java.nio.file.Paths - 如何在迭代时跳过无法访问的文件/文件夹

Question

I am writing code to iterate through all folders that i can access. However my program stops when on folder is inaccessible.

How do i bypass that folder and keep looking for others? Or, in other words, how do i show folders and files i have access to?

i am using java.nio.file.Paths (Java 8).

Here's my code:

import java.io.IOException;
import java.nio.file.FileVisitOption;
import java.nio.file.Files;
import java.nio.file.Paths;

// Test File D:\TEST\test.jpg
public class TestIteration{

    // Main
    public static void main(String[] args) throws Exception {
        // Iterate through folders
        String rootFolder = "c:\\";    
        WalkDirTree(rootFolder); // Walks through directory tree and print names of directories/files.      
    }


    // Prints all file/directory names in the entire directory tree
    private static void WalkDirTree(String rootFolder) throws Exception {                   
        Files.walk(Paths.get(rootFolder)).forEach(path -> {
            System.out.println(path);
        });

        System.out.println("_______________________________________DONE");
    }

}

Answer 1

If by inaccessible you're referring to "not readable", then I reckon you can use Files#isReadable ; from its documentation:

Tests whether a file is readable. This method checks that a file exists and that this Java virtual machine has appropriate privileges that would allow it open the file for reading. Depending on the implementation, this method may require to read file permissions, access control lists, or other file attributes in order to check the effective access to the file. Consequently, this method may not be atomic with respect to other file system operations.

Your code would look like:

Files.walk(Paths.get(rootFolder)).filter(Files::isReadable).forEach(path -> {
    System.out.println(path);
});

Answer 2

While streams are certainly beautiful, you might need to deal with each inaccessible file individually.

In that case, you could choose to have a simple for loop by using the FileUtils.listFiles method from org.apache.commons.io

String[] extensions = {"png","txt"}; // file extensions you might want to target
Collection fileObjects= FileUtils.listFiles(new File("dirPath"),extensions,true);
for (Object obj : fileObjects){
     File file = (File) obj;
     if (!Files.isReadable(file.toPath())) continue; // or do smth else
}

If you wish to target all files regardless their extensions, then pass null instead of the a String array.

If you do not wish recursive search, then pass false instead of true