## 抽取JDBC工具类 ： JDBCUtils
* 目的：简化书写
* 分析：
1. 注册驱动也抽取
2. 抽取一个方法获取连接对象
* 需求：不想传递参数（麻烦），还得保证工具类的通用性。
* 解决：配置文件
jdbc.properties
driver=
url=
user=
password=
**切记：值后面不要有多余空格！！！**
3. 抽取一个方法释放资源
* 代码实现：
emp表 sql语句
-- ----------------------------
-- Table structure for emp
-- ----------------------------
DROP TABLE IF EXISTS `emp`;
CREATE TABLE `emp` (
`id` int(11) NOT NULL,
`ename` varchar(50) CHARACTER SET utf8 COLLATE utf8_general_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 = utf8 COLLATE = utf8_general_ci ROW_FORMAT = Dynamic;
-- ----------------------------
-- Records of emp
-- ----------------------------
INSERT INTO `emp` VALUES (1001, '孙悟空', 4, 1004, '2000-12-17', 8000.00, NULL, 20);
INSERT INTO `emp` VALUES (1002, '卢俊义', 3, 1006, '2001-02-20', 16000.00, 3000.00, 30);
INSERT INTO `emp` VALUES (1003, '林冲', 3, 1006, '2001-02-22', 12500.00, 5000.00, 30);
INSERT INTO `emp` VALUES (1004, '唐僧', 2, 1009, '2001-04-02', 29750.00, NULL, 20);
INSERT INTO `emp` VALUES (1005, '李逵', 4, 1006, '2001-09-28', 12500.00, 14000.00, 30);
INSERT INTO `emp` VALUES (1006, '宋江', 2, 1009, '2001-05-01', 28500.00, NULL, 30);
INSERT INTO `emp` VALUES (1007, '刘备', 2, 1009, '2001-09-01', 24500.00, NULL, 10);
INSERT INTO `emp` VALUES (1008, '猪八戒', 4, 1004, '2007-04-19', 30000.00, NULL, 20);
INSERT INTO `emp` VALUES (1009, '罗贯中', 1, NULL, '2001-11-17', 50000.00, NULL, 10);
INSERT INTO `emp` VALUES (1010, '吴用', 3, 1006, '2001-09-08', 15000.00, 0.00, 30);
INSERT INTO `emp` VALUES (1011, '沙僧', 4, 1004, '2007-05-23', 11000.00, NULL, 20);
INSERT INTO `emp` VALUES (1012, '李逵', 4, 1006, '2001-12-03', 9500.00, NULL, 30);
INSERT INTO `emp` VALUES (1013, '小白龙', 4, 1004, '2001-12-03', 30000.00, NULL, 20);
INSERT INTO `emp` VALUES (1014, '关羽', 4, 1007, '2002-01-23', 13000.00, NULL, 10);
Emp.java 实体类
package cn.domain;
import java.util.Date;
/*
* 封装Emp表的实体类
*/
public class Emp {
private int id;
private String ename;
private int job_id;
private int mgr;
private Date joindate;
private double salary;
private double bonus;
private int dept_id;
/**
* @return the id
*/
public int getId() {
return id;
}
/**
* @param id the id to set
*/
public void setId(int id) {
this.id = id;
}
/**
* @return the ename
*/
public String getEname() {
return ename;
}
/**
* @param ename the ename to set
*/
public void setEname(String ename) {
this.ename = ename;
}
/**
* @return the job_id
*/
public int getJob_id() {
return job_id;
}
/**
* @param job_id the job_id to set
*/
public void setJob_id(int job_id) {
this.job_id = job_id;
}
/**
* @return the mgr
*/
public int getMgr() {
return mgr;
}
/**
* @param mgr the mgr to set
*/
public void setMgr(int mgr) {
this.mgr = mgr;
}
/**
* @return the joindate
*/
public Date getJoindate() {
return joindate;
}
/**
* @param joindate the joindate to set
*/
public void setJoindate(Date joindate) {
this.joindate = joindate;
}
/**
* @return the salary
*/
public double getSalary() {
return salary;
}
/**
* @param salary the salary to set
*/
public void setSalary(double salary) {
this.salary = salary;
}
/**
* @return the dept_id
*/
public int getDept_id() {
return dept_id;
}
/**
* @param dept_id the dept_id to set
*/
public void setDept_id(int dept_id) {
this.dept_id = dept_id;
}
/**
* @return the bonus
*/
public double getBonus() {
return bonus;
}
/**
* @param bonus the bonus to set
*/
public void setBonus(double bonus) {
this.bonus = bonus;
}
@Override
public String toString() {
return "Emp [id=" + id + ", ename=" + ename + ", job_id=" + job_id + ", mgr=" + mgr + ", joindate=" + joindate
+ ", salary=" + salary + ", bonus=" + bonus + ", dept_id=" + dept_id + "]";
}
}
JDBCUtils.java
package cn.utils;
import java.io.FileNotFoundException;
import java.io.FileReader;
import java.io.IOException;
import java.io.InputStream;
import java.net.URL;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;
/**
* JDBC工具类
* @author
*/
public class JDBCUtils {
private static String url = "";
private static String user = "";
private static String password = "";
private static String driver = "";
/**
* 文件的读取，只需要读取一次即可拿到这些值。使用静态代码块
*/
static {
//读取资源文件，获取值
try {
//1.创建Properties集合类
Properties pro = new Properties();
//获取src路径下的文件的方式-->ClassLoader 类加载器
ClassLoader classloader = JDBCUtils.class.getClassLoader();
URL res = classloader.getResource("jdbc.properties");
String path = res.getPath();
System.out.println(path);
//2.加载文件
//pro.load(new FileReader("F:\\workspace2\\20200116\\src\\jdbc.properties"));
pro.load(new FileReader(path));
//3.获取数据，赋值
url = pro.getProperty("url");
user = pro.getProperty("user");
password = pro.getProperty("password");
driver = pro.getProperty("driver");
//4.注册驱动
Class.forName(driver);
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
/**
* 获取连接
* @return 连接对象
* @throws SQLException
*/
public static Connection getConnection() throws SQLException {
return DriverManager.getConnection(url,user, password);
}
/**
* 释放资源
* @param stmt
* @param conn
*/
public static void close(Statement stmt,Connection conn) {
if(stmt!=null) {
try {
stmt.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(conn!=null) {
try {
conn.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
public static void close(ResultSet rs,Statement stmt,Connection conn) {
if(rs!=null) {
try {
rs.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(stmt!=null) {
try {
stmt.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
if(conn!=null) {
try {
conn.close();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
}
}
package cn.jdbc;
import java.sql.Connection;
import java.sql.Date;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;
import cn.domain.Emp;
import cn.utils.JDBCUtils;
/*
* * 定义一个方法，查询emp表的数据将其封装为对象，然后装载集合，返回。
*/
public class Jdbcdemo8 {
/**
* 演示JDBC工具类
*
* @return
*/
public List<Emp> findAll2() {
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
List<Emp> list = null;
try {
/*
* // 1.注册驱动 Class.forName("com.mysql.jdbc.Driver"); // 2.获取连接 conn =
* DriverManager.getConnection("jdbc:mysql:///db2", "root", "123456");
*/
conn = JDBCUtils.getConnection();
// 3.定义sql
String sql = "select * from emp ";
// 4.获取执行sql对象
stmt = conn.createStatement();
// 5.执行sql
rs = stmt.executeQuery(sql);
// 6.遍历结果集，封装对象，装载集合
Emp emp = null;
list = new ArrayList<Emp>();
while (rs.next()) {
// 获取数据
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 bonus = rs.getDouble("bonus");
int dept_id = rs.getInt("dept_id");
// 创建emp对象,并赋值
emp = new Emp();
emp.setId(id);
emp.setEname(ename);
emp.setJob_id(job_id);
emp.setMgr(mgr);
emp.setJoindate(joindate);
emp.setSalary(salary);
emp.setBonus(bonus);
emp.setDept_id(dept_id);
//装载集合
list.add(emp);
}
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
// if(rs!=null) {
// try {
// rs.close();
// } catch (SQLException e) {
// // TODO Auto-generated catch block
// e.printStackTrace();
// }
// }
//
// if(stmt!=null) {
// try {
// stmt.close();
// } catch (SQLException e) {
// // TODO Auto-generated catch block
// e.printStackTrace();
// }
// }
//
// if(conn!=null) {
// try {
// conn.close();
// } catch (SQLException e) {
// // TODO Auto-generated catch block
// e.printStackTrace();
// }
// }
JDBCUtils.close(rs, stmt, conn);
}
return list;
}
public static void main(String[] args) {
List<Emp> list = new Jdbcdemo8().findAll2();
System.out.println(list);
}
}
* 练习：
* 需求：
1. 通过键盘录入用户名和密码
2. 判断用户是否登录成功
* select * from user where username = "" and password = "";
* 如果这个sql有查询结果，则成功，反之，则失败
* 步骤：
1. 创建数据库表 user
CREATE TABLE USER(
id INT PRIMARY KEY AUTO_INCREMENT,
username VARCHAR(32),
PASSWORD VARCHAR(32)
);
INSERT INTO USER VALUES(NULL,'zhangsan','123');
INSERT INTO USER VALUES(NULL,'lisi','234');
2. 代码实现：
package cn.jdbc;
import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Scanner;
import cn.utils.JDBCUtils;
/**
* * 练习：
* 需求：
1. 通过键盘录入用户名和密码
2. 判断用户是否登录成功
*
*/
public class Jdbcdemo9 {
/**
* 登录方法
* @return
*/
public boolean login(String username,String password) {
if(username == null || password == null) {
return false;
}
//连接数据库判断是否登录成功
Connection conn = null;
Statement stmt = null;
ResultSet rs = null;
try {
//1.获取连接
conn = JDBCUtils.getConnection();
//2.定义sql
String sql = "select * from user where username = '"+username+"' and password = '"+password+"' ";
//3.获取执行sql的对象
stmt = conn.createStatement();
//4.执行查询
rs = stmt.executeQuery(sql);
//5.判断
return rs.next();
} catch (SQLException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} finally {
JDBCUtils.close(rs, stmt, conn);
}
return false;
}
public static void main(String[] args) {
//1.键盘录入，接受用户名和密码
Scanner sc = new Scanner(System.in);
System.out.println("请输入用户名");
String username = sc.nextLine();
System.out.println("请输入密码");
String password = sc.nextLine();
//2.调用方法
boolean flag = new Jdbcdemo9().login(username, password);
//3.判断结果，输出不同 语句
if(flag) {
//登录成功
System.out.println("登录成功");
}else {
//登录失败
System.out.println("用户名或密码错误");
}
}
}
