How to convert a HashMap to a K/V-String in Java 8 with Streams

Question

I want to create a string of the key value pairs of my HashMap<String, String> m as fast as possible.

I tried:

StringBuffer buf = new StringBuffer();
buf.append("[");
for (String key : m.keySet()) {
   buf.append(key);
   buf.append("=");
   buf.append(m.get(key));
   buf.append(";");
}
buf.append("]");

With Java8 I tried:

m.entrySet().stream()
            .map(entry -> entry.getKey() + " = " + entry.getValue())
            .collect(Collectors.joining("; " , "[" , "]"));

Is there any faster, better code to do that? It seems to be costly to append the keys and Values in the map function, doesn't it?

Answer 1

map -> map.entrySet().stream().map(Entry::toString).collect(joining(";", "[", "]"))

(Note that I omitted the imports.)

Like Luiggi Mendoza said:

I would not worry about performance in this case unless it's a critical part of the system and it's pointed out as a bottleneck by usage of a profiler or a similar tool. If you haven't done this before and you think this code is not optimal, then I̶ ̶k̶n̶o̶w̶ ̶t̶h̶a̶t̶ maybe you're wrong and should test it first.