用于检查for循环内条件的最短代码

Question

What is the shortest form for this code?

List<String> supported = Arrays.asList("...");
boolean isSupported = false;
for(String s : supported) {
    if(url.startsWith(s)) {
       isSupported = true;
       break;
    }
}

Or this is the shortest form to check condition inside a for-loop ?

Answer 1

如果您使用的是Java 8，则可以在Stream API的帮助下一行完成此操作：

boolean isSupported = supported.stream().anyMatch(s -> url.startsWith(s));

Answer 2

The Java 8 answer given by @Azel +1 is lean and is probably the best answer that can be given with your current design. However, I have had similar problems to yours in the past, and have found it better to identify URLs by their hosts, rather than just by an arbitrary beginning substring. What I ended up doing was to create a map of hosts. Then, I compared each incoming URL against that Map , something like this:

Map<String, Integer> hosts = new HashMap<>();
hosts.add("google.com", 1);
hosts.add("stackoverflow.com", 1);
hosts.add("wordpress.com", 1);

URL url = new URL("http://www.google.com");
String host = url.getHost();

if (hosts.containsKey(host)) {
    System.out.println("Found " + url + " in list of approved hosts.");
}

The basic idea here is that we don't even need to iterate a list of approved domains, we can just do a constant time lookup against a whitelist (or maybe blacklist).

In practice, you might use a Java properties file to store the list of known hosts, and then load it when you need it.

Answer 3

This is the shortest for array

boolean isSupported = false;
for(String s : supported)
  if(isSupported = url.startsWith(s)) break;

Answer 4

You can create a method to make it easier. I'm assuming you're using an array, but this will also work with a list.

boolean containsURL(String[] array, URL url) {
    for (String s : array)
        if (url.startsWith(s))
            return true;
    return false;
}

isSupported = containsURL(supported, url);