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How to download a file from Google Cloud Storage and return it in Spring controller

I have a Spring Boot application.
Users can login to my application and upload files.
All the files of users are stored in a Google Cloud Storage.
Now, I want the users to be able to download their files.
So, I have to download the files form the Cloud Storage.
I don't know how my controller should look.
With my current code I'm getting an empty file. The upload is already made and the connection is fine as well.
public static Blob downloadFile(Storage storage, String fileName){
Blob blob = storage.get(BUCKET_NAME, fileName);
return blob;
}
#RequestMapping(value = "/downloadFileTest")
#ResponseBody
public void downloadFile(HttpSession session,
HttpServletResponse response) {
Storage storage = de.msm.msmcenter.service.cloudstorage.Authentication.getStorage();
Blob blob = de.msm.msmcenter.service.cloudstorage.Authentication.downloadFile(storage,"test.txt");
ReadChannel readChannel = blob.reader();
InputStream inputStream = Channels.newInputStream(readChannel);
try {
response.setContentType("application/force-download");
response.setHeader("Content-Disposition", "attachment; filename=test.txt");
IOUtils.copy(inputStream, response.getOutputStream());
response.flushBuffer();
inputStream.close();
} catch (Exception e){
e.printStackTrace();
}
}
I actually want to be able to download any file, not only txt.
When the user opens the link, the file with the name test.txt gets downloaded but it's empty..

It seems like you just want to give access to the user to be able to download the file.
A solution for that would be to use a Signed URL, which can let you provide the user with an URL to access/download the object for a limited time. If you redirect the user directly to that URL the download would start immediately.

Thank you #Mayeru
I changed my code to :
public static String downloadFile(Storage storage, String fileName){
Blob blob = storage.get(BUCKET_NAME, fileName);
String PATH_TO_JSON_KEY = "/your/path";
URL signedUrl = null;
try {
signedUrl = storage.signUrl(BlobInfo.newBuilder(BUCKET_NAME, fileName).build(),
1, TimeUnit.DAYS, SignUrlOption.signWith(ServiceAccountCredentials.fromStream(
new FileInputStream(PATH_TO_JSON_KEY))));
} catch (IOException e) {
e.printStackTrace();
}
return signedUrl.toString();
}

#add this line to you spring-boot application.properties file
spring.cloud.gcp.credentials.location=classpath:key.json
// read/download objects
public static ResponseEntity<byte[]> getObjectFromGCP(String yourfileName) throws IOException {
String objectNameWithLocation ="your file location with file name in GCP bucket";
//create your storage object with your credentials
Credentials credentials = GoogleCredentials.fromStream(new
ClassPathResource("key.json").getInputStream());
Storage storage = StorageOptions.newBuilder().setCredentials(credentials).build().getService();
BlobId blobId = BlobId.of(bucketName, objectNameWithLocation);
Blob blob = storage.get(blobId);
return ResponseEntity.ok().contentType(MediaType.valueOf(FileTypeMap.getDefaultFileTypeMap().getContentType(yourfileName)))
.body(blob.getContent(BlobSourceOption.generationMatch()));
}

How to get resources directory path using java

I am testing test in cucumber which i want to upload file from testData to S3 bucket:
String bucket = bucketname+ "/ADL";
String ActualFilesPathForComparison = Environment.getInstance().getValue(DATAINPUTPATH);
temp = ActualFilesPathForComparison+inputPath+ File.separator+ file;
s3.uploadFile(bucket, file, new File (temp));
public void uploadFile(String bucketName, String fileKeyName, File localFilePath) {
try {
this.s3.putObject((new PutObjectRequest(bucketName, fileKeyName, localFilePath)).withCannedAcl(CannedAccessControlList.PublicRead));
} catch (Exception var5) {
throw new RuntimeException("Upload file failed.", var5);
}
}
I have this file:
src\main\resources\testData\testInputsFile\testLZInputUnZippedFiles\Log.csv
when i run the test i am getting from the debug:
localFilePath = testData\testInputsFile\testLZInputUnZippedFiles\Log_WithHeader.csv
And getting excption:
com.amazonaws.SdkClientException: Unable to calculate MD5 hash: testData\testInputsFile\testLZInputUnZippedFiles\Log_WithHeader.csv (The system cannot find the path specified)
what should i fixed? i want to avoid to copy the file outside from the src.

To access a file named "my.properties" which is inside src/main/resources/, you just need to do:
File propertiesFile = new File(this.getClass().getClassLoader().getResource("my.properties").getFile());

Could not save file on disk in controller

I have following controller:
#PostMapping(value = "/load_attachment")
public DeferredResult uploadingPost(#RequestParam("attachment") MultipartFile[] uploadingFiles, #RequestParam("stoneId") String stoneId) throws IOException {
logger.info("Upload {} files for stone: {}", uploadingFiles.length, stoneId);
for (MultipartFile uploadedFile : uploadingFiles) {
File file = new File(uploadedFile.getOriginalFilename());
uploadedFile .transferTo(file);
logger.info("path:{}", file.getAbsolutePath()); // I expect to find files here
}
}
No exceptions happens but I could not find files on file system.

In your case, Application server doesn't application server inside folder path so you should specify it manually!...
for (MultipartFile uploadedFile : uploadingFiles) {
File file = new File("path/to/your/server/application/directory"+uploadedFil‌e.getOriginalFilenam‌e());
uploadedFile .transferTo(file);
logger.info("path:{}", file.getAbsolutePath()); // I expect to find files here
}
for further reference https://www.programcreek.com/java-api-examples/index.php?class=org.springframework.web.multipart.MultipartFile&method=transferTo

Generating pdf with wkhtmltopdf and download the pdf

I am working in a old project.The project is in Spring MVC .In the project I have to generate a pdf file from a jsp page and store in a location and download that file. For that I am using wkhtmltopdf tool to convert the one specific jsp page into pdf format. Using wkhtmltopdf sometime works fine, it generate the pdf in specific location, but sometime it require more time. Also when I am trying to download the file from specific location , sometime it download a 0KB size file or sometime the downloaded file can't be open (with some size) but sometime download perfectly. If I check the file at define location, it exist and open normally.
Here is my code in controller class.
#RequestMapping(value="/dwn.htm",method=RequestMethod.GET)
public void dwAppFm(HttpSession session,HttpServletRequest request,HttpServletResponse response,#RequestParam String id) throws IOException,InterruptedException
{
final int BUFFER_SIZES=4096;
ServletContext context=request.getServletContext();
String savePath="/tmp/";//PDF file Generate Path
String fileName="PDFFileName"; //Pdf file name
FileInputStream inputStream=null;
BufferedInputStream bufferedInputStream=null;
OutputStream outputStream=null;
printApp(id,fileName);
Thread.sleep(1000);
printApp(id,fileName);
File download=new File(savePath+fileName+".pdf");
while(!download.canRead())
{
Thread.sleep(1000);
printApp(id,fileName);
download=new File(savePath+fileName+".pdf");
}
if(download.canRead()){//if the file can read
try{
Thread.sleep(1000);
inputStream=new FileInputStream(download);
bufferedInputStream=new BufferedInputStream(inputStream);
String mimeType = context.getMimeType(savePath+fileName+".pdf");
if (mimeType == null) {
mimeType = "application/octet-stream";
}
System.out.println("MIME type: " + mimeType);
response.setContentType(mimeType);
response.setContentLength((int)download.length());
String headerKey="Content-Disposition";
String headerValue=String.format("attachment;filename=\"%s\"", download.getName());
response.setHeader(headerKey, headerValue);
outputStream=response.getOutputStream();
byte[] buffer=new byte[BUFFER_SIZES];
int bytesRead=-1;
while ((bytesRead = bufferedInputStream.read(buffer)) != -1) {
outputStream.write(buffer, 0, bytesRead);
}
}catch(Exception e)
{
e.printStackTrace();
}
finally
{
try{
if(inputStream!=null)inputStream.close();
if(bufferedInputStream!=null)bufferedInputStream.close();
if(outputStream!=null)outputStream.close();
}
catch(Exception e)
{
e.printStackTrace();
}
}
}
}
public void printApp(String id,String fileName)
{
try{
String urlPath="http://localhost:8080/proj";
urlPath+="/genApp.htm?id="+id;//generate url to execute wkhtmltopdf
String wxpath="/home/exm/wkhtmltopdf";//the path where wkhtmltopdf located
String save="/tmp/"+fileName+".pdf";//File save Pathname
Process process=null;
process=Runtime.getRuntime().exec(wxpath+" "+urlPath+" "+save);
}catch(Exception e)
{}
}
#RequestMapping(value="/genApp.htm",method=RequestMethod.GET)
public String getApplicationPDF(HttpServletRequest request,HttpSession session,#RequestParam String id)
{
UDets uDets=uService.getAllById(Long.parseLong(id));//Methods to get details
request.setAttribute("uDets",uDets );
return "makeApp";//Name of the jsp page
}
In my code I have use Thread.sleep(1000) and printApp(id,fileName) method three times , since sometime wkhtmltopdf fail to generate pdf in certain time and then probability of downloading 0KB file is more. I haven't share the jsp page since the jsp page contain simple jsp page code of lots of line (the size of the generated pdf file is two page).
So the problem is what should I change in my code so that the pdf file generated and download without a failure also in heavy load in server.
If there is any best procedure or idea please share.
I don't like to use itext, since the jsp page contain complex design. Any advise is also appreciable and also thanks in advance.

I would say that your code is flawed not just a little but big time. You are checking if a file can be read, if not you start again a proces writing to the same file (at least twice). At some time you will endup with multiple processes trying to write to the same file, resulting in strange behavior.
I would refactor the printApp method to return the Process it created. Then call waitFor on that process. If it returns 0 and doesn't get interrupted it completed successfully and you should be able to download the file.
#RequestMapping(value="/dwn.htm",method=RequestMethod.GET)
public void dwAppFm(HttpSession session,HttpServletRequest request,HttpServletResponse response,#RequestParam String id) throws IOException,InterruptedException
{
String savePath="/tmp/";//PDF file Generate Path
String fileName="PDFFileName.pdf"; //Pdf file name
File download = new File(savePath, fileName);
try {
Process process = printApp(id, download.getPath());
int status = process.waitFor();
if (status == 0) {
response.setContentType("application/pdf");
response.setContentLength((int)download.length());
String headerKey="Content-Disposition";
String headerValue=String.format("attachment;filename=\"%s\"", download.getName());
StreamUtils.copy(new FileInputStream(download), response.getOutputStream())
} else {
// do something if it fails.
}
} catch (IOException ioe) {
// Do something to handle exception
} catch (InterruptedException ie) {
// Do something to handle exception
}
}
}
public Process printApp(String id, String pdf) throws IOException {
String urlPath="http://localhost:8080/proj";
urlPath+="/genApp.htm?id="+id;//generate url to execute wkhtmltopdf
String wxpath="/home/exm/wkhtmltopdf";//the path where wkhtmltopdf located
String command = wxpath+" "+urlPath+" "+pdf;
return Runtime.getRuntime().exec(command);
}
Something like the code above should to the trick.

file upload with spring MVC

I am uploading file using spring MVC and jquery. Inside my class method I have written
#RequestMapping(value="attachFile", method=RequestMethod.POST)
public #ResponseBody List<FileAttachment> upload(
#RequestParam("file") MultipartFile file,
HttpServletRequest request,
HttpSession session) {
String fileName = null;
InputStream inputStream = null;
OutputStream outputStream = null;
//Save the file to a temporary location
ServletContext context = session.getServletContext();
String realContextPath = context.getRealPath("/");
fileName = realContextPath +"/images/"+file.getOriginalFilename();
//File dest = new File(fileName);
try {
//file.transferTo(dest);
inputStream = file.getInputStream();
outputStream = new FileOutputStream(fileName);
inputStream.close();
outputStream.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
Its uploading the file correctly I am using
ServletContext context = session.getServletContext();
String realContextPath = context.getRealPath("/");
to get the path. My first question is , Is this the correct way to get the path and it stores the file somewhere at
workspace/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/wtpwebapps/myproject/images
and when I am trying to display this image on my jsp page using the following code
<img src="<%=request.getRealPath("/") + "images/images.jpg" %>" alt="Upload Image" />
It does not display the image, Its generating the following html
<img src="/home/name/workspace/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/wtpwebapps/myproject/images/images.jpg" alt="Upload Image">
Am I doing the things right? In my project I have to upload large number of files everyday.
Please let me know if you need anything else to understand my question

It will be better if you upload your files in some directory by absolute path(e.g. C:\images\) instead of relative (your approach). Usually, web apps runs on linux mathines on production and it is good practice to make save path configurable.
Create some application property which will holds save path for files(in xml or property file).