Class.forName("com.mysql.jdbc.Driver")的作用

传统的使用jdbc来访问数据库的流程为：

public class JDBCTest {
	public static void main(String[] args) {
		Connection connection = null;
		PreparedStatement preparedStatement = null;
		ResultSet resultSet = null;

		try {
			Class.forName("com.mysql.jdbc.Driver");
			connection = DriverManager.getConnection("jdbc:mysql:///mybatis?characterEncoding=utf-8", "root", "123456");
			String sql = "select * from user where username=?";
			preparedStatement = connection.prepareStatement(sql);
			preparedStatement.setString(1,"王五");
			resultSet = preparedStatement.executeQuery();
			while (resultSet.next()) {
				System.out.println(resultSet.getString("id")+" "+resultSet.getString("username"));
			}
		} catch (Exception e) {
			e.printStackTrace();
		}finally {
			if (resultSet != null) {
				try {
					resultSet.close();
				} catch (SQLException e) {
					e.printStackTrace();
				}
			}
			if (preparedStatement != null) {
				try {
					preparedStatement.close();
				} catch (SQLException e) {
					e.printStackTrace();
				}
			}
			if (connection != null) {
				try {
					connection.close();
				} catch (SQLException e) {
					e.printStackTrace();
				}
			}
		}
	}
}

for(DriverInfo aDriver : registeredDrivers) {
    // If the caller does not have permission to load the driver then
    // skip it.
    if(isDriverAllowed(aDriver.driver, callerCL)) {
        try {
            println("    trying " + aDriver.driver.getClass().getName());
            Connection con = aDriver.driver.connect(url, info);
            if (con != null) {
                // Success!
                println("getConnection returning " + aDriver.driver.getClass().getName());
                return (con);
            }
        } catch (SQLException ex) {
            if (reason == null) {
                reason = ex;
            }
        }
    } else {
        println("    skipping: " + aDriver.getClass().getName());
    }
}

public class Driver extends NonRegisteringDriver implements java.sql.Driver {
    public Driver() throws SQLException {
    }

    static {
        try {
            DriverManager.registerDriver(new Driver());
        } catch (SQLException var1) {
            throw new RuntimeException("Cant register driver!");
        }
    }
}