print directory tree

Question

I have to print a directory tree (like tree command), example:

 .
 +---A
 |   +---IMAGES
 |       +---BACKUP
 +---ADOKS
 |   +---ROZDZIAL_2
 |   +---ROZDZIAL         


        

Answer 1

I was testing the solution with the most upticks written by @tan70 however it caused a null pointer exception on printing my home directory. I did some investigation and found that listFiles() can return null.

public File[] listFiles()

Returns an array of abstract pathnames denoting the files in the directory denoted by this abstract pathname.

If this abstract pathname does not denote a directory, then this method returns null. Otherwise an array of File objects is returned, one for each file or directory in the directory

/**
 * Pretty print the directory tree and its file names.
 *
 * @param path
 * @return
 */
public static String printDirectoryTree(String path) {
    File folder = new File(path);
    if (!folder.isDirectory()) {
        throw new IllegalArgumentException("folder is not a Directory");
    }
    int indent = 0;
    StringBuilder sb = new StringBuilder();
    printDirectoryTree(folder, indent, sb);
    return sb.toString();
}

private static void printDirectoryTree(File folder, int indent, StringBuilder sb) {

    if (folder != null && folder.isDirectory() && folder.listFiles() != null) {
        sb.append(getIndentString(indent));
        sb.append("+--");
        sb.append(folder.getName());
        sb.append("/");
        sb.append("\n");

        for (File file : folder.listFiles()) {
            if (file.isDirectory()) {
                printDirectoryTree(file, indent + 1, sb);
            } else {
                printFile(file, indent + 1, sb);
            }
        }
    }
}

private static void printFile(File file, int indent, StringBuilder sb) {
    sb.append(getIndentString(indent));
    sb.append("+--");
    if (file != null) {
        sb.append(file.getName());
    } else {
        sb.append("null file name");
    }
    sb.append("\n");
}

private static String getIndentString(int indent) {
    StringBuilder sb = new StringBuilder();
    for (int i = 0; i < indent; i++) {
        sb.append("|  ");
    }
    return sb.toString();
}