public static <K, V> String mkString(Map<K, V> map, String begin, String end,
                                         String keyValueSeparator, String elementSeparator) {
        StringBuilder bld = new StringBuilder();
        bld.append(begin);
        String prefix = "";
        for (Map.Entry<K, V> entry : map.entrySet()) {
            bld.append(prefix).append(entry.getKey()).
                    append(keyValueSeparator).append(entry.getValue());
            prefix = elementSeparator;
        }
        bld.append(end);
        return bld.toString();
    }
Converts a {@code Map} class into a string, concatenating keys and values
 Example:
     {@code mkString({ key: "hello", keyTwo: "hi" }, "|START|", "|END|", "=", ",")
         => "|START|key=hello,keyTwo=hi|END|"}
clients/src/main/java/org/apache/kafka/common/utils/Utils.java