how to check if the file path is invalid/does not exist in java

Question

My task is to save a file in the path specified by the end user (must be an absolute path). Am currently facing three different scenarios as in below:

Path name is invalid (cannot be created) - for ex, path name provided by user : sfg rgdf gfggdgfudf
Path name is invalid (but, it can be created) - for ex : C:\Parent\Child\GrandChildren (here C:\Parent exists whereas Child\GrandChildren does not.
Path name is valid (i.e. directory exists) - for ex : C:\Parent\Test

For the first case, I need to save the file in a default location. For the second, I need to create directories and save the file. And for the last, I'll save in the specified path.

Below is my code snippet which is saving the file in default location for both first and second scenarios. Am having difficulty to distinguish between first and second. java.io.File.mkdirs works for the second case, but not for the first. Please ignore my poor code as am new to this programming language. Any inputs would be much appreciated.

//User input must be absolute path
String  saveToFolder = "kut igeiguye jh";
String defaultFolder = "C:\\Parent\\Data";
try{
    File file = new File(saveToFolder);
    if(!file.exists()){
        saveToFolder = defaultFolder;
    }
    file.mkdirs();
    }catch(Exception e){
    saveToFolder = defaultFolder;
    }
//code to save data in path **saveToFolder**

Why do you think `sfg rgdf gfggdgfudf`is an invalid path? It is valid. It points to the directory named `sfg rgdf gfggdgfudf`in the current directory. — JB Nizet, Aug 31 '17 at 11:29
Check out Christopher Oezbek's answer here, he lists the invalid path characters, so you can filter the string like myFolderPath.contains(":") or myFolderPath.matches("regex_for_invalid_characters") https://stackoverflow.com/questions/1976007/what-characters-are-forbidden-in-windows-and-linux-directory-names — Razor, Aug 31 '17 at 11:32

Rishi Saraf · Answer 1 · 2017-08-31T11:40:35.820

1) For 1st case use regex to determine if path is valid or not

String regularExpression = "([a-zA-Z]:)?(\\[a-zA-Z0-9_-]+)+\\?" ; // this regex for windows. If you are running in linux then regex will be different.

    Pattern pattern = Pattern.compile(regularExpression);

    boolean isMatched = Pattern.matches(regularExpression,saveToFolder);

2) Check if path is valid or not again using 1st method. If its valid check if folder exists or not.

File f = new File(saveToFolder);
if (f.exists() && f.isDirectory()) {
   ...
}

3) If path is valid by first method and if it exists second method .

This is platform-dependent. – Klitos Kyriacou Aug 31 '17 at 11:38 — Klitos Kyriacou, Aug 31 '17 at 11:38

score 1 · Answer 2 · answered Aug 31 '17 at 11:34

1

kut igeiguye jh is happily accepted by most file systems out there. If you don't want spaces in your path/filenames, you already need to check the validity by yourself e.g. using a Regular Expression.

answered Aug 31 '17 at 11:34

Lothar

5,323
1
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am using absolute path and in which case **kut igeiguye jh** is invalid for me. – user8478502 Aug 31 '17 at 12:07

score 0 · Accepted Answer · answered Aug 31 '17 at 13:07

Appreciate all those who added their inputs. I made few changes to my code which works. One of my assignments requirement was that my program must take absolute path as input. With my below code, am able to save data in default location for case 1; New folders are being created and file is being saved in the newly created folder for case 2; And saving the file in specified path for case 3.

    String  saveToFolder = "kut igeiguye jh";
    String defaultFolder = "C:\\Parent\\Data";

    try{
        File file = new File(saveToFolder);
        boolean dirCreated = file.mkdirs();
        if(!dirCreated || (file.getParent().equals(null))){
            saveToFolder = defaultFolder;
        }
    }catch(Exception e){
        saveToFolder = defaultFolder;
    }

    System.out.println("save to folder : " +saveToFolder);

score 0 · Answer 4 · answered Aug 31 '17 at 14:08

you can use isFile() to valid over exists(). I have not checked for all cases but this should help you.

public static void checkPath(){
    String saveToFolder = "file/User.txt";
    String defaultFolder = "file/data/";
    try{
        File file = new File(saveToFolder);
        if(!file.isFile()){
           saveToFolder = defaultFolder;
           System.out.println("File not found");
         }
         file.mkdirs();
         }catch(Exception e){
            saveToFolder = defaultFolder;
         }
    }

DodgyCodeException · Answer 5 · 2017-08-31T14:34:31.940

Java NIO make this simple. The method Files.createDirectories succeeds whether the directory already exists or didn't exist and has been created.

try {
    Files.createDirectories(Paths.get(saveToFolder));
}
catch (IOException e) {
    System.err.println("Using default folder due to the following exception: " + e);
    saveToFolder = defaultFolder;
}

If you really want to check whether the user entered an absolute path, just use Path.isAbsolute().

how to check if the file path is invalid/does not exist in java

5 Answers5