JDBC之第一个较为规范的JDBC程序

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1、工具类的设计，设计成final，不被继承

package cn.itcast.jdbc;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;/** * Jdbc工具类 */public final class JdbcUtils {//省略localhost:3306private static String url = "jdbc:mysql:///jdbc";private static String username = "root";private static String password = "root";/** * 构造器私用,防止直接创建对象, * 当然通过反射可以创建 */private JdbcUtils(){}//保证只是注册一次驱动static{try {Class.forName("com.mysql.jdbc.Driver");} catch (ClassNotFoundException e) {throw new ExceptionInInitializerError(e);}}/** * 获取连接 * @return * @throws SQLException */public static Connection getConnection() throws SQLException {return DriverManager.getConnection(url, username, password);}/** * 释放资源 */public static void free(ResultSet rs, Statement st, Connection conn) {//规范的关系连接的方式try{if(rs != null) {rs.close();}} catch (SQLException e) {e.printStackTrace();}finally{try{if(st != null) {st.close();}} catch (SQLException e) {e.printStackTrace();}finally {if(conn != null) {try {conn.close();} catch (SQLException e) {e.printStackTrace();}}}}}}

2、主类中的代码

package cn.itcast.jdbc;import java.sql.Connection;import java.sql.DriverManager;import java.sql.ResultSet;import java.sql.SQLException;import java.sql.Statement;/** * 第一个JDBC程序 */public class Base {public static void main(String[] args) throws SQLException, ClassNotFoundException {template();}/** * 比较严谨的实现方式 * @throws ClassNotFoundException  * @throws SQLException  */public static void template() throws ClassNotFoundException, SQLException {Connection conn = null;Statement st = null;ResultSet rs = null;try {//建立连接conn = JdbcUtils.getConnection();//创建语句st = conn.createStatement();//执行语句rs = st.executeQuery("select * from user");//处理结果集while(rs.next()) {System.out.println(rs.getObject(1) + "\t" + rs.getObject(2) + "\t"+ rs.getObject(3) + "\t" + rs.getObject(4));}} finally {JdbcUtils.free(rs, st, conn);}}}

运行结果：

1 zhangsan 2017-06-30 100.0

2 lisi 2017-06-06 200.0

3 wangwu 2017-05-30 300.0

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