Add loading object to file and reading object from file

src/FileManager.java

@@ -1,8 +1,7 @@
-import java.io.File;
-import java.io.FileWriter;
-import java.io.IOException;
+import java.io.*;
 import java.util.Scanner;
 
+// TODO: close scanner etc after use
 public class FileManager {
     public static void writeFile(String fileLocation, String writeString) throws IOException {
         File newFile = new File(fileLocation);
@@ -22,4 +21,16 @@ public class FileManager {
             return fileReader.useDelimiter("\\Z").next();
         }
     }
+
+    public static Object readObjectFromFile(String fileLocation, String allowedObject) throws IOException, ClassNotFoundException {
+        FileInputStream fileStream = new FileInputStream(fileLocation);
+        SafeObjectInputStream objectStream = new SafeObjectInputStream(fileStream, allowedObject);
+        return objectStream.readObject();
+    }
+
+    public static void writeObjectToFile(String fileLocation, Object o) throws IOException {
+        FileOutputStream fileStream = new FileOutputStream(fileLocation);
+        ObjectOutputStream objectStream = new ObjectOutputStream(fileStream);
+        objectStream.writeObject(o);
+    }
 }

src/SafeObjectInputStream.java

@@ -0,0 +1,24 @@
+import java.io.IOException;
+import java.io.InputStream;
+import java.io.ObjectInputStream;
+import java.io.ObjectStreamClass;
+
+public class SafeObjectInputStream extends ObjectInputStream {
+
+    String allowedClass;
+
+    public SafeObjectInputStream(InputStream in, String allowedClass) throws IOException {
+        super(in);
+        this.allowedClass = allowedClass;
+    }
+
+    // local files are generally assumed to be safe, but this additional check slightly hardens the application against using arbitrary attacks to exploit
+    // please note that it is still insecure; don't use in sensitive contexts!
+    @Override
+    protected Class<?> resolveClass(ObjectStreamClass desc) throws IOException, ClassNotFoundException {
+        if (!desc.getName().equals(allowedClass)) {
+            throw new SecurityException();
+        }
+        return super.resolveClass(desc);
+    }
+}

src/UtilityFunction.java

@@ -1,4 +1,6 @@
 import java.awt.event.KeyEvent;
+import java.io.IOException;
+import java.io.ObjectInputStream;
 import java.lang.reflect.Array;
 import java.util.ArrayList;