valid tests save and getFromSave sudoku

app/src/main/java/sudoku/io/SudokuSerializer.java

@@ -1,6 +1,9 @@
 package sudoku.io;
 
 import java.io.*;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Paths;
 import java.util.ArrayList;
 import java.util.List;
 
@@ -101,26 +104,68 @@ public class SudokuSerializer {
 		return jsonRoot;
 	}
 
-	public static void saveMultiDoku(final MultiDoku doku) {
+	/**
+	 * Save a serialized MultiDoku in a JSON file.
+	 * @param doku MultiDoku, MultiDoku to save.
+	 * @return int, number of the save.
+	 */
+	public static int saveMultiDoku(final MultiDoku doku) {
 
 		JSONObject jsonRoot = serializeSudoku(doku);
 
 		File f = new File("save", "save.json");
-		InputStream is = null;
-		int i = 1;
+		int i = 0;
 
 		while (f.exists()) {
-			String newName = "save-" + i + ".json";
+			String newName = "save-" + ++i + ".json";
 			f = new File("save", newName);
-			i++;
 		}
 
 		try (FileWriter file = new FileWriter(f)) {
 			file.write(jsonRoot.toString(3));
-			//file.flush();
 		} catch (IOException e) {
 			e.fillInStackTrace();
 		}
+		return i;
+	}
+
+	/**
+	 * Get a MultiDoku from a pre-existing json save file.
+	 * @param numberSave int, number of the save file to open.
+	 * @return MultiDoku, MultoDoku contained in the file.
+	 * @throws Exception when the given save file does not exist.
+	 */
+	public static MultiDoku getSavedMultiDoku(int numberSave) throws Exception {
+		String fileName;
+		if (numberSave < 1) {
+			fileName = "save.json";
+		} else {
+			fileName = "save-" + numberSave + ".json";
+		}
+
+		File f = new File("save", fileName);
+		String fileContent;
+
+		if (!f.exists()) {
+			throw new Exception("This save does not exist.");
+		} else {
+			fileContent = new String(Files.readAllBytes(Paths.get("save/" + fileName)));
+			/*
+			try {
+				FileReader file = new FileReader(f);
+				char[] rawFileContent = {};
+				int length = 1000;
+				while (file.read(rawFileContent, 0, length) != -1) {
+					rawFileContent = new char[]{};
+					length = length * 10;
+				}
+				fileContent = new String(rawFileContent);
+			} catch (IOException e) {
+				throw new Exception("Error reading file.");
+			}
+			*/
+			return deserializeSudoku(fileContent);
+		}
 	}
 
 	public static MultiDoku deserializeSudoku(final String json) {