How to iterate nested lists with lambda streams?

Question

I\'m trying to refactor the following code to lambda expressions with `stream, especially the nested foreach loops:

public static Result match (Response rsp) {
          


        

Answer 1

A little bit late but here is a readable approach:

   Result = rsp.getFirstNodes()
        .stream()
        .flatMap(firstNode -> firstNode.getSndNodes.stream())
        .filter(secondNode::isValid))
        .findFirst()
        .map(node -> this.parseNode(node)).orElse(null);

Explanation: you get all the firstNodes and stream() them up. Out a each firstNode you bring n SndNodes. You check each SndNodes to see find the first one that is valid. If there is no valid SndNode then we'll get a null. If there is one, it'll get parsed into a Result

the parseMethod() doesn't change from the original:

public Result parseNode(SndNode node){
        try {
        ...
        ... // attempt to parsed node 
    } catch (ParseException e) {
        throw new ParseException;
    }   
}