I am new in java web application, (Java EE, JSF).
I tried to change the contents of a csv file on the client computer with a java web application, so that the client does not have to download a new file, because the file is already in the set to be used for applications in the client. so I just wanted to rewrite the csv file.
Could it be done in java web application? If yes, please give me an example. I am very grateful if there is a better solution.
No, absolutely not. You can't change the contents of a file on a client computer from a web browser. The best you could do is have them upload a version of a file and then send them another version to download. Giving write access to the filesystem would be a massive security hole.
Place the CSV on a network share somewhere. The client can edit it, the back-end server can edit it. Requires more infrastructure, of course, but may work depending on the type of application.
Not that I think this is what you want, but if the 'client computer' was also acting as the server (i.e. was the host running Jetty/Tomcat/whatever), then you could modify files on it using the java IO api.
Again, very likely not what you want, just saying it would work.
Related
I would like to write a web application (in django) which scans the client/remote computers (assumption is windows) and retrieve the list of software's(mainly browsers) installed. Looking for suggestions to implement it.
Is this possible without asking the user to download any scritps/exe's?
If so, is it possible via java script?
I am planning to use python/django to write the entire app. Any input would be much appreciated.
EDIT : Comments on feasibility in java also much appreciated
Short answer: No, it is not possible
Long answer: This is something that any sane (operating) system designer / administrator would try to prevent - scanning of local system by a web page. However, you could use a plug-in component, such as a java applet, to do so - but in practice you probably would need to handle each client platform (OS) separately, since each of them has a different way of storing the information of installed software
You want to access the data from the client side so from the conceptual/logically its not good to access the client system. You have to use some medium which run on client side on behalf of server.
JavaScript and JavaApplet is good in this. You can get the data by JavaScript or Applet and in backend you can send data to the server.
You cannot do this unless you have some signed control installed on the client computer; or have them download a program which runs (separate from a browser) and sends the information to your server, where your django app can access it.
This is not possible using javascript (as it runs in a sandbox).
"Scanning" a client from a server may be possible if you break their security or get them to break it for you through some extension (see windows udate, for example). Either way, it's evil.
I have exported some Processing code (outputs sensor data to a textbox) to an
applet that includes the .jar and .html files. I have tried to insert this html on a
simple website that I created and the java applet doesn't work. Do I have to somehow
modify the html? I know that the .jar files are already in the same directory and
are referenced appropriately in the exported html code. Is there a better approach
to posting to a website? Thank you
I don't think that it is possible, due to security restrictions on applet communication.
More than likely you will have to write a small client/server program using sockets.
The idea would be to transmit the the output from your locally running client application to your applet(server) which would receive and display the data.
You could use any language with socket support obviously(Flash, PHP, etc.), but I assume you will want to stick with Java.
I'm looking into a small project just now where we have a need for a very very basic news article system. Ideally, this is a simple XML file that will be written to with some news, and then parsed to display on the homepage. This file is on the server, of course.
My question is how to allow a client browser to write to this XML file, given that the server will not have PHP enabled?
I know of TiddlyWiki which uses a .JAR file to allow the writes, but are there any other methods I should try?
Since FTP seems to be enabled/supported, your best bet is to create an applet which does the job. FTP connectivity can fairly simple be done by Apache Commons Net FTPClient. Your only problem is that the FTP connection details needs to be embedded in the applet somehow and that anyone with bad intent can extract it from the applet's source code since applets are downloaded into the client machine.
Without some serverside code, you will not be able to write files to the server.
You need a "PHP/Java/FTP-Server/something else"-backend serverprocess to take the content and write it to a file.
Apache supports HTTP PUT, and some browsers support it in XMLHttpRequest. So long as you are willing to limit editors to browsers that support it, you could use that without installing additional software on the server or using a plugin on the client.
FTP would definitely work, depending on how well the user doing the updates is familiar with it.
If the upload solution needs to be browser-based, you could perhaps run an FTP applet and have the user remember the connection details/password.
We have a web application which which is deployed and used within an intranet. The application reads in text files from a specified location on the web server itself.
Now we have a requirement of reading in text files from other machines as well, so i'm exploring possible options to implement this. Possible options i've been thinking of are:
Maybe start a ftp server on each local machine and then write a servlet to ftp given machines n read-in data.
Maybe run some utility program thats would read in file contents and push it back to the server using xml etc ?)
Ne help about above/or new ideas would be highly appreciated!
Technologies i'm using are :
Tomcat/Struts/JSP/AJAX.
P.S i want to handle non NFS situations as well!
Thanks,
Abhishek.
apart from the fact that I don't know whats the purpose of the application you're building, and knowing it is a Web-app, why not have users upload the specific files you want to process?, or even better, if they are configuration files, you might put them all in one single location, let's say just one machine. That might be better than having your app stuck just because some machine is not accessible.
I have an idea for you.... You may expose web service on each machine where from you want to get logs.These web services will read log files and send to your web application in bytes. You web application will call these service periodically and will take latest data. your entire system would work like a distributed system. you need to ensure that log file should generate with the name in uniform format - for eg.. log-24-12-2010.log or log24122010.log (if your log file generates on daily basis) - so that web services can form the right name of log and access it.
I recommand you to use RESTful web services because they are pretty easy for such purposes. Use JAX-RS APIs to develop such services.
I hope you would get my idea a little bit.
~~ Priyanjan
I am really looking for implementation advice as I have entered a new realm that I am not familiar with.
At the simplest level, I would like to find a way that I can read/write to a users machine from my web server. For this to work, I think I will have to install some sort of "plugin" on the users machine which can receive (or poll?) the server for instructions.
The above is the line of thought that I currently have, maybe using JAVA to do this. This needs to work on Linux, Mac and Windows OS.
I am really looking for advice on the above, is it a good idea? Is there a better way of doing this? Is there something out there already that I can build on top of?
I really appreciate all input and advice as this is something I have not done before.
Thanks all
For Java, you could launch a client application via Java Web Start that will be able to perform a limited set of operations on the file system.
If this is too restrictive, then you would need to provide a link to a download of a client application that would be installed / executed on the user's desktop machine.
I'm assuming you want to read and write specific files on the users' machine that are not normally accessible (i.e. not temp files, or files in a sandbox). And you want to do this from your webserver.
As you looking for cross platform, I'd go with java. Given that your needs are simple (read/write files from remote commands) you could probably target JRE 1.4, which is now many years old, but is installed on ca. 98% of desktops (source).
Here's an overview of how you can approach this:
Create a java applet or Java Web Start application that fetches a list of commands from a URL. The URL can contain any specific identification that you need to identify the machine, such as the users ID (see below for alternatives.)
Your webserver generates the list of commands that the applet should execute - create file, read file, write file and sends these as the response.
Sign the applet/application, so that it can escape the restrictions of the sandbox. To do this, you need to obtain a certificate. More on this later.
Inform and educate your users about what the applet is doing. E.g. a page on your site about why they are being asked to trust your certificate and what the implications are.
You can implement this as an applet or an application, the bulk of the work is pretty much the same. I talk about applet, but remember it applies equally to application.
In more detail:
The applet requests a list of commands from a URL. To hamper attempts at using your applet on another malicious site, you should use HTTPS to fetch the list of commands so that the server is authenticated. The URL should be hard-coded into your applet, so that any attempts to change this will break the signing. How you communicate the commands to the applet via the URL is up to you, e.g. you can use XML or use RMI and simply send over the list of commands as an object.
I mentioned using the userid to identify the machine - using the machine's MAC address is also a possibility. See how to get the mac address of the host.
Once you have the list of commands, your applet executes these using java file I/O apis. See File, FileReader/FileWriter in the javadocs. You include appropriate logging so the applets actions can be audited later if necessary. Once the applet has executed the commands, it sends the result of the commands back to the server, either as a POST operation, or another RMI method call, if you settle on RMI.
If you want to continually send commands from the server, then the applet can poll the URL/invoke the RMI method regularly. A Timer can help with this.
With communciation errors, it will be necessary for the client to request the list of commands more than once. Thus each time you produce a list of commands from the server, it is given an id. The server gives out the same list with the same id until it receives acknowledgement from the applet that the commands have been executed.
To sign the applet, you should obtain an rsa certificate from a certficiate authority. You can self-sign, but then you are opening the door to others modifying your app and impersonating your certificate. Details on obtaining and using certificates are given here.
If you don't know java, then all of this may not make a huge amount of sense, and it's not a trivial project to get started on, particularly considering the implications for your users if your implementation has holes and defects.
It may be wise to exercise caution: although you can do this, doesn't necessarily mean you should. I imagine that most expert users would frown on the use of this app, and would not accept the certificate. And then there is culpability - if your app accidentally deletes a critical file through a bug, misconfiguration, human error etc, how will you be prepared for that?
For the user, a web browser plugin may be the easiest, since the user won't have to manage yet another running application, however it has its limitation such as having to develop a plugin for each browser. In addition, the user would need their browser running.
You could have the user install a desktop application, which they would have to keep running, so installing it as a service might be ideal.
You could also use a plugin as a wedge between the web browser and a desktop application, which is how Flash works.
To really know you will have to answer the "why" question, why do you wan tot do this.
If you are just trying to store some state on the user's machine that you need to have locally then for small things you can fall back on cookies, or for larger needs you can use the new Web Database features in HTML5 http://dev.w3.org/html5/webdatabase/
If you need to access specific files then you are actually going to have to circumvent the security sand boxing that Java does when run on a webpage. I will leave that for others to go into, I don't know how to do it off hand myself.
In my opinion, Applet will be a better solution. I have made one applet which downloads a zip file from the server on client machine into temp folder, extracts the zip file into a directory specified by client (browser user) and then deletes the zip file.
thanks.
The lowest hanging fruit might be to provide WebDAV access through your web server to a given set of files, as this allows the users to see the files as a part of their usual filesystem with all their usual tools. You then do not have to do all that functionality.
Looks like Slide can deploy on Tomcat, and JBoss has ModeShape.
Will that be useful enough?