Only fetch checksums for final gradle releases during build

This is a follow up to #2775
I frequently experience build failures due to connection errors.

After some debugging with wireshark, netstat and
`-Djdk.httpclient.HttpClient.log=all` I suspect that I'm getting rate
throttled.

Somewhere between 150 and 200 requests, the connections either get
closed by the remote or almost stall.

To mitigate the issue, this excludes nightly, snapshot, rc and broken
gradle releases. The biggest impact has cutting out RC releases:

total versions: 386
without nightly: 385
without RCs: 173
without broken: 172

Note that this still doesn't completely fix the issue for me, but it
helps reduce the chance for it happening.

org.eclipse.jdt.ls.core/pom.xml

@@ -52,12 +52,12 @@
 								import groovy.json.JsonOutput
 
 								import java.net.http.HttpClient
+								import java.net.http.HttpClient.Redirect
 								import java.net.http.HttpRequest
 								import java.net.http.HttpResponse.BodyHandlers
 								import java.util.concurrent.CompletableFuture
 								import java.util.stream.Collectors;
 
-
 								def checksumsFile = new File(project.basedir.absolutePath, "gradle/checksums/checksums.json")
 								if (System.getProperty("eclipse.jdt.ls.skipGradleChecksums") != null && checksumsFile.exists()) {
 									println "Skipping gradle wrapper validation checksums ..."
@@ -77,42 +77,24 @@
 									String wrapperChecksumUrl;
 									String sha256
 								}
-								HttpClient client = HttpClient.newHttpClient()
+
+								HttpClient client = HttpClient.newBuilder()
+									.followRedirects(Redirect.NORMAL)
+									.build();
 								def futures = []
 								versions.each {
-									if (it.wrapperChecksumUrl == null) {
+									if (it.wrapperChecksumUrl == null || it.nightly || it.snapshot || it.rcFor != "" || it.broken) {
 										return
 									}
 									HttpRequest request = HttpRequest.newBuilder().uri(URI.create(it.wrapperChecksumUrl)).build()
-									futures.add(client.sendAsync(request, BodyHandlers.ofString()).thenApply { response ->
-										if (response.statusCode() == 301) {
-											String newUrl = response.headers().firstValue("location").orElse(null)
-											if (newUrl != null) {
-												HttpRequest newRequest = HttpRequest.newBuilder()
-														.uri(URI.create(newUrl))
-														.build()
-												try {
-													String sha256 = client.send(newRequest, BodyHandlers.ofString()).body()
-													return new Checksum(wrapperChecksumUrl: it.wrapperChecksumUrl, sha256: sha256)
-												} catch (IOException | InterruptedException e) {
-													return null
-												}
-											} else {
-												return null
-											}
-										} else {
-											// Return the body of the original response
-											return new Checksum(wrapperChecksumUrl: it.wrapperChecksumUrl, sha256: response.body())
-										}
-									})
+									future = client.sendAsync(request, BodyHandlers.ofString()).thenApply { response ->
+										return new Checksum(wrapperChecksumUrl: it.wrapperChecksumUrl, sha256: response.body())
+									}
+									futures.add(future)
 								}
 
-								def checksums = CompletableFuture.allOf(futures.toArray(new CompletableFuture[0]))
-										.thenApply { v ->
-											futures.stream().map({ f ->
-												f.join()
-											}).collect(Collectors.toList())
-										}.get()
+								CompletableFuture.allOf(futures.toArray(new CompletableFuture[0])).get()
+								def checksums = futures.stream().map({ f -> f.join() }).collect(Collectors.toList())
 
 								def json = JsonOutput.toJson(checksums)
 								checksumsFile.write(JsonOutput.prettyPrint(json))