I would like to get a list of files with a specific extension in a directory. In the API (Java 6), I see a method File.listFiles(FileFilter)
which would do this.
Since I need a specific extension, I created a FileNameExtensionFilter
. However I get a compilation error when I use listFiles
with this. I assumed that since FileNameExtensionFilter implements FileFilter
, I should be able to do this. Code follows:
FileNameExtensionFilter filter = new FileNameExtensionFilter("text only","txt");
String dir = "/users/blah/dirname";
File f[] = (new File(dir)).listFiles(filter);
The last line shows a compilation error:
method listFiles(FileNameFilter) in type File is not applicable for arguments of type FileNameExtensionFilter
I am trying to use listFiles(FileFilter)
, not listFiles(FileNameFilter)
. Why does the compiler not recognize this?
This works if I write my own extension filter extending FileFilter
. I would rather use FileNameExtensionFilter
than write my own. What am I doing wrong?
Here's something I quickly just made and it should perform far better than File.getName().endsWith(".xxxx");
import java.io.File;
import java.io.FileFilter;
public class ExtensionsFilter implements FileFilter
{
private char[][] extensions;
private ExtensionsFilter(String[] extensions)
{
int length = extensions.length;
this.extensions = new char[length][];
for (String s : extensions)
{
this.extensions[--length] = s.toCharArray();
}
}
@Override
public boolean accept(File file)
{
char[] path = file.getPath().toCharArray();
for (char[] extension : extensions)
{
if (extension.length > path.length)
{
continue;
}
int pStart = path.length - 1;
int eStart = extension.length - 1;
boolean success = true;
for (int i = 0; i <= eStart; i++)
{
if ((path[pStart - i] | 0x20) != (extension[eStart - i] | 0x20))
{
success = false;
break;
}
}
if (success)
return true;
}
return false;
}
}
Here's an example for various images formats.
private static final ExtensionsFilter IMAGE_FILTER =
new ExtensionsFilter(new String[] {".png", ".jpg", ".bmp"});
Is there a specific reason you want to use FileNameExtensionFilter
? I know this works..
private File[] getNewTextFiles() {
return dir.listFiles(new FilenameFilter() {
@Override
public boolean accept(File dir, String name) {
return name.toLowerCase().endsWith(".txt");
}
});
}
The FileNameExtensionFilter
class is intended for Swing to be used in a JFileChooser
.
Try using a FilenameFilter
instead. For example:
File dir = new File("/users/blah/dirname");
File[] files = dir.listFiles(new FilenameFilter() {
public boolean accept(File dir, String name) {
return name.toLowerCase().endsWith(".txt");
}
});
One-liner in java 8 syntax:
pdfTestDir.listFiles((dir, name) -> name.toLowerCase().endsWith(".txt"));
Duh.... listFiles requires java.io.FileFilter. FileNameExtensionFilter extends javax.swing.filechooser.FileFilter. I solved my problem by implementing an instance of java.io.FileFilter
Edit: I did use something similar to @cFreiner's answer. I was trying to use a Java API method instead of writing my own implementation which is why I was trying to use FileNameExtensionFilter. I have many FileChoosers in my application and have used FileNameExtensionFilters for that and I mistakenly assumed that it was also extending java.io.FileFilter.
With java lambdas (available since java 8) you can simply convert javax.swing.filechooser.FileFilter
to java.io.FileFilter
in one line.
javax.swing.filechooser.FileFilter swingFilter = new FileNameExtensionFilter("jpeg files", "jpeg");
java.io.FileFilter ioFilter = file -> swingFilter.accept(file);
new File("myDirectory").listFiles(ioFilter);
Source: Stackoverflow.com