Here you can find the source of checkConnection()
private static boolean checkConnection() throws SQLException
//package com.java2s; /**/*from w ww . ja va2s .c o m*/ * Java Settlers - An online multiplayer version of the game Settlers of Catan * Copyright (C) 2003 Robert S. Thomas <thomas@infolab.northwestern.edu> * Portions of this file Copyright (C) 2009-2010,2012 Jeremy D Monin <jeremy@nand.net> * * This program is free software; you can redistribute it and/or * modify it under the terms of the GNU General Public License * as published by the Free Software Foundation; either version 3 * of the License, or (at your option) any later version. * * This program is distributed in the hope that it will be useful, * but WITHOUT ANY WARRANTY; without even the implied warranty of * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the * GNU General Public License for more details. * * You should have received a copy of the GNU General Public License * along with this program. If not, see <http://www.gnu.org/licenses/>. * * The maintainer of this program can be reached at jsettlers@nand.net **/ import java.io.BufferedReader; import java.io.FileNotFoundException; import java.io.FileReader; import java.io.IOException; import java.sql.Connection; import java.sql.Driver; import java.sql.DriverManager; import java.sql.PreparedStatement; import java.sql.SQLException; import java.sql.Statement; import java.util.ArrayList; import java.util.List; import java.util.Properties; public class Main { /** * The db driver instance, if we dynamically loaded its JAR. * Otherwise null, use {@link #dbURL} to connect instead. *<P> * Used because {@link DriverManager#registerDriver(Driver)} won't work * if the classloader is different, which it will be for dynamic loading. *<P> * Set in {@link #initialize(String, String, Properties)}. * Used in {@link #connect(String, String, String)}. * @since 1.1.15 */ private static Driver driverinstance = null; /** * db connection, or <tt>null</tt> if never initialized or if cleaned up for shutdown. * If this is non-null but closed, most queries will try to recreate it via {@link #checkConnection()}. * Set in {@link #connect(String, String, String)}, based on the {@link #dbURL} * from {@link #initialize(String, String, Properties)}. * Cleared in {@link #cleanup(boolean) cleanup(true)}. */ private static Connection connection = null; /** * Retain the URL (default, or passed via props to {@link #initialize(String, String, Properties)}). * Used in {@link #connect(String, String, String)}. *<P> * If {@link #driverinstance} != null, go through it to connect to dbURL. * @since 1.1.09 */ private static String dbURL = null; /** * This flag indicates that the connection should be valid, yet the last * operation failed. Methods will attempt to reconnect prior to their * operation if this is set. */ private static boolean errorCondition = false; /** Cached username used when reconnecting on error */ private static String userName; /** Cached password used when reconnecting on error */ private static String password; private static String CREATE_ACCOUNT_COMMAND = "INSERT INTO users VALUES (?,?,?,?,?);"; private static String RECORD_LOGIN_COMMAND = "INSERT INTO logins VALUES (?,?,?);"; private static String USER_PASSWORD_QUERY = "SELECT password FROM users WHERE ( users.nickname = ? );"; private static String HOST_QUERY = "SELECT nickname FROM users WHERE ( users.host = ? );"; private static String LASTLOGIN_UPDATE = "UPDATE users SET lastlogin = ? WHERE nickname = ? ;"; private static String SAVE_GAME_COMMAND = "INSERT INTO games VALUES (?,?,?,?,?,?,?,?,?,?);"; private static String ROBOT_PARAMS_QUERY = "SELECT * FROM robotparams WHERE robotname = ?;"; private static PreparedStatement createAccountCommand = null; private static PreparedStatement recordLoginCommand = null; private static PreparedStatement userPasswordQuery = null; private static PreparedStatement hostQuery = null; private static PreparedStatement lastloginUpdate = null; private static PreparedStatement saveGameCommand = null; /** Query all robot parameters for a bot name; {@link #ROBOT_PARAMS_QUERY}. * Used in {@link #retrieveRobotParams(String)}. */ private static PreparedStatement robotParamsQuery = null; /** * Checks if connection is supposed to be present and attempts to reconnect * if there was previously an error. Reconnecting closes the current * {@link #connection}, opens a new one, and re-initializes the prepared statements. * * @return true if the connection is established upon return */ private static boolean checkConnection() throws SQLException { if (connection != null) { try { return (!errorCondition) || connect(userName, password, null); } catch (IOException ioe) { // will not occur, connect script is null return false; } } return false; } /** * Opens a new connection and initializes the prepared statements. * {@link #initialize(String, String, Properties)} and {@link #checkConnection()} use this to get ready. * Uses {@link #dbURL} and {@link #driverinstance}. *<P> * If <tt>setupScriptPath</tt> != null, it will be ran before preparing statements. * That way, it can create tables used by the statements. * * @param user DB username * @param pswd DB user password * @param setupScriptPath Full path or relative path to SQL script to run at connect, or null * @throws IOException if <tt>setupScriptPath</tt> wasn't found, or if any other IO error occurs reading the script * @throws SQLException if any connect error, missing table, or SQL error occurs * @return true on success; will never return false, instead will throw a sqlexception */ private static boolean connect(final String user, final String pswd, final String setupScriptPath) throws SQLException, IOException { if (driverinstance == null) { connection = DriverManager.getConnection(dbURL, user, pswd); } else { Properties props = new Properties(); props.put("user", user); props.put("password", pswd); connection = driverinstance.connect(dbURL, props); } errorCondition = false; userName = user; password = pswd; if (setupScriptPath != null) runSetupScript(setupScriptPath); // may throw IOException, SQLException // prepare PreparedStatements for queries createAccountCommand = connection .prepareStatement(CREATE_ACCOUNT_COMMAND); recordLoginCommand = connection .prepareStatement(RECORD_LOGIN_COMMAND); userPasswordQuery = connection .prepareStatement(USER_PASSWORD_QUERY); hostQuery = connection.prepareStatement(HOST_QUERY); lastloginUpdate = connection.prepareStatement(LASTLOGIN_UPDATE); saveGameCommand = connection.prepareStatement(SAVE_GAME_COMMAND); robotParamsQuery = connection.prepareStatement(ROBOT_PARAMS_QUERY); return true; } /** * Load and run a SQL script. * Typically DDL commands to create or alter tables, indexes, etc. * @param setupScriptPath Full path or relative path to the SQL script filename * @throws FileNotFoundException if file not found * @throws IOException if any other IO error occurs * @throws SQLException if any unexpected database problem * @since 1.1.15 */ private static void runSetupScript(final String setupScriptPath) throws FileNotFoundException, IOException, SQLException { if (!checkConnection()) return; // also may throw SQLException final boolean isSqlite = (dbURL.startsWith("jdbc:sqlite:")); FileReader fr = new FileReader(setupScriptPath); BufferedReader br = new BufferedReader(fr); List<String> sqls = new ArrayList<String>(); // Read 1 line at a time, with continuations; build a list try { StringBuilder sb = new StringBuilder(); for (String nextLine = br.readLine(); nextLine != null; nextLine = br .readLine()) { // Reminder: java String.trim removes ascii whitespace (including tabs) but not unicode whitespace. // Character.isWhitespace is true for both ascii and unicode whitespace, except non-breaking spaces. if ((nextLine.length() == 0) || (nextLine.trim().length() == 0)) continue; // <-- skip empty lines -- if (nextLine.startsWith("--")) continue; // <-- skip comment lines with no leading whitespace -- if (isSqlite && nextLine.toLowerCase().startsWith("use ")) continue; // <-- sqlite doesn't support "USE" // If starts with whitespace, append it to sb (continue previous line). // Otherwise, add previous sb to the sqls list, and start a new sb containing nextLine. if (Character.isWhitespace(nextLine.codePointAt(0))) { if (sb.length() > 0) sb.append("\n"); // previous line's readLine doesn't include the trailing \n } else { sqls.add(sb.toString()); sb.delete(0, sb.length()); } sb.append(nextLine); } // don't forget the last command sqls.add(sb.toString()); // done reading the file try { br.close(); } catch (IOException eclose) { } try { fr.close(); } catch (IOException eclose) { } } catch (IOException e) { try { br.close(); } catch (IOException eclose) { } try { fr.close(); } catch (IOException eclose) { } throw e; } // No errors: Run the built list of SQLs for (String sql : sqls) { if (sql.trim().length() == 0) continue; Statement cmd = connection.createStatement(); cmd.executeUpdate(sql); cmd.close(); } } }