couldn't find relevant question on SO I'm asking a new one. I can create a file using FileWriter class, but it requires to specify the path for that file (physically creates the file). What I want to achieve is to create a file like in-memory, without specyfying the path or saving it on the disk and then upload it into the online form with selenium webdriver, is that somehow possible?
But there also is another problem, html fileUpload element will accept the path such as:
driver.findElement(By.id("Content_CV")).sendKeys("C:\\Users\\name\\Documents\\my_cv.pdf");
but will it accept the file itself? Probably not, so assuming that some of you knows how to create a file without saving it on the disk, would there be a way of providing path to that file anyway (given its virtual location)?
I'm trying to figure it out and I did some google research, yet here I am. Thanks for any attempt of help :)
If your question is just how to create a temporary file without caring about how to name it and where to create it without overwriting existing files, then you can simply use File.createTempFile. This will create an actual new temporary file on disk in the directory designated by the operating system for that purpose. You might also want to have a look at File.deleteOnExit.
If you are not looking for a java solution, you can simply create the file in a RAM drive
Software for this exist for all mayor operating systems.
Have a look at the wikipedia link above for more information.
Related
Linux Api has O_TMPFILE flag to be specified with open system call creating unnamed temporary file which cannot be opened by any path. So we can use this to write data to the file "atmoically" and the linkat the given file to the real path. According to the open man page it can be implemented as simple as
char path[1000];
int fd = open("/tmp", O_TMPFILE | O_WRONLY, S_IWUSR);
write(fd, "123456", sizeof("123456"));
sprintf(path, "/proc/self/fd/%d", fd);
linkat(AT_FDCWD, path, AT_FDCWD, "/tmp/1111111", AT_SYMLINK_FOLLOW);
Is there a Java alternative (probably non crossplatform) to do atomic write to a file without writing Linux-specific JNI function? Files.createTempFile does completely different thing.
By atomic write I mean that either it cannot be opened and be read from or it contains all the data required to be writted.
I don't believe Java has an API for this, and it seems to depend on both the OS and filesystem having support, so JNI might be the only way, and even then only on Linux.
I did a quick search for what Cygwin does, seems to be a bit of a hack just to make software work, creating a file with a random name then excluding it only from their own directory listing.
I believe the closest you can get in plain Java is to create a file in some other location (kinda like a /proc/self/fd/... equivalent), and then when you are done writing it, either move it or symbolic link it from the final location. To move the file, you want it on the same filesystem partition so the file contents don't actually need to be copied. Programs watching for the file in say /tmp/ wouldn't see it until the move or sym link creation.
You could possibly play around with user accounts and filesystem permissions to ensure that no other (non SYSTEM/root) program can see the file initially even if they tried to look wherever you hid it.
I have an app that accesses words from a csv text files. Since they usually do not change I have them placed inside a .jar file and read them using .getResourceAsStream call. I really like this approach since I do not have to place a bunch of files onto a user's computer - I just have one .jar file.
The problem is that I wanted to allow "admin" to add or delete the words within the application and then send the new version of the app to other users. This would happen very rarely (99.9% only read operations and 0.1% write). However, I found out that it is not possible to write to text files inside the .jar file. Is there any solution that would be appropriate for what I want and if so please explain it in detail as I'm still new to Java.
It is not possible because You can't change any content of a jar which is currently used by a JVM.
Better Choose alternate solution like keeping your jar file and text file within the same folder
I have been coding for about a month and I have found ways to adapt around ever problem but one. The problem as you can probably see by the title is how to make a way to make game saves. I am currently creating a very simple game that has about 5 classes of my code and maybe 2 of Java Swing GUI.
I know how I would like to go about the saving process but I have no idea how to do it in my code. How I would like to go about doing this is by making the code print a Number or Integer to a file to represent a Level. For example if you completed level 1 the number in the file would be 1. I have tried some templates for this but none of them work.
I understand how to write to a file but my problem is reading it from a jar or even creating a file then reading it from a place on the computer. I need to know how to find a file URL for different computers because some use Docs and Settings and other Users. Please could someone help.
Since the jar is read only, it can only contain the 'default settings'. See this answer for the general strategy to deal with such a embedded-resource.
Speaking of which (embedded resources) see the info. page for more details on how to access them.
Here is an example of storing and reading a Properties file from the 'current directory'.
As mentioned by #MadProgrammer though, it is safest to put the settings file into a (sub-directory) of user.home, as seen in this answer.
But a properties file is just one option. You might also serialize an object, or write the file in a custom format that your app. knows how to read, for the first two off the top of my head.
Besides 'serialize (in some form) in a File', there is also the Preferences API, or for desktop applications launched using Java Web Start, the PersistenceService. Here is a demo. of the service.
I need to know how to find a file url for different computers because
some use Docs and Settings and other Users
The System property user.home points to the user's home directory
File userHome = new File(System.getProperty("user.home"));
Is there any way in Java to write out to a temporary file securely?
As far as I can tell, the only way to create a temporary file (createTempFile) does't actually open it at the same time, so there's a race condition between file open & file write. Am I missing something? I couldn't find the C source code behind createFileExclusively(String) in UnixFileSystem.java, but I doubt it can really do anything since the file open occurs in the Java code after the temp file is created (unless it tries to do something with file locks?).
The problem
Between when the temporary file is created & you open it, a malicious attacker could unlink that temporary file & put malicious stuff there. For example, an attacker could create a named pipe to read sensitive data. Or similarly if you eventually copy the file by reading it, then the named pipe could just ignore everything written & supply malicious content to be read.
I remember reading of numerous examples of temporary file attacks in the past 10+ years that exploit the race condition between when the name appears in the namespace and when the file is actually opened.
Hopefully a mitigating factor is that Java set's the umask correctly so a less-privileged user can't read/write to the file and typically the /tmp directory restricts permissions properly so that you can't perform an unlink attack.
Of course if you pass a custom directory for the temporary file that's owned by a less-privileged user who's compromised, the user could do an unlink attack against you. Hell, with inotify, it's probably even easier to exploit the race condition than just a brute force loop that does a directory listing.
http://kurt.seifried.org/2012/03/14/creating-temporary-files-securely/
Java
use java.io.File.createTempFile() – some interesting info at http://www.veracode.com/blog/2009/01/how-boring-flaws-become-interesting/
for directories there is a helpful posting at How to create a temporary directory/folder in Java?
Java 7
for files use java.io.File.createTempFile()
for directories use createTempDirectory()
http://docs.oracle.com/javase/7/docs/api/java/nio/file/Files.html
Since Java 7 we have OpenOption.
An object that configures how to open or create a file.
Objects of this type are used by methods such as newOutputStream, newByteChannel, FileChannel.open, and AsynchronousFileChannel.open when opening or creating a file.
Of particular interest is StandardOpenOptions.CREATE_NEW.
Create a new file, failing if the file already exists. The check for the existence of the file and the creation of the file if it does not exist is atomic with respect to other file system operations.
So, you can do something like this:
FileChannel mkstemp() {
Path path = Files.createTempFile(null, null);
Files.delete(path);
return FileChannel.open(path, WRITE, CREATE_NEW);
}
Implementing the same template behaviour is left as exercise to the reader.
Keep in mind that on many systems, just because a file doesn't have a name doesn't at all mean it's inaccessible. For example, on Linux open file descriptors are available in /proc/<pid>/fd/<fdno>. So you should make sure that your use of temporary files is secure even if someone knows / has a reference to the open file.
You might get a more useful answer if you specify exactly what classes of attacks you are trying to prevent.
Secure against other ordinary userid's? Yes, on any properly functioning multi-user system.
Secure against the your own userid or the superuser? No.
I have a text file i want to include in my Android application, it is not a string file it is a standard text file. It contains data that defines the characteristics of a "map" that is drawn on a board. The file is not an XML file so i am unsure where i should put it or if this isn't good file structure for android? Are you suppose to do this? If you are then under what directory are you suppose to put them? How then are you suppose to access the file? I know how to use FileInputStreams and FileOutputStreams i just need to know how to access the file. All relevant answers are welcome and appreciated!
Use assets or raw folder in your android folders structure to keep that file. For more info read this
You have to put your file in the assets folder as Waqas said.
Now to access it you do it like that.
I give you an example using BufferedReader
BufferedReader reader = new BufferedReader(
new InputStreamReader(getAssets().open("YourTextFile.txt")));
Be careful. In my case, I don't know why for now, I cannot read text files bigger than ~1MB and I had to split them in multiple small files. It seems other had the same problem of file size but I didn't find any information about that on Android developer site. If any one knows more about this ....
FOLLOW UP
My problem with the 1MB was due to a know bug/limitation of earlier versions of Android. Since using recent versions of Android, that problem is not present anymore.
I would just like to add to the accepted answer (I don't have enough reputation to comment unfortunately.) The link there to the tutorial that explains how to set up the res/raw method or the assets method is mostly good, but there's actually a MUCH easier way. Look at the function described there called LoadFile. That function is rather verbose. Lets say all you need is an InputStream variable so that you can read and write to a file. Then delete everything after line 77! Also you don't need the resource id at all! You can use this function:
//get the file as a stream
iS = resources.openRawResource(R.raw.mygpslog)
Now all you have to do is return iS and you will have your much desired file handle.
For reference, the tutorial is right here -> http://www.41post.com/3985/programming/android-loading-files-from-the-assets-and-raw-folders