fixed some issues

src/main/java/com/cpsc329pm/DataStorage.java

@@ -2,6 +2,8 @@ package com.cpsc329pm;
 
 import java.io.*;
 import java.util.*;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.logging.Logger;
 
 import com.fasterxml.jackson.databind.*;