Develop Reference

How to get a random file from a random folder

This is not a duplicate of "Counting the number of files in a directory using Java", since the main question here is "How to get a random file from a random folder". Counting the number of files was just an optional question for improvement.
I have a folder "testfiles" in my project directory, which contains a lot of others folders. Those folders all have names like "alice-g" (firstname and then first letter from lastname). Each of those folders contains some other folders, not always the same number. And in each of those last folders, i got a bunch of files, all named with number ("1.", "2.", "3." and so on).
What i want to do is going into this "testfiles" directory, randomly select a folder, get his name, then randomly select another folder in it and finally select a random file in this folder (and get his name).
I have found this post which say we can pick a random file from a folder this way:
File[] files = dir.listFiles();
Random rand = new Random();
File file = files[rand.nextInt(files.length)];
This sound clear and easy to me. However, since all my files have "easy numbered names", i wonder if there is a way to do this without making a list of all files. Getting the total number of files in the directory should be enough to me, since their names are just number with a "."
Second, this solve the problem of selecting a random file, but not of selecting a random directory (and get his name).
EDIT:
I also found this post which says that a "good solution" (fast) to count the number of files OR directories in a directory is:
File hugeDir = new File("/tmp/huge-dir");
int numberFiles = hugeDir.list().length;
I totally didn't know that we could create a File object with a directory. Seems weird to me. However, i guess it can solve both of my question: to select a random directory and get his name, i do:
//Get a random client name according to directories names:
private static String getRandomClient() {
File testFiles = new File("testfiles"); //directory where all my testfiles are (in other directories)
Random rand = new Random();
String[] dirNames = testFiles.list(); //making a list() seems to be faster than making a listFiles().
File randomNamedDirectory = new File(dirNames[rand.nextInt(dirNames.length)]);
String randomDirName = randomNamedDirectory.getName();
return randomDirName;
}
Then i want to get a random file from a random directory from this client Directory:
//Get a random File Path from the client Directory:
private static String getRandomFilePath(String clientDirectory) {
File clientDir = new File("testfiles\\"+clientDirectory); //client Directory.
System.out.println(clientDir);
Random rand = new Random();
String[] dirNames = clientDir.list(); //This return null!?
System.out.println(dirNames);
File randomDirectory = new File(dirNames[rand.nextInt(dirNames.length)]);
int numberFiles = randomDirectory.list().length;
String randomFile = rand.nextInt(numberFiles) + "."; //All files are named with their number and a .
String filePath = clientDir + "\\" + randomDirectory +"\\" + randomFile;
return filePath;
}
The first function works well; however, in the second one, the list of Directories Names is null. Since it's just the same code as before, i don't understand why.

So, after some research, i found out that:
1. It seems that there is not really a better solution than making a list of the files. However, using list() instead of listFiles() seems to be a bit faster (see the post cited in the EDIT part of the question)
The "partial solution" i give in my question have some stupid mistakes in it (like, using \ instead of / ). Here is a "minimal and complete" solution:
.
import java.io.File;
public class main {
public static void main(String[] args) throws Exception{
String client = getRandomClient();
String filePath = getRandomFilePath(client);
File file = new File(filePath);
}
//Get a random client name according to directories names:
private static String getRandomClient() {
File testFiles = new File("maildir"); //directory where all my testfiles are (in other directories)
Random rand = new Random();
String[] dirNames = testFiles.list();
File randomNamedDirectory = new File(dirNames[rand.nextInt(dirNames.length)]);
String randomDirName = randomNamedDirectory.getName();
return randomDirName;
}
//Get a random File Path from the client Directory:
private static String getRandomFilePath(String clientDirectory) {
File clientDir = new File("maildir/"+clientDirectory); //client Directory.
System.out.println(clientDir);
Random rand = new Random();
String[] dirNames = clientDir.list();
File randomDirectory = new File(clientDir +"/" + dirNames[rand.nextInt(dirNames.length)]);
int numberFiles = randomDirectory.list().length;
String randomFile = rand.nextInt(numberFiles) + "."; //All files are named with their number and a .
String filePath = randomDirectory + "/" + randomFile;
return filePath;
}

Unable to save the uploaded file into specific directory

I want to upload files and save them into specific directory.And i am new to files concept.When i uploading files from my page they are saved in another directory(C:\Users\ROOTCP~1\AppData\Local\Temp\multipartBody989135345617811478asTemporaryFile) and not in specified directory.I am unable to set it.Please help me in finding a solution.For all help thanks in advance.
public static Result uploadHoFormsByHeadOffice() throws Exception {
Logger.info("#C HoForms -->> uploadHoFormsByHeadOffice() -->> ");
final String basePath = System.getenv("INVOICE_HOME");
play.mvc.Http.MultipartFormData body = request().body()
.asMultipartFormData(); // get Form Body
StringBuffer fileNameString = new StringBuffer(); // to save file path
// in DB
String formType = body.asFormUrlEncoded().get("formType")[0];// get formType from select Box
FilePart upFile = body.getFile("hoFiles");//get the file details
String fileName = upFile.getFilename();//get the file name
String contentType = upFile.getContentType();
File file = upFile.getFile();
//fileName = StringUtils.substringAfterLast(fileName, ".");
// path to Upload Files
File ftemp= new File(basePath +"HeadOfficeForms\\"+formType+"");
//File ftemp = new File(basePath + "//HeadOfficeForms//" + formType);
File f1 = new File(ftemp.getAbsolutePath());// play
ftemp.mkdirs();
file.setWritable(true);
file.setReadable(true);
f1.setWritable(true);
f1.setReadable(true);
//HoForm.create(fileName, new Date(), formType);
Logger.info("#C HoForms -->> uploadHoFormsByHeadOffice() <<-- Redirecting to Upload Page for Head Office");
return redirect(routes.HoForms.showHoFormUploadPage());
}
}
I really confused why the uploaded file is saved in this(C:\Users\ROOTCP~1\AppData\Local\Temp\multipartBody989135345617811478asTemporaryFile) path.

You're almost there.
File file = upFile.getFile(); is the temporary File you're getting through the form input. All you've got to do is move this file to your desired location by doing something like this: file.renameTo(ftemp).
Your problem in your code is that you're creating a bunch of files in memory ftemp and f1, but you never do anything with them (like writing them to the disk).
Also, I recommend you to clean up your code. A lot of it does nothing (aforementioned f1, also the block where you're doing the setWritable's). This will make debugging a lot easier.

I believe when the file is uploaded, it is stored in the system temporary folder as the name you've provided. It's up to you to copy that file to a name and location that you prefer. In your code you are creating the File object f1 which appears to be the location you want the file to end up in.
You need to do a file copy to copy the file from the temporary folder to the folder you want. Probably the easiest way is using the apache commons FileUtils class.
File fileDest = new File(f1, "myDestFileName.txt");
try {
FileUtils.copyFile(ftemp, fileDest);
}
catch(Exception ex) {
...
}

Attempting to append number chars in a filename to a new file

I am attempting in Java to grab a file name, select the first eight characters from this file name and then append them to a new file name, I'm not entirely sure how to go about this and I'm not entirely sure my approach is even the correct way to go about this but here is my attempt so far: (Above this I have code to copy a new file from one directory to another this works)
for (String file : files) {
File srcFile = new File(src, file);
String fileName = null;
new File(fileName).getName();
String fileNames;
fileNames = "Split after 8 characters!";
if (fileNames.length() > 16)
fileNames = fileNames.substring(0, 8) + "...";
File destFile = new File(dest, file);
copyFolder(srcFile,destFile);
fileName.renameTo(fileNames);
}
The only thing giving me an error at the moment is the .renameTo at the bottom and the error given is
cannot find symbol symbol: method renameTo(String) location:
variable fileName of type String Dereferencing null pointer

Text input and output java

I am trying to read 2 files after i read the files i want to get their contents and manipulate the contents of the two files then update a new file which is the output. The files are in the same folder as the program but the program always throws a FileNotFoundException.
Below is my code:-
import java.io.*;
import java.util.Scanner;
public class UpdateMaster {
public static void main(String[] args)
{
String master = "Customer.dat";
String trans = "Transactns.dat";
String newMaster = "Temp.txt";
Scanner inputStreamMaster = null;
Scanner inputStreamTrans = null;
PrintWriter inputStreamNewMaster = null;
try
{
inputStreamMaster = new Scanner(new File(master));
inputStreamTrans = new Scanner(new File(trans));
inputStreamNewMaster = new PrintWriter(newMaster);
}
catch(FileNotFoundException e)
{
System.out.println("Error: you opend a file that does not exist.");
System.exit(0);
}
catch(IOException e)
{
System.out.println("Error.");
System.exit(0);
}
do
{
String transLine = inputStreamTrans.nextLine();
String masterLine = inputStreamMaster.nextLine();
String[] transLineArr = transLine.split(",");
String[] masterLineArr = masterLine.split(",");
int trAccNo = Integer.parseInt(transLineArr[0]);
int sales = Integer.parseInt(transLineArr[1]);
int masterAccNo = Integer.parseInt(masterLineArr[0]);
int balance = Integer.parseInt(masterLineArr[1]);
while(masterAccNo== trAccNo){
inputStreamNewMaster.println(trAccNo+ " , "+masterAccNo);
masterLine = inputStreamMaster.nextLine();
masterLineArr = masterLine.split(",");
masterAccNo = Integer.parseInt(masterLineArr[0]);
balance = Integer.parseInt(masterLineArr[1]);
}
balance = balance + sales;
inputStreamNewMaster.println(masterAccNo+ " , "+balance);
}while(inputStreamTrans.hasNextLine());
inputStreamMaster.close();
inputStreamTrans.close();
inputStreamNewMaster.close();
//System.out.println(" the line were written to "+ newMaster);
}
}

Like #Ankit Rustagi said in the comments, you need the full path of the files if you want to keep the current implementation.
However, there is a solution where you only need the file names: use BufferedReader / BufferedWriter. See here an example on how to use these classes (in the example it uses the full path but it works without it too).

Use absolute path
String master = "C:/Data/Customer.dat";
String trans = "C:/Data/Transactns.dat";
String newMaster = "C:/Data/Temp.txt";

The code works for me, i guess you misspelled some filename(s) or your files are in the wrong folder. I created your files on the same level as the src or the project. Also this is the folder where the files are exspected.

There's nothing wrong with using relative paths like tihis. What's happening is that your program is looking for the files in the directory where you execute the program, which doesn't have to be the folder of the program. You can confirm this by logging the absolute path of the files before you try to read them. For example:
File masterFile = new File(master);
System.out.printf("Using master file '%s'%n", masterFile.getAbsolutePath());
inputStreamMaster = new Scanner(masterFile);
In general you should not hardcode file paths but allow the user to specify them in someway, for example using command line arguments, a configuration file with a well known path, or an interactive user interface.
There is a way to locate the program's class file but it's a little tricky because Java allows classes to be loaded from compressed archives that may be located in remote systems. It's better to solve this problem in some other manner.

Try this:
String current = new java.io.File( "." ).getCanonicalPath();
System.out.println("I look for files in:"+current);
To see what directory your program expects to find its input files. If it shows the correct directory, check spelling of filenames. Otherwise, you have a clue as to what's gone wrong.

Java: renameTo() function failing

Java
The code below was written to read all files in, and send the data to another method (setOutput()), and then call a method to rename the last read file to another directory, and then delete the original. Everything seems to work up until the smdrCleanup() method is called. The renameTo() is failing.
From what I understand, if a FileReader is wrapped in a BufferedReader, I only need to call BufferedReader.close() to release the last read file... which I am doing here.
I have also seen where if the file were still "open", being scanned by anti-virus programs, or otherwise locked by a process, the renameTo() function would fail. I have used Process Explorer to review what may have it locked, and I don't see anything locking it.
I have my method setup to throw any kind of IOExceptions, but I am not getting any exceptions. Everything runs, but the console merely says that the file was not copied.
I am running Eclipse Helios Release 2, Windows 7 Ultimate, local administrator, UAC disabled.
Any help would be greatly appreciated.
public void smdrReader(String path, String oldPath) throws IOException
{
output = null; //nullify the value of output to avoid duplicate data
File folder = new File(path); //setting the directory for raw data files
File[] listOfFiles = folder.listFiles(); //array of files within the folder/directory
//For loop to iterate through the available files, open, & read contents to String Buffer.
for (int i = 0; i < listOfFiles.length; i++)
{
if (listOfFiles[i].isFile()) //verifying next entry in array is a file
{
File fileName = new File(listOfFiles[i].getName());//getting file name from array iteration
StringBuffer fileData = new StringBuffer(2048);//establishing StringBuffer for reading file contents into
BufferedReader reader = new BufferedReader(new FileReader(path + fileName));//reader to actually access/read file
String readData = String.valueOf(reader);//String variable being set to value of the reader
fileData.append(readData);//appending data from String variable into StringBuffer variable
setOutput(fileData);//setting the value of "output" to the value of StringBuffer
fileData.delete(0, i);
reader.close();//closing the reader (closing the file)
smdrCleanup(oldPath,fileName.toString());//calling method to move processed file and delete original
}
}
}
//method to rename input file into another directory and delete the original file to avoid duplicate processing
public void smdrCleanup(String oldPathPassed, String fileNamePassed) throws IOException
{
File oldFile = new File(oldPathPassed);//establishing File object for path to processed folder
File fileName = new File(fileNamePassed);//establishing File object for the fileName to rename/delete
String oldFilePath = oldFile.toString();
boolean success = fileName.renameTo(new File(oldFilePath + "\\" + fileName + ".old"));//attempting to rename file
if (!success) //checking the success of the file rename operation
{
System.out.println("The File Was NOT Successfully Moved!");//reporting error if the file cannot be renamed
}
else
{
fileName.delete();//deleting the file if it was successfully renamed
}
}

oldFile.toString(); returns the full path of the file including its file name, so if your old file path is c:\path\to\file.txt, oldFilePath + "\\" + fileName + ".old" will be c:\path\to\file.txt\file.txt.old.
Since there is no folder c:\path\to\file.txt, it fails. change it to
boolean success = fileName.renameTo(new File(oldFilePath + ".old"));
And you should be good to go.

File.renameTo can fail for any number of reasons:
Many aspects of the behavior of this
method are inherently
platform-dependent: The rename
operation might not be able to move a
file from one filesystem to another,
it might not be atomic, and it might
not succeed if a file with the
destination abstract pathname already
exists. The return value should always
be checked to make sure that the
rename operation was successful.
But there's not much feedback on why it fails. Before calling renameTo, verify that the file you're moving exists, and the parent directory you are moving it to also exists, and canWrite(). Are these on the same disk volume? If not, it might fail.
*EDIT: Code sample added *
Try something like the following. Modifications:
Accepts File objects instead of Strings
Uses 2-arg File constructor to create a child File object in a parent directory
Better error checking
This might give you some clues into what is failing.
public void smdrCleanup(File oldPathPassed, File fileNamePassed) throws IOException {
if (!oldPathPassed.exists() || !oldPathPassed.isDirectory() || !oldPathPassed.canWrite() ) throw new IOException("Dest is not a writable directory: " + oldPathPassed);
if (!fileNamePassed.exists()) throw new IOException("File does not exist: " + fileNamePassed);
final File dest = new File(oldPathPassed, fileNamePassed + ".old");
if (dest.exists()) throw new IOException("File already exists: " + dest);
boolean success = (fileNamePassed).renameTo(dest);//attempting to rename file
if (!success) //checking the success of the file rename operation
{
throw new IOException("The File Was NOT Successfully Moved!");
} else {
// file was successfully renamed, no need to delete
}
}