Develop Reference

What is the meaning of LinkOption.NOFOLLOW_LINKS and when to use it?

I want to check if a directory is exist by using the notExists(Path path, LinkOption... options) and Im confused with the LinkOption.NOFOLLOW_LINKS although after I googled I still not quite get when to use it. Here are my codes:
import java.io.*;
import java.nio.file.Files;
import java.nio.file.*;
import java.util.ArrayList;
public class Test
{
public static void main(String[] args) throws IOException
{
Path source = Paths.get("Path/Source");
Path destination = Paths.get("Path/Destination");
ArrayList<String> files = new ArrayList<String>();
int retry = 3;
// get files inside source directory
files = getFiles(source);
// move all files inside source directory
for (int j=0; j < files.size(); j++){
moveFile(source,destination,files.get(j),retry);
}
}
// move file to destination directory
public static void moveFile(Path source, Path destination, String file, int retry){
while (retry>0){
try {
// if destination path not exist, create directory
if (Files.notExists(destination, LinkOption.NOFOLLOW_LINKS)) {
// make directory
Files.createDirectories(destination);
}
// move file to destination path
Path temp = Files.move(source.resolve(file),destination.resolve(file));
// if successfully, break
if(temp != null){
break;
}
// else, retry
else {
--retry;
}
} catch (Exception e){
// retry if error occurs
--retry;
}
}
}
// get all file names in source directory
public static ArrayList<String> getFiles(Path source){
ArrayList<String> filenames = new ArrayList<String>();
File folder = new File(source.toString());
File[] listOfFiles = folder.listFiles(); // get all files inside the source directory
for (int i = 0; i < listOfFiles.length; i++) {
if (listOfFiles[i].isFile()) {
filenames.add(listOfFiles[i].getName()); // add file's name into arraylist
}
}
return filenames;
}
}
The result of using LinkOption.NOFOLLOW_LINKS and not using it are the same (The files are transferred to the destination). So, Im guessing for my case, i can ignore the Link option? also, in what situation will i be needing that? Thanks!

So, Im guessing for my case, i can ignore the Link option?
You can only follow a link if the link exists.
So if you are testing to make sure a directory doesn't exist, there are two outcomes.
it exists, so there is no need to follow the link.
it doesn't exist, so there is nothing to follow.
in what situation will i be needing that?
Did you look at my answer in the link I provided you? I tried to give a simple example.

How do I conditionally get code to loop back to specific point in code in java?

I am creating an application that automatically sorts and organizes files into a database​. I have written my code to read files within the imported folder one at a time, and process them into the DB. However, I am having trouble looping this process, so that I can process files that are nested in any amount of folders within the original folder that the user wants to input.
I simply need to instruct my program to go back to a specific part of my code and start running from there again.
Another possible way to solve this issue would be to create a way to list out all of the individual files within folder (including all the files within subfolders), and I could easily fit that into my program too.
I tried using labeled continue, return, and break keywords based off of an answer I got online, but I never expected those to succeed in looping my code back to a specific spot.
JFileChooser chooser = new JFileChooser();
chooser.setSelectedFiles(null);
chooser.setFileSelectionMode(JFileChooser.FILES_AND_DIRECTORIES);
chooser.showOpenDialog(null);
//Getting file paths from within folder
File f = chooser.getSelectedFile();
String file = f.getAbsolutePath();
if (f.isDirectory()) {
//Need to loop back to here
File folder = new File(file);
File[] listOfFiles = folder.listFiles();
for (int i = 0; i < listOfFiles.length; i++) {
if (listOfFiles[i].isDirectory()) {
//Code here is run if there is a folder within a folder. I tested it too
//I want the code here to loop back above where it says "Need to loop back to here"
}
if (listOfFiles[i].isFile()) { //Once I list the files from within the folder, their information gets assigned variable here, and the rest of my program sorts it and saves it to DB accordingly.
//Everything below here is not important, but it might be helpful to see what happens each file with the folders.
System.out.println(listOfFiles[i]);
String filename = (listOfFiles[i].getName()); //For Files
Long filemodified = (listOfFiles[i].lastModified());
String filepath = (listOfFiles[i].getAbsolutePath());
Long filesizeraw = (listOfFiles[i].length());
long filehashcode = (listOfFiles[i].hashCode());
String fileparent = (listOfFiles[i].getParent());
Currently, there is no error message. It would process any individual files directly in the imported file (not nested in any folder within the folder), but wouldn't get to any of the files that are in folders within folders.

Another possible way to solve this issue would be to create a way to list out all of the individual files within folder (including all the files within subfolders), and I could easily fit that into my program too
Although this doesn't do the SQLite inserts, the following class extracts a list (of File objects) the files (thus file name and path are available via the File object).
public class FTS {
private ArrayList<File> mFileList; //Resultant list of Files extracted
private String mBaseDirectory; // The Directory to search
private long mSubDirectoryCount; // The count of the subdirectories
//Constructor
public FTS(String directory) {
this.mBaseDirectory = directory;
this.mSubDirectoryCount = 0;
buildFileListing(this.mBaseDirectory);
}
//
private void buildFileListing(String directory) {
// Initialise the ArrayList for the result
if (mFileList == null) {
mFileList = new ArrayList(){};
}
//Get the File (directory to process)
File dir = new File(directory);
// Get the List of the Directories contents
String[] filelist = dir.list();
// If empty (null) then return
if (filelist == null) {
return;
}
// Loop through the directory list
for (String s: filelist) {
//get the current list item as a file
File f = new File(dir.getAbsolutePath() + File.separator + s);
// is it a file or directory?
if (f.isFile() && !f.isDirectory()) {
this.mFileList.add(f); // If a file then add the file to the extracted list
} else {
// If a directory then increment the count of the subdirectories processed
mSubDirectoryCount++;
// and then recursively call this method to process the directory
buildFileListing(f.getAbsolutePath());
}
}
}
// return the list of extracted files
public ArrayList<File> getFileList() {
return this.mFileList;
}
// return the number of sub-directories processed
public long getSubDirectoryCount() {
return this.mSubDirectoryCount;
}
}
An example usage of the above is :-
public class Main {
/**
* #param args the command line arguments
*/
public static void main(String[] args) {
// TODO code application logic here
FTS fileTreeSearch;
String BaseDirectory = "E:" + File.separator;
List<File> files = (fileTreeSearch = new FTS(BaseDirectory)).getFileList();
System.out.println("Extracted " + String.valueOf(files.size()) + " files, from " + String.valueOf(fileTreeSearch.getSubDirectoryCount()) + " sub-directories of " + BaseDirectory);
/* this commented out code would process all the extracted files
for (File f: files) {
System.out.println("File is " + f.getName() + "\t\t path " + f.getAbsolutePath());
}
*/
}
}
Example output from running the above :-
Extracted 186893 files, from 54006 sub-directories of E:\

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.

How to make Java list only writable files

I need to know how to know how to make Java's File.list(); method list only the files I am able to access or how to filter them out, cause now it lists files like $RecycleBin or Documents and Settings (I am on Win7) basically files I am unable to see in Win Explorer. Many Thanks.

The following will do it:
File[] subDirs = dir.listFiles( new FileFilter() {
#Override public boolean accept( File f ) {
return f.canWrite();
} } );
You could also use CanWriteFileFilter of apache.commons.io (http://commons.apache.org/proper/commons-io/apidocs/org/apache/commons/io/filefilter/CanWriteFileFilter.html)
Example, showing how to print out a list of the current directory's writable files:
File dir = new File(".");
String[] files = dir.list( CanWriteFileFilter.CAN_WRITE );
for ( int i = 0; i < files.length; i++ ) {
System.out.println(files[i]);
}

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;
}