I have a created and signed an applet where i need to read from C: of the client computer. When i run the applet from netbeans am able to read C: But when i embed that applet to the browser it cant find the C: drive.
How can i achieve this?
According to Oracle documentation Sandbox applets cannot access client resources such as the local filesystem (...)
Also, privileged applets do not have the security restrictions that are imposed on sandbox applets and can run outside the security sandbox.
Therefore, what you need is a privileged applet.
Since you have already signed the applet and still have problems you can try running the code as privileged code as presented here.
Note: Signed applet will request trust from the user, usually in a little dialog box in the browser. Maybe check if you have set an "always block" setting in your browser in the past ?
Related
I have to call .exe file on client.
But I dont understand sevler-client communication using Applets.
So few Q:
1.Can I do my task using Applets?
2.Does applets jar methods called on server?
Thanks in advance.
Applet does not maintain a state-full communication between client and server.
It is a Java application that runes inside the browser and has an access to a local system resources (if signed) and existing browser session, i.e. can use the same cookies to perform HTTP calls within the same Server-Side session.
1) Yes, you can do you task in Applet as in any other java application, however, in case of Applet it must be signed with the digital signature: http://www.oracle.com/technetwork/java/javase/tech/java-code-signing-1915323.html#60
2) No. All the classpath dependencies Applet may have, will be downloaded and cached on the client machine. See http://docs.oracle.com/javase/tutorial/deployment/deploymentInDepth/index.html
File system access is often not allowed as applets can (should) run in a sandbox limited-privileges environment. So running an exe file is possible only if the applet has proper permissions. Typically they are given such permissions when signed.
That being said, try not to use applets and write proper Java applications instead. You can always wrap the Java app in an applet, so that it is started from the applet.
Not so sure what you mean by the second question.
I've implemented a Java package with functionality to operate a POS printer and cash drawer connected to the workstation via USB. I've also implemented an applet to utilize the functionality of this package with the hopes of having it invoked by a POS website.
When the applet is run from within Eclipse, all goes well. When the applet is run from within a browser it seems that my package is unable to access the peripherals connected via USB. I get an error from the third party (JavaPOS) code stating:
jpos.JposException: The device
communications channel could not be
opened, check the device and retry.
The applet is signed with a self-cert. I'd post some code but the error is thrown from somewhere buried in manufacturer-specific drivers for the POS printer in use.
I'm assuming the issue is that, from within the browser sandbox, the applet does not have access to the peripherals connected via USB.
Could this be the case? If so, is there anyway to access USB peripherals from within a signed Applet?
If an applet can't access USB peripherals, how could a web site invoke code that can?
Do signed java applets have access to USB peripherals when run in the browser sandbox?
To address this specific question (and avoid the specific technologies involved in the comments following), yes Signed Java Applets have access to USB Peripherals. The "sandbox" is what you have capability to "break out of" when you run a signed applet.
But for security reasons, simply signing the applet does not automatically give access to items outside of the sandbox.
PrivelegedAction seems to be the preferred method for accessing privileged system components, such as the printer. More about these privileged actions is provided by Oracle here: http://docs.oracle.com/javase/7/docs/api/java/security/AccessController.html
In addition, there are several consideration when doing something like this from a web browser as Java cares where the action originates from.
public function writeFile() {
...
FileWriter fw = new FileWriter(...);
...
}
public void init() {
writeFile();
}
For example, if you were to write a file to the filesystem (i.e. $HOME/Desktop/text.txt) using the FileWriter class in the applet init() method, a Signed Applet would generally allow it. Wrapping this into a PrivilegedAction would be better, and checking permission first using AccessController.checkPermission(...) would be ideal.
However, FileWriter gets blocked when it's called directly from JavaScript (instead of from init()):
var myapplet = document.getElementById('myapplet');
myapplet.writeFile(); // Blocked by Security Framework
To circumvent this issue, some chose to use PrivelegedAction, however if the action takes a long time, you'll notice it blocks the UI, which is very bad practice in a web page (and can deadlock the browser).
public void init() {
...
AccessController.doPrivileged(new PrivilegedAction() {
public Object run() {
writeFile();
return null;
}
});
...
}
Furthermore, your question asks specifically about accessing a USB peripheral, which is generally done by iterating through the Human Interface Devices. HID is not something Java directly supports natively (yet, as of writing this/JRE7). So yes, a signed applet CAN talk to your USB peripherals, but you would need to use some form of Java Native Interfacing (JNI) to properly "access" them. JNI can be a mess to support cross-platform (i.e. distributing DLLs and SOs with your JAR) so...
What most Java Applets do is access the locally installed printers and use the standard Java Printing libraries. This is how we do it over at the qz-print project and you're free to review our source code here: https://github.com/qzindustries/qz-print/tree/master/qz-print/src/qz which uses threads fired by init() and boolean flags to fire all privileged functions.
I am not sure of the answer to your question, but have an experiment that should shed further light on the matter.
In the opening lines of the Applet.init() call System.setSecurityManager(null). Then try to connect to the USB.
If the applet is trusted, the call to setSecurityManager(null) will succeed, and remove the last remnants of the SecurityManager. (Yes, even trusted applets have a security manager, it is just much less restrictive that the security manager for sand-boxed apps.)
If the USB is now discovered, it indicates a change in the trusted security manager. There have been a number of such changes in recent times.
Note that I am not suggesting putting code like this into production. If your applet is running in the same JRE as other applets, nullifying the SM could also elevate the privileges of the other applets.
I had a similar problem with an Epson TM-H6000III on XP and Win7 32bit using JRE 1.6. Administrators could use the device, but "Users" could not. Java console was reporting:
Sep 23, 2011 3:38:47 PM com.xxxx.printer.epson.EpsonPrinter findPrinter
INFO: Error opening PrinterIII: jpos.JposException:
Could not connect to service with logicalName =
PrinterIII: Exception.message=Property or stream open error.
It appears the JRE installation had permission issues. Reinstalling JRE quickly cleared the problem.
I received feedback from the Star Micronics team that their '...javapos drivers do not support web browser printing.'
BTW, System.setSecurityManager(null) turned out to be a great way to disambiguate any issues I was having that seemed to be related to security. Thanks Andrew.
Is it possible to create a web-chatting application using java Applet ??
As far as I know, using Java Applet we cannot access Web Server due to Sandbox restriction.
But I'm not very sure about this ..
A sand-boxed applet can 'phone home' to its own server with no problems. It is only accessing other servers that requires trust.
as far as I remember we can access server from which we downloaded this applet without problems. Another opportunity is to try to sign the code to make it trusted.
I have a java applet that is downloaded to a user's browser when they visit a webpage and allows them resumable file uploads to my server. Obviously, this requires the applet to access the user's hard disk, which I understand is outside the regular sandbox applets can run in. The user sees a security warning popup which asks for their permission to allow this applet to run.
I have signed the applet using verisign and the link from where is applet is fetched is over SSL with a versigned cert. None of these make the warning go away.
Is there a way to make all warnings go away? Can anyone explain what is going on behind the scenes?
JNLP has a FileOpenService which allows the untrusted Java Webstart applications to show a File Open dialog to the user and access the file the user selected:
http://docs.oracle.com/javase/1.5.0/docs/guide/javaws/jnlp/javax/jnlp/FileOpenService.html
You can't avoid this message, it would be a security issue if you could.
Granting Applets Permission
If you tried to run the applet example, you undoubtedly saw errors when you clicked the Click Me button. This is because the Java 2 Platform security does not permit an applet to write to and read from files without explicit permission.
An applet has no access to local system resources unless it is specifically granted the access. So for the FileUIAppl program to read from text.txt and write to text.txt, the applet has to be given the appropriate read or write access permission for each file.
Access permission is granted with a policy file, and appletviewer is launched with the policy file to be used for the applet being viewed.
What you can do is having a configuration (a policy file) to allow this applet to use some files. But you would have to do this manually (for obvious security reasons). Check the link below.
Resources :
oracle.com - Applets, File Access and Permissions
i am doing a master project on how java applet works with web browsers.Can anyone give me details or any link that can be useful.How the web browser interacts with the java applet.
Download the source of Mozilla (Firefox, e.g.)
Read the code that integrates the JRE for applets.
Ask more questions when specific issues arise.
Maybe a simple answer will be enough and it won't require reverse-engineering Mozilla.
Until recently, applets did not interact much with the browser. The browser sent only 'start', 'stop' and 'resize' events to the applet and the applet could order the browser to open new web pages. With the Java 6 update 10, there is a possibility to call Applet functions from JavaScript and to call JavaScript from an Applet, as long as they are on the same page.
The browser creates a 'sandbox' to run the applet. The sandbox limits the access rights of the applet (e.g. applet can connect to TCP ports only on the web server, cannot access files directly on the client file system, etc.). Besides these limitations, an applet is like an autonomous application running on the client box.
You can find info on applets at 'http://java.sun.com/applets/' and 'http://java.sun.com/docs/books/tutorial/deployment/applet/index.html'