TileCache.java
/*
* *************************************************************************************************************************************************************
*
* MapView: a JavaFX map renderer for tile-based servers
* http://tidalwave.it/projects/mapview
*
* Copyright (C) 2024 - 2025 by Tidalwave s.a.s. (http://tidalwave.it)
*
* *************************************************************************************************************************************************************
*
* Licensed under the Apache License, Version 2.0 (the "License"); you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software distributed under the License is distributed on an "AS IS" BASIS, WITHOUT WARRANTIES OR
* CONDITIONS OF ANY KIND, either express or implied. See the License for the specific language governing permissions and limitations under the License.
*
* *************************************************************************************************************************************************************
*
* git clone https://bitbucket.org/tidalwave/mapview-src
* git clone https://github.com/tidalwave-it/mapview-src
*
* *************************************************************************************************************************************************************
*/
package it.tidalwave.mapviewer.javafx.impl;
import java.lang.ref.SoftReference;
import jakarta.annotation.Nonnull;
import java.util.Map;
import java.util.Optional;
import java.util.concurrent.BlockingQueue;
import java.util.concurrent.ConcurrentHashMap;
import java.util.concurrent.ExecutorService;
import java.util.concurrent.Executors;
import java.util.concurrent.LinkedBlockingQueue;
import java.util.concurrent.TimeUnit;
import java.util.stream.IntStream;
import java.nio.charset.StandardCharsets;
import java.nio.file.Files;
import java.nio.file.Path;
import java.net.URI;
import java.net.http.HttpClient;
import java.net.http.HttpRequest;
import java.net.http.HttpResponse;
import javafx.scene.image.Image;
import javafx.application.Platform;
import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
import it.tidalwave.mapviewer.javafx.MapView;
import lombok.extern.slf4j.Slf4j;
import static it.tidalwave.mapviewer.impl.NameMangler.mangle;
import static java.net.http.HttpClient.Redirect.ALWAYS;
/***************************************************************************************************************************************************************
*
* A cache for tiles.
*
* @author Fabrizio Giudici
*
**************************************************************************************************************************************************************/
@Slf4j
public class TileCache
{
/** The queue of tiles to be downloaded. */
@Nonnull
private final BlockingQueue<Tile> tileQueue;
/** Options of the map view. */
@Nonnull
private final MapView.Options options;
/** The thread pool for downloading tiles. */
@Nonnull
private final ExecutorService executorService;
/** Whether the downloader thread should be stopped. */
private volatile boolean stopped = false;
/** This is important to avoid flickering then the TileGrid recreates tiles. */
private final Map<URI, SoftReference<Image>> memoryImageCache = new ConcurrentHashMap<>();
/** The placeholder used while the tile image has not been loaded yet. */
private final Image waitingImage = new Image(TileCache.class.getResource("/hold-on.gif").toExternalForm());
/***********************************************************************************************************************************************************
*
**********************************************************************************************************************************************************/
@SuppressFBWarnings("RV_RETURN_VALUE_IGNORED_BAD_PRACTICE")
public TileCache (@Nonnull final MapView.Options options)
{
this.options = options;
tileQueue = new LinkedBlockingQueue<>(options.tileQueueCapacity());
final var poolSize = options.poolSize();
executorService = Executors.newFixedThreadPool(poolSize);
IntStream.range(0, poolSize).forEach(i -> executorService.submit(this::tileLoader));
}
/***********************************************************************************************************************************************************
* {@return the number of tiles in the download queue}.
**********************************************************************************************************************************************************/
public int getPendingTileCount()
{
return tileQueue.size();
}
/***********************************************************************************************************************************************************
* Loads a tile in background.
* @param tile the tile to download
**********************************************************************************************************************************************************/
public final void loadTileInBackground (@Nonnull final Tile tile)
{
final var imageRef = memoryImageCache.get(tile.getUri());
final var image = (imageRef == null) ? null : imageRef.get();
if (image != null)
{
tile.setImage(image);
}
else
{
final var localPath = resolveCachedTilePath(tile);
if (Files.exists(localPath))
{
loadImageFromCache(tile, localPath);
}
else
{
tile.setImage(waitingImage);
if (tileQueue.offer(tile))
{
log.debug("Tiles in download queue: {}", tileQueue.size());
}
else
{
log.warn("Download queue full, discarding: {}", tile);
}
}
}
}
/***********************************************************************************************************************************************************
* Clears the queue of pending tiles, retaining only those for the given zoom level.
* @param zoom the zoom level to retain
**********************************************************************************************************************************************************/
public void retainPendingTiles (final int zoom)
{
log.debug("retainPendingTiles({})", zoom);
tileQueue.removeIf(tile -> tile.getZoom() != zoom);
}
/***********************************************************************************************************************************************************
*
**********************************************************************************************************************************************************/
public void dispose()
throws InterruptedException
{
log.debug("dispose()");
stopped = true;
executorService.shutdown();
executorService.awaitTermination(10, TimeUnit.SECONDS);
}
/***********************************************************************************************************************************************************
* The main loop that downloads the tiles.
**********************************************************************************************************************************************************/
private void tileLoader()
{
while (!stopped)
{
try
{
log.debug("waiting for next tile to load... queue size = {}", tileQueue.size());
final var tile = tileQueue.take();
final var uri = tile.getUri();
final var localPath = resolveCachedTilePath(tile);
if (!Files.exists(localPath) && options.downloadAllowed())
{
downloadTile(localPath, uri);
}
if (!Files.exists(localPath))
{
Platform.runLater(() -> tile.setImage(null));
}
else
{
Platform.runLater(() -> loadImageFromCache(tile, localPath));
}
}
catch (InterruptedException ignored)
{
log.info("tileLoader interrupted");
}
catch (Exception e) // defensive
{
log.error("", e);
}
}
log.info("tileLoader terminated");
}
/***********************************************************************************************************************************************************
* Loads an image from the cache.
* @param tile the tile
* @param path the path of the cache file
**********************************************************************************************************************************************************/
private void loadImageFromCache (@Nonnull final Tile tile, @Nonnull final Path path)
{
log.debug("Loading tile from cache: {}", path);
final var image = new Image(path.toUri().toString());
memoryImageCache.put(tile.getUri(), new SoftReference<>(image));
tile.setImage(image);
}
/***********************************************************************************************************************************************************
* {@return the path of the cached tile}.
* @param tile the tile
**********************************************************************************************************************************************************/
@Nonnull
private Path resolveCachedTilePath (@Nonnull final Tile tile)
{
return options.cacheFolder().resolve(tile.getSource().getCachePrefix()).resolve(mangle(tile.getUri().toString()));
}
/***********************************************************************************************************************************************************
* Downloads a tile and stores it.
* @param localPath the file to store the tile into
* @param uri the uri of the tile
**********************************************************************************************************************************************************/
@SuppressFBWarnings("REC_CATCH_EXCEPTION")
private static void downloadTile (@Nonnull final Path localPath, @Nonnull final URI uri)
{
try (final var client = HttpClient.newBuilder().followRedirects(ALWAYS).build())
{
Files.createDirectories(localPath.getParent());
final var request = HttpRequest.newBuilder()
.GET()
.header("User-Agent", "curl/8.7.1")
.header("Accept", "*/*")
.uri(uri)
.build();
final var response = client.send(request, HttpResponse.BodyHandlers.ofByteArray());
switch (response.statusCode())
{
case 200:
final var bytes = response.body();
Files.write(localPath, bytes);
log.debug("written {} bytes to {}", bytes.length, localPath);
break;
case 503:
log.warn("status code 503 for {}, should re-schedule; {}", uri, response.headers().map());
getErrorBody(response).ifPresent(log::warn);
// TODO: should reschedule, but not immediately, and also count for a max number of attempts
// TOOD: could use a different placeholder image?
break;
default:
log.error("status code {} for {}; {}", response.statusCode(), uri, response.headers().map());
getErrorBody(response).ifPresent(log::error);
}
}
catch (Exception e) // defensive
{
log.error("", e);
}
}
/***********************************************************************************************************************************************************
*
**********************************************************************************************************************************************************/
@Nonnull
private static Optional<String> getErrorBody (@Nonnull final HttpResponse<byte[]> response)
{
return response.headers()
.firstValue("Content-type")
.filter(ct -> ct.startsWith("text/"))
.map(r -> new String(response.body(), StandardCharsets.UTF_8)); // TODO: charset should be get from response
}
}