How do I get the file extension of a file in Java

Question

Just to be clear  I m not looking for the MIME type   Let s say I have the following input   path to file foo txt  I d like a way to break this input up  specifically into  txt for the extension   Is there any built in way to do this in Java   I would like to avoid writing my own parser

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This particular question gave me a lot of trouble then i found a very simple solution for this problem which i m posting here   file getName   toLowerCase   endsWith   txt      That s it

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How about REGEX version   static final Pattern PATTERN   Pattern compile                  Matcher m   PATTERN matcher path   if  m find          System out println  File path name      m group 1        System out println  Extention      m group 2        or with null extension supported   static final Pattern PATTERN       Pattern compile            File separator                              File separator               class Separated       String path  name  ext     Separated parsePath String path        Separated res   new Separated        Matcher m   PATTERN matcher path       if  m find              if  m group 1     null                res path   m group 2               res name   m group 3               res ext   m group 5             else               res path   m group 6               res name   m group 7                       return res      Separated sp   parsePath   root docs readme txt    System out println  path      sp path   System out println  name      sp name   System out println  Extention      sp ext     result for  nix  path   root docs  name  readme Extention  txt  for windows  parsePath  c  windows readme txt    path  c  windows  name  readme Extention  txt

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Here s a method that handles  tar gz properly  even in a path with dots in directory names   private static final String getExtension final String filename      if  filename    null  return null    final String afterLastSlash   filename substring filename lastIndexOf        1     final int afterLastBackslash   afterLastSlash lastIndexOf         1    final int dotIndex   afterLastSlash indexOf      afterLastBackslash     return  dotIndex    -1         afterLastSlash substring dotIndex   1       afterLastSlash is created to make finding afterLastBackslash quicker since it won t have to search the whole string if there are some slashes in it   The char   inside the original String is reused  adding no garbage there  and the JVM will probably notice that afterLastSlash is immediately garbage in order to put it on the stack instead of the heap

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How about JFileChooser  It is not straightforward as you will need to parse its final output     JFileChooser filechooser   new JFileChooser    File file   new File  your txt    System out println  the extension type   filechooser getTypeDescription file      which is a MIME type     OK   I forget that you don t want to know its MIME type   Interesting code in the following link  http   download oracle com javase tutorial uiswing components filechooser html        Get the extension of a file        public static String getExtension File f        String ext   null      String s   f getName        int i   s lastIndexOf            if  i  gt  0  amp  amp   i  lt  s length   - 1            ext   s substring i 1  toLowerCase              return ext      Related question  How do I trim a file extension from a String in Java

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Just a regular-expression based alternative  Not that fast  not that good    Pattern pattern   Pattern compile                 Matcher matcher   pattern matcher fileName    if  matcher find          String ext   matcher group 1

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If on Android  you can use this   String ext   android webkit MimeTypeMap getFileExtensionFromUrl file getName

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In this case  use FilenameUtils getExtension from Apache Commons IO Here is an example of how to use it  you may specify either full path or just file name   import org apache commons io FilenameUtils           String ext1   FilenameUtils getExtension  quot  path to file foo txt quot       returns  quot txt quot  String ext2   FilenameUtils getExtension  quot bar exe quot       returns  quot exe quot   Maven dependency   lt dependency gt     lt groupId gt commons-io lt  groupId gt     lt artifactId gt commons-io lt  artifactId gt     lt version gt 2 6 lt  version gt   lt  dependency gt   Gradle Groovy DSL implementation  commons-io commons-io 2 6   Gradle Kotlin DSL implementation  quot commons-io commons-io 2 6 quot    Others https   search maven org artifact commons-io commons-io 2 6 jar

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As is obvious from all the other answers  there s no adequate  built-in  function  This is a safe and simple method   String getFileExtension File file        if  file    null            return               String name   file getName        int i   name lastIndexOf           String ext   i  gt  0   name substring i   1            return ext

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String extension   com google common io Files getFileExtension  fileName jpg

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Do you really need a  parser  for this   String extension        int i   fileName lastIndexOf       if  i  gt  0        extension   fileName substring i 1       Assuming that you re dealing with simple Windows-like file names  not something like archive tar gz   Btw  for the case that a directory may have a      but the filename itself doesn t  like  path to a file   you can do  String extension        int i   fileName lastIndexOf       int p   Math max fileName lastIndexOf       fileName lastIndexOf          if  i  gt  p        extension   fileName substring i 1

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I found a better way to find extension by mixing all above answers  public static String getFileExtension String fileLink             String extension          Uri uri   Uri parse fileLink           String scheme   uri getScheme            if  scheme    null  amp  amp  scheme equals ContentResolver SCHEME CONTENT                 MimeTypeMap mime   MimeTypeMap getSingleton                extension   mime getExtensionFromMimeType CoreApp getInstance   getContentResolver   getType uri              else               extension   MimeTypeMap getFileExtensionFromUrl fileLink                      return extension         public static String getMimeType String fileLink            String type   CoreApp getInstance   getContentResolver   getType Uri parse fileLink            if   TextUtils isEmpty type   return type          MimeTypeMap mime   MimeTypeMap getSingleton            return mime getMimeTypeFromExtension FileChooserUtil getFileExtension fileLink

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Test     public void getFileExtension String fileName         String extension   null        List lt String gt  list   new ArrayList lt  gt           do            extension    FilenameUtils getExtension fileName             if extension  null                 break                        if  extension isEmpty                   list add     extension                         fileName   FilenameUtils getBaseName fileName          while   extension isEmpty           Collections reverse list         System out println list toString

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Java has a built-in way of dealing with this  in the java nio file Files class  that may work for your needs   File f   new File   path to file foo txt    String ext   Files probeContentType f toPath     if ext equalsIgnoreCase  txt    do whatever    Note that this static method uses the specifications found here to retrieve  content type   which can vary

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private String getFileExtension File file        String name   file getName        int lastIndexOf   name lastIndexOf           if  lastIndexOf    -1            return        empty extension           return name substring lastIndexOf

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Here s the version with Optional as a return value  cause you can t be sure the file has an extension     also sanity checks      import java io File  import java util Optional   public class GetFileExtensionTool        public static Optional lt String gt  getFileExtension File file            if  file    null                throw new NullPointerException  file argument was null                      if   file isFile                  throw new IllegalArgumentException  getFileExtension File file                           called on File object that wasn t an actual file                           perhaps a directory or device    file had path                          file getAbsolutePath                       String fileName   file getName            int i   fileName lastIndexOf               if  i  gt  0                return Optional of fileName substring i   1              else               return Optional empty

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Modified from EboMike s answer  String extension     path to file foo txt  substring   path to file foo txt  lastIndexOf          extension should have   txt  in it when run

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try this   String   extension    adadad adad adnandad jpg  split                          adadad adad adnandad   jpg   extension 1     jpg

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How about  using Java 1 5 RegEx        String   split   fullFileName split             String ext   split split length - 1

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In order to take into account file names without characters before the dot  you have to use that slight variation of the accepted answer   String extension        int i   fileName lastIndexOf       if  i  gt   0        extension   fileName substring i 1          file doc    gt   doc   file doc gz    gt   gz    doc    gt   doc

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If you plan to use Apache commons-io and just want to check the file s extension and then do some operation you can use this here is a snippet   if FilenameUtils isExtension file getName    java          someoperation

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My dirty and may tiniest using String replaceAll    replaceAll                  1     Note that first   is greedy so it will grab most possible characters as far as it can and then just last dot and file extension will be left

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String path     Users test test txt   String extension        if  path contains            extension   path substring path lastIndexOf          return   txt   if you want only  txt   make path lastIndexOf        1

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This is a tested method  public static String getExtension String fileName        char ch      int len      if fileName  null                  len   fileName length     0                  ch   fileName charAt len-1           ch            in the case of a directory              ch          in the case of   or            return         int dotInd   fileName lastIndexOf               sepInd   Math max fileName lastIndexOf       fileName lastIndexOf             if  dotInd lt  sepInd           return         else         return fileName substring dotInd 1  toLowerCase        And test case    Test public void testGetExtension         assertEquals     getExtension  C         assertEquals  ext   getExtension  C ext         assertEquals  ext   getExtension  A B C ext         assertEquals     getExtension  A B C ext          assertEquals     getExtension  A B C ext            assertEquals  bin   getExtension  A B C bin         assertEquals  hidden   getExtension   hidden         assertEquals  dsstore   getExtension   user home  dsstore         assertEquals     getExtension   strange          assertEquals  3   getExtension  1 2 3         assertEquals  exe   getExtension  C   Program Files  x86   java  bin  javaw exe

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If you use Guava library  you can resort to Files utility class  It has a specific method  getFileExtension    For instance   String path    c  path to file foo txt   String ext   Files getFileExtension path   System out println ext     prints txt   In addition you may also obtain the filename with a similar function  getNameWithoutExtension     String filename   Files getNameWithoutExtension path   System out println filename     prints foo

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If you use Spring framework in your project  then you can use StringUtils import org springframework util StringUtils   StringUtils getFilenameExtension  quot YourFileName quot

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Without use of any library  you can use the String method split as follows            String   splits   fileNames get i  split                  String extension                if splits length  gt   2                        extension   splits splits length-1

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I like the simplicity of spectre s answer  and linked in one of his comments is a link to another answer that fixes dots in file paths  on another question  made by EboMike   Without implementing some sort of third party API  I suggest   private String getFileExtension File file         String name   file getName   substring Math max file getName   lastIndexOf                   file getName   lastIndexOf         lt  0   0   Math max file getName   lastIndexOf                   file getName   lastIndexOf              int lastIndexOf   name lastIndexOf           if  lastIndexOf    -1            return        empty extension           return name substring lastIndexOf   1      doesn t return     with extension     Something like this may be useful in  say  any of ImageIO s write methods  where the file format has to be passed in   Why use a whole third party API when you can DIY

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Getting File Extension from File Name         The extension separator character      private static final char EXTENSION SEPARATOR                The Unix separator character      private static final char UNIX SEPARATOR                The Windows separator character      private static final char WINDOWS SEPARATOR                 The system separator character      private static final char SYSTEM SEPARATOR   File separatorChar          Gets the extension of a filename      lt p gt     This method returns the textual part of the filename after the last dot     There must be no directory separator after the dot      lt pre gt     foo txt      -- gt   txt     a b c jpg    -- gt   jpg     a b txt c    -- gt        a b c        -- gt         lt  pre gt      lt p gt     The output will be the same irrespective of the machine that the code is running on         param filename the filename to retrieve the extension of      return the extension of the file or an empty string if none exists      public static String getExtension String filename        if  filename    null            return null            int index   indexOfExtension filename       if  index    -1            return           else           return filename substring index   1                   Returns the index of the last extension separator character  which is a dot      lt p gt     This method also checks that there is no directory separator after the last dot     To do this it uses   link  indexOfLastSeparator String   which will    handle a file in either Unix or Windows format      lt p gt     The output will be the same irrespective of the machine that the code is running on         param filename  the filename to find the last path separator in  null returns -1     return the index of the last separator character  or -1 if there    is no such character     public static int indexOfExtension String filename        if  filename    null            return -1            int extensionPos   filename lastIndexOf EXTENSION SEPARATOR       int lastSeparator   indexOfLastSeparator filename       return  lastSeparator  gt  extensionPos   -1   extensionPos             Returns the index of the last directory separator character      lt p gt     This method will handle a file in either Unix or Windows format     The position of the last forward or backslash is returned      lt p gt     The output will be the same irrespective of the machine that the code is running on         param filename  the filename to find the last path separator in  null returns -1     return the index of the last separator character  or -1 if there    is no such character     public static int indexOfLastSeparator String filename        if  filename    null            return -1            int lastUnixPos   filename lastIndexOf UNIX SEPARATOR       int lastWindowsPos   filename lastIndexOf WINDOWS SEPARATOR       return Math max lastUnixPos  lastWindowsPos       Credits   Copied from Apache FileNameUtils Class - http   grepcode com file repo1 maven org maven2 commons-io commons-io 1 3 2 org apache commons io FilenameUtils java FilenameUtils getExtension 28java lang String 29

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Here is another one-liner for Java 8    String ext   Arrays stream fileName split         reduce  a b  - gt  b  orElse null    It works as follows    Split the string into an array of strings using     Convert the array into a stream Use reduce to get the last element of the stream  i e  the file extension

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Here I made a small method  however not that secure and doesnt check for many errors   but if it is only you that is programming a general java-program  this is more than enough to find the filetype  This is not working for complex filetypes  but those are normally not used as much        public static String getFileType String path          String fileType   null         fileType   path substring path indexOf     path lastIndexOf       1  toUpperCase           return fileType

[java] How do I get the file extension of a file in Java?

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