Develop Reference

Java - Recursively populating array of directories - avoiding NullPointerException when accessing system protected folder [duplicate]

File f=new File("C:/");
File fList[] = f.listFiles();
When i use this it list all system file as well as hidden files.
and this cause null pointer exception when i use it to show in jTree like this:
public void getList(DefaultMutableTreeNode node, File f) {
if(f.isDirectory()) {
DefaultMutableTreeNode child = new DefaultMutableTreeNode(f);
node.add(child);
File fList[] = f.listFiles();
for(int i = 0; i < fList.length; i++)
getList(child, fList[i]);
}
}
What should i do so that it do not give NullPointerException and show only non hidden and non system files in jTree?

Do this for hidden files:
File root = new File(yourDirectory);
File[] files = root.listFiles(new FileFilter() {
#Override
public boolean accept(File file) {
return !file.isHidden();
}
});
This will not return hidden files.
As for system files, I believe that is a Windows concept and therefore might not be supported by File interface that tries to be system independent. You can use Command line commands though, if those exist.
Or use what #Reimeus had in his answer.
Possibly like
File root = new File("C:\\");
File[] files = root.listFiles(new FileFilter() {
#Override
public boolean accept(File file) {
Path path = Paths.get(file.getAbsolutePath());
DosFileAttributes dfa;
try {
dfa = Files.readAttributes(path, DosFileAttributes.class);
} catch (IOException e) {
// bad practice
return false;
}
return (!dfa.isHidden() && !dfa.isSystem());
}
});
DosFileAttributes was introduced in Java 7.

If running under Windows, Java 7 introduced DosFileAttributes which enables system and hidden files to be filtered. This can be used in conjunction with a FileFilter
Path srcFile = Paths.get("myDirectory");
DosFileAttributes dfa = Files.readAttributes(srcFile, DosFileAttributes.class);
System.out.println("System File? " + dfa.isSystem());
System.out.println("Hidden File? " + dfa.isHidden());

If you are trying to list all files in C:/ please keep in mind that there are other files also which are neither hidden nor system files, but that still won't open because they require special privileges/permissions. So:
String[] files = file.list();
if (files!=null) {
for (String f : files) open(f);
}
So just compare if the array is null or not and design your recursion in such a way that it just skips those files whose array for the list() function is null.
private void nodes(DefaultMutableTreeNode top, File f) throws IOException {
if (f.isDirectory()) {
File[] listFiles = f.listFiles();
if (listFiles != null) {
DefaultMutableTreeNode b1[] = new DefaultMutableTreeNode[listFiles.length];
for (int i = 0; i < b1.length; i++) {
b1[i] = new DefaultMutableTreeNode(listFiles[i].toString());
top.add(b1[i]);
File g = new File(b1[i].toString());
nodes(b1[i], g);
}
}
}
Here is the code I used to create a window file explorer using jtree.

Iterate large set of files in a directory

I have a directory with 100,000 files and I need to iterate them all to read a value. Right now I use listFiles() to load all files in a array and then iterate one by one. But is there a memory efficient way to do this without loading in a array?
File[] tFiles = new File(Dir).listFiles();
try {
for (final File tFile : tFiles) {
//Process files one by one
}
}

Since Java 7, you can use the file visitor pattern to visit the contents of a directory recursively.
The documentation for the FileVisitor interface is here.
This allows you to iterate over files without creating a large array of File objects.
Simple example to print out your file names:
Path start = Paths.get(new URI("file:///my/folder/"));
Files.walkFileTree(start, new SimpleFileVisitor<Path>() {
#Override
public FileVisitResult visitFile(Path file, BasicFileAttributes attrs)
throws IOException
{
System.out.println(file);
return FileVisitResult.CONTINUE;
}
#Override
public FileVisitResult postVisitDirectory(Path dir, IOException e)
throws IOException
{
if (e == null) {
System.out.println(dir);
return FileVisitResult.CONTINUE;
}
else {
// directory iteration failed
throw e;
}
}
});

Java 8 lazily loaded stream version:
Files.list(new File("path to directory").toPath()).forEach(path -> {
File file = path.toFile();
//process your file
});

If you want to avoid the excessive boilerplate that comes with JDK's FileVisitor, you can use Guava. Files.fileTreeTraverser() gives you a TreeTraverser<File> which you can use for traversing the files in the folder (or even sub-folders):
for (File f : Files.fileTreeTraverser()
.preOrderTraversal(new File("/parent/folder"))) {
// do something with each file
}

List of files inside a zip folder and its subfolder

I am looking a way to get the list of files inside a zip file. I created a method to get the list of files inside a directory but I am also looking a way to get files inside a zip as well instead of showing just zip file.
here is my method:
public ArrayList<String> listFiles(File f, String min, String max) {
try {
// parse input strings into date format
Date minDate = sdf.parse(min);
Date maxDate = sdf.parse(max);
//
File[] list = f.listFiles();
for (File file : list) {
double bytes = file.length();
double kilobytes = (bytes / 1024);
if (file.isFile()) {
String fileDateString = sdf.format(file.lastModified());
Date fileDate = sdf.parse(fileDateString);
if (fileDate.after(minDate) && fileDate.before(maxDate)) {
lss.add("'" + file.getAbsolutePath() +
"'" + " Size KB:" + kilobytes + " Last Modified: " +
sdf.format(file.lastModified()));
}
} else if (file.isDirectory()) {
listFiles(file.getAbsoluteFile(), min, max);
}
}
} catch (Exception e) {
e.getMessage();
}
return lss;
}

After having searched for a better answer for a while, I finally found a better way to do this. You can actually do the same thing in a more generic way using the Java NIO API (Since Java 7).
// this is the URI of the Zip file itself
URI zipUri = ...;
FileSystem zipFs = FileSystems.newFileSystem(zipUri, Collections.emptyMap());
// The path within the zip file you want to start from
Path root = zipFs.getPath("/");
Files.walkFileTree(root, new SimpleFileVisitor<Path>() {
#Override
public FileVisitResult visitFile(Path path, BasicFileAttributes attrs) throws IOException {
// You can do anything you want with the path here
System.out.println(path);
// the BasicFileAttributes object has lots of useful meta data
// like file size, last modified date, etc...
return FileVisitResult.CONTINUE;
}
// The FileVisitor interface has more methods that
// are useful for handling directories.
});
This approach has the advantage that you can travers ANY file system this way: your normal windows or Unix filesystem, the file system contain contained within a zip or a jar, or any other really.
You can then trivially read the contents of any Path via the Files class, using methods like Files.copy(), File.readAllLines(), File.readAllBytes(), etc...

You can use ZipFile.entries() method to read the list of files via iteration as below:
File[] fList = directory.listFiles();
for (File file : fList)
{
ZipFile myZipFile = new ZipFile(fList.getName());
Enumeration zipEntries = myZipFile.entries();
while (zipEntries.hasMoreElements())
{
System.out.println(((ZipEntry) zipEntries.nextElement()).getName());
// you can do what ever you want on each zip file
}
}

Filtering files in a directory in Java

public class Sorter {
String dir1 = ("C:/Users/Drew/Desktop/test");
String dir2 = ("C:/Users/Drew/Desktop/");
public void SortingAlgo() throws IOException {
// Declare files for moving
File sourceDir = new File(dir1);
File destDir = new File(dir2);
//Get files, list them, grab only mp3 out of the pack, and sort
File[] listOfFiles = sourceDir.listFiles();
if(sourceDir.isDirectory()) {
for(int i = 0; i < listOfFiles.length; i++) {
//list Files
System.out.println(listOfFiles[i]);
String ext = FilenameUtils.getExtension(dir1);
System.out.println(ext);
}
}
}
}
I am trying to filter out only .mp3's in my program. I'm obviously a beginner and tried copying some things off of Google and this website. How can I set a directory (sourceDir) and move those filtered files to it's own folder?

File provides an ability to filter the file list as it's begin generated.
File[] listOfFiles = sourceDir.listFiles(new FileFilter() {
#Override
public boolean accept(File pathname) {
return pathname.getName().toLowerCase().endsWith(".mp3");
}
});
Now, this has a number of benefits, the chief among which is you don't need to post-process the list, again, or have two lists in memory at the same time.
It also provides pluggable capabilities. You could create a MP3FileFilter class for instance and re-use it.

I find the NIO.2 approach using GLOBs or custom filter the cleanest solution. Check out this example on how to use GLOB or filter example in the attached link:
Path directoryPath = Paths.get("C:", "Program Files/Java/jdk1.7.0_40/src/java/nio/file");
if (Files.isDirectory(directoryPath)) {
try (DirectoryStream<Path> stream = Files.newDirectoryStream(directoryPath, "*.mp3")) {
for (Path path : stream) {
System.out.println(path);
}
} catch (IOException e) {
throw new RuntimeException(e);
}
}
For more information about content listing and directory filtering visit Listing and filtering directory contents in NIO.2

if(ext.endWith(".mp3")){
//do what ever you want
}

Java: How to read directory folder, count and display no of files and copy to another folder?

I have to read a folder, count the number of files in the folder (can be of any type), display the number of files and then copy all the files to another folder (specified).
How would I proceed?

i Have to read a folder, count the number of files in the folder (can
be of any type) display the number of files
You can find all of this functionality in the javadocs for java.io.File
and then copy all the files to another folder (specified)
This is a bit more tricky. Read: Java Tutorial > Reading, Writing and Creating of Files
(note that the mechanisms described there are only available in Java 7 or later. If Java 7 is not an option, refer to one of many previous similar questions, e.g. this one: Fastest way to write to file? )

you have all the sample code here :
http://www.exampledepot.com
http://www.exampledepot.com/egs/java.io/GetFiles.html
File dir = new File("directoryName");
String[] children = dir.list();
if (children == null) {
// Either dir does not exist or is not a directory
} else {
for (int i=0; i<children.length; i++) {
// Get filename of file or directory
String filename = children[i];
}
}
// It is also possible to filter the list of returned files.
// This example does not return any files that start with `.'.
FilenameFilter filter = new FilenameFilter() {
public boolean accept(File dir, String name) {
return !name.startsWith(".");
}
};
children = dir.list(filter);
// The list of files can also be retrieved as File objects
File[] files = dir.listFiles();
// This filter only returns directories
FileFilter fileFilter = new FileFilter() {
public boolean accept(File file) {
return file.isDirectory();
}
};
files = dir.listFiles(fileFilter);
The copying http://www.exampledepot.com/egs/java.io/CopyDir.html :
// Copies all files under srcDir to dstDir.
// If dstDir does not exist, it will be created.
public void copyDirectory(File srcDir, File dstDir) throws IOException {
if (srcDir.isDirectory()) {
if (!dstDir.exists()) {
dstDir.mkdir();
}
String[] children = srcDir.list();
for (int i=0; i<children.length; i++) {
copyDirectory(new File(srcDir, children[i]),
new File(dstDir, children[i]));
}
} else {
// This method is implemented in Copying a File
copyFile(srcDir, dstDir);
}
}
However is very easy to gooole for this stuff :)

I know this is too late but below code worked for me. It basically iterates through each file in directory, if found file is a directory then it makes recursive call. It only gives files count in a directory.
public static int noOfFilesInDirectory(File directory) {
int noOfFiles = 0;
for (File file : directory.listFiles()) {
if (file.isFile()) {
noOfFiles++;
}
if (file.isDirectory()) {
noOfFiles += noOfFilesInDirectory(file);
}
}
return noOfFiles;
}