BIG feat,fix,refactor: use database and some minor refactoring which also fixes memory issues and * related to PersistentDataUtilities

src/main/java/me/chayapak1/chomens_bot/plugins/DatabasePlugin.java

@@ -0,0 +1,53 @@
+package me.chayapak1.chomens_bot.plugins;
+
+import com.google.common.util.concurrent.ThreadFactoryBuilder;
+import me.chayapak1.chomens_bot.Bot;
+import me.chayapak1.chomens_bot.Configuration;
+import me.chayapak1.chomens_bot.Main;
+
+import java.sql.*;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+
+public class DatabasePlugin {
+    // is it OK to have a completely separate ExecutorService to do the executions?
+    public static final ExecutorService executorService = Executors.newFixedThreadPool(
+            Runtime.getRuntime().availableProcessors(),
+            new ThreadFactoryBuilder().setNameFormat("ExecutorService (database) #%d").build()
+    );
+
+    public Connection connection;
+
+    public DatabasePlugin (Configuration config) {
+        try {
+            connection = DriverManager.getConnection(
+                    "jdbc:mysql://" + config.database.address + "/chomens_bot",
+                    config.database.username,
+                    config.database.password
+            );
+        } catch (SQLException e) {
+            e.printStackTrace();
+            return;
+        }
+
+        for (Bot bot : Main.bots) bot.database = this;
+    }
+
+    public boolean execute (String query) throws SQLException {
+        final Statement statement = connection.createStatement();
+
+        return statement.execute(query);
+    }
+
+    public ResultSet query (String query) throws SQLException {
+        final Statement statement = connection.createStatement();
+
+        return statement.executeQuery(query);
+    }
+
+    public int update (String query) throws SQLException {
+        final Statement statement = connection.createStatement();
+
+        return statement.executeUpdate(query);
+    }
+}