Update streaming example to use IoMulti to demonstrate proper NIO usage. (helidon-io#6604)

Fixes helidon-io#2844

Author: romain-grecourt

examples/webserver/streaming/src/main/java/io/helidon/webserver/examples/streaming/ServerFileReader.java

@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2018, 2021 Oracle and/or its affiliates.
+ * Copyright (c) 2018, 2023 Oracle and/or its affiliates.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -16,11 +16,21 @@
 
 package io.helidon.webserver.examples.streaming;
 
+import java.io.IOException;
+import java.io.UncheckedIOException;
 import java.net.URISyntaxException;
+import java.net.URL;
+import java.nio.channels.ReadableByteChannel;
+import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.Paths;
+import java.util.Arrays;
+import java.util.concurrent.ScheduledExecutorService;
 import java.util.logging.Logger;
 
+import io.helidon.common.configurable.ScheduledThreadPoolSupplier;
+import io.helidon.common.http.DataChunk;
+import io.helidon.common.reactive.IoMulti;
 import io.helidon.webserver.Routing;
 import io.helidon.webserver.ServerRequest;
 import io.helidon.webserver.ServerResponse;
@@ -34,12 +44,16 @@
  */
 public class StreamingService implements Service {
     private static final Logger LOGGER = Logger.getLogger(StreamingService.class.getName());
-
+    private final ScheduledExecutorService executor = ScheduledThreadPoolSupplier.create().get();
     private final Path filePath;
 
     StreamingService() {
+        URL resource = getClass().getResource(LARGE_FILE_RESOURCE);
+        if (resource == null) {
+            throw new IllegalStateException("Resource not found: " + LARGE_FILE_RESOURCE);
+        }
         try {
-            filePath = Paths.get(getClass().getResource(LARGE_FILE_RESOURCE).toURI());
+            filePath = Paths.get(resource.toURI());
         } catch (URISyntaxException e) {
             throw new RuntimeException(e);
         }
@@ -48,20 +62,45 @@ public class StreamingService implements Service {
     @Override
     public void update(Routing.Rules routingRules) {
         routingRules.get("/download", this::download)
-                .post("/upload", this::upload);
+                    .post("/upload", this::upload);
     }
 
     private void upload(ServerRequest request, ServerResponse response) {
         LOGGER.info("Entering upload ... " + Thread.currentThread());
-        request.content().subscribe(new ServerFileWriter(response));
+        Path tempFilePath = createTempFile("large-file", ".tmp");
+        request.content()
+               .map(DataChunk::data)
+               .flatMapIterable(Arrays::asList)
+               .to(IoMulti.writeToFile(tempFilePath)
+                          .executor(executor)
+                          .build());
         LOGGER.info("Exiting upload ...");
     }
 
     private void download(ServerRequest request, ServerResponse response) {
         LOGGER.info("Entering download ..." + Thread.currentThread());
         long length = filePath.toFile().length();
-        response.headers().add("Content-Length", String.valueOf(length));
-        response.send(new ServerFileReader(filePath));
+        response.headers().contentLength(length);
+        response.send(IoMulti.multiFromByteChannelBuilder(newByteChannel(filePath))
+                             .executor(executor)
+                             .build());
         LOGGER.info("Exiting download ...");
     }
+
+    @SuppressWarnings("SameParameterValue")
+    private static Path createTempFile(String prefix, String suffix) {
+        try {
+            return Files.createTempFile(prefix, suffix);
+        } catch (IOException ex) {
+            throw new UncheckedIOException(ex);
+        }
+    }
+
+    private static ReadableByteChannel newByteChannel(Path path) {
+        try {
+            return Files.newByteChannel(path);
+        } catch (IOException ex) {
+            throw new UncheckedIOException(ex);
+        }
+    }
 }