List all files from a directory recursively with Java

Question

I have this function that prints the name of all the files in a directory recursively  The problem is that my code is very slow because it has to access a remote network device with every iteration   My plan is to first load all the files from the directory recursively and then after that go through all files with the regex to filter out all the files I don t want  Does anyone have a better suggestion   public static printFnames String sDir      File   faFiles   new File sDir  listFiles       for File file  faFiles       if file getName   matches                    System out println file getAbsolutePath                if file isDirectory             printFnames file getAbsolutePath                     This is just a test later on I m not going to use the code like this  instead I m going to add the path and modification date of every file which matches an advanced regex to an array

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In Java 8  it s a 1-liner via Files find   with an arbitrarily large depth  eg 999  and BasicFileAttributes of isRegularFile    public static printFnames String sDir        Files find Paths get sDir   999   p  bfa  - gt  bfa isRegularFile    forEach System out  println       To add more filtering  enhance the lambda  for example all jpg files modified in the last 24 hours    p  bfa  - gt  bfa isRegularFile      amp  amp  p getFileName   toString   matches       jpg      amp  amp  bfa lastModifiedTime   toMillis    gt  System currentMillis   - 86400000

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public class GetFilesRecursive       public static List  lt String gt  getFilesRecursively File dir           List  lt String gt  ls   new ArrayList lt String gt             for  File fObj   dir listFiles                  if fObj isDirectory                      ls add String valueOf fObj                    ls addAll getFilesRecursively fObj                                 else                   ls add String valueOf fObj                                            return ls            public static List  lt String gt  getListOfFiles String fullPathDir            List  lt String gt  ls   new ArrayList lt String gt              File f   new File fullPathDir           if  f exists                  if f isDirectory                      ls add String valueOf f                    ls addAll getFilesRecursively f                            else               ls add fullPathDir                     return ls             public static void main String   args            List  lt String gt  ls   getListOfFiles   Users srinivasab Documents            for  String file ls                System out println file                     System out println ls size

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Another optimized code  import java io File  import java util ArrayList  import java util List   public class GetFilesRecursive       public static List  lt String gt  getFilesRecursively File dir           List  lt String gt  ls   new ArrayList lt String gt             if  dir isDirectory                for  File fObj   dir listFiles                      if fObj isDirectory                          ls add String valueOf fObj                        ls addAll getFilesRecursively fObj                                     else                       ls add String valueOf fObj                                                   else             ls add String valueOf dir             return ls             public static void main String   args            List  lt String gt  ls   getFilesRecursively new File   Users srinivasab Documents             for  String file ls                System out println file                     System out println ls size

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This Function will probably list all the file name and its path from its directory and its subdirectories    public void listFile String pathname        File f   new File pathname       File   listfiles   f listFiles        for  int i   0  i  lt  listfiles length  i              if  listfiles i  isDirectory                  File   internalFile   listfiles i  listFiles                for  int j   0  j  lt  internalFile length  j                      System out println internalFile j                    if  internalFile j  isDirectory                          String name   internalFile j  getAbsolutePath                        listFile name                                              else               System out println listfiles i

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With Java 7 a faster way to walk thru a directory tree was introduced with the Paths and Files functionality  They re much faster then the  old  File way   This would be the code to walk thru and check path names with a regular expression   public final void test   throws IOException  InterruptedException       final Path rootDir   Paths get  path to your directory where the walk starts            Walk thru mainDir directory     Files walkFileTree rootDir  new FileVisitor lt Path gt                 First  minor  speed up  Compile regular expression pattern only one time          private Pattern pattern   Pattern compile                      Override         public FileVisitResult preVisitDirectory Path path                  BasicFileAttributes atts  throws IOException                boolean matches   pattern matcher path toString    matches                    TODO  Put here your business logic when matches equals true false              return  matches   FileVisitResult CONTINUE FileVisitResult SKIP SUBTREE                      Override         public FileVisitResult visitFile Path path  BasicFileAttributes mainAtts                  throws IOException                boolean matches   pattern matcher path toString    matches                    TODO  Put here your business logic when matches equals true false              return FileVisitResult CONTINUE                      Override         public FileVisitResult postVisitDirectory Path path                  IOException exc  throws IOException                  TODO Auto-generated method stub             return FileVisitResult CONTINUE                      Override         public FileVisitResult visitFileFailed Path path  IOException exc                  throws IOException               exc printStackTrace                    If the root directory has failed it makes no sense to continue             return path equals rootDir   FileVisitResult TERMINATE FileVisitResult CONTINUE

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Just so you know isDirectory   is quite a slow method  I m finding it quite slow in my file browser  I ll be looking into a library to replace it with native code

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Java s interface for reading filesystem folder contents is not very performant  as you ve discovered    JDK 7 fixes this with a completely new interface for this sort of thing  which should bring native level performance to these sorts of operations   The core issue is that Java makes a native system call for every single file   On a low latency interface  this is not that big of a deal - but on a network with even moderate latency  it really adds up   If you profile your algorithm above  you ll find that the bulk of the time is spent in the pesky isDirectory   call - that s because you are incurring a round trip for every single call to isDirectory     Most modern OSes can provide this sort of information when the list of files folders was originally requested  as opposed to querying each individual file path for it s properties    If you can t wait for JDK7  one strategy for addressing this latency is to go multi-threaded and use an ExecutorService with a maximum   of threads to perform your recursion   It s not great  you have to deal with locking of your output data structures   but it ll be a heck of a lot faster than doing this single threaded   In all of your discussions about this sort of thing  I highly recommend that you compare against the best you could do using native code  or even a command line script that does roughly the same thing    Saying that it takes an hour to traverse a network structure doesn t really mean that much   Telling us that you can do it native in 7 second  but it takes an hour in Java will get people s attention

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Java 8  public static void main String   args  throws IOException            Path start   Paths get  C   data              try  Stream lt Path gt  stream   Files walk start  Integer MAX VALUE                 List lt String gt  collect   stream                  map String  valueOf                   sorted                    collect Collectors toList                  collect forEach System out  println

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The more efficient way I found in dealing with millions of folders and files is to capture directory listing through DOS command in some file and parse it  Once you have parsed data then you can do analysis and compute statistics

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this will work just fine     and its recursive   File root   new File  ROOT PATH    for   File file   root listFiles          getFilesRecursive file       private static void getFilesRecursive File pFile        for File files   pFile listFiles                  if files isDirectory                          getFilesRecursive files                     else                          do your thing                 you can either save in HashMap and use it as                per your requirement

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it feels like it s stupid access the   filesystem and get the contents for   every subdirectory instead of getting   everything at once    Your feeling is wrong  That s how filesystems work  There is no faster way  except when you have to do this repeatedly or for different patterns  you can cache all the file paths in memory  but then you have to deal with cache invalidation i e  what happens when files are added removed renamed while the app runs

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Assuming this is actual production code you ll be writing  then I suggest using the solution to this sort of thing that s already been solved - Apache Commons IO  specifically FileUtils listFiles    It handles nested directories  filters  based on name  modification time  etc    For example  for your regex   Collection files   FileUtils listFiles    dir     new RegexFileFilter               DirectoryFileFilter DIRECTORY      This will recursively search for files matching the        regex  returning the results as a collection   It s worth noting that this will be no faster than rolling your own code  it s doing the same thing - trawling a filesystem in Java is just slow  The difference is  the Apache Commons version will have no bugs in it

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This is a very simple recursive method to get all files from a given root   It uses the Java 7 NIO Path class   private List lt String gt  getFileNames List lt String gt  fileNames  Path dir        try DirectoryStream lt Path gt  stream   Files newDirectoryStream dir             for  Path path   stream                if path toFile   isDirectory                      getFileNames fileNames  path                 else                   fileNames add path toAbsolutePath   toString                     System out println path getFileName                                   catch IOException e            e printStackTrace              return fileNames

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One more example of listing files and directories using Java 8 filter public static void main String   args     System out println  quot Files   quot            try               Files walk Paths get  quot   quot                         filter Files  isRegularFile                       filter c - gt                              c getFileName   toString   substring c getFileName   toString   length  -4  contains  quot  jpg quot                                                              c getFileName   toString   substring c getFileName   toString   length  -5  contains  quot  jpeg quot                                              forEach System out  println              catch  IOException e            System out println  quot No jpeg or jpg files quot                       System out println  quot  nDirectories   n quot            try               Files walk Paths get  quot   quot                         filter Files  isDirectory                       forEach System out  println              catch  IOException e                System out println  quot No Jpeg files quot

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I personally like this version of FileUtils  Here s an example that finds all mp3s or flacs in a directory or any of its subdirectories   String   types     mp3    flac    Collection lt File gt  files2   FileUtils listFiles  path to your dir  types   true

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import java io     public class MultiFolderReading    public void checkNoOfFiles  String filename  throws IOException        File dir new File filename       File files   dir listFiles     files array stores the list of files   for int i 0 i lt files length i                  if files i  isFile      check whether files i  is file or directory                       System out println  File    files i  getName                 System out println                       else if files i  isDirectory                          System out println  Directory    files i  getName                 System out println                checkNoOfFiles files i  getAbsolutePath                        public static void main String   args  throws IOException        MultiFolderReading mf new MultiFolderReading        String str  E   file        mf checkNoOfFiles str

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In Guava you don t have to wait for a Collection to be returned to you but can actually iterate over the files  It is easy to imagine a IDoSomethingWithThisFile interface in the signature of the below function   public static void collectFilesInDir File dir        TreeTraverser lt File gt  traverser   Files fileTreeTraverser        FluentIterable lt File gt  filesInPostOrder   traverser preOrderTraversal dir       for  File f  filesInPostOrder          System out printf  File   s n   f getPath         TreeTraverser also allows you to between various traversal styles

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The fast way to get the content of a directory using Java 7 NIO    import java nio file DirectoryStream  import java nio file Files  import java nio file FileSystems  import java nio file Path        Path dir   FileSystems getDefault   getPath  filePath    DirectoryStream lt Path gt  stream   Files newDirectoryStream  dir    for  Path path   stream       System out println  path getFileName        stream close

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This will work fine  public void displayAll File path             if path isFile             System out println path getName          else          System out println path getName                      File files     path listFiles            for File dirOrFile  files               displayAll dirOrFile

[java] List all files from a directory recursively with Java

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