You can use tools like Jackson to serialize and deserialize maps to json an vice versa.

Example

@Test
public void loadMapFromFileAndSaveIt(){
    Map<Object, Object> map = loadMap("map.json");
    map.put("8", "8th");
    map.remove("7");
    saveMap(map,"/path/to/map2.txt");
}

private Map<Object, Object> loadMap(String string) {
    ObjectMapper mapper = new ObjectMapper(); //should be initialized outside!
    try (InputStream in = Thread.currentThread().getContextClassLoader().getResourceAsStream("map.json")) {
        return mapper.readValue(in, HashMap.class);
    }catch (Exception e) {
        throw new RuntimeException(e);
    }
}

private void saveMap(Map<Object, Object> map,String path) {
    try (PrintWriter out = new PrintWriter(path)) {
        out.println(toString(map));
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}

public String toString(Object obj) {
    try (StringWriter w = new StringWriter();) {
        new ObjectMapper().configure(SerializationFeature.INDENT_OUTPUT, true).writeValue(w, obj);
        return w.toString();
    } catch (Exception e) {
        throw new RuntimeException(e);
    }
}

If the file map.json on your classpath contains

{
 "1":"1th",
 "2":"2th",
 "3":"3th",
 "4":"4th",
 "5":"5th",
 "6":"6th",
 "7":"7th"
}

The code above will modify it and writes it to a file /path/to/map2.txt that will contain the modified map.

{
  "1" : "1th",
  "2" : "2th",
  "3" : "3th",
  "4" : "4th",
  "5" : "5th",
  "6" : "6th",
  "8" : "8th"
}