Java 27 and 26: runnable demos and captured output for every JEP, plus version lanes

Co-Authored-By: Claude Sonnet 5 <[email protected]> Claude-Session: https://claude.ai/code/session_01B38FGKKam5SCGgwgduVAh3
2026-09-21 15:08:50 +00:00
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+import com.sun.net.httpserver.HttpsConfigurator;
+import com.sun.net.httpserver.HttpsServer;
+import java.io.FileInputStream;
+import java.net.InetSocketAddress;
+import java.net.URI;
+import java.net.http.HttpClient;
+import java.net.http.HttpOption;
+import java.net.http.HttpRequest;
+import java.net.http.HttpResponse;
+import java.security.KeyStore;
+import javax.net.ssl.KeyManagerFactory;
+import javax.net.ssl.SSLContext;
+import javax.net.ssl.TrustManagerFactory;
+
+/**
+ * JEP 517 (Java 26): HTTP/3 for the HTTP Client API. The sandbox cannot reach a real HTTP/3 server (no UDP egress),
+ * so this shows the half that is checkable everywhere: a client that PREFERS HTTP/3 talking to a server that does not
+ * speak it (the JDK's own HttpsServer, HTTP/1.1) quietly falls back, and says so in response.version().
+ * args: keystore path, password
+ * Chapter: docs/11-recap-26.md
+ */
+public class Http3Fallback {
+    public static void main(String[] args) throws Exception {
+        KeyStore ks = KeyStore.getInstance("PKCS12");
+        try (var in = new FileInputStream(args[0])) { ks.load(in, args[1].toCharArray()); }
+        KeyManagerFactory kmf = KeyManagerFactory.getInstance("SunX509"); kmf.init(ks, args[1].toCharArray());
+        TrustManagerFactory tmf = TrustManagerFactory.getInstance("SunX509"); tmf.init(ks);
+        SSLContext ctx = SSLContext.getInstance("TLS"); ctx.init(kmf.getKeyManagers(), tmf.getTrustManagers(), null);
+
+        HttpsServer server = HttpsServer.create(new InetSocketAddress("127.0.0.1", 0), 0);
+        server.setHttpsConfigurator(new HttpsConfigurator(ctx));
+        server.createContext("/", ex -> { byte[] b = "hello".getBytes(); ex.sendResponseHeaders(200, b.length); ex.getResponseBody().write(b); ex.close(); });
+        server.start();
+        int port = server.getAddress().getPort();
+        try (HttpClient client = HttpClient.newBuilder().sslContext(ctx).version(HttpClient.Version.HTTP_3).build()) {
+            HttpRequest req = HttpRequest.newBuilder(URI.create("https://localhost:" + port + "/")).GET().build();
+            HttpResponse<String> r = client.send(req, HttpResponse.BodyHandlers.ofString());
+            System.out.println("client asked for : " + client.version());
+            System.out.println("server answered  : " + r.version() + " " + r.statusCode() + " " + r.body());
+
+            HttpRequest strict = HttpRequest.newBuilder(URI.create("https://localhost:" + port + "/")).GET()
+                    .setOption(HttpOption.H3_DISCOVERY, HttpOption.Http3DiscoveryMode.HTTP_3_URI_ONLY).build();
+            try {
+                client.send(strict, HttpResponse.BodyHandlers.ofString());
+                System.out.println("HTTP_3_URI_ONLY  : unexpectedly succeeded");
+            } catch (Exception e) {
+                System.out.println("HTTP_3_URI_ONLY  : " + e.getClass().getName() + ": " + e.getMessage());
+            }
+        } finally {
+            server.stop(0);
+        }
+    }
+}