JDBC05JDBC工具类3

每次都要注册驱动、获取连接等重复的代码，重复比较繁琐，所以抽取JDBC工具类 ： JDBCUtils

1、目的

　简化书写

2、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

　　　　　　url=

　　　　　　user=

　　　　　　password=

　　3. 抽取一个方法释放资源

3、代码实现

　src根路径下创建一个jdbc.properties文件

url=jdbc:mysql:///db3
user=root
password=root
driver=com.mysql.jdbc.Driver

package com.itcast.jdbc;

import java.util.Date;

/**
 * 封装Emp表数据的JavaBean
 */
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;

    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 getBonus() {
        return bonus;
    }

    public void setBonus(double bonus) {
        this.bonus = bonus;
    }

    public int getDept_id() {
        return dept_id;
    }

    public void setDept_id(int dept_id) {
        this.dept_id = dept_id;
    }

    @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 +
                '}';
    }
}

package com.itcast.jdbc;

import com.sun.scenario.effect.impl.sw.sse.SSEBlend_SRC_OUTPeer;

import java.io.*;
import java.net.URL;
import java.sql.*;
import java.util.Properties;

/**
 * JDBC工具类
 *
 */
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。
        //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(加载字节码文件进内容，可获取src下资源文件的路径)
        ClassLoader classLoader = JDBCUtils.class.getClassLoader();
        URL resource = classLoader.getResource("jdbc.properties");//以src为根路径
        String path = resource.getPath();
        System.out.println(path);

        try {
            //2. 加载文件
//            pro.load(new FileReader("/Users/alsc/Desktop/lj/workspace/day05_jdbc/jdbc/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 (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }
    }

    /**
     * 获取连接
     * @return 连接对象
     */
    public static Connection getConnection() throws SQLException {
        return DriverManager.getConnection(url,user,password);
    }

    /**
     * 释放资源
     * @param stat
     * @param conn
     */
    public static void close(Statement stat, Connection conn){
        if(stat != null){
            try {
                stat.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
        if(conn != null){
            try {
                conn.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }

    /**
     * 释放资源
     * @param rs
     * @param stat
     * @param conn
     */
    public static void close(ResultSet rs,Statement stat, Connection conn){
        if(rs != null){
            try {
                rs.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
        if(stat != null){
            try {
                stat.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
        if(conn != null){
            try {
                conn.close();
            } catch (SQLException throwables) {
                throwables.printStackTrace();
            }
        }
    }
}

package com.itcast.jdbc;

import java.sql.*;
import java.util.ArrayList;
import java.util.List;

public class JDBCDemo9 {

    public static void main(String[] args) {
        List<Emp> list = new JDBCDemo9().findAll2();
        System.out.println(list);
        System.out.println(list.size());
    }

    /**
     * 查询所有emp对象
     * @return
     */
    public List<Emp> findAll(){
        Connection conn = null;
        Statement stat = 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:///db3", "root", "root");

            //3. 定义sql
            String sql = "select * from emp";
            //4. 获取执行sql的对象 Statement
            stat = conn.createStatement();
            //5. 执行sql
            rs = stat.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");//这是java.sql.Date，是java.util.Date的子类
                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 (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            //7. 释放资源
            //避免空指针异常
            if(rs != null){
                try {
                    rs.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if(stat != null){
                try {
                    stat.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
            if(conn != null){
                try {
                    conn.close();
                } catch (SQLException e) {
                    e.printStackTrace();
                }
            }
        }
        return list;
    }

    /**
     * 演示JDBC工具类
     * @return
     */
    public List<Emp> findAll2(){
        Connection conn = null;
        Statement stat = null;
        ResultSet rs = null;
        List<Emp> list = null;

        try {
            //1. 注册驱动
            //2. 获取连接
            conn = JDBCUtils.getConnection();
            //3. 定义sql
            String sql = "select * from emp";
            //4. 获取执行sql的对象 Statement
            stat = conn.createStatement();
            //5. 执行sql
            rs = stat.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");//这是java.sql.Date，是java.util.Date的子类
                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) {
            e.printStackTrace();
        } finally {
            //7. 释放资源
            //避免空指针异常
            JDBCUtils.close(rs,stat,conn);
        }
        return list;
    }
}

　

　输出结果：

　

4、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. db4数据库中创建数据库表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","1234");

　　2. 代码实现

package cn.itcast.jdbc;

import java.sql.Connection;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Scanner;

/**
 * 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 JDBCDemo10 {

    public static void main(String[] args) {
        //1. 键盘录入，接收用户名和密码
        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
        JDBCDemo10 jdbcDemo10 = new JDBCDemo10();
        boolean flag = jdbcDemo10.login(username,password);

        //3. 判断结果，输出不同语句
        if(flag){
            System.out.println("登录成功！");
        }else{
            System.out.println("用户名或密码错误！");
        }
    }

    /**
     * 登录方法
     */
    public boolean login(String username,String password){

        if(username == null && password == null){
            return false;
        }
        Connection conn = null;
        Statement stat = null;
        ResultSet rs = null;
        //连接数据库判断是否登录成功
        //1. 获取连接
        try {
            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
            stat = conn.createStatement();
            //4. 执行查询
            rs = stat.executeQuery(sql);
            //5. 判断
            return rs.next();//如果有下一行则返回true
        } catch (SQLException e) {
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stat, conn);
        }
        return false;
    }
}

　执行结果：

　      

 但是存在一个问题，用户名不是数据库的用户名有可能会登录成功，需要PreparedStatement去解决