Unable to open resources in directories which end with an exclamation mark (!)

Question

The getResourceAsStream-method returns null whenever running the executable jar in a directory which ends with a exclamation mark.

For the following example, I have a Eclipse project the following directory structure:

src\ (Source Folder)
    main\ (Package)
        Main.java
    res\ (Source Folder)
        images\
            Logo.png

I'm reading the Logo.png as follows:

public static void main(String[] args) throws IOException {
    try (InputStream is = Main.class.getClassLoader().getResourceAsStream("images/Logo.png")) {
        Image image = ImageIO.read(is);
        System.out.println(image);
    }   
}

See the attachment for 2 test cases. First, the executable jar is started from the directory "D:\test123!@#" without any problems. Secondly, the executable jar is started from the directory "D:\test123!@#!!!", with problems.

Are directories ending with an exclamation mark not supported? Is the code wrong?

Thanks in advance.

Answer 1

Probably because of this bug or any of the many similar bugs in the Java bug database:

https://bugs.java.com/bugdatabase/view_bug?bug_id=4523159

The reason is that "!/" in a jar URL is interpreted as the separator between the JAR file name and the path within the JAR itself. If a directory name ends with !, the "!/" character sequence at the end of the directory is incorrectly interpreted. In your case, you are actually trying to access a resource with the following URL:

jar:file:///d:/test1231@#!!!/test.jar!/images/Logo.png

The bug has been open for almost 12 years and is not likely to be fixed. Actually I don't know how it can be fixed without breaking other things. The problem is the design decision to use ! as a character with a special meaning (separator) in the URL scheme for JAR files:

jar:<URL for JAR file>!/<path within the JAR file>

Since the exclamation mark is an allowed character in URLs, it may occur both in the URL to the JAR file itself, as well as in the path within the JAR file, making it impossible in some cases to find the actual "!/" separator.