I´m using the FileServlet from Omnifaces:
http://showcase.omnifaces.org/servlets/FileServlet
It works fine and all my images appears in my webapp.
But now I would like to change the link from the image because I would like to avoid that someone enter the path from another image:
For example:
The path from one image is:
myapp/imagesservlet/mypic1.jpg
-> Someone can enter
myapp/imagesservlet/mypic2.jpg -> and got another image.
My files are stored as:
mypic like mypic1.jpg, mypic2.jpg.....
Is there any chance to change the path and got also the correct image?
Just use unpredictable autogenerated filenames. E.g. imgur also does that. This responsibility is actually beyond the OmniFaces FileServlet as all it does is just inspecting the passed-in filename and serving it up. You should change the passed-in filename to be an autogenerated one. Save if necessary the original filename somewhere else, e.g. in a SQL database, if necessary along with other metadata (content type, size, etc) so it can more efficiently be indexed and searched.
How to autogenerate a random string in Java is already covered in this Q&A: How to generate a random alpha-numeric string?
Related
I want to make some basic math stuff like Sum in Diagrams.net (old Draw.io).Is it possible ?
Exemple : I create a new parameter on a shape, like "Elec : T16" and make several copy on this shape. Is it possible to have a Text which can give me the total of the shape with this parameter ?
Best Regards.
I search a lot in the Diagrams.net blog but anything relevent.
This is not supported.
Regards,
I also wanted to do something similar and while it doesn't seem possible to do it completely in the software (as of v20.3.0), I did find a bit of a workaround: If you add properties to the shape data, then do File > Export As > XML, the properties will be there in the XML data. You can then count them one of two ways:
Open the XML file with a text editor like Notepad++, do a find on the value you want to count. If you choose "Find All" it will tell you how many times it appears.
Use a programming language like Python to read through the file and count the instances of that value.
Example:
I created a red circle in a new diagram, edited the text to say "RedCircle" and used Edit Data to add a property called TestValue, to which I assigned a value of 1. When I exported to XML it contained this element:
<object label="RedCircle" TestValue="1" id="6byQ5fOap-RXn7mFit_J-1">
Notes
When you export, make sure you turn off the Compressed option, this will create an unusable file.
Don't use Save As > XML, this will also use compression.
Diagrams.net natively saves in a compressed XML format, with only slight differences between that and the other compressed XML options, but it seems happy to also read in the exported uncompressed XML. I didn't test but if you go the programming route and want to take it a step further, it seems you could have the program update the value of a given "counter" element with the count, then open the XML file in diagrams.net to see the updated value and save it as a native .drawio file or publish in whatever format you like.
Edit: I discovered that under File > Properties you can turn off the compression on the actual .drawio file. If you do that you can just work from this file instead of exporting, but you might want to check the size of your file with and without it.
I'm sure a plugin could be created to do all of that within the app itself, but the other methods are enough for me at this point.
Hope this helps you!
Looking at this
http://www.dotnetperls.com/ashx
I might have bits of code like this:
string file = context.Request.QueryString["file"];
if (file == "logo")
{
r.WriteFile("Logo1.png");
}
else
{
r.WriteFile("Flower1.png");
}
That should allow me to see different things depending on URL that I enter in a browser, for example:
http://www.dotnetperls.com/?file=logo
http://www.dotnetperls.com/?file=sth_else_eg_flower
The problem I am facing now is how, knowing just http://www.dotnetperls.com/?file can I read what the all the assumed options of the file variable are? In this case it would be "logo" and anything else.
What I have in reality is http://www.somewebstie.com/somefile.ashx?somevariable=. I can Google up the string to get few results (i.e. http://www.somewebstie.com/somefile.ashx?somevariable=abcde or http://www.somewebstie.com/somefile.ashx?somevariable=xyz) thus I know it exists and is somehow searchable. I just would like to know all the other "abcde" and "xyz". If I try just http://www.somewebstie.com/somefile.ashx I get a singe line error saying that I am giving a wrong variable and I cannot see anything important in the source of the site.
What might be important here - I have zero knowledge about web technologies.
You can't get this information. Its all hidden in the code implementation. There is no published format (by default) that will show you all of the available options the code is looking for.
I am using file upload mechanism to upload file for an employee and converting it into byte[] and passing it to varBinary(Max) to store into database.
Now I what I have to do is, if any file is already uploaded for employee, simply read it from table and show file name. I have only one column to store a file and which is of type VarBinary.
Is it possible to get all file information from VarBinary field?
Any other way around, please let me know.
If you're not storing the filename, you can't retrieve it.
(Unless the file itself contains its filename in which case you'd need to parse the blob's contents.)
If the name of the file (and any other data about the file that's not part of the file's byte data) needs to be used later, then you need to save that data as well. I'd recommend adding a column for the file name, perhaps one for its type (mime type or something like that for properly sending it back to the client's browser, etc.) and maybe even one for size so you don't have to calculate that on the fly for each file (useful when displaying a grid of files and not wanting to touch the large blob field in the query that populates the grid).
Try to stay away from using the file name for system-internal identity purposes. It's fine for allowing the users to search for a file by name, select it, etc. But when actually making the request to the server to display the file it's better to use a simple integer primary key from the table to actually identify it. (On a side note, it's probably a good idea to put a unique constraint on the file name column.)
If you also need help displaying the file to the user, you'll probably want to take the approach that's tried and true for displaying images from a database. Basically it involves having a resource (generally an .aspx page, but could just as well be an HttpHandler instead) which accepts the file ID as a query string parameter and outputs the file.
This resource would have no UI (remove everything from the .aspx except the Page directive) and would manually manipulate the response headers (this is where you'd set the content type from the file's type), write the byte stream to the client, and end the response. From the client's perspective, something like ~/MyContent/MyFile.aspx?fileID=123 would be the file. (You can suggest a file name to the browser for saving purposes in the response headers, which you'd probably want to do with the file's stored name.)
There's no shortage of quick tutorials (some several years old, it's been around for a while) on how to do this with images. Just remember that there's essentially no difference from the server's perspective if it's an image or any other kind of file. All the server needs to do is send the type in the response headers and write the file's bytes to the client. How the client handles the file is up to the browser. In the vast majority of cases, the browser will know what to do (display an image, display via a plugin a PDF, save a .doc, etc.).
i use such code
string.Format("<img src='{0}'><br>", u.Avatar);
u.Avatar-it's like '/img/path/pic.jpg'
but in this site i can upload new image instead old pic.jpg. so picture new, but name is old. and browser show OLD picture (cache). if i put random number like /img/path/pic.jpg?123 then works fine, but i need it only ufter upload, not always. how can i solve this?
string imgUrl = _
string.Format("<img src='{0}?{1}'><br>", _
u.Avatar, _
FunctionThatLookupFileSystemForItsLastModified(u.Avatar).Ticks.ToString());
Instead of linking to the images directly, consider setting up a generic HTTP handler to serve the images.
MSDN: HTTP Handlers and HTTP Modules Overview
Stack Overflow: How to use output caching on .ashx handler
Append DateTime.Now.Ticks to the image url:
string imgUrl =
string.Format("<img src='{0}?{1}'><br>", u.Avatar,DateTime.Now.Ticks);
EDIT: I don' think this best practice are even a practice I would use. This is just a suggestion given the limited information given in case the Random implementation isn't truly Random.
Read your post again,,, sorry for general answer.
To workaround it do following
On Application_Start create a Dictionary with uploaded images save it on Application object, set it to null. Once you upload an image add it to this Dictionary. Wrap every place avatars appear on your website with function that evaluates image in Dictionary if found return imagename.jpg?randomnumber and then delete it from a Dictionary else return just an imagename.jpg.
This is going to be heavy because you will need to check each image in Dictionary but this will do exactly what you need.
You can set cache dependancy using the System.Web.Caching.CacheDependency namespace.
This can set the dependancy on the file uploaded, and will release the cache for that file automatically when the file changes.
There are lots of articles and stuff on MSDN and other places so I will not go into details on all that level of detail.
You can do inserts, deletes and other management of cache using the tools available.
(and this does not require you to change the file names or tack on stuff - it knows by the file system that the file changed)
I am allowing users of the admin panel of my website to upload photos, its a simple process where I check the validity of the image and then save it to a folder, then I also have to record a couple of database records for that image to be able to retrieve it later, my saving function is as follows...
The function that uploads and saves the picture in the folder with a name i construct in another function:
My_HTMLInputFile.PostedFile.SaveAs(HttpContext.Current.Server.MapPath("~/photos\" & pta.FileName))
And the function that creates the database record for that same picture:
Public Function InsertPhoto() As Integer
Dim pta As New GKPTableAdapters.tblPhotosTableAdapter
Return pta.InsertPhoto(PhotoCaption, PhotoDescription, ("http://www.myURL.com/photos/" & FileName), IsDefault, IsPicture)
End Function
Now I know that what I am doing is full of best-practices violations, so please point me out to what I should do, keep in mind that the users might delete the pictures later, so I wanna make sure that I can delete the database and file of the picture, and the whole issue of the path is confusing me :P
Thanks in advance.
Something I've noticed right off the bet is that you are hardcoding the FULL PATH to the image.
I'd just store the image name, and then prepend the relative path when i display it in the application
If you allow your users to delete the files via your application, you should delete the record in the database, and then delete the file itself by using File.Delete method
You may also want to look at your file name generation. If you use an md5 hash of the image data as the file name, for example, you can prevent people from uploading duplicate images and you also don't have to think of a way to generate "unique" names for the images.
Exposing your photos directory directly to the internet may be a bad idea if there are images in there that the public should not see and your naming policy is predictable. People will start guessing image URLs and stumble upon something they are not allowed to see.