src/main/java/com/github/wnameless/json/flattener/JsonFlattener.java
public JsonFlattener withSeparator(char separator) {
    isTrue(!Character.toString(separator).matches("[\"\\s]"),
        "Separator contains illegal chracter(%s)",
        Character.toString(separator));
    isTrue(!leftBracket.equals(separator) && !rightBracket.equals(separator),
        "Separator(%s) is already used in brackets",
        Character.toString(separator));

    this.separator = separator;
    flattenedMap = null;
    return this;
  }
public JsonFlattener withSeparator(char separator) {
    isTrue(!Character.toString(separator).matches("[\"\\s]"),
        "Separator contains illegal chracter(%s)",
        Character.toString(separator));
    isTrue(!leftBracket.equals(separator) && !rightBracket.equals(separator),
        "Separator(%s) is already used in brackets",
        Character.toString(separator));

    this.separator = separator;
    flattenedMap = null;
    return this;
  }
A fluent setter to setup the separator within a key in the flattened JSON.
The default separator is a dot(.).

@param separator
any character
@return this {@link JsonFlattener}