FileNotFoundException异常。 工作并不同时工作？

Question

I have the following code in a static class called Methods that is archived in a jar:

System.out.println(Methods.class.getResource("tagdict.txt")); // 1
URL test = Methods.class.getResource("tagdict.txt");          // 2
System.out.println(test.getPath());                           // 3
TagDictionary dict = new POSDictionary(test.getPath());       // 4

The first System.out (1) says:

rsrc:de/fhg/scai/bio/harsha/classificationworkflow/tagdict.txt

The second System.out (2) says:

de/fhg/scai/bio/harsha/classificationworkflow/tagdict.txt

Line 4 throws a

java.io.FileNotFoundException: de/fhg/scai/bio/harsha/classificationworkflow/tagdict.txt (No such file or directory)

The file tagdict.txt is placed in the same package as the Method.class , which is de/fhg/scai/bio/harsha/classificationworkflow .

I do not understand why line 4 throws a FileNotFoundException even though the file was found already inside the jar.

Answer 1

Line 3 just prints out the path component of the URL returned by getResource . It doesn't actually check if that path represents a real file on disk.

It looks like the POSDictionary constructor is trying to create a File using the path string passed to it, and this path doesn't actually represent an on-disk file, therefore throwing the exception.

I do not understand why line 4 throws a FileNotFoundException even though the file was found already inside the jar.

Because if the resource is in a JAR, then it's not a file. Such resources can only be accessed by opening input streams directly from the URL object, or by using getResourceAsStream() instead of getResource() . They can't be accessed using java.io.File , since they're not actual disk files.