diff -r e70a0e3555fb -r 576e7a2861ae src/main/java/de/uapcore/sudoku/DocumentHandler.java
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/main/java/de/uapcore/sudoku/DocumentHandler.java	Sat Jul 25 14:01:28 2020 +0200
@@ -0,0 +1,104 @@
+/*
+ * Copyright 2013 Mike Becker. All rights reserved.
+ * 
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions are met:
+ * 
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 
+ * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS"
+ * AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT HOLDER OR CONTRIBUTORS BE
+ * LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
+ * CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
+ * SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
+ * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
+ * POSSIBILITY OF SUCH DAMAGE.
+ */
+
+package de.uapcore.sudoku;
+
+import java.io.*;
+import java.util.regex.Matcher;
+import java.util.regex.Pattern;
+
+/**
+ *
+ * @author mike
+ */
+public class DocumentHandler {
+    
+    private String filename;
+    
+    public void load(Field field) throws IOException {
+        if (!isFilenameSet()) {
+            throw new IOException("no filename supplied");
+        }
+        int row = 0;
+        try (BufferedReader in = new BufferedReader(
+                new InputStreamReader(new FileInputStream(filename)))) {
+            Pattern pat = Pattern.compile("^\\s*(?:[1-9_] ){8}[1-9_]\\s*$");
+            String line;
+            while ((line = in.readLine()) != null) {
+                if (line.matches("^\\s*$")) {
+                    continue;
+                }
+                Matcher m = pat.matcher(line);
+                if (m.matches()) {
+                    String c[] = line.trim().split(" ");
+                    if (c.length != 9) {
+                        break;
+                    }
+                    for (int i = 0 ; i < 9 ; i++) {
+                        field.setCellValue(i, row,
+                                c[i].equals("_") ? 0 : Integer.valueOf(c[i]));
+                    }
+                    row++;
+                } else {
+                    break;
+                }
+            }
+            if (row != 9) {
+                throw new IOException("Kein Sudoku-Feld enthalten!");
+            }
+        }
+        field.setAllCellsModified(false);
+    }
+    
+    public void save(Field field) throws IOException {
+        if (!isFilenameSet()) {
+            throw new IOException("no filename supplied");
+        }
+        
+        try (BufferedWriter out = new BufferedWriter(
+                new OutputStreamWriter(new FileOutputStream(filename)))) {
+            for (int i = 0 ; i < 9 ; i++) {
+                int[] row = field.getRow(i);
+                for (int j = 0 ; j < 9 ; j++) {
+                    out.append(row[j] > 0 ? Character.forDigit(row[j], 10):'_');
+                    out.append(j == 8 ? '\n': ' ');
+                }
+            }
+        }
+    }
+    
+    public void setFilename(String filename) {
+        this.filename = filename;
+    }
+    
+    public void clearFilename() {
+        filename = null;
+    }
+    
+    public boolean isFilenameSet() {
+        return filename != null;
+    }
+}