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How to create a file in java without random numbers getting added to the filename and delete after use?

I have to create a temp file in the /tmp directory the code that I am using is adding random numbers to the filename. I have to use the name of the file in order to do something. With the random number, I am not able to use that file. The code I wrote is :
File dir = new File("/tmp");
String prefix = "temp";
String suffix = ".txt";
File tempFile = File.createTempFile(prefix, suffix, dir);
After using the file with the correct file name I also have to delete it how can I do that?

If you need to access the File again, you can store the path of the file to be accessed at another time.
You can get the absolute path file using:
tempFile.getAbsolutePath();
To answer your question about deleting the file after you are finished using it, you can either use the detete() or deleteOnExit() methods of File.

If your code needs a predictable filename, and you want that file to be cleaned up automatically when the program ends, don’t use a temp file (they have a random name - it’s just how they work) but rather just use deleteOnExit() with a regular file:
File file = new File("some/filename.ext");
file.deleteOnExit();

How to avoid delete the Temp files using java?

I have a simple code to generate the temp files and store the some values(I don't want to store the files in normal storage area)
In future, I want to use that file and get the data from that file (its not a problem if the user manually delete the files).
But I don't want to delete the files automatically. when read this link, I get some information, generally temp files not deleted
when you explicitly call deleteOnExit() but when my JVM finish the work temp file deleted automatically.
//create a temp file
File temp = File.createTempFile("demo_", ".txt");
String path = temp.getParent();
//count the file which names starts with "demo"
File f = new File(path);
File[] matchingFiles = f.listFiles(new FilenameFilter() {
public boolean accept(File dir, String name) {
return name.startsWith("demo") && name.endsWith(".txt");
}
});
// Print count array elements
System.out.println("Length : " + matchingFiles.length + " ");
Here I never call the deleteOnExit() (but file delete automtically)OR JVM automatically delete the file? By the way its deleted automatically if is it possible
to avoid deleting the file? or any other ways to do my requirement?

File.createTempFile only creates files with unique names, other than that they are just regular files. They are not deleted automatically. It is explained in File.createTempFile API: This method provides only part of a temporary-file facility. To arrange for a file created by this method to be deleted automatically, use the deleteOnExit method

How to specify a directory when creating a File object?

This should be a really simple question but Google + my code isn't working out.
In Eclipse on Windows, I want my program to look inside a certain folder. The folder is directly inside the Project folder, on the same level as .settings, bin, src, etc. My folder is called surveys, and that's the one I want my File object to point at.
I don't want to specify the full path because I want this to run on both of my computers. Just the path immediately inside my Project.
I'm trying this code but it isn't working - names[] is coming back null. And yes I have some folders and test junk inside surveys.
File file = new File("/surveys");
String[] names = file.list();
for(String name : names)
{
if (new File("/surveys/" + name).isDirectory())
{
System.out.println(name);
}
}
I'm sure my mistake is within the String I'm passing to File, but I'm not sure what's wrong?

In your question you didn't specify what platform you are running on. On non-Windows, a leading slash signifies an absolute path. Best to remove the leading slash. Try this:
File file = new File("surveys");
System.out.println("user.dir=" + System.getProperty("user.dir"));
System.out.println("file is at: " + file.getCanonicalPath());
String[] names = file.list();
for(String name : names)
{
if (new File(file, name).isDirectory())
{
System.out.println(name);
}
}
Make sure the in your run configuration, the program is running from the projects directory (user.dir = <projects>)

Make sure that your file is a directory before using file.list() on it, otherwise you will get a nasty NullPointerException.
File file = new File("surveys");
if (file.isDirectory()){
...
}
OR
if (names!=null){
...
}

If you checked the full path of your file with
System.out.println(file.getCanonicalPath())
the picture would immediately become clear. File.getCanonicalPath gives you exactly the full path. Note that File normalizes the path, eg on Windows "c:/file" is converted to "C:\file".

Creating temp Folder in java

I need to create a temp folder where I can put some temp files for processing. I am not sure if I would have Read/Write access in the folder where my application jar would be executed.
Is it best to create the temp folder in the System's temp Directory ?
When I use the File tempFolder = File.createTempFile("fooo",""); Where is the folder created ? When I cd into the temp folder in my mac I am not able to see a folder by name fooo.

You are almost done with create tempfolder, see this:
import java.io.File;
import java.io.IOException;
public class TempFolder {
public static void main(String[] args) throws IOException {
File file = File.createTempFile("my_prefix", "");
System.out.println(file.getAbsolutePath() + " isFile: " + file.isFile() + " isDir:" + file.isDirectory());
file.delete();
file.mkdir();
System.out.println(file.getAbsolutePath() + " isFile: " + file.isFile() + " isDir:" + file.isDirectory());
}
}
first createTempFile will make a real file for you, just remove it and make a directory using the same name.
I use osx, too. My result is:
/var/folders/aQ/aQLNlFLOF28xewK2A7i0X++++TM/-Tmp-/my_prefix8720723534029791962 isFile: true isDir:false
/var/folders/aQ/aQLNlFLOF28xewK2A7i0X++++TM/-Tmp-/my_prefix8720723534029791962 isFile: false isDir:true

When you call File tempFolder = File.createTempFile("fooo","") it will return a File object. You can then call
tempFolder.getAbsolutePath();
linked here
and this will give you the location. At a guess I would say it was in /tmp/ which you can get to in from the Finder
choose Go to Folder
from the Go menu type /tmp/
This will take you to folders that are hidden as well.
I know in windows you can type %temp% in the windows explorer address bar to take you to the temp directory. I am not sure if there is anything like this on OSX

You should use File.createTempFile().
Where it gets created depends on your environment. Try printing out the full path of such a file if your are interested.
On my Mac (10.8.2) the system Java created a file in "/var/folders/qj/v2cqt0t91h1b4rzj1s0pc_780000gp/T/" just now.

Try printing out tempFolder.getAbsolutePath(). It should give you the path where this folder is created.

Java File.renameTo(File) not working

I'm trying to list a directory's contents, and rename certain files.
public void run(String dirName) {
try {
File parDir = new File(dirName);
File[] dirContents = parDir.listFiles();
// Rename if necessary
for(File f : dirContents) {
System.out.println("f is:\n" + f.toString());
String name = f.getName();
String subbedName = name.replaceAll("\uFFFD", "_");
System.out.println("\n" + "name = " + name + ", subbedName = " + subbedName + "\n");
if(!name.equals(subbedName)) {
File newFile = new File(f.getParentFile(), subbedName);
System.out.println("newFile is:\n" + newFile.toString());
if(!f.renameTo(newFile))
System.out.println("Tried to change file name but couldn't.");
}
}
}
catch(Exception exc1) {
System.out.println("Something happened while listing and renaming directory contents: " + exc1.getMessage());
}
}
When I run this, I get "Tried to change file name but couldn't." I don't believe that Java is considering these files to be "open", so I don't think that's the reason. I've even ran chmod 777 myDir where myDir is the value of the dirName string passed into the run method.
What am I missing here? Why won't Java rename these file(s)? These are CentOS machines.
Edit: Added printouts for both f and newFile, which is as follows:
f is:
/root/path/to/mydir/test�.txt
newFile is:
/root/path/to/mydir/test_.txt

You need to create your new File object with the full pathname of those files. So
String name = f.getName(); // gets the name without the directory
should likely be:
String name = f.getAbsolutePath();
(your search/replace may need to change)

The problem is that f.getName() returns the last name component of the path that is represented by f. You then massage this String and turn it back into a File. But the File now represents a path relative to the current directory, not the directory containing the original path.
As a result your code is actually attempting to rename the files from dirName into the application's current directory. That could fail because files already exist in the current directory with those names, or because the dirName and the current directory are in different file systems. (You cannot rename a file from one filesystem to another ... you have to copy it.)
Please note that a File in Java represents a pathname, not a file or a folder. In your code, the f objects are the pathnames for file system objects (either files or folders) in the directory denoted by the String dirname. Each of these f objects will have a directory part.
There is more than one way to fix your code; for example
change name = f.getName() to name = f.toString()
change new File(subbedName) to new File(f.getParentFile(), subbedName)
I have an alternative / additional theory.
The pathname of the file containing the \uFFFD character is coming out as "mojibake"; i.e. the kind of garbled text that you get when you display encoded text using the wrong encoding. And since we are seeing 3 characters of garbled text, I suspect that it is attempting to display the UTF-8 rendering of \uFFFD as Latin-1.
So my theory is that the same think is happening when the File.renameTo method is converting f to the form that it is going to provide to the system call. For some reason that is no clear to me, Java could be using the wrong encoding, and as a result producing a "name" for the original file that doesn't match the name of the file in the file system. That would be sufficient to cause the rename to fail.
Possibly related questions / links:
File name charset problem in java
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4733494 (Note that Sun decided this was not a Java bug, and most of the "me too" comments on the bug report are from people who do not understand the explanation ...)

f.getName(); only returns the name of the folder, not the full path. So subbedName becomes a relative path file. Try something with f.getCanonicalPath() instead.