JDBC连接到数据库查询打印数据

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<Emp> 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<Emp> all = new Jdbc08().findAll();
        all.forEach(System.out::println);
        System.out.println(all.size()+"条记录");
    }
    public List<Emp> findAll(){//查询所有emp数据
        Connection conn =null;
        Statement statement =null;
        ResultSet rs =null;
        List<Emp> 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;