Store HashMap keys and values to two separate string variables in Java

I need to store all keys into single string variable each key separated by a comma and also I need to do the same for all values

Here is my code

HashMap<String, Object> yourHashMap = new Gson().fromJson(dynamicJson, HashMap.class);
    
yourHashMap.forEach((k, v) -> {
    //System.out.println("Key: " + k );
    String result = k + ",";
    System.out.println("Keys : "+result);
});

Actual output Keys : name,
message,

> Expected output : Keys : name, message
>
> Values : "Message1", "Message Content"

Using these outputs I'm going to create CSV file it uses keys as header and values as rows

You can use Collectors.joining() to add comma separation

String keys = map.keySet().stream().collect(Collectors.joining(", "));
String values = map.values().stream().map(obj -> String.valueOf(obj)).collect(Collectors.joining(", "));

, main function

    public static void main(String[] args) {
        Map<String, String> map = new HashMap<>();
        map.put("key1", "val1");
        map.put("key2", "val2");
        map.put("key3", "val3");
        map.put("key4", "val4");
        String keys = map.keySet().stream().collect(Collectors.joining(", "));
        String values = map.values().stream().map(obj -> String.valueOf(obj)).collect(Collectors.joining(", "));
        System.out.println("Keys: " + keys);
        System.out.println("Values: " + values);
    }

, output

Keys: key1, key2, key3, key4
Values: val1, val2, val3, val4

    HashMap<String, Object> yourHashMap = new Gson().fromJson(dynamicJson, HashMap.class);
    LinnkedHashSet<String> keys = new LinnkedHashSet<>();
    LinnkedHashSet<String> values = new LinnkedHashSet<>();
    yourHashMap.forEach((k, v) -> {
            keys.add(k);
            values.add(v);
       });
    System.out.println("keys: "+String.join(",",keys) +
                       "\n values: "+ String.join(",",values));

Use String.join

HashMap<String, String> yourHashMap = ....
String keys = String.join(",", yourHashMap.keySet());
String values = String.join(",", yourHashMap.values());