Adds an update checker for alerting about new updates

src/main/java/net/knarcraft/stargate/Stargate.java

@@ -21,6 +21,7 @@ import net.knarcraft.stargate.portal.PortalRegistry;
 import net.knarcraft.stargate.thread.BlockChangeThread;
 import net.knarcraft.stargate.thread.ChunkUnloadThread;
 import net.knarcraft.stargate.thread.StarGateThread;
+import net.knarcraft.stargate.utility.UpdateChecker;
 import org.bukkit.Server;
 import org.bukkit.command.PluginCommand;
 import org.bukkit.configuration.file.FileConfiguration;
@@ -55,6 +56,8 @@ public class Stargate extends JavaPlugin {
     private static PluginManager pluginManager;
     private static StargateConfig stargateConfig;
 
+    private static String updateAvailable = null;
+
     /**
      * Empty constructor necessary for Spigot
      */
@@ -74,6 +77,26 @@ public class Stargate extends JavaPlugin {
         super(loader, descriptionFile, dataFolder, file);
     }
 
+    /**
+     * Stores information about an available update
+     *
+     * <p>If a non-null version is given, joining admins will be alerted about the new update.</p>
+     *
+     * @param version <p>The version of the new update available</p>
+     */
+    public static void setUpdateAvailable(String version) {
+        updateAvailable = version;
+    }
+
+    /**
+     * Gets information about an available update
+     *
+     * @return <p>The version number if an update is available. Null otherwise</p>
+     */
+    public static String getUpdateAvailable() {
+        return updateAvailable;
+    }
+
     /**
      * Gets an instance of this plugin
      *
@@ -334,6 +357,9 @@ public class Stargate extends JavaPlugin {
         runThreads();
 
         this.registerCommands();
+
+        //Check for any available updates
+        UpdateChecker.checkForUpdate();
     }
 
     /**

src/main/java/net/knarcraft/stargate/utility/UpdateChecker.java

@@ -0,0 +1,87 @@
+package net.knarcraft.stargate.utility;
+
+import net.knarcraft.stargate.Stargate;
+import org.bukkit.scheduler.BukkitScheduler;
+
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStream;
+import java.net.URL;
+import java.util.logging.Level;
+
+/**
+ * The update checker is responsible for looking for new updates
+ */
+public final class UpdateChecker {
+
+    private final static String APIResourceURL = "https://api.spigotmc.org/legacy/update.php?resource=97784";
+    private final static String updateNotice = "A new update is available: %s (You are still on %s)";
+
+    private UpdateChecker() {
+
+    }
+
+    /**
+     * Checks if there's a new update available, and alerts the user if necessary
+     */
+    public static void checkForUpdate() {
+        BukkitScheduler scheduler = Stargate.getInstance().getServer().getScheduler();
+        scheduler.runTaskAsynchronously(Stargate.getInstance(), UpdateChecker::queryAPI);
+    }
+
+    /**
+     * Queries the spigot API to check for a newer version, and informs the user
+     */
+    private static void queryAPI() {
+        try {
+            InputStream inputStream = new URL(APIResourceURL).openStream();
+            BufferedReader reader = FileHelper.getBufferedReaderFromInputStream(inputStream);
+            //There should only be one line of output
+            String newVersion = reader.readLine();
+            reader.close();
+
+            String oldVersion = Stargate.getPluginVersion();
+            //If there is a newer version, notify the user
+            if (isVersionHigher(oldVersion, newVersion)) {
+                Stargate.getConsoleLogger().log(Level.INFO, Stargate.getBackupString("prefix") +
+                        getUpdateAvailableString(newVersion, oldVersion));
+                Stargate.setUpdateAvailable(newVersion);
+            }
+        } catch (IOException e) {
+            Stargate.debug("UpdateChecker", "Unable to get newest version.");
+        }
+    }
+
+    /**
+     * Gets the string to display to a user to alert about a new update
+     *
+     * @param newVersion <p>The new available plugin version</p>
+     * @param oldVersion <p>The old (current) plugin version</p>
+     * @return <p>The string to display</p>
+     */
+    public static String getUpdateAvailableString(String newVersion, String oldVersion) {
+        return String.format(updateNotice, newVersion, oldVersion);
+    }
+
+    /**
+     * Decides whether one version number is higher than another
+     *
+     * @param oldVersion <p>The old version to check</p>
+     * @param newVersion <p>The new version to check</p>
+     * @return <p>True if the new version is higher than the old one</p>
+     */
+    public static boolean isVersionHigher(String oldVersion, String newVersion) {
+        String[] oldVersionParts = oldVersion.split("\\.");
+        String[] newVersionParts = newVersion.split("\\.");
+        int versionLength = Math.max(oldVersionParts.length, newVersionParts.length);
+        for (int i = 0; i < versionLength; i++) {
+            int oldVersionNumber = oldVersionParts.length > i ? Integer.parseInt(oldVersionParts[i]) : 0;
+            int newVersionNumber = newVersionParts.length > i ? Integer.parseInt(newVersionParts[i]) : 0;
+            if (newVersionNumber != oldVersionNumber) {
+                return newVersionNumber > oldVersionNumber;
+            }
+        }
+        return false;
+    }
+
+}