/**     * 1 在方法中固化连接参数     *      * @return 数据库连接     */     public Connection getConnection() {     Connection conn = null;     try {     Class.forName("com.mysql.jdbc.Driver");       conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/test", "root", "");       return conn;       } catch (Exception e) {     e.printStackTrace();     }     return null;     }       /**     * 2 通过方法参数方式传递连接参数     *      * @return 数据库连接     */     public Connection getConnection(String driver, String url, String user, String password) {       Connection conn = null;       try {     Class.forName(driver);     conn = DriverManager.getConnection(url, user, password);       return conn;       } catch (Exception e) {     e.printStackTrace();     }       return null;     }       /**     * 3 通过properties配置文件的方式灵活配置连接参数，properties中的属性名固化     *      * @return 数据库连接     */     public Connection openConnection() {       Connection conn = null;     String driver = "";     String url = "";     String user = "";     String password = "";     Properties props = new Properties();     try {     props.load(this.getClass().getClassLoader()     .getResourceAsStream("db.properties"));     url = props.getProperty("mysql_url");     driver = props.getProperty("mysql_driver");     user = props.getProperty("mysql_user");     password = props.getProperty("mysql_password");       Class.forName(driver);     conn = DriverManager.getConnection(url, user, password);       return conn;     } catch (Exception e) {     e.printStackTrace();     }       return null;     }