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webapps/examples/WEB-INF/classes/websocket/snake/SnakeTimer.java

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+/*
+ * Licensed to the Apache Software Foundation (ASF) under one or more
+ * contributor license agreements.  See the NOTICE file distributed with
+ * this work for additional information regarding copyright ownership.
+ * The ASF licenses this file to You 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.
+ */
+package websocket.snake;
+
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.Timer;
+import java.util.TimerTask;
+import java.util.concurrent.ConcurrentHashMap;
+
+import org.apache.juli.logging.Log;
+import org.apache.juli.logging.LogFactory;
+
+/**
+ * Sets up the timer for the multi-player snake game WebSocket example.
+ */
+public class SnakeTimer {
+
+    private static final Log log =
+            LogFactory.getLog(SnakeTimer.class);
+
+    private static Timer gameTimer = null;
+
+    private static final long TICK_DELAY = 100;
+
+    private static final ConcurrentHashMap<Integer, Snake> snakes =
+            new ConcurrentHashMap<>();
+
+    protected static synchronized void addSnake(Snake snake) {
+        if (snakes.size() == 0) {
+            startTimer();
+        }
+        snakes.put(Integer.valueOf(snake.getId()), snake);
+    }
+
+
+    protected static Collection<Snake> getSnakes() {
+        return Collections.unmodifiableCollection(snakes.values());
+    }
+
+
+    protected static synchronized void removeSnake(Snake snake) {
+        snakes.remove(Integer.valueOf(snake.getId()));
+        if (snakes.size() == 0) {
+            stopTimer();
+        }
+    }
+
+
+    protected static void tick() {
+        StringBuilder sb = new StringBuilder();
+        for (Iterator<Snake> iterator = SnakeTimer.getSnakes().iterator();
+                iterator.hasNext();) {
+            Snake snake = iterator.next();
+            snake.update(SnakeTimer.getSnakes());
+            sb.append(snake.getLocationsJson());
+            if (iterator.hasNext()) {
+                sb.append(',');
+            }
+        }
+        broadcast(String.format("{\"type\": \"update\", \"data\" : [%s]}",
+                sb.toString()));
+    }
+
+    protected static void broadcast(String message) {
+        for (Snake snake : SnakeTimer.getSnakes()) {
+            try {
+                snake.sendMessage(message);
+            } catch (IllegalStateException ise) {
+                // An ISE can occur if an attempt is made to write to a
+                // WebSocket connection after it has been closed. The
+                // alternative to catching this exception is to synchronise
+                // the writes to the clients along with the addSnake() and
+                // removeSnake() methods that are already synchronised.
+            }
+        }
+    }
+
+
+    public static void startTimer() {
+        gameTimer = new Timer(SnakeTimer.class.getSimpleName() + " Timer");
+        gameTimer.scheduleAtFixedRate(new TimerTask() {
+            @Override
+            public void run() {
+                try {
+                    tick();
+                } catch (RuntimeException e) {
+                    log.error("Caught to prevent timer from shutting down", e);
+                }
+            }
+        }, TICK_DELAY, TICK_DELAY);
+    }
+
+
+    public static void stopTimer() {
+        if (gameTimer != null) {
+            gameTimer.cancel();
+        }
+    }
+}