I am new to web application world. I have made an app and ready to deploy on Heroku. I have tested and it is working.
Problem is that I have static 62 text files (each 1KB, so total 62 KB size) which I feed data (numbers) from the files and display on web page.
I am using java for back-end / js, JQuery, CSS, ajax, etc for front-end.
Application is working fine and I have tested for the deployment on Heroku.
Originally, I used external sever for the data and fetch the data from the server and display it on my web application.
However, the sever connection wants to keep the confidentiality, so I was recommended to use static files.
The files only include numbers. ex) 356, 200, 100, 280,....etc
So here are my questions.
1) How can I upload 62 text files (each 1KB) on Heroku?
(I don't know about django, Ruby on rails.. what so ever???? All answers are about those. but I do NOT think I am USING those. but I don't know, I am very newbie.)
2) when my app on Heroku try to use data from the text files on Heroku (after I figure out how to upload), How my connection URL can be in java code to fetch the data from those text files (I mean usually there are url address I am giving )
Current to code to fetch data from the server.. I am doing like this
String addressURL = "http://url_address_bla:xxxx/data/bla";
URL url = new URL(addressURL);
//then I open the file and read the file..etc
Thanks in advance.
Related
I want to upload large files to my backend which I created with gqlgen.
To do that, I want to use multipart requests to keep only one endpoint.
(Client implementation e.g. apollo-upload-client)
There is an example and documentation on how to upload files using gqlgen using multipart requests. However, this only works for small files. When I try to upload large files (only 500mb in this case) I get a connection reset error. (I get the same error in my implementation and the example gqlgen provided)
Does anyone know a solution for this?
Our application is entirely built on websockets. We don't do any HTTP request-reply. However, we are stuck with file download. If i receive file content via websockets can I wrote to local folder on user computer ?
If it makes a difference, we are only supporting Chrome so not issue if it doesn't work on other browsers.
Also, I know i can do this via HTTP. Trying to avoid it and stick to websockets since thats how the entire app is.
Thanks a lot in advance!
The solution depends on size of your file.
If size is less than about 50 MB, I would encode file's content to base64 string on the server and send this string to the client. Client should receive parts of the string, concat them to single result, and store. After receiving whole string, add link (tag <a>) to your page with attribute href set to "data:<data_type>;base64,<base64_encoded_file_content>". <data_type> is a mime type of your file, for example "text/html" or "image/png". Suggest file name by adding download attribute set to name of file (doesn't work for Chrome on OS X).
Unfortunately I have no solution for large files. Currently there is only FileEntry API that allows to write files with JS, but according to documentation it is supported only by Chrome v13+, learn more here https://developer.mozilla.org/en-US/docs/Web/API/FileEntry.
so I am working on a school project in which we have designed a web application that takes in much user info and creates a pdf then should display that pdf to the user so they can print it off or save it. We are using Play! Framework 2.1.3 as our framework and server and Java for the server side. I create the pdf with Apache's PDFbox library. Every thing works as it should in development mode ie launching it on a localhost with plays run command. the issue is when we put it up to the server and launch with plays start command I it seems to take a snapshot of the directory (or at least the assets/public folder) which is where I am housing the output.pdf file/s (i have attempted to move the file elsewhere but that still seems to result in a 404 error). Initially I believed this to be something with liunx machine we were deploying to which was creating a caching problem and have tried many of the tricks to defeat the browser from caching the pdf
like using javascript to append on a time stamp to the filename,
using this cache-control directive in the play! documentation,
"assets.cache./public/stylesheets/output.pdf"="max-age=0",
then I tried to just save the pdf as a different filename each time and pass back the name of that file and call it directly through the file structure in the HTML
which also works fine with the run command but not the start.
finally I came to the conclusion that when the start command is issued it balls up the files so only the files that are there when the start command is issued can be seen.
I read the documentation here
http://www.playframework.com/documentation/2.1.x/Production
which then I noticed this part
When you run the start command, Play forks a new JVM and runs the
default Netty HTTP server. The standard output stream is redirected to
the Play console, so you can monitor its status.
so it looks like the fact that it forks a new JVM is what is causing my pain.
so my question really is can this be gotten around in some way that a web app can create and display a pdf form? (if I cannot get this to work my only solution
that I can see is that I will have to simulate the form with HTML and fill it out from there) --which I really think is a bad way to do this.
this seems like something that should have a solution but I cannot seem to find or come up with one please help.
i have looked here:
http://www.playframework.com/documentation/2.1.x/JavaStream
the answer may be in there but Im not getting it to work I am pretty novice with this Play! Framework still
You are trying to deliver the generated PDF file to the user by placing it in the assets directory, and putting a link to it in the HTML. This works in development mode because Play finds the assets in the directory. It won't work in production because the project is wrapped up into a jar file when you do play dist, and the contents of the jar file can't be modified by the Play application. (In dev mode, Play has a classpath entry for the directory. In production, the classpath points to the jar file).
You are on the right lines with JavaStream. The way forward is:
Generate the PDF somewhere in your local filesystem (I recommend the temp directory).
Write a new Action in your Application object that opens the file you generated, and serves it instead of a web page.
Check out the Play docs for serving files. This approach also has the advantage that you can specify the filename that the user sees. There is an overloaded function Controller.ok(File file, String filename) for doing this. (When you generate the file, you should give it a unique name, otherwise each request will overwrite the file from a previous request. But you don't want the user to see the unique name).
I'm new and just developing on J2EE.
I am modifying an existing application (an OpenSource project).
I need to save an image on a client sent by the server, but I do not know how.
This activity must be done in a transparent manner without affecting the existing operation of the application.
From the tests done I get this error:
java.lang.IllegalStateException: getWriter () has Already Been Called for this response.
How should carry out this task, according to your own opinion?
How do I save on the client, locally, the image?
Update:
Thanks for the answers.
My problem is that:
the image is generated on the server, but not for direct client request (there is no link to click on web page), the picture is composed using other services on the Internet.
reconstruct the image on the server.
This image must be sent to the client to be saved locally.
so I'd like it to appear a window where you assign the destination image
plus I'd like the rest of the application were not affected by this activity.
The application is yet on production.
Thank you very much for your response.
From the tests done I get this error: java.lang.IllegalStateException: getWriter () has Already Been Called for this response.
In other words, you were trying to mix the binary data of the image with the character data of the HTML output, or you were trying to do this in a JSP instead of a Servlet. This is indeed not going to work. You need to send either the image or the HTML page exclusively in response to fully separate requests.
In your JSP/HTML page just have a link to the image, like so:
click to download image
Then, in a servlet listening on an url-pattern of /imageservlet/*, you just get the image as InputStream from some datasource (e.g. from local disk file system as FileInputStream) and then write it to the OutputStream of the response the usual Java IO way.
You only need to set at least the Content-Disposition response header to attachment to make sure that the client get a Save As popup dialogue, else it will be displayed straight in the browser. Setting the Content-Type and Content-Length are also important so that the browser knows what the server is sending and can predict how long the download may take.
response.setHeader("Content-Type", getServletContext().getMimeType(file.getName()));
response.setHeader("Content-Length", String.valueOf(file.length()));
response.setHeader("Content-Disposition", "attachment;filename=\"" + file.getName() + "\"");
You can find complete basic servlet example in this article.
Note: you cannot control where the client would save the image, this would be a security hole. This way websites would be able to write malicious files on client's disk unaskingly.
Update: as per your update, there are two options:
You need to let the client itself fire two HTTP requests (I've answered this in your subsequent question)
Create a client side application which does all the task directly at the client side and then embed this in your webpage, for example a Java Applet. With an applet you have full control over the client environment. You can execute almost all Java code you'd like to execute and you can write files to disk directly without asking client for the location to save. You only need to sign the applet by a 3rd party company or the client needs to confirm a security warning before running.
Its up to the browser how all types of output are handled. Web pages are given a content type of html which the browser understands and ends up rendering ass a page that we can see. Images are given content type of image/jpeg etc which are rendered as images when in a page etc. To force a download prompt one needs to use a content type of a binary file rather than that of an image so the browser forces the download rather than shows the image. To ensure this use something like "application/octetstream"... i cant recall exactly but its easy to google for.
How to use External Directory to Store Images.
And how i access that images thru my Web application ?
I am using Jboss as an application Server.
Web application is in Java,Jsp.
Presently images stored in WAR file.
After google i got the solution
C:\jboss-4.0.0\server\default\deploy\jbossweb-tomcat55.sar\server.xml
Then restart the server and access the
http://localhost:8080/contextname/images
Please provide comments
I've answered similar question before: Simplest way to serve static data from outside the application server in a Java web application
To summarize there are basically two ways:
Add a new Context to the server.xml denoting the absolute location where the images are.
Create a Servlet which gets an InputStream of the image using FileInputStream and writes it the usual Java IO way to the OutputStream of the response, along with at least Content-Type, Content-Length and Content-Disposition headers.
See the link for more detailed answers and code examples.