Trying to use getResourceAsStream() and failing

Question

I am trying to replace all instances of using Files and FileReaders and replace them with InputStreams and appropriate readers in preparation for packing the app in a jar - however, when I try to use ClassLoader.getSystemClassLoader().getResourceAsStream() with the same path that the File approach managed to find, it fails due to failing to find the file.

The code I use and output:

The text in the file:

e:Easy
definitions/easy_level_definitions.txt
h:Hard
definitions/hard_level_definitions.txt
d:Derp
definitions/derp_level_definitions.txt

Code:

    String line;
    File f = new File("src/resources/level_sets.txt");
    BufferedReader reader1 = null;
    try {
        reader1 = new BufferedReader(new FileReader(f));
        while ((line = reader1.readLine()) != null) {
            System.out.println(line);
        }
    } catch (FileNotFoundException e) {
        e.printStackTrace();
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            if (reader1 != null) {
                reader1.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }
    line = null;
    InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("src/resources/level_sets.txt");
    BufferedReader reader = new BufferedReader(new InputStreamReader(is));
    try {
        while ((line = reader.readLine()) != null) {
            System.out.println(line);
        }
    } catch (IOException e) {
        e.printStackTrace();
    } finally {
        try {
            if (reader != null) {
                reader.close();
            }
        } catch (IOException e) {
            e.printStackTrace();
        }
    }

Output:

e:Easy
definitions/easy_level_definitions.txt
h:Hard
definitions/hard_level_definitions.txt
d:Derp
definitions/derp_level_definitions.txt
Exception in thread "main" java.lang.NullPointerException
    at java.io.Reader.<init>(Unknown Source)
    at java.io.InputStreamReader.<init>(Unknown Source)
    at Testing.main(Testing.java:34)

Answer 1

The "src" folder is only available in your IDE. Once the app is packaged, it wont exist anymore and the resource will be available at the root of the classpath. Use this:

InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("/level_sets.txt");

Answer 2

This is hard to know because it looks like you're not using standard Maven-style directories and it's not totally apparent what your classpath is, but it would seem like you should use /level_sets.txt or maybe /src/level_sets.txt, not src/resources/level_sets.txt. The argument is giving the location of the resource in the classpath, it seems very unlikely that the src directory would be part of the classpath, and it's unclear whether resources would be.

The leading slash says to look directly under the root of the classpath.

As part of the build process typically files get copied from a src directory to a target directory (could be named bin or classes). Your code needs to look relative to the target directory, not under src.

Answer 3

 InputStream is = ClassLoader.getSystemClassLoader().getResourceAsStream("src/resources/level_sets.txt");

Your path starts with "src/". Try to replace it with the binary folder (bin or classes).