Recursively list files in Java

Question

How do I recursively list all files under a directory in Java  Does the framework provide any utility      I saw a lot of hacky implementations  But none from the framework or nio

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Kotlin has FileTreeWalk for this purpose  For example   dataDir walkTopDown   filter    it isDirectory   joinToString   n           it toRelativeString dataDir      it length         Will produce a text list of all the non-directory files under a given root  one file per line with the path relative to the root and length

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Apart from the recursive traversal one can use a Visitor based approach as well   Below code is uses Visitor based approach for the traversal It is expected that the input to the program is the root directory to traverse   public interface Visitor       void visit DirElement d       void visit FileElement f      public abstract class Element       protected File rootPath      abstract void accept Visitor v         Override     public String toString             return rootPath getAbsolutePath             public class FileElement extends Element       FileElement final String path            rootPath   new File path               Override     void accept final Visitor v            v visit this            public class DirElement extends Element implements Iterable lt Element gt        private final List lt Element gt  elemList      DirElement final String path            elemList   new ArrayList lt Element gt             rootPath   new File path           for  File f   rootPath listFiles                  if  f isDirectory                      elemList add new DirElement f getAbsolutePath                    else if  f isFile                      elemList add new FileElement f getAbsolutePath                                          Override     void accept final Visitor v            v visit this              public Iterator lt Element gt  iterator             return elemList iterator             public class ElementWalker       private final String rootDir      ElementWalker final String dir            rootDir   dir             private void traverse             Element d   new DirElement rootDir           d accept new Walker                public static void main final String   args            ElementWalker t   new ElementWalker  C   temp            t traverse               private class Walker implements Visitor           public void visit final DirElement d                System out println d               for Element e d                    e accept this                                    public void visit final FileElement f                System out println f

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With Java 7 you can use the following class   import java io IOException  import java nio file FileVisitResult  import java nio file Files  import java nio file Path  import java nio file Paths  import java nio file SimpleFileVisitor  import java nio file attribute BasicFileAttributes   public class MyFileIterator extends SimpleFileVisitor lt Path gt        public MyFileIterator String path  throws Exception               Files walkFileTree Paths get path   this               Override     public FileVisitResult visitFile Path file              BasicFileAttributes attributes  throws IOException               System out println  File      file           return FileVisitResult CONTINUE              Override     public FileVisitResult preVisitDirectory Path dir              BasicFileAttributes attributes  throws IOException               System out println  Dir      dir           return FileVisitResult CONTINUE

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Ready to run  import java io File   public class Filewalker        public void walk  String path              File root   new File  path            File   list   root listFiles             if  list    null  return           for   File f   list                 if   f isDirectory                       walk  f getAbsolutePath                      System out println   Dir     f getAbsoluteFile                                else                   System out println   File     f getAbsoluteFile                                         public static void main String   args            Filewalker fw   new Filewalker            fw walk  c

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I came up with this for printing all the files file names recursively   private static void printAllFiles String filePath File folder        if filePath  null            return            File   files   folder listFiles        for File element   files            if element isDirectory                  printAllFiles filePath element             else               System out println   FileName    element getName

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private void fillFilesRecursively File file  List lt File gt  resultFiles            if  file isFile                  resultFiles add file             else               for  File child   file listFiles                      fillFilesRecursively child  resultFiles

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FileUtils have iterateFiles and listFiles methods  Give them a try   from commons-io   Edit  You can check here for a benchmark of different approaches  It seems that the commons-io approach is slow  so pick some of the faster ones from here  if it matters

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Java 8 provides a nice stream to process all files in a tree   Files walk Paths get path            filter Files  isRegularFile           forEach System out  println     This provides a natural way to traverse files  Since it s a stream you can do all nice stream operations on the result such as limit  grouping  mapping  exit early etc   UPDATE  I might point out there is also Files find which takes a BiPredicate that could be more efficient if you need to check file attributes   Files find Paths get path              Integer MAX VALUE              filePath  fileAttr  - gt  fileAttr isRegularFile             forEach System out  println     Note that while the JavaDoc eludes that this method could be more efficient than Files walk it is effectively identical  the difference in performance can be observed if you are also retrieving file attributes within your filter  In the end  if you need to filter on attributes use Files find  otherwise use Files walk  mostly because there are overloads and it s more convenient   TESTS  As requested I ve provided a performance comparison of many of the answers  Check out the Github project which contains results and a test case

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Here a simple but perfectly working solution using recursion   public static List lt Path gt  listFiles String rootDirectory        List lt Path gt  files   new ArrayList lt  gt         listFiles rootDirectory  files        return files     private static void listFiles String path  List lt Path gt  collectedFiles        File root   new File path       File   files   root listFiles         if  files    null                return             for  File file   files                if  file isDirectory                          listFiles file getAbsolutePath    collectedFiles             else                       collectedFiles add file toPath

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just write it yourself using simple recursion   public List lt File gt  addFiles List lt File gt  files  File dir        if  files    null          files   new LinkedList lt File gt          if   dir isDirectory                  files add dir           return files             for  File file   dir listFiles            addFiles files  file       return files

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I think this should do the work   File dir   new File dirname   String   files   dir list      This way you have files and dirs  Now use recursion and do the same for dirs  File class has isDirectory   method

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base on  Michael answer  add check whether listFiles return null static Stream lt File gt  files File file        return file isDirectory                 Optional ofNullable file listFiles    map Stream  of  orElseGet Stream  empty  flatMap MainActivity  files                Stream of file      or use Lightweight-Stream-API  which support Android5  amp  Android6 static Stream lt File gt  files File f        return f isDirectory     Stream ofNullable f listFiles    flatMap MainActivity  files    Stream of f

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Example outputs   csv files in directory recursive searching Subdirectories using Files find   from java nio   String path    C  Daten ibiss ferret        logger debug  Path     path       try  Stream lt Path gt  fileList   Files find Paths get path   Integer MAX VALUE               filePath  fileAttr  - gt  fileAttr isRegularFile    amp  amp  filePath toString   endsWith  csv               List lt String gt  someThingNew   fileList sorted   map String  valueOf  collect Collectors toList             for  String t   someThingNew                t toString                logger debug  Filename     t                      Posting this example  as I had trouble understanding howto pass the filename parameter in the  1 example given by Bryan  using foreach on Stream-result -   Hope this helps

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Non-recursive BFS with a single list  particular example is searching for   eml files        final FileFilter filter   new FileFilter              Override         public boolean accept File file                return file isDirectory      file getName   endsWith   eml                             BFS recursive search     List lt File gt  queue   new LinkedList lt File gt         queue addAll Arrays asList dir listFiles filter          for  ListIterator lt File gt  itr   queue listIterator    itr hasNext               File file   itr next            if  file isDirectory                  itr remove                for  File f  file listFiles filter   itr add f

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No external libraries needed  Returns a Collection so you can do whatever you want with it after the call   public static Collection lt File gt  listFileTree File dir        Set lt File gt  fileTree   new HashSet lt File gt         if dir  null  dir listFiles    null           return fileTree            for  File entry   dir listFiles              if  entry isFile    fileTree add entry           else fileTree addAll listFileTree entry              return fileTree

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The accepted answer is great  however it breaks down when you want to do IO inside the lambda   Here is what you can do if your action declares IOExceptions   You can treat the filtered stream as an Iterable  and then do your action in a regular for-each loop  This way  you don t have to handle exceptions inside a lambda   try  Stream lt Path gt  pathStream   Files walk Paths get path            filter Files  isRegularFile          for  Path file    Iterable lt Path gt   pathStream  iterator               something that throws IOException         Files copy file  System out             Found that trick here  https   stackoverflow com a 32668807 1207791

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I would go with something like    public void list File file        System out println file getName         File   children   file listFiles        for  File child   children            list child             The System out println is just there to indicate to do something with the file  there is no need to differentiate between files and directories  since a normal file will simply have zero children

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Lists all files with provided extensions with option to scan subfolders  recursive    public static ArrayList lt File gt  listFileTree File dir boolean recursive            if  null    dir     dir isDirectory                  return new ArrayList lt  gt                       final Set lt File gt  fileTree   new HashSet lt File gt             FileFilter fileFilter   new FileFilter                 private final String   acceptedExtensions   new String    quot jpg quot    quot png quot    quot webp quot    quot jpeg quot                  Override             public boolean accept File file                    if  file isDirectory                          return true                                    for  String extension   acceptedExtensions                        if  file getName   toLowerCase   endsWith extension                             return true                                                          return false                                   File   listed   dir listFiles fileFilter           if listed  null               for  File entry   listed                    if  entry isFile                          fileTree add entry                     else if recursive                       fileTree addAll listFileTree entry true                                                      return new ArrayList lt  gt  fileTree

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This code is ready to run  public static void main String    args        File   files   new File  D     listFiles        if  files    null          getFiles files      public static void getFiles File   files        for  File file   files            if  file isDirectory                  getFiles file listFiles               else               System out println  File      file

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In Java 8  we can now use the Files utility to walk a file tree  Very simple   Files walk root toPath           filter path - gt   Files isDirectory path          forEach path - gt  System out println path

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Another way you can do even if someone already provide Java 8 walk   This one will provide you all files recursively    private Stream lt File gt  files File file        return file isDirectory                 Arrays stream file listFiles    flatMap this  files                Stream of file

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Based on stacker answer  Here is a solution working in JSP without any external libraries so you can put it almost anywhere on your server    lt  DOCTYPE html gt   lt    page session  false    gt   lt    page import  java util      gt   lt    page import  java io      gt   lt    page contentType  text html  charset UTF-8    gt    lt        public List lt String gt  files   new ArrayList lt String gt                     Fills files array with all sub-files             public void walk  File root             File   list   root listFiles             if  list    null  return           for   File f   list                 if   f isDirectory                       walk  f                              else                   files add f getAbsolutePath                                     gt   lt       files clear        File jsp   new File request getRealPath request getServletPath          File dir   jsp getParentFile        walk dir       String prefixPath   dir getAbsolutePath            gt    Then you just do something like        lt ul gt           lt   for  String file   files      gt               lt   if  file matches        apk ipa mobileprovision         gt                   lt li gt  lt   file replace prefixPath       gt  lt  li gt               lt       gt           lt       gt       lt  ul gt

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I prefer using a queue over recursion for this kind of simple traversion   List lt File gt  allFiles   new ArrayList lt File gt     Queue lt File gt  dirs   new LinkedList lt File gt     dirs add new File   start dir      while   dirs isEmpty        for  File f   dirs poll   listFiles          if  f isDirectory            dirs add f         else if  f isFile            allFiles add f

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public static String getExten String path        int i   path lastIndexOf           if  i  gt  0           return path substring i             else return  quot  quot     public static List lt String gt  GetAllFiles String path  List lt String gt fileList       File file   new File path            File   files   file listFiles        for File folder files            if extensions contains getExten folder getPath                    fileList add folder getPath                         File   direcs   file listFiles File  isDirectory       for File dir direcs            GetAllFiles dir getPath   fileList             return fileList          This is a simple recursive function that should give you all the files  extensions is a list of string that contains only those extensions which are accepted  Example extensions     quot  txt quot   quot  docx quot   etc

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You can use below code to get a list of files of specific folder or directory recursively   public static void main String args               recusiveList  D                 public static void recursiveList String path             File f   new File path           File   fl   f listFiles            for  int i   0  i  lt  fl length  i                  if  fl i  isDirectory    amp  amp   fl i  isHidden                      System out println fl i  getAbsolutePath                     recusiveList fl i  getAbsolutePath                   else                   System out println fl i  getName

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Java 7 will have has Files walkFileTree      If you provide a starting point and a file visitor  it will invoke various methods on the file visitor as it walks through the file in the file tree  We expect people to use this if they are developing a recursive copy  a recursive move  a recursive delete  or a recursive operation that sets permissions or performs another operation on each of the files    There is now an entire Oracle tutorial on this question

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My version  of course I could have used the built in walk in Java 8   -      public static List lt File gt  findFilesIn File rootDir  Predicate lt File gt  predicate            ArrayList lt File gt  collected   new ArrayList lt  gt             walk rootDir  predicate  collected           return collected             private static void walk File dir  Predicate lt File gt  filterFunction  List lt File gt  collected            Stream of listOnlyWhenDirectory dir                    forEach file - gt  walk file  filterFunction  addAndReturn collected  file  filterFunction                private static File   listOnlyWhenDirectory File dir            return dir isDirectory     dir listFiles     new File                 private static List lt File gt  addAndReturn List lt File gt  files  File toAdd  Predicate lt File gt  filterFunction            if  filterFunction test toAdd                 files add toAdd                     return files

[java] Recursively list files in Java

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