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

user_298758 0
Viewed 800817

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.

io file java
32 Answers

If you use Spring framework in your project, then you can use StringUtils

import org.springframework.util.StringUtils;

StringUtils.getFilenameExtension("YourFileName")
user_40499830

Here is another one-liner for Java 8. 

String ext = Arrays.stream(fileName.split("\\.")).reduce((a,b) -> b).orElse(null)

It works as follows:

  1. Split the string into an array of strings using "."
  2. Convert the array into a stream
  3. Use reduce to get the last element of the stream, i.e. the file extension
user_72773220 
    private String getExtension(File file)
        {
            String fileName = file.getName();
            String[] ext = fileName.split("\\.");
            return ext[ext.length -1];
        }
Admin1

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('\\')) < 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?

user_20897600

The fluent way:

public static String fileExtension(String fileName) {
    return Optional.of(fileName.lastIndexOf(".")).filter(i-> i >= 0)
            .filter(i-> i > fileName.lastIndexOf(File.separator))
            .map(fileName::substring).orElse("");
}
user_75672940

try this.

String[] extension = "adadad.adad.adnandad.jpg".split("\\.(?=[^\\.]+$)"); // ['adadad.adad.adnandad','jpg']
extension[1] // jpg
user_89060770 
  @Test
    public void getFileExtension(String fileName){
      String extension = null;
      List<String> list = new ArrayList<>();
      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());
    }
user_2198650

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 && 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));
    }
user_39941270
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