GP-28 Add File Reader solution to exercise/completed

Author: shryhus

3-0-java-core/src/main/java/com/bobocode/file_reader/FileReaderException.java

@@ -0,0 +1,7 @@
+package com.bobocode.file_reader;
+
+public class FileReaderException extends RuntimeException {
+    public FileReaderException(String message, Exception e) {
+        super(message, e);
+    }
+}

3-0-java-core/src/main/java/com/bobocode/file_reader/FileReaders.java

@@ -2,6 +2,17 @@
 
 import com.bobocode.util.ExerciseNotCompletedException;
 
+import java.io.IOException;
+import java.net.URISyntaxException;
+import java.net.URL;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.util.Objects;
+import java.util.stream.Stream;
+
+import static java.util.stream.Collectors.joining;
+
 /**
  * {@link FileReaders} provides an API that allow to read whole file into a {@link String} by file name.
  */
@@ -14,6 +25,27 @@ public class FileReaders {
      * @return string that holds whole file content
      */
     public static String readWholeFile(String fileName) {
-        throw new ExerciseNotCompletedException(); //todo
+        Path filePath = createPathFromFileName(fileName);
+        try (Stream<String> fileLinesStream = openFileLinesStream(filePath)) {
+            return fileLinesStream.collect(joining("\n"));
+        }
+    }
+
+    private static Path createPathFromFileName(String fileName) {
+        Objects.requireNonNull(fileName);
+        URL fileUrl = FileReaders.class.getClassLoader().getResource(fileName);
+        try {
+            return Paths.get(fileUrl.toURI());
+        } catch (URISyntaxException e) {
+            throw new FileReaderException("Invalid file URL",e);
+        }
+    }
+
+    private static Stream<String> openFileLinesStream(Path filePath) {
+        try {
+            return Files.lines(filePath);
+        } catch (IOException e) {
+            throw new FileReaderException("Cannot create stream of file lines!", e);
+        }
     }
 }