How do I iterate through the files in a directory in Java

Question

I need to get a list of all the files in a directory  including files in all the sub-directories  What is the standard way to accomplish directory iteration with Java

User · Answer

I like to use Optional and streams to have a net and clear solution  i use the below code to iterate over a directory  the below cases are handled by the code   handle the case of empty directory Laziness  but as mentioned by others  you still have to pay attention for outOfMemory in case you have huge folders     File directoryFile   new File  quot put your path here quot        Stream lt File gt  files   Optional ofNullable directoryFile   directoryFile                                                            listFiles File  isDirectory      filter only directories change with null if you don t need to filter                                    stream                                     flatMap Arrays  stream     flatmap from Stream lt File   gt  to Stream lt File gt

User · Answer

It s a tree  so recursion is your friend  start with the parent directory and call the method to get an array of child Files   Iterate through the child array   If the current value is a directory  pass it to a recursive call of your method   If not  process the leaf file appropriately

User · Answer

To add with  msandiford answer  as most of the times when a file tree is walked u may want to execute a function as a directory or any particular file is visited  If u are reluctant to using streams  The following methods overridden can be implemented  Files walkFileTree Paths get Krawl INDEXPATH   EnumSet of FileVisitOption FOLLOW LINKS   Integer MAX VALUE      new SimpleFileVisitor lt Path gt               Override         public FileVisitResult preVisitDirectory Path dir  BasicFileAttributes attrs                  throws IOException                      Do someting before directory visit                 return FileVisitResult CONTINUE                     Override         public FileVisitResult visitFile Path file  BasicFileAttributes attrs                  throws IOException                      Do something when a file is visited                 return FileVisitResult CONTINUE                     Override         public FileVisitResult postVisitDirectory Path dir  IOException exc                  throws IOException                      Do Something after directory visit                  return FileVisitResult CONTINUE

User · Answer

If you are using Java 1 7  you can use java nio file Files walkFileTree        For example   public class WalkFileTreeExample      public static void main String   args        Path p   Paths get   usr        FileVisitor lt Path gt  fv   new SimpleFileVisitor lt Path gt             Override       public FileVisitResult visitFile Path file  BasicFileAttributes attrs            throws IOException           System out println file           return FileVisitResult CONTINUE                      try         Files walkFileTree p  fv         catch  IOException e          e printStackTrace                   If you are using Java 8  you can use the stream interface with java nio file Files walk        public class WalkFileTreeExample      public static void main String   args        try  Stream lt Path gt  paths   Files walk Paths get   usr             paths forEach System out  println         catch  IOException e          e printStackTrace

User · Answer

For Java 7   there is also https   docs oracle com javase 7 docs api java nio file DirectoryStream html  Example taken from the Javadoc   List lt Path gt  listSourceFiles Path dir  throws IOException      List lt Path gt  result   new ArrayList lt  gt        try  DirectoryStream lt Path gt  stream   Files newDirectoryStream dir      c h cpp hpp java              for  Path entry  stream               result add entry                 catch  DirectoryIteratorException ex              I O error encounted during the iteration  the cause is an IOException        throw ex getCause            return result

User · Answer

As noted  this is a recursion problem   In particular  you may want to look at  listFiles      In the java File API here   It returns an array of all the files in a directory   Using this along with   isDirectory     to see if you need to recurse further is a good start

User · Answer

You can use File isDirectory   to test if the given file  path  is a directory  If this is true  then you just call the same method again with its File listFiles   outcome  This is called recursion  Here s a basic kickoff example  package com stackoverflow q3154488   import java io File   public class Demo        public static void main String    args            File dir   new File  quot  path to dir quot            showFiles dir listFiles                public static void showFiles File   files            for  File file   files                if  file isDirectory                      System out println  quot Directory   quot    file getAbsolutePath                     showFiles file listFiles        Calls same method again                else                   System out println  quot File   quot    file getAbsolutePath                                      Note that this is sensitive to StackOverflowError when the tree is deeper than the  JVM s stack can hold  If you re already on Java 8 or newer  then you d better use Files walk   instead which utilizes tail recursion  package com stackoverflow q3154488   import java io File  import java nio file Files  import java nio file Path  import java nio file Paths   public class DemoWithJava8        public static void main String    args  throws Exception           Path dir   Paths get  quot  path to dir quot            Files walk dir  forEach path - gt  showFile path toFile                 public static void showFile File file            if  file isDirectory                  System out println  quot Directory   quot    file getAbsolutePath               else               System out println  quot File   quot    file getAbsolutePath

User · Answer

You can also misuse File list FilenameFilter   and variants  for file traversal  Short code and works in early java versions  e g      list files in dir new File dir  list new FilenameFilter         public boolean accept File dir  String name            String file   dir getAbsolutePath     File separator   name          System out println file           return false

User · Answer

Check out the FileUtils class in Apache Commons - specifically iterateFiles      Allows iteration over the files in given directory  and optionally its subdirectories

User · Answer

Using org apache commons io FileUtils  File file   new File  F  Lines           Collection lt File gt  files   FileUtils listFiles file  null  true        for File file2   files       System out println file2 getName                      Use false if you do not want files from sub directories

[java] How do I iterate through the files in a directory in Java?

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