********";
           NSString *savePath = @"/Users/your_username/Desktop/myfile.txt"; // 请替换为您的用户名
           
           // 创建 URL 对象
           NSURL *url = [NSURL URLWithString:fileURL];
           
           // 创建下载任务
           NSURLSessionDataTask *task = [[NSURLSession sharedSession] dataTaskWithURL:url completionHandler:^(NSData *data, NSURLResponse *response, NSError *error) {
               // 错误处理
               if (error) {
                   NSLog(@"Error during download: %@", error.localizedDescription);
                   return;
               }
               
               // 检查数据
               if (!data) {
                   NSLog(@"No data received.");
                   return;
               }
               
               // 保存文件
               NSError *writeError = nil;
               BOOL success = [data writeToURL:[NSURL fileURLWithPath:savePath] options:NSDataWritingAtomic error:&writeError];
               if (success) {
                   NSLog(@"Download completed!");
               } else {
                   NSLog(@"Error saving file: %@", writeError.localizedDescription);
               }
           }];
           
           // 启动任务
           [task resume];
           
           // 让主线程继续运行以便异步请求能够完成
           [[NSRunLoop currentRunLoop] run];
       }
       return 0;
   }

其他场景

import com.aliyun.oss.*;
import com.aliyun.oss.common.auth.*;
import com.aliyun.oss.model.GeneratePresignedUrlRequest;
import java.net.URL;
import java.util.*;
import java.util.Date;

public class Demo {
    public static void main(String[] args) throws Throwable {
        // 以华东1（杭州）的外网Endpoint为例，其它Region请按实际情况填写。
        String endpoint = "https://oss-cn-hangzhou.aliyuncs.com";
        // 从环境变量中获取访问凭证。运行本代码示例之前，请确保已设置环境变量OSS_ACCESS_KEY_ID和OSS_ACCESS_KEY_SECRET。
        EnvironmentVariableCredentialsProvider credentialsProvider = CredentialsProviderFactory.newEnvironmentVariableCredentialsProvider();
		    // 填写Bucket名称，例如examplebucket。
        String bucketName = "examplebucket";
        // 填写Object完整路径，例如exampleobject.txt。Object完整路径中不能包含Bucket名称。
        String objectName = "exampleobject.txt";
        // 填写Object的versionId。
        String versionId = "CAEQARiBgID8rumR2hYiIGUyOTAyZGY2MzU5MjQ5ZjlhYzQzZjNlYTAyZDE3****";
        // 填写Bucket所在地域。以华东1（杭州）为例，Region填写为cn-hangzhou。
        String region = "cn-hangzhou";

        // 创建OSSClient实例。
        ClientBuilderConfiguration clientBuilderConfiguration = new ClientBuilderConfiguration();
        clientBuilderConfiguration.setSignatureVersion(SignVersion.V4);        
        OSS ossClient = OSSClientBuilder.create()
        .endpoint(endpoint)
        .credentialsProvider(credentialsProvider)
        .clientConfiguration(clientBuilderConfiguration)
        .region(region)               
        .build();

        try {
            // 创建请求。
            GeneratePresignedUrlRequest generatePresignedUrlRequest = new GeneratePresignedUrlRequest(bucketName, objectName);
            // 设置HttpMethod为GET。
            generatePresignedUrlRequest.setMethod(HttpMethod.GET);
            // 设置签名URL过期时间，单位为毫秒。本示例以设置过期时间为1小时为例。
            Date expiration = new Date(new Date().getTime() + 3600 * 1000L);
            generatePresignedUrlRequest.setExpiration(expiration);
            // Object的versionId。
            Map<String, String> queryParam = new HashMap<String, String>();
            queryParam.put("versionId", versionId);
            generatePresignedUrlRequest.setQueryParameter(queryParam);
            // 生成签名URL。
            URL url = ossClient.generatePresignedUrl(generatePresignedUrlRequest);
            System.out.println(url);
        } catch (OSSException oe) {
            System.out.println("Caught an OSSException, which means your request made it to OSS, "
                    + "but was rejected with an error response for some reason.");
            System.out.println("Error Message:" + oe.getErrorMessage());
            System.out.println("Error Code:" + oe.getErrorCode());
            System.out.println("Request ID:" + oe.getRequestId());
            System.out.println("Host ID:" + oe.getHostId());
        } catch (ClientException ce) {
            System.out.println("Caught an ClientException, which means the client encountered "
                    + "a serious internal problem while trying to communicate with OSS, "
                    + "such as not being able to access the network.");
            System.out.println("Error Message:" + ce.getMessage());
        } finally {
            if (ossClient != null) {
                ossClient.shutdown();
            }
        }
    }
}

相关文档

• 关于使用签名URL下载文件的完整示例代码，请参见GitHub示例。

• 关于使用签名URL下载文件的API接口说明，请参见GeneratePresignedUrlRequest。