Use string replace inside java 8 foreach

Question

I have already look at this questions, but my problem is a little different.

I have a "baseString", n HashMap and an output string. I want to fill the baseString with the hashmap, to construct a json call parameters.

I have already done it with Java 7, in this way:

HashMap<String,Integer> element= getAllElement();

String baseElem="{\"index\":{}}\r\n" + 
        "{\"name\":\"$name$\",\"age\":$age$}";

String result=baseElem;

for (Map.Entry<String, Integer> entry : element.entrySet()) {

    result=result.replace("$name$", entry.getKey());
    result=result.replace("$age$", entry.getValue().toString());
    result=result+baseElem;
}
result= result.replace(baseElem, "");

Now I want to the same with Java 8, I have tried in this way:

element.forEach((k,v)->{
            result=result.replaceAll("$name$", k);
            result=result.replaceAll("$age$", v.toString());
            result=result+baseElem;
        });

But for each result I have an error

"Local variable result defined in an enclosing scope must be final or effectively final"

So the question is: I can do that in some kind of way with Java 8 and streams? Or there is no way, and so I can use the simple Java 7 for?

Answer 1

Your approach is going entirely into the wrong direction. This is not only contradicting the functional programming style, the Stream API adopts. Even the loop is horribly inefficient, performing repeated string concatenation and replace operations on the growing result string.

You did a Shlemiel the painter’s algorithm

You actually only want to perform a replace operation on the baseElem template for each map entry and join all results. This can be expressed directly:

Map<String,Integer> element = getAllElement();

String baseElem = "{\"index\":{}}\r\n{\"name\":\"$name$\",\"age\":$age$}";

String result = element.entrySet().stream()
    .map(e -> baseElem.replace("$name$", e.getKey())
                      .replace("$age$",  e.getValue().toString()))
    .collect(Collectors.joining());