jdbc to mysql 樣本(1)最佳化之單例模式

建立BaseBetter.java

package cn.dzj.demo.jdbc;import java.sql.*;/** * Create Date:2013-6-24 Author : Dzj E-mail : 625065470@qq.com */public class BaseBetter {public static void main(String[] args) throws ClassNotFoundException {// TODO Auto-generated method stubtry {jdbcTemplate();} catch (Exception e) {// TODO Auto-generated catch blocke.printStackTrace();}}public static void jdbcTemplate() throws Exception {Connection conn = null;Statement stm = null;ResultSet rs = null;try {// build connection//conn = JdbcUtils.getConnection();conn = JdbcUtilSingle.getInstance().getConnection();  //call// create statementstm = conn.createStatement();// execute SQLrs = stm.executeQuery("Select * from persons;");// while getwhile (rs.next()) {System.out.println(rs.getObject(1) + "," + rs.getObject(2));}} finally {JdbcUtils.free(conn, stm, rs);}}}

建立JdbcUtilSingle.java

package cn.dzj.demo.jdbc;import java.sql.*;/** * Create Date:2013-6-24 Author : Dzj E-mail : 625065470@qq.com */public final class JdbcUtilSingle {public String url = "jdbc:mysql://localhost:3306/PIMS";public String username = "root";public String password = "123456";public static JdbcUtilSingle instance = null;static {try {Class.forName("com.mysql.jdbc.Driver");} catch (ClassNotFoundException e) {throw new ExceptionInInitializerError(e);}}private JdbcUtilSingle() {}public static JdbcUtilSingle getInstance() {synchronized (JdbcUtilSingle.class) {if (instance == null) {instance = new JdbcUtilSingle();}}return instance;}public Connection getConnection() throws SQLException {return DriverManager.getConnection(url, username, password);}public void free(Connection conn, Statement st, ResultSet rs) {try {if (rs != null) {rs.close();}} catch (SQLException e) {e.printStackTrace();} finally {try {if (st != null) {st.close();}} catch (SQLException e) {e.printStackTrace();} finally {try {if (conn != null) {conn.close();}} catch (SQLException e) {e.printStackTrace();}}}}}