Question

我正在使用 java 代码和 aws sdk 从我的 aws s3 中的存储桶下载文件 (zip)。但是，下载的文件已损坏。手动下载文件有效。

我比较了文件的内容并注意到损坏的文件包含某种未编码的字符看到这个：

用于下载的代码如下：

public boolean downloadFile(String bucketName,  String fileNameOnServer, String localFileName )
    {
        S3Object object =null;
        InputStream objectData =null;
        try
        {
            object = s3.getObject(new GetObjectRequest(bucketName, fileNameOnServer));
            objectData = object.getObjectContent();
        }
        catch(Exception e)
        {
            LoggingService.writeToLog("Error001 downloading file "+bucketName+"/"+fileNameOnServer+" to "+localFileName, e, LogModule.CommonUtils,LogLevel.Error);
            return false;
        }
        try
        {
            FileWriter fw = new FileWriter(localFileName, true);
            BufferedWriter bw = new BufferedWriter(fw);
            try
            {
                BufferedReader reader = new BufferedReader(new InputStreamReader(object.getObjectContent()));
                String line;                                                
                while( (line = reader.readLine() ) !=null)
                {
                    bw.write(line);
                    bw.newLine();
                }
                LoggingService.writeToLog("file from "+bucketName+"/"+fileNameOnServer+" "+" downloaded to "+bucketName + " successfully",  LogModule.CommonUtils,LogLevel.Info);
                return true;
            }
            catch(IOException e)
            {
                LoggingService.writeToLog("Error downloading file "+bucketName+"/"+fileNameOnServer+" to "+localFileName, e, LogModule.CommonUtils,LogLevel.Error);
                return false;
            }
            finally
            {
                objectData.close();
                bw.close();
                object.close();
            }

        }
        catch(IOException e)
        {
            LoggingService.writeToLog("Error opening local file "+localFileName+" for writing ", e, LogModule.CommonUtils,LogLevel.Error);
            return false;
        }
    }

Answer 1

InputStreamReader 的文档包括：

<块引用>

InputStreamReader 是从字节流到字符流的桥梁：它读取字节并使用指定的字符集将它们解码为字符。它使用的字符集可以通过名称指定或明确给出，或者可以接受平台的默认字符集。

换句话说，它试图将数据视为文本数据。对于 zip 文件中的二进制数据，这几乎肯定会损坏数据。相反，如果你直接读写字节，你会传递它们而不改变它们：

package com.exampleapp.app;

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.S3Object;
import com.amazonaws.services.s3.model.S3ObjectInputStream;
import java.io.BufferedInputStream;
import java.io.BufferedOutputStream;
import java.io.File;
import java.io.FileOutputStream;
import java.io.InputStream;
import java.io.IOException;
import java.io.OutputStream;

public class App
{
    public static void main(String[] args)
    {
        downloadFile("example-bucket", "example-key.zip", "local-file.zip");
    }

    static AmazonS3 s3 = AmazonS3ClientBuilder.standard().withRegion(Regions.DEFAULT_REGION).build();

    public static boolean downloadFile(String bucketName,  String fileNameOnServer, String localFileName )
    {
        S3Object object = null;
        InputStream objectData = null;
        InputStream reader = null;
        OutputStream writer = null;
        try
        {
            object = s3.getObject(new GetObjectRequest(bucketName, fileNameOnServer));
            objectData = object.getObjectContent();
        }
        catch(Exception e)
        {
            System.out.println("Error001 downloading file "+bucketName+"/"+fileNameOnServer+" to "+localFileName);
            return false;
        }
        try
        {
            File file = new File(localFileName);
            try
            {
                reader = new BufferedInputStream(object.getObjectContent());
                writer = new BufferedOutputStream(new FileOutputStream(file));
                int read = -1;
                while ( ( read = reader.read() ) != -1 )
                {
                    writer.write(read);
                }
                System.out.println("file from "+bucketName+"/"+fileNameOnServer+" "+" downloaded to "+bucketName + " successfully");
                return true;
            }
            catch(IOException e)
            {
                System.out.println("Error downloading file "+bucketName+"/"+fileNameOnServer+" to "+localFileName);
                return false;
            }
            finally
            {
                object.close();
                writer.flush();
                writer.close();
                reader.close();
            }

        }
        catch(IOException e)
        {
            System.out.println("Error opening local file "+localFileName+" for writing ");
            return false;
        }
    }
}

Answer 2

Photo Spring BOOT 应用程序现在支持下载图像。它完美地工作。您应该使用适用于 Java V2 的 AWS 开发工具包。这是示例应用程序：

当我打开下载的图像时 - 它有效且未损坏：

从 Amazon S3 存储桶下载此图像的代码位于 Spring 控制器中：

  @RequestMapping(value = "/downloadphoto", method = RequestMethod.GET)
    void buildDynamicReportDownload(HttpServletRequest request, HttpServletResponse response) {
        try {

            //Get the photo object name
            String photoKey = request.getParameter("photoKey");
            byte[] photoBytes = s3Client.getObjectBytes("myphotobucket", photoKey) ;
            InputStream is = new ByteArrayInputStream(photoBytes);

            //define the required information to download the image
            response.setContentType("image/png");
            response.setHeader("Content-disposition", "attachment; filename="+photoKey);
            org.apache.commons.io.IOUtils.copy(is, response.getOutputStream());
            response.flushBuffer();

        } catch (Exception e) {
            e.printStackTrace();
        }
    }

V2 S3 代码在这里。注意它读取一个对象并返回一个字节[]。

public byte[] getObjectBytes (String bucketName, String keyName) {

        s3 = getClient();

        try {
            // create a GetObjectRequest instance
            GetObjectRequest objectRequest = GetObjectRequest
                    .builder()
                    .key(keyName)
                    .bucket(bucketName)
                    .build();

            // get the byte[] from this AWS S3 object
            ResponseBytes<GetObjectResponse> objectBytes = s3.getObjectAsBytes(objectRequest);
            byte[] data = objectBytes.asByteArray();
            return data;

        } catch (S3Exception e) {
            System.err.println(e.awsErrorDetails().errorMessage());
            System.exit(1);
        }
        return null;
    }

最后是 Javascript 调用

function DownloadImage(){

    //Post the values to the controller
    var photo =  $('#photo').val();
    window.location="../downloadphoto?photoKey=" + photo ;
}

此示例将被更新，因此所有这些代码都在示例文档中。

https://github.com/awsdocs/aws-doc-sdk-examples/tree/master/javav2/usecases/creating_photo_analyzer_app

通过 AWS SDK 从 AWS S3 存储桶下载文件会损坏文件

2 个答案: