transform xml string by lambda java8

Question

I have String as XML. I'm trying to transform String by regexp:

public String replaceValueByTag(final String source, String tag, String value) {
     return replaceFirst(source, "(?<=<" + tag + ">).*?(?=</" + tag + ">)", value);
}

then create map with tag, new value:

Map<String, String> params = TAGS.stream().collect(toMap(tag -> tag, tag -> substringByTag(request, tag)));

and use map to replace values in XML:

public String getConfirm(String request) {
    String[] answer = {template}; 
    Map<String, String> params = TAGS.stream().collect(toMap(tag -> tag, tag -> substringByTag(request, tag)));   
    params.entrySet().forEach(entry -> answer[0] = replaceValueByTag(answer[0], entry.getKey(), entry.getValue()));
    return answer[0];
}

How to write lambda expression without saving in array (lambda takes String , converts it by map and returns a String )?

Answer 1

You can use reduce to apply all the elements of the Stream of map entries on your template String.

I'm not sure, though, how the combiner should look like (ie how to combine two partially transformed String s into a String that contains all transformations), but if a sequential Stream is sufficient, you don't need the combiner:

String result = 
    params.entrySet()
          .stream()
          .reduce(template,
                  (t,e) -> replaceValueByTag(t, e.getKey(), e.getValue()),
                  (s1,s2)->s1); // dummy combiner

Answer 2

instead of using an intermediate map you could directly apply the terminal operation, I'll use the .reduce() operation like @Eran suggested:

String result = TAGS.stream()
     .reduce(
         template, 
         (tmpl, tag) -> replaceValueByTag(tmpl, tag, substringByTag(request, tag),
         (left, right) -> left) // TODO: combine them
     );

This way you wont have as much overhead.