JDBC連接到數據庫查詢打印數據

通過一天的視頻學習,認識了jdbc的連接原理前來小結:

游標讀取數據庫表的行一次讀取一個,getXxx()方法讀取表的列一個數據  

next()方法可以讓游標下移

可以把數據庫的表看做是一個類,每條記錄就是一個對象,所以要封裝表

測試類 Jdbc08 .java

/**
 * 練習查詢 db4的emp數據然后打印
 * 定義一個方法,查詢emp表的數據將其封裝為對象,然后裝在集合.
 * 1.定義類emp類
 * 2.定義方法public  返回List<Emp> findAll()
 * 3.實現方法 select * from emp
 * @author 三只堅果
 * @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()+"條記錄");
    }
    public List<Emp> findAll(){//查詢所有emp數據
        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是游標指向一行,getXxx("參數")指中列的一個數據,所以選中一個數據
            //遍歷結果,封裝對象裝在集合
            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");
                //封裝對象
                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 {//釋放資源
            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 封裝類  ALT+INSERT  IDEA快捷鍵自動生成!!!

package HeiMaSQL02.emp08;

import java.util.Date;

/**
 * 封裝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 數據庫表  (數據庫都給你備好了!夠意思吧!!!)

/*
 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, '訂單', 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, '發', 2, 1009, '2001-09-01', 24500.00, NULL, 10);
INSERT INTO `emp` VALUES (1008, '豬發', 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, '吳讓她', 3, 1006, '2001-09-08', 15000.00, 0.00, 30);
INSERT INTO `emp` VALUES (1011, '沙讓他', 4, 1004, '2007-05-23', 11000.00, NULL, 20);
INSERT INTO `emp` VALUES (1012, '李讓他', 4, 1006, '2001-12-03', 9500.00, NULL, 30);
INSERT INTO `emp` VALUES (1013, '餓龍', 4, 1004, '2001-12-03', 30000.00, NULL, 20);
INSERT INTO `emp` VALUES (1014, '餓', 4, 1007, '2002-01-23', 13000.00, NULL, 10);

SET FOREIGN_KEY_CHECKS = 1;