I am developing a GWT application. This application is running in a server. Well, I implement a button which calls a method that generates a local file in server side. However I would like to download/generate this file in client side. How could I do this in GWT?
Thanks
In our project we created a file on server on demand. When the file has been successful created we send notification to browser and created a link.
See servlet code:
public class DownloadServlet extends HttpServlet {
private FileManager fileManager;
#Override
protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
String encodedFileName = req.getRequestURI().substring(
req.getContextPath().length() + req.getServletPath().length() + 1);
String decodedFileName = URLDecoder.decode(encodedFileName, "utf-8");
File downloadableFile = fileManager.toFile(decodedFileName);
ServletOutputStream os = resp.getOutputStream();
try {
InputStream is = FileUtils.openInputStream(downloadableFile);
try {
IOUtils.copy(is, os);
} finally {
is.close();
}
} finally {
os.close();
}
}
}
private native void Download(String filename, String text)/*-{
var pom = document.createElement('a');
pom.setAttribute('href', 'data:text/plain;charset=utf-8,' + encodeURIComponent(text));
pom.setAttribute('download', filename);
document.body.appendChild(pom);
pom.click();
document.body.removeChild(pom); }-*/;
Use JSNI method inside GWT code , provide the file name you want to download in addition to JSON string as text (String) , this method will download a file with specified content in text variable to client browser.
Current situation is, that not all browsers are able to work with local file system, so there is no universal solution in GWT. Also as far as I know FilesSstem API is not finished.
As alternative you can keep using serverside generated files, or use Flash plugin to generate and store files (you will have to create a Flash app, and create some API to control it from GWT).
You should definitely have a look at Aki Miyazaki’s HTML5 file download code for GWT.
It works on the client side as you requested.
AFAIK, as of now, it only works in Chrome, but this is supposed to change as other browsers implement the download attribute.
You can do that using Data URIs:
Make your GWT RPC method return the file content or the data to generate the file.
On the client side, format a Data URI with the file content received or generate the data content.
Use Window.open to open a file save dialog passing the formatted DataURI.
Take a look at this reference, to understand the Data URI usage:
Export to csv in jQuery
Related
I am trying to download a file from the drive using google drive api
Steps to reproduce :
Step 1:
Click on :https://developers.google.com/drive/v3/reference/files/export#try-it
Step 2:
I have provided fileid and mimetype
I gave fileid and mime type as "application/vnd.google-apps.spreadsheet" and click on execute.i got this error:
"code":403,
"message":"Export requires alt=media to download the exported content."
public static void downloadFile(Drive service,String fileId) throws IOException{
OutputStream outputStream = new ByteArrayOutputStream();
//OutputStream outputStream = new FileOutputStream("/Users/xxxxx/Downloads/driveFile.xls");
//service.get
service.files().export(fileId,"application/vnd.openxmlformats-officedocument.spreadsheetml.sheet")
.executeMediaAndDownloadTo(outputStream);
}
Based on the error you are getting...
https://developers.google.com/drive/v3/web/manage-downloads
Try adding "?alt=media" to your GET request. My guess is you are missing something in the input parameters or possibly do not have access to the media (not logged in maybe?). I can't help more without seeing the actual code you are attempting to call, or the request you are making.
I have Spring MVC web app running on Tomcat.
I upload a file and save it in the /tmp folder on the file system.
Then I need to show a link to that file in the view (Thymeleaf), so that the user can download the file by clicking on the link. How to do that?
I've heard about configuring Tomcat to allow a specific context to link to a folder on the FS, but not sure how to do that or if that is the only solution. Please help.
The way I approach this is slightly different. Basically I use two controller actions for handling file uploads, one for uploading, and for downloading (viewing) files.
So upload action would save files to some preconfigured directory on the file system, I assume you already have that part working.
Then declare download action similar to this
#Controller
public class FileController {
#RequestMapping("/get-file/{filename}")
public void getFileAction(#RequestParam filename, HttpServletResponse response) {
// Here check if file with given name exists in preconfigured upload folder
// If it does, write it to response's output stream and set correct response headers
// If it doesn't return 404 status code
}
}
If you want to make impossible to download file just by knowing the name, after uploading file, save some meta info to the database (or any other storage) and assign some hash (random id) to it. Then, in getFileAction, use this hash to look for file, not the original filename.
Finally, I would discourage using /tmp for file uploads. It depends on the system/application used, but generally temp directory are meant, as name suggest, for temporary data. Usually it is guaranteed data in the temp directory will stay for "reasonable time", but applications must take into account that content of temp directory can be deleted anytime.
This is the precisely setup that worked for me (Tomcat 8, SpringMVC, boot):
server.xml:
<Context docBase="C:\tmp\" path="/images" />
In the controller:
public String createNewsSource(#ModelAttribute("newsSource") NewsSource source, BindingResult result, Model model,
#RequestParam("attachment") final MultipartFile attachment) {
new NewsSourceValidator().validate(source, result);
if (result.hasErrors()) {
return "source/addNewSource";
}
if (!attachment.isEmpty()) {
try {
byte[] bytes = attachment.getBytes();
BufferedOutputStream stream = new BufferedOutputStream(
new FileOutputStream(new File("/tmp/" + attachment.getOriginalFilename())));
stream.write(bytes);
stream.close();
} catch (Exception e) {
e.printStackTrace();
}
}
source.setLogo("images/" + attachment.getOriginalFilename());
newsSourceService.createNewsSourceIfNotExist(source);
return "redirect:/sources/list";
}
As you can see I am saving the file to /tmp, but in the DB (source.setLogo()), I am pointing to images as mapped in server.xml
Here's where I found about Tomcat config:
If the images are all located outside the webapp and you want to have
Tomcat's DefaultServlet to handle them, then all you basically need to
do in Tomcat is to add the following Context element to
/conf/server.xml inside tag:
This way they'll be accessible through http://example.com/images/....
SO answer to a similar question
So I pushed my java app to a server, pretty excited about that.
Now I want to test something, how can I save the posted data to my servlet to a file, and the filename should be a unique guid.
I have this so far:
public class TestServlet extends javax.servlet.http.HttpServlet {
protected void doPost(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)
throws javax.servlet.ServletException, IOException {
}
protected void doGet(javax.servlet.http.HttpServletRequest request, javax.servlet.http.HttpServletResponse response)
throws javax.servlet.ServletException, IOException {
PrintWriter printWriter = response.getWriter();
printWriter.print("hello, world from testservlet!");
}
}
So assuming the http posted data (say around 50K) will be posted to the field 'payload', how can I grab the posted text, and save it to a file, with the filename being a GUID.
Does java have a construct to clean up an open file, like in c#:
using(var file = new ....)
{
// write to file
}
That closes the connection and cleans up memory etc.
Also, do I need to set special permissions for tomcat to save this file?
I just set things up by default right now (just playing around on a VPS) using ubuntu 11, installed tomcat6.
Thanks.
You can user request to read the "payload", see the API doc for ServletRequest:
request.getParameter("payload");
You can use File to create the file, see AP doc:
File newFile = new File("fileName");
boolean isCreated = newfile.createNewFile();
You can write to the file as follows,
BufferedWriter out = new BufferedWriter(new FileWriter(newFile));
out.write(payLoad);
out.close();
For GUID you see this Create a GUID in Java
And for the clean up, you don't have to worry about it in Java, it's Garbage Collector ( What is the garbage collector in Java? ) does it for you automatically when the reference goes out of scope.
But you should close the resources like out.close to release it back to the system when you are done with it.
Also, do I need to set special permissions for tomcat to save this file?
You do not need to do that because tomcat is just a server, it's more related to the file system (OS). I use Glassfish on Unix and I don't need to do anything like that to create file.
Now I want to test something, how can I save the posted data to my servlet to a file, and the filename should be a unique guid.
Use File#createTempFile() to create a file with an unique ID in the given folder.
File file = File.createTempfile("prefix-", ".ext", "/path/to/files");
// ...
See also:
Saving uploaded file in specific location
Does java have a construct to clean up an open file, like in c#: using?
Only in Java 7 which is already been out for some time.
try (FileWriter writer = new FileWriter(file)) {
writer.write(content);
}
which is equivalent to
FileWriter writer = null;
try {
writer = new FileWriter(file);
writer.write(content);
} finally {
if (writer != null) writer.close();
}
See also:
"using" keyword in java
Also, do I need to set special permissions for tomcat to save this file?
The user who has started Tomcat should indeed have the file write permissions on the given directory.
In the future please ask separate questions in separate SO questions.
Java 7 has a new try with resources construct that will take care of closing the file for you. Otherwise... just close the file; no big deal.
As far as "special permissions", as long as the user Tomcat is running under can access the directory in question, there's no issue. I'd recommend against storing it under the webapp directories, though (and if it's deployed as a war you may not be able to anyway). Keep uploaded files in a known, but separate, directory.
A webpage contains a link to an executable (i.e. If we click on the link, the browser will download the file on your local machine).
Is there any way to achieve the same functionality with Java?
Thank you
Yes there is.
Here a simple example:
You can have a JSF(Java Server Faces) page, with a supporting backing bean that contains a method annotated with #PostConstruct This means that any action(for example downloading), will occur when the page is created.
There is already a question very similar already, have a look at: Invoke JSF managed bean action on page load
You can use Java's, URL class to download a file, but it requires a little work. You will need to do the following:
Create the URL object point at the file
Call openStream() to get an InputStream
Open the file you want to write to (a FileOutputStream)
Read from the InputStream and write to the file, until there is no more data left to read
Close the input and output streams
It doesn't really matter what type of file you are downloading (the fact that it's an executable file is irrelevant) since the process is the same for any type of file.
Update: It sounds like what you actually want is to plug the URL of a webpage into the Java app, and have the Java app find the link in the page and then download that link. If that is the case, the wording of your question is very unclear, but here are the basic steps I would use:
First, use steps 1 and 2 above to get an InputStream for the page
Use something like TagSoup or jsoup to parse the HTML
Find the <a> element that you want and extract its href attribute to get the URL of the file you need to download (if it's a relative URL instead of absolute, you will need to resolve that URL against the URL of the original page)
Use the steps above to download that URL
Here's a slight shortcut, based on jsoup (which I've never used before, I'm just writing this from snippets stolen from their webpage). I've left out a lot of error checking, but hey, I usually charge for this:
Document doc = Jsoup.connect(pageUrl).get();
Element aElement = doc.getElementsByTag("a").first() // Obviously you may need to refine this
String newUrl = aElement.attr("abs:href"); // This is a piece of jsoup magic that ensures that the destination URL is absolute
// assert newUrl != null
URL fileUrl = new URL(newUrl);
String destPath = fileUrl.getPath();
int lastSlash = destPath.lastIndexOf('/');
if (lastSlash != -1) {
destPath = destPath.substring(lastSlash);
}
// Assert that this is really a valid filename
// Now just download fileUrl and save it to destPath
The proper way to determine what the destination filename should be (unless you hardcode it) is actually to look for the Content-Disposition header, and look for the bit after filename=. In that case, you can't use openStream() on the URL, you will need to use openConnection() instead, to get a URLConnection. Then you can use getInputStream() to get your InputStream and getRequestProperty("Content-Disposition") to get the header to figure out your filename. In case that header is missing or malformed, you should then fall-back to using the method above to determine the destination filename.
You can do this using apache commons IO FileUtils
http://commons.apache.org/io/apidocs/org/apache/commons/io/FileUtils.html#copyURLToFile(java.net.URL, java.io.File)
Edit:
I was able to successfully download a zip file from source forge site (it is not empty), It did some thing like this
import java.io.File;
import java.net.URL;
import org.apache.commons.io.FileUtils;
public class Test
{
public static void main(String args[])
{
try {
URL url = new URL("http://sourceforge.net/projects/gallery/files/gallery3/3.0.2/gallery-3.0.2.zip/download");
FileUtils.copyURLToFile(url, new File("test.zip"));
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
I was able successfully download tomcat.exe too
URL url = new URL("http://archive.apache.org/dist/tomcat/tomcat-6/v6.0.16/bin/apache-tomcat-6.0.16.exe");
I want to output the content of some analysis done by my java application (on Google App Engine) to a PDF using PDFJet library... I want that the file should be directly created on the end user's pc. Is it possible to do this, and any code sample would be appreciated.
Thanks,
Arvind.
in your servlet,
public void doGet(HttpServletRequest request, HttpServletResponse response) {
// set content type so client will see the file download dialog
response.setContentType("application/pdf");
// generate pdf content
PDF pdf = new PDF(response.getOutputStream());
...
// writes file to client
pdf.flush();
pdf.close();
}
disclaimer: i didnt test the above code.