Why does `getResourceAsStream` sometimes load a resource even when there is a typo in the resource path?

Question

I have a Jar (we'll call it a.jar) with a resource in it at path foo/bar.txt and a function as follows:

object FooBarLoader {
    fun loadFooBarText() = javaClass.getResourceAsStream("foo//bar.txt")
        ?.bufferedReader()
        ?.readLines()
        ?.joinToString("\n")
} 

When I test the function in a unit test (JUnit 4, running with Gradle 6), it loads the text from the resource file despite the obvious typo (the // in the middle of the resource path).

I also have a CLI application (in b.jar) that has a dependency on a.jar. When the CLI application calls loadFooBarText(), it got a null result due to the resource not being found. This was fixed by fixing the typo (// -> /) in the function in a.jar. No other changes were needed to fix it.

So, my question is why did the wrong path work in one situation (unit tests of a.jar) and not the other (call from b.jar)?

Answer 1

How do you run the unit test with a.jar ? Just run it in your IDE or use command java -jar a.jar ?

If you ran it just in IDE，I think difference is the search path between local files and zip files .

Your first application searches the file in your target directory and the second application searches it in the jar which is a compressed file.

When searching files in local path, command will be changed to right one by system.

The two commands below are the same in both Windows/Linux.

cd work//abc/ddd

cd work/abc/ddd

But when searching files in a jar file which is actually compressed zip file, path should be a restrict written or else the program will find nothing.