[Java] Read the file in src / main / resources

It took a while to read the file in src / main / resources in Java, so it's a reminder.

1. Get with absolute path from root

src/main/resources/sample1.txt

sample1

src/main/java/Foo.java

public void sample1() {
    String path = "src/main/resources/sample1.txt";
    try (BufferedReader br = Files.newBufferedReader(Paths.get(path))) {

        System.out.println(br.readLine());

    } catch (IOException e) {
        e.printStackTrace();
    }
}

Execution result

sample1

2. Get relative to the classpath

src/main/resources/sample2.txt

sample2

src/main/java/Foo.java

public void sample2() {
    String path = "/sample2.txt";
    //Foo for static methods.class.Write like getResourceAsStream(Foo is the class name)
    try (InputStream is = getClass().getResourceAsStream(path);
        BufferedReader br = new BufferedReader(new InputStreamReader(is))) {

        System.out.println(br.readLine());

    } catch (IOException e) {
        e.printStackTrace();
    }
}

Execution result

sample2

important point

In 1 and 2, when testing, the behavior when there is a file with the same name in src / test / resources is different.

src/test/resources/sample1.txt

test1

src/test/resources/sample2.txt

test2

src/test/java/FooTest.java

public class FooTest {
  @Test
  public void testInput() throws Exception {
    Foo foo = new Foo();
    foo.sample1();  // src/main/resources/sample1.Read txt
    foo.sample2();  // src/test/resources/sample2.Read txt
  }
}

Execution result

sample1
test2

In the case of 1, it is natural because the path is written directly, but sample1.txt under the src / main / resources directory is read. In case of 2, sample2.txt under the src / test / resources directory is read in preference to src / main / resources.

If there is no sample2.txt in the src / test / resources directory, sample2.txt under the src / main / resources directory will be read as it is.

Summary

Should I use Class # getResourceAsStream for the time being? I would appreciate it if you could let me know if you have any problems.

reference: Getting resources [Java] Difference in how to get files on the classpath

Digression

When I got the absolute path via Class # getResource instead of Class # getResourceAsStream and passed it to Paths # get, I got java.nio.file.InvalidPathException.

String filename= "/sample2.txt";
String filepath = getClass().getResource(filename).getPath();
Path path = Paths.get(filepath); // java.nio.file.InvalidPathException

It seems that the drive letter part needs to be escaped in the Windows environment, and I was able to get it by replacing it as follows.

String filename= "/sample2.txt";
String filepath = getClass().getResource(filename).getPath();
Path path = Paths.get(filepath .replaceFirst("^/(.:/)", "$1")); // OK

Reference: create Java NIO file path problem