In this post we'll see how to read or list all the files in a directory using Java. Suppose you have folder with files in it and there are sub-folders with files in those sub-folders and you want to read or list all the files in the folder recursively.
Here is a folder structure used in this post to read the files. Test, Test1 and Test2 are directories here and then you have files with in those directories.
Test
abc.txt
Test1
test.txt
test1.txt
Test2
xyz.txt
Java Example to read all the files in a folder recursively
There are two ways to list all the files in a folder; one is using the listFiles() method of the File class which is there in Java from 1.2.
Another way to list all the files in a folder is to use Files.walk() method which is a recent addition in Java 8.
import java.io.BufferedReader;
import java.io.File;
import java.io.FileReader;
import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.nio.file.Paths;
import java.util.List;
import java.util.stream.Stream;
public class ListFiles {
public static void main(String[] args) {
File folder = new File("G:\\Test");
ListFiles listFiles = new ListFiles();
System.out.println("reading files before Java8 - Using listFiles() method");
listFiles.listAllFiles(folder);
System.out.println("-------------------------------------------------");
System.out.println("reading files Java8 - Using Files.walk() method");
listFiles.listAllFiles("G:\\Test");
}
// Uses listFiles method
public void listAllFiles(File folder){
System.out.println("In listAllfiles(File) method");
File[] fileNames = folder.listFiles();
for(File file : fileNames){
// if directory call the same method again
if(file.isDirectory()){
listAllFiles(file);
}else{
try {
readContent(file);
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
// Uses Files.walk method
public void listAllFiles(String path){
System.out.println("In listAllfiles(String path) method");
try(Stream<Path> paths = Files.walk(Paths.get(path))) {
paths.forEach(filePath -> {
if (Files.isRegularFile(filePath)) {
try {
readContent(filePath);
} catch (Exception e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
});
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
public void readContent(File file) throws IOException{
System.out.println("read file " + file.getCanonicalPath() );
try(BufferedReader br = new BufferedReader(new FileReader(file))){
String strLine;
// Read lines from the file, returns null when end of stream
// is reached
while((strLine = br.readLine()) != null){
System.out.println("Line is - " + strLine);
}
}
}
public void readContent(Path filePath) throws IOException{
System.out.println("read file " + filePath);
List<String> fileList = Files.readAllLines(filePath);
System.out.println("" + fileList);
}
}
Output
reading files before Java8 - Using listFiles() method In listAllfiles(File) method read file G:\Test\abc.txt Line is - This file is in Test folder. In listAllfiles(File) method read file G:\Test\Test1\test.txt Line is - This file test is under Test1 folder. read file G:\Test\Test1\test1.txt Line is - This file test1 is under Test1 folder. In listAllfiles(File) method read file G:\Test\Test2\xyz.txt Line is - This file xyz is under Test2 folder. ------------------------------------------------- reading files Java8 - Using Files.walk() method In listAllfiles(String path) method read file G:\Test\abc.txt [This file is in Test folder.] read file G:\Test\Test1\test.txt [This file test is under Test1 folder.] read file G:\Test\Test1\test1.txt [This file test1 is under Test1 folder.] read file G:\Test\Test2\xyz.txt [This file xyz is under Test2 folder.]
Here we have two overloaded listAllFiles() methods. First one takes File instance as argument and use that instance to read files using the File.listFiles() method. In that method while going through the list of files under a folder you check if the next element of the list is a file or a folder. If it is a folder then you recursively call the listAllFiles() method with that folder name. If it is a file you call the readContent() method to read the file using BufferedReader.
Another version of listAllFiles() method takes String as argument. In this method whole folder tree is traversed using the Files.walk() method. Here again you verify if it is a regular file then you call the readContent() method to read the file.
Note that readContent() method is also overloaded one takes File instance as argument and another Path instance as argument.
If you just want to list the files and sub-directories with in the directory then you can comment the readContent() method.
That's all for this topic Read or List All Files in a Folder in Java. If you have any doubt or any suggestions to make please drop a comment. Thanks!
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