Im currently building an web-app that allows users to upload content via blobstore and to later download it.
However, the servlet that takes care of the download is called BlobServiceServlet
and whenever a user downloads a blob, the filename is changed to "BlobServiceServlet" and the extension is also changed sometimes to .bin. Does anyone know how to fix this problem?
Add a "Content-disposition" header to the response.
See http://en.wikipedia.org/wiki/MIME#Content-Disposition for an example.
E.g., in the handler,
self.response.headers['Content-Disposition'] = 'attachment; filename=foo.doc'
Just an additional info.
This is the code to let the browser know the file size:
BlobInfoFactory blobInfoFactory = new BlobInfoFactory(DatastoreServiceFactory.getDatastoreService());
BlobInfo blobInfo = blobInfoFactory.loadBlobInfo(blobKey);
resp.setContentLength(new Long(blobInfo.getSize()).intValue());
resp.setHeader("content-type", blobInfo.getContentType());
resp.setHeader("content-disposition", "attachment;filename=" + blobInfo.getFilename());
blobstoreService.serve(blobKey, resp);
Note that if you have files with more than 1MB in size, the file size is not sent to browser. GAE reads the blob 1MB at a time and overwrites the file size header in the response.
I found all this information here:
http://www.mail-archive.com/google-appengine#googlegroups.com/msg29314.html
Related
I'm using Spring model.addAttribute to set the ByteArrayOutputStream value and send it to JSP . Please advise how to trigger the download option from JSP once that response JSP page loaded. I know how to do that by download file from server, But my idea is not to store anything in the server, instead do all using the ByteStream so that we can avoid IO throughput.
Here is my controller class that will send the byte stream to JSP to display or download
ByteArrayOutputStream fDoc = new ByteArrayOutputStream();
fDoc = fileDownloader.geDownload(docID); //this will have the document stream
model.addAtrribute("doc",fDoc);
return "responseJSP"
Once the responseJSP loaded , I need to show the download option and let the user to download and save it as doc/docx in local .
Is there any other easy way I can render it in client side ?
I create data in the server (gae) and I want to store it in Blobstore. I saw many answers on how to do this giving a BlobStore URL to the client, but there is no client or HTTP request: it's just an asynchronous task.
Then I guess I should use createUploadUrl(), and instead of giving this URL to a client, from my code HTTP Post my data to it via URL Fetch. This looks weird, isn't there another API for this?
Let's say that the files I want in Blobstore are already stored in my GCS default bucket. Can I just tell Blobstore about them using the gcs location "/gs/bucketname/file"? I tried this by
GcsFilename filename = new GcsFilename(bucketName, fileId);
String gcsKey = "/gs/" + bucketName + "/" + filename.getObjectName();
BlobKey blobKey = blobstoreService.createGsBlobKey(gcsKey);
GcsOutputChannel outputChannel = gcsService.createOrReplace(filename, GcsFileOptions.getDefaultInstance());
ObjectOutputStream oout = new ObjectOutputStream(Channels.newOutputStream(outputChannel));
oout.writeObject(myDataObjectToPersist);
oout.close();
// ...at some other point I have checked the file is correctly stored in
// GCS and I can fetch it using /gs/bucket/fileId
// but it doesn't seem to be in Blobstore, so when
InputStream stream = new BlobstoreInputStream(new BlobKey(blobKey.keyString))
// ... this gives a BlobstoreInputStream$BlobstoreIOException: BlobstoreInputStream received an invalid blob key...
Is this something conceptually wrong - like if I use GcsOutputChannel to save it I will not get it from Blobstore even if I create a BlobKey, or is it something that could work but I just did something wrong?
1K thanks
Why would you want to store the file in blobstore as opposed to writing and reading it directly from GCS?
Yes, you can create a BlobKey for a file stored in GCS, and can use the key in some of the blobstore API (such as fetchData and serve) but unfortunately not in all.
Some of the blobstore API (such as BlobstoreInputStream) depends on BlobInfo and that is not created when using the GCS client.
I have a java class that generates a PDF file to a folder in my computer. I have managed to connect this class to a link on a web application and when i click this link it generates the pdf and writes it to the folder on my computer. I would want to change this and have the link send the pdf to the browser instead. How can i do this? The class does not use any HttpRequests or similar and the link isnt a hypertext link atm. Im looking for the most straight forward way to send a pdf to the browser.
/* Java Code */
response.setContentType("application/pdf");
response.setHeader("Content-Disposition", "attachment; filename=path/to/file.pdf");
i print it (any kind of file) to the response stream from a byte array, inside a servlet
if(content != null)
{
response.setContentType( "application/octet-stream" );
response.setHeader("Content-Disposition", "attachment; filename=\"" + fname + "\"");
response.setContentLength(content.length);
out.write(content);
}//where content is byte[]
You should be able to write the pdf to a stream, you can pass it the output stream from your response.
There are several ways to do that:
Put PDF file on some place available from Web, and then redirect user to URL, which will lead him to PDF file (if your web server supports this). Redirection may be easily done with "Location" HTTP header.
Send PDF file in HTTP response stream. Note, that you will have to set corresponding Mime-type in HTTP header. Implementation depends on web server / web framework you are using in your application.
Even though it's not part of HTTP 1.1/RFC2616 webapps that wish to force a resource to be downloaded (rather than displayed) in a browser can use the Content-Disposition header like this:
Content-Disposition: attachment; filename=FILENAME
Even tough it's only defined in RFC2183 and not part of HTTP 1.1 it works in most web browsers as wanted.
So from the client side, everything is good enough.
However on the server-side, in my case, I've got a Java webapp and I don't know how I'm supposed to set that header, especially in the following case...
I'll have a file (say called "bigfile") hosted on an Amazon S3 instance (my S3 bucket shall be accessible using a partial address like: files.mycompany.com/) so users will be able to access this file at files.mycompany.com/bigfile.
Now is there a way to craft a servlet (or a .jsp) so that the Content-Disposition header is always added when the user wants to download that file?
What would the code look like and what are the gotchas, if any?
I got this working as Pointy pointed out. Instead of linking directly to the asset - in my case pdfs - one now links to a JSP called download.jsp which takes and parses GET parameters and then serves out the pdf as a download.
Download here
Here's the jsp code I used. Its working in IE8, Chrome and Firefox:
<%#page session="false"
contentType="text/html; charset=utf-8"
import="java.io.IOException,
java.io.InputStream,
java.io.OutputStream,
javax.servlet.ServletContext,
javax.servlet.http.HttpServlet,
javax.servlet.http.HttpServletRequest,
javax.servlet.http.HttpServletResponse,
java.io.File,
java.io.FileInputStream"
%>
<%
//Set the headers.
response.setContentType("application/x-download");
response.setHeader("Content-Disposition", "attachment; filename=downloaded.pdf");
[pull the file path from the request parameters]
File file = new File("[pdf path pulled from the requests parameters]");
FileInputStream fileIn = new FileInputStream(file);
ServletOutputStream outstream = response.getOutputStream();
byte[] outputByte = new byte[40096];
while(fileIn.read(outputByte, 0, 40096) != -1)
{
outstream.write(outputByte, 0, 40096);
}
fileIn.close();
outstream.flush();
outstream.close();
%>
You wouldn't have a URL that was a direct reference to the file. Instead, you'd have a URL that leads to your servlet code (or to some sort of action code in your server-side framework). That, in turn, would have to access the file contents and shovel them out to the client, after setting up the header. (You'd also want to remember to deal with cache control headers, as appropriate.)
The HttpServletResponse class has APIs that'll let you set all the headers you want. You have to make sure that you set up the headers before you start dumping out the file contents, because the headers literally have to come first in the stream being sent out to the browser.
This is not that much different from a situation where you might have a servlet that would generate a download on-the-fly.
edit I'll leave that stuff above here for posterity's sake, but I'll note that there is (or might be) some way to hand over some HTTP headers to S3 when you store a file, such that Amazon will spit those back out when the file is served out. I'm not exactly sure how you'd do that, and I'm not sure that "Content-disposition" is a header that you can set up that way, but I'll keep looking.
Put a .htaccess file in the root folder with the following line:
Header set Content-Disposition attachment
I just found this via google.
And I had a simmilar problem, but I still want to use a Servlet (as I generate the Content).
However the following line is all you need in a Servlet.
response.setHeader("Content-Disposition", "attachment; filename=downloadedData.json");
I have Java webserver (no standard software ... self written). Everything seems to work fine, but when I try to call a page that contains pictures, those pictures are not displayed. Do I have to send images with the output stream to the client? Am I missing an extra step?
As there is too much code to post it here, here is a little outline what happens or is supposed to happen:
1. client logs in
2. client gets a session id and so on
3. the client is connected with an output stream
4. we built the response with the HTML-Code for a certain 'GET'-request
5. look what the GET-request is all about
6. send html response || file || image (not working yet)
So much for the basic outline ...
It sends css-files and stuff, but I still have a problem with images!
Does anybody have an idea? How can I send images from a server to a browser?
Thanks.
I check requests from the client and responses from the server with charles. It sends the files (like css or js) fine, but doesn't with images: though the status is "200 OK" the transfer-encoding is chunked ... I have no idea what that means!? Does anybody know?
EDIT:
Here is the file-reading code:
try{
File requestedFile = new File( file );
PrintStream out = new PrintStream( this.getHttpExchange().getResponseBody() );
// File wird geschickt:
InputStream in = new FileInputStream( requestedFile );
byte content[] = new byte[(int)requestedFile.length()];
in.read( content );
try{
// some header stuff
out.write( content );
}
catch( Exception e ){
e.printStackTrace();
}
in.close();
if(out!=null){
out.close();
System.out.println( "FILE " + uri + " SEND!" );
}
}
catch ( /*all exceptions*/ ) {
// catch it ...
}
Your browser will send separate GET image.png HTTP 1.1 requests to your server, you should handle these file-gets too. There is no good way to embed and image browser-independent in HTML, only the <img src="data:base64codedimage"> protocol handler is available in some browsers.
As you create your HTML response, you can include the contents of the external js/css files directly between <script></script> and <style></style> tags.
Edit: I advise to use Firebug for further diagnostics.
Are you certain that you send out the correct MIME type for the files?
If you need a tiny OpenSource webserver to be inspired by, then have a look at http://www.acme.com/java/software/Acme.Serve.Serve.html which serves us well for ad-hoc server needs.
Do I have to send those external files
or images with the output stream to
the client?
The client will make separate requests for those files, which your server will have to serve. However, those requests can arrive over the same persisten connection (a.k.a. keepalive). The two most likely reasons for your problem:
The client tries to send multiple requests over a persistent connection (which is the default with HTTP 1.1) and your server is not handling this correctly. The easiest way to avoid this is to send a Connection: close header with the response.
The client tries to open a separate connection and your server isn't handling it correctly.
Edit:
There's a problem with this line:
in.read( content );
This method is not guaranteed to fill the array; it will read an arbitrary number of bytes and return that number. You have to use it in a loop to make sure everything is read. Since you have to do a loop anyway, it's a good idea to use a smaller array as a buffer to avoid keeping the whole file in memory and running into an OutOfMemoryError with large files.
Proabably step #4 is where you are going wrong:
// 4. we built the response with the HTML-Code for a certain 'GET'-request
Some of the requests will be a 'GET /css/styles.css' or 'GET /js/main.js' or 'GET /images/header.jpg'. Make sure you stream those files in those circumstances - try loading those URLs directly.
Images (and css/js files) are requested by the browser as completely separate GET requests to the page, so there's definitely no need to "send those ... with the output stream". So if you're getting pages served up ok, but images aren't being loaded, my first guess would be that you're not setting your response headers appropriately (for example, setting the Content-Type of the response to text/html), so the browser isn't interpreting it as a proper page & therefore not loading the images.
Some other things to try if that doesn't work:
Check if you can access an image directly
Use something like firebug or fiddler to check whether the browser is actually requesting the image/css/js files & that all your request/response headers look ok
Use an existing web server!