implement getting resource file as input stream

src/main/java/ResourceApi.java

@@ -0,0 +1,16 @@
+import java.io.InputStream;
+
+public class ResourceApi {
+
+    public InputStream getFileFromResourceAsStream(String fileName) {
+        //ClassLoader classLoader = getClass().getClassLoader();
+        ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
+        InputStream inputStream = classLoader.getResourceAsStream(fileName);
+
+        if (inputStream == null) {
+            throw new IllegalArgumentException("file not found! " + fileName);
+        } else {
+            return inputStream;
+        }
+    }
+}

src/test/java/ResourceApiTest.java

@@ -0,0 +1,39 @@
+import org.junit.jupiter.api.BeforeAll;
+import org.junit.jupiter.api.Test;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.InputStreamReader;
+
+import static org.junit.jupiter.api.Assertions.assertThrowsExactly;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+class ResourceApiTest {
+
+    private static ResourceApi resourceApi;
+
+    @BeforeAll
+    static void init() {
+        resourceApi = new ResourceApi();
+    }
+
+    @Test
+    void getFileFromResourceAsStream() throws IOException {
+        assertThrowsExactly(IllegalArgumentException.class,
+                () -> resourceApi.getFileFromResourceAsStream("does_not_exist"));
+
+        InputStream is = resourceApi.getFileFromResourceAsStream("german_wordlist.txt");
+
+        BufferedReader in = new BufferedReader(new InputStreamReader(is));
+        String inputLine;
+        StringBuffer response = new StringBuffer();
+
+        while ((inputLine = in.readLine()) != null) {
+            response.append(inputLine + "\n");
+        }
+        in.close();
+
+        assertTrue(response.toString().contains("Alleinherrschaft"));
+    }
+}