JDBC连接到数据库查询打印数据

2024-06-30 19:30| 来源: 网络整理| 查看: 265

通过一天的视频学习,认识了jdbc的连接原理前来小结:

游标读取数据库表的行一次读取一个,getXxx()方法读取表的列一个数据

next()方法可以让游标下移

可以把数据库的表看做是一个类,每条记录就是一个对象,所以要封装表

测试类 Jdbc08 .java

/** * 练习查询 db4的emp数据然后打印 * 定义一个方法,查询emp表的数据将其封装为对象,然后装在集合. * 1.定义类emp类 * 2.定义方法public 返回List findAll() * 3.实现方法 select * from emp * @author 三只坚果 * @date 2019/9/14 21:17 */ public class Jdbc08 { public static void main(String[] args) { List all = new Jdbc08().findAll(); all.forEach(System.out::println); System.out.println(all.size()+"条记录"); } public List findAll(){//查询所有emp数据 Connection conn =null; Statement statement =null; ResultSet rs =null; List list=null; try { Class.forName("com.mysql.jdbc.Driver"); conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/db4", "root", "123"); String sql="select * from emp"; statement = conn.createStatement(); rs = statement.executeQuery(sql);//rs是游标指向一行,getXxx("参数")指中列的一个数据,所以选中一个数据 //遍历结果,封装对象装在集合 Emp emp=null; list= new ArrayList(); while (rs.next()){ int id = rs.getInt("id"); String ename = rs.getString("ename"); int job_id = rs.getInt("job_id"); int mgr = rs.getInt("mgr"); Date joindate = rs.getDate("joindate"); double salary = rs.getDouble("salary"); double bouns = rs.getDouble("bonus"); int dept_id = rs.getInt("dept_id"); //封装对象 emp=new Emp(); emp.setId(id); emp.setEname(ename); emp.setJob_id(job_id); emp.setMgr(mgr); emp.setJoindate(joindate); emp.setSalary(salary); emp.setBouns(bouns); emp.setDept_id(dept_id); list.add(emp); } } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (SQLException e) { e.printStackTrace(); }finally {//释放资源 if (rs!=null){ try { rs.close(); } catch (SQLException e) { e.printStackTrace(); } } if (statement!=null){ try { statement.close(); } catch (SQLException e) { e.printStackTrace(); } } if (conn!=null){ try { conn.close(); } catch (SQLException e) { e.printStackTrace(); } } } return list; } } /** * 晚安! * @author BinPeng * @date 2019/9/14 22:04 */

Emp.java 封装类 ALT+INSERT IDEA快捷键自动生成!!!

package HeiMaSQL02.emp08; import java.util.Date; /** * 封装Emp表 * @author BinPeng * @date 2019/9/14 21:24 */ public class Emp { private int id; private String ename; private int job_id; private int mgr; private Date joindate; private double salary; private double bouns; private int dept_id; @Override public String toString() { return "Emp{" + "id=" + id + ", ename='" + ename + '\'' + ", job_id=" + job_id + ", mgr=" + mgr + ", joindate=" + joindate + ", salary=" + salary + ", bouns=" + bouns + ", dept_id=" + dept_id + '}'; } public int getId() { return id; } public void setId(int id) { this.id = id; } public String getEname() { return ename; } public void setEname(String ename) { this.ename = ename; } public int getJob_id() { return job_id; } public void setJob_id(int job_id) { this.job_id = job_id; } public int getMgr() { return mgr; } public void setMgr(int mgr) { this.mgr = mgr; } public Date getJoindate() { return joindate; } public void setJoindate(Date joindate) { this.joindate = joindate; } public double getSalary() { return salary; } public void setSalary(double salary) { this.salary = salary; } public double getBouns() { return bouns; } public void setBouns(double bouns) { this.bouns = bouns; } public int getDept_id() { return dept_id; } public void setDept_id(int dept_id) { this.dept_id = dept_id; } }

emp 数据库表 (数据库都给你备好了!够意思吧!!!)

/* Navicat MySQL Data Transfer Source Server : first Source Server Type : MySQL Source Server Version : 50725 Source Host : localhost:3306 Source Schema : db4 Target Server Type : MySQL Target Server Version : 50725 File Encoding : 65001 Date: 14/09/2019 22:15:35 */ SET NAMES utf8mb4; SET FOREIGN_KEY_CHECKS = 0; -- ---------------------------- -- Table structure for emp -- ---------------------------- DROP TABLE IF EXISTS `emp`; CREATE TABLE `emp` ( `id` int(11) NOT NULL, `ename` varchar(50) CHARACTER SET utf8mb4 COLLATE utf8mb4_unicode_ci NULL DEFAULT NULL, `job_id` int(11) NULL DEFAULT NULL, `mgr` int(11) NULL DEFAULT NULL, `joindate` date NULL DEFAULT NULL, `salary` decimal(7, 2) NULL DEFAULT NULL, `bonus` decimal(7, 2) NULL DEFAULT NULL, `dept_id` int(11) NULL DEFAULT NULL, PRIMARY KEY (`id`) USING BTREE, INDEX `emp_jobid_ref_job_id_fk`(`job_id`) USING BTREE, INDEX `emp_deptid_ref_dept_id_fk`(`dept_id`) USING BTREE, CONSTRAINT `emp_deptid_ref_dept_id_fk` FOREIGN KEY (`dept_id`) REFERENCES `dept` (`id`) ON DELETE RESTRICT ON UPDATE RESTRICT, CONSTRAINT `emp_jobid_ref_job_id_fk` FOREIGN KEY (`job_id`) REFERENCES `job` (`id`) ON DELETE RESTRICT ON UPDATE RESTRICT ) ENGINE = InnoDB CHARACTER SET = utf8mb4 COLLATE = utf8mb4_unicode_ci ROW_FORMAT = Dynamic; -- ---------------------------- -- Records of emp -- ---------------------------- INSERT INTO `emp` VALUES (1001, '啦啦', 4, 1004, '2000-12-17', 8000.00, NULL, 20); INSERT INTO `emp` VALUES (1002, '吖吖', 3, 1006, '2001-02-20', 16000.00, 3000.00, 30); INSERT INTO `emp` VALUES (1003, '啊吖', 3, 1006, '2001-02-22', 12500.00, 5000.00, 30); INSERT INTO `emp` VALUES (1004, '订单', 2, 1009, '2001-04-02', 29750.00, NULL, 20); INSERT INTO `emp` VALUES (1005, '李方法', 4, 1006, '2001-09-28', 12500.00, 14000.00, 30); INSERT INTO `emp` VALUES (1006, '宋方法', 2, 1009, '2001-05-01', 28500.00, NULL, 30); INSERT INTO `emp` VALUES (1007, '发', 2, 1009, '2001-09-01', 24500.00, NULL, 10); INSERT INTO `emp` VALUES (1008, '猪发', 4, 1004, '2007-04-19', 30000.00, NULL, 20); INSERT INTO `emp` VALUES (1009, 'utah', 1, NULL, '2001-11-17', 50000.00, NULL, 10); INSERT INTO `emp` VALUES (1010, '吴让她', 3, 1006, '2001-09-08', 15000.00, 0.00, 30); INSERT INTO `emp` VALUES (1011, '沙让他', 4, 1004, '2007-05-23', 11000.00, NULL, 20); INSERT INTO `emp` VALUES (1012, '李让他', 4, 1006, '2001-12-03', 9500.00, NULL, 30); INSERT INTO `emp` VALUES (1013, '饿龙', 4, 1004, '2001-12-03', 30000.00, NULL, 20); INSERT INTO `emp` VALUES (1014, '饿', 4, 1007, '2002-01-23', 13000.00, NULL, 10); SET FOREIGN_KEY_CHECKS = 1;

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