在特定情况下使用 Java Stream 映射和过滤响应代码

Question

My question is regarding lambda with JAVA8 and use of the filters. It is done via Selenium of Java for testing for different response codes.

How can I use Lambda in greatest possible way to transform following function with Streams?

The code which I wanted to refactor is as follows into Streams , lambda of Java 8:

        for (int i = 0; i < links.size(); i++) {
        if (!(links.get(i).getAttribute("href") == null) && !(links.get(i).getAttribute("href").equals(""))) {
            // Find HTTP Status-Code
            try {
                statusCode = getResponseCode(links.get(i).getAttribute("href").trim());
            } catch (IOException e) {
                e.printStackTrace();
            }
            // Check broken link
            if (statusCode== 404) {
                System.out.println("Broken of Link# "+i+" "+links.get(i).getAttribute("href"));
            }
            else if (statusCode== 400) {
                System.out.println("Bad Request# "+i+" "+links.get(i).getAttribute("href"));
            }
            else if (statusCode== 401) {
                System.out.println("Unauthorized# "+i+" "+links.get(i).getAttribute("href"));
            }
            else if (statusCode== 403) {
                System.out.println("Forbidden# "+i+" "+links.get(i).getAttribute("href"));
            }
            else if (statusCode== 500) {
                System.out.println("Internal server error# "+i+" "+links.get(i).getAttribute("href"));
            }
        }

    }

What I have for now is:

List<AbstractMap.SimpleImmutableEntry<String,Integer>> variablename =
    links.stream().map(WebElement::getAttribute("href"));

I was trying to do something along the lines of filtering out everything that is not 500,403,401,400,404 and only keeping the mapping or a Pair of that like (linkString, responseCode), but I am having a bit of troubles exactly how I could do it properly with Lambda?

EDIT1: I didn't meant to put everything via stream, just to make as much use of it as I can in this example

Answer 1

It's fairly simple if you take it piece by piece, so:

// create a set of codes you want to include
Set<Integer> acceptableCodes = new HashSet<>(Arrays.asList(404, 400, 401, 403, 500)); 

// for (int i = 0; i < links.size(); i++) {
links.stream()

// convert to the href value as that's all we need later on
.map(link -> link.getAttribute("href"))

// filter out anything without a href
//   if (!(links.get(i).getAttribute("href") == null) && !(links.get(i).getAttribute("href").equals(""))) {
.filter(href -> href != null)
.filter(href -> !href.equals(""))

// filter out non-matching status codes
.filter(href -> acceptableCodes.contains(getResponseCode(href))
.map(link -> new LinkWithCode(href , getResponseCode(href))
.collect(toList());

Putting it together without the comments so you can read it easier:

Set<Integer> acceptableCodes = new HashSet<>(Arrays.asList(404, 400, 401, 403, 500)); 
links.stream()
    .map(link -> link.getAttribute("href"))
    .filter(href -> href != null)
    .filter(href -> !href.equals(""))
    .filter(href -> acceptableCodes.contains(getResponseCode(href))
    .map(link -> new LinkWithCode(href , getResponseCode(href))
    .collect(toList());

LinkWithCode is a class you'll need to create to hold the link and the status code. This assumes getResponseCode isn't a heavyweight operation as it's happening twice.

Caveat: I haven't tested this or put it in an IDE so you might have some tidy up to do.