Java File exists Case sensitive .jpg and .JPG

Question

I use this function to detect if my file exists or not. While I have some image stored as .jpg, .JPG, .png, and .PNG. But it always return .jpg or .png as true even if the real file has extension .JPG or .PNG.

After I render it to my webpage it throws an error "Failed to load resource: the server responded with a status of 404 (Not Found)".

public static String getPhotoFileExtension(int empKey){     try{         String[] types = {".jpg",".JPG",".png", ".PNG"};         for(String t : types)         {             String path = "/"+Common.PHOTO_PATH + empKey + t;             File f = new File(Sessions.getCurrent().getWebApp()                     .getRealPath(path));             if(f.isFile())                  return t;         }     }catch (Exception e) {         e.printStackTrace();     }     return ""; } 

Answer 1

So you want to get the real case sensitive names of files stored in your filesystem. Lets imaging we have the following paths:

• on Linux: using ext4 (which is case sensitive) /testFolder/test.PnG
• on Windows using NTFS (which is not case sensitive) c:\testFolder\test.PnG

Now lets create some Java File Objects to each Image File.

// on Linux File f1 = new File("/testFolder/test.png"); File f2 = new File("/testFolder/test.PNG"); File f3 = new File("/testFolder/test.PnG"); f1.exists(); // false f2.exists(); // false f3.exists(); // true  // on Windows File f1 = new File("c:\\testFolder\\test.png"); File f2 = new File("c:\\testFolder\\test.PNG"); File f3 = new File("c:\\testFolder\\test.PnG"); f1.exists(); // true f2.exists(); // true f3.exists(); // true 

Your problem is that all calls of File like File.exists are redirected to the java.io.FileSystem class that represents real Operating System calls of your File System by the JVM. So you cannot distinguish on Windows Machines between test.PNG and test.png. Neither do Windows itself.

But even on Windows each File has a defined name in the File System that could be for example: test.PnG. You will see this in your Windows Explorer or in Command Line if you type dir c:\testFolder.

So what you can do in Java is use the File.list method on the parent directory that results in the Operating System list call for all files in this directory with their real names.

File dir = new File("c://testFolder//"); for(String fileName : dir.list())     System.out.println(fileName); // OUTPUT: test.PnG 

or if you prefer File Objects

File dir = new File("c://testFolder//"); for(File file : dir.listFiles())     System.out.println(file.getName()); // OUTPUT: test.PnG 

You can use this to write your own exists Method that is case sensitive on all operating systems

public boolean exists(File dir, String filename){     String[] files = dir.list();     for(String file : files)         if(file.equals(filename))             return true;     return false; } 

Use it like this:

File dir = new File("c:\\testFolder\\"); exists(dir, "test.png");   // false exists(dir, "test.PNG");   // false exists(dir, "test.PnG");   // true 

EDIT: I have to admit that I was wrong. There is a way to get the real name of a File. I always overlooked the method File.getCanonicalPath.
Again our example: We have that File c:\testFolder\test.PnG.

File f = new File("c://testFolder//test.png"); System.out.println(f.getCanonicalPath()); // OUTPUT: C:\testFolder\test.PnG 

With that knowledge you can write a simple test method for the case sensitive extension without iterating all files.

public boolean checkExtensionCaseSensitive(File _file, String _extension) throws IOException{     String canonicalPath = _file.getCanonicalPath();     String extension = "";     int i = canonicalPath.lastIndexOf('.');     if (i > 0) {         extension = canonicalPath.substring(i+1);         if(extension.equals(_extension))             return true;     }     return false; } 

Use it like this:

File f = new File("c://testFolder//test.png");     checkExtensionCaseSensitive(f, "png"); // false checkExtensionCaseSensitive(f, "PNG"); // false checkExtensionCaseSensitive(f, "PnG"); // true