How to convert my Database class to Singleton - singleton

Question

I'm a beginner in java and i'm practicing Singleton.
I'm trying to figure out how to convert my Database class to Singleton.
Also, part of my issue is how to use the Database class without passing the properties in the constructor.
public class Database {
public static final String DB_DRIVER_KEY = "db.driver";
public static final String DB_URL_KEY = "db.url";
public static final String DB_USER_KEY = "db.user";
public static final String DB_PASSWORD_KEY = "db.password";
private static Logger LOG = Logger.getLogger(Database.class.getName());
private static final Database theInstance = new Database();
private static Connection connection;
private static Properties properties;
private Database() {
}
public static void init(Properties properties) {
if (Database.properties == null) {
LOG.debug("Loading database properties from db.properties");
Database.properties = properties;
}
}
public static Connection getConnection() throws SQLException {
if (connection != null) {
return connection;
}
try {
connect();
} catch (ClassNotFoundException e) {
throw new SQLException(e);
}
return connection;
}
private static void connect() throws ClassNotFoundException, SQLException {
String dbDriver = properties.getProperty(DB_DRIVER_KEY);
LOG.debug(dbDriver);
Class.forName(dbDriver);
System.out.println("Driver loaded");
connection = DriverManager.getConnection(properties.getProperty(DB_URL_KEY),
properties.getProperty(DB_USER_KEY), properties.getProperty(DB_PASSWORD_KEY));
LOG.debug("Database connected");
}
/**
* Close the connections to the database
*/
public void shutdown() {
if (connection != null) {
try {
connection.close();
connection = null;
} catch (SQLException e) {
LOG.error(e.getMessage());
}
}
}
/**
* Determine if the database table exists.
*
* #param tableName
* #return true is the table exists, false otherwise
* #throws SQLException
*/
public static boolean tableExists(String tableName) throws SQLException {
DatabaseMetaData databaseMetaData = getConnection().getMetaData();
ResultSet resultSet = null;
String rsTableName = null;
try {
resultSet = databaseMetaData.getTables(connection.getCatalog(), "%", "%", null);
while (resultSet.next()) {
rsTableName = resultSet.getString("TABLE_NAME");
if (rsTableName.equalsIgnoreCase(tableName)) {
return true;
}
}
} finally {
resultSet.close();
}
return false;
}
/**
* #return the theinstance
*/
public static Database getTheinstance() {
return theInstance;
}
}

Answer 1

Well this little bit change into your existing class to make you understand.
public class Database {
public static final String DB_DRIVER_KEY = "db.driver";
public static final String DB_URL_KEY = "db.url";
public static final String DB_USER_KEY = "db.user";
public static final String DB_PASSWORD_KEY = "db.password";
private static Logger LOG = Logger.getLogger(Database.class.getName());
private static Database theInstance;
private static Connection connection;
private static Properties properties;
private Database() {
}
public static void init(Properties properties) {
if (Database.properties == null) {
LOG.debug("Loading database properties from db.properties");
Database.properties = properties;
}
}
public static Connection getConnection() throws SQLException {
if (connection != null) {
return connection;
}
try {
connect();
} catch (ClassNotFoundException e) {
throw new SQLException(e);
}
return connection;
}
private static void connect() throws ClassNotFoundException, SQLException {
String dbDriver = properties.getProperty(DB_DRIVER_KEY);
LOG.debug(dbDriver);
Class.forName(dbDriver);
System.out.println("Driver loaded");
connection = DriverManager.getConnection(
properties.getProperty(DB_URL_KEY),
properties.getProperty(DB_USER_KEY),
properties.getProperty(DB_PASSWORD_KEY));
LOG.debug("Database connected");
}
/**
* Close the connections to the database
*/
public void shutdown() {
if (connection != null) {
try {
connection.close();
connection = null;
} catch (SQLException e) {
LOG.error(e.getMessage());
}
}
}
/**
* Determine if the database table exists.
*
* #param tableName
* #return true is the table exists, false otherwise
* #throws SQLException
*/
public static boolean tableExists(String tableName) throws SQLException {
DatabaseMetaData databaseMetaData = getConnection().getMetaData();
ResultSet resultSet = null;
String rsTableName = null;
try {
resultSet = databaseMetaData.getTables(connection.getCatalog(),
"%", "%", null);
while (resultSet.next()) {
rsTableName = resultSet.getString("TABLE_NAME");
if (rsTableName.equalsIgnoreCase(tableName)) {
return true;
}
}
} finally {
resultSet.close();
}
return false;
}
/**
* #return the theinstance
*/
public static Database getInstance() {
if(theInstance == null){
theInstance = new Database();
}
return theInstance;
}
}