UncleJokerly

JavaEE项目学习——JDBC入门基础知识

环境

1.Eclipse Java Photon

2.MySQL 8.0（DBMS可用自带的黑框框也可用Navicat 12，不过是收费的）

3.JDK 1.8.0

4.jar包：mysql_connector_java 8.0.13

（由于我的环境都是自己装的（船新版本，过程中遇到了很多小麻烦Orz），过程中需要的mysql_connector_java可从MySQL官网下载，不明白的可以参考这篇博客：如何在MySQL官网下载jar包附8.0jar包百度云地址）

(jar包的使用：包放在新建文件夹lib里，右键jar包--构建路径--配置构建路径)

JDBC概述

Java DataBase Connection Java数据库连接，实现Java代码与数据库之间的数据交互。

1.将Java代码中的数据保存到数据库

2.将数据库中的数据查询到Java代码

JDBC步骤

1.建立连接（数据库服务器ip，数据库port，用户名，密码）

2.准备需要执行的SQL指令

3.通过数据库连接加载SQL指令

4.执行SQL指令，获取执行结果

5.处理结果

6.关闭连接

理解并记住这六个步骤我们就可以开始实现JDBC了。

首先我们需要自己建立一个数据库，这里我使用MySQL建了两个数据库:db_qzone和db_sims。

create table tb_users(
   qq varchar(11) primary key,
   pwd varchar(16) not null,
   nick varchar(20) not null,
   sex char(2) not null,
   age int,
   remark varchar(100)
);

create table tb_articles(
   art_id int primary key auto_increment,
   art_title varchar(50) not null,
   art_content text not null,
   art_time datetime not null,
   art_type char(4) not null,
   art_qq varchar(11) not null,
   constraint FK_ARTICLES_USERS foreign key(art_qq)references tb_users(qq)
);

create table tb_albums(
   album_id int primary key auto_increment,
   album_name varchar(20) not null,
   album_desc varchar(200),
   album_time datetime not null,
   album_cover varchar(100),
   album_qq varchar(11) not null,
   constraint FK_ALBUMS_USERS foreign key(album_qq)references tb_users(qq)
);

create table tb_photos(
   photo_id int primary key auto_increment,
   photo_url varchar(100) not null,
   photo_desc varchar(40),
   photo_time datetime not null,
   photo_aid int not null,
   constraint FK_PHOTOS_ALBUMS foreign key(photo_aid)references tb_albums(album_id)
);


create table tb_students(
   stu_num char(5) primary key,
   stu_name varchar(20) not null,
   stu_sex char(2) not null,
   stu_age int not null,
   stu_tel char(11) not null unique
);

create table tb_courses(
   course_id char(8) primary key,
   course_name varchar(50) not null,
   course_score float not null
);

create table tb_student_course(
   snum char(5) not null,
   cid char(8) not null,
   primary key(snum,cid),
   constraint FK_SC_STUDENT foreign key(snum) references tb_students(stu_num),
   constraint FK_SC_COURSE foreign key(cid) references tb_courses(course_id)
);


insert into tb_students(stu_num,stu_name,stu_sex,stu_age,stu_tel)
values('stu1','joker','GG',21,'17630642952');
insert into tb_students(stu_num,stu_name,stu_sex,stu_age,stu_tel)
values('stu2','aoker','GG',21,'17630642953');
insert into tb_students(stu_num,stu_name,stu_sex,stu_age,stu_tel)
values('stu3','boker','GG',21,'17630642954');
insert into tb_students(stu_num,stu_name,stu_sex,stu_age,stu_tel)
values('stu4','coker','GG',21,'17630642955');
insert into tb_students(stu_num,stu_name,stu_sex,stu_age,stu_tel)
values('stu5','doker','GG',21,'17630642956');


insert into tb_courses(course_id,course_name,course_score)
values('course1','math',138.8);
insert into tb_courses(course_id,course_name,course_score)
values('course2','english',139.8);
insert into tb_courses(course_id,course_name,course_score)
values('course3','chinese',138.9);

insert into tb_student_course(snum,cid)
values('stu1','course1');
insert into tb_student_course(snum,cid)
values('stu2','course3');
insert into tb_student_course(snum,cid)
values('stu3','course2');

嵌套查询：
select * from tb_courses where course_id in (select cid from tb_student_course where snum='stu1');

效果部分截图如下：

建好数据库以后我们就要实现Java代码对数据库的操作了。

JDBC实现

（名词解释：DAO： data access object数据访问对象 DTO ： Data Transfer Object数据传输对象 utils:工具集）

1.创建Java项目“jdbc_0100”

2.在项目的src中创建名为“com.joker.jdbc.dto”的package

3.在“com.joker.jdbc.dto”包中创建名为“Student”类

PS：当我们需要对某张数据表进行操作的时候，首先要创建一个类（实体类/JavaBean），用于存储从数据表中查询出的记录。所以创建实体类要求如下：(“要想调用类的方法就需要类的对象”--脑子里又冒出了这句话)

* 1.类中属性的个数和类型要与对应的数据表保持一致

* 2.提供无参构造器和带有所有参数的构造器

* 3.提供所有属性的get和set方法

* 4.重写toString方法：右键--source--Generate toString--OK

package com.joker.jdbc.dto;

import java.io.Serializable;

/**
 * 1.类中属性的个数和类型要与对应的数据表保持一致
 * 2.提供无参构造器 和 带有参数的构造器
 * 3.提供所有属性的get和set方法
 * 4.重写toString方法：右键--source--Generate toString--OK
 * 
 * 5.实现序列化接口
 * 6.重写equals方法
 * 7.重写hashcode方法
 * @author 25213
 *
 */

public class Student {
	
	private String stuNum;
	private String stuName;
	private String stuSex;
	private int stuAge;
	private String stuTel;
	
	@Override
	public String toString() {
		return "Student [stuNum=" + stuNum + ", stuName=" + stuName + ", stuSex=" + stuSex + ", stuAge=" + stuAge
				+ ", stuTel=" + stuTel + "]";
	}

	public Student() {
	}

	public Student(String stuNum, String stuName, String stuSex, int stuAge, String stuTel) {
		super();
		this.stuNum = stuNum;
		this.stuName = stuName;
		this.stuSex = stuSex;
		this.stuAge = stuAge;
		this.stuTel = stuTel;
	}

	public String getStuNum() {
		return stuNum;
	}

	public void setStuNum(String stuNum) {
		this.stuNum = stuNum;
	}

	public String getStuName() {
		return stuName;
	}

	public void setStuName(String stuName) {
		this.stuName = stuName;
	}

	public String getStuSex() {
		return stuSex;
	}

	public void setStuSex(String stuSex) {
		this.stuSex = stuSex;
	}

	public int getStuAge() {
		return stuAge;
	}

	public void setStuAge(int stuAge) {
		this.stuAge = stuAge;
	}

	public String getStuTel() {
		return stuTel;
	}

	public void setStuTel(String stuTel) {
		this.stuTel = stuTel;
	}
	
	
	
}

（这个代码就是写完五个属性以后右键快捷键自动生成的）

测试一下：

package com.joker.jdbc.dto;


//测试Student类是否正确
public class Test {
	public static void main(String[] args) {
		Student s = new Student("stu10","zoker","GG",28,"15858585588");
		System.out.println(s);
	}
}

4.在项目的src中创建名为“com.joker.jdbc.dao”的package

5.在“com.joker.jdbc.dao”包中创建名为“StudentDAO”类，对学生表的所有数据库操作都在此类中完成。【对数据库中每个操作都单独定义一个方法完成】

6.JDBC实现操作

7.测试

注意在第二步准备SQL语句过程中时注意SQL注入问题：

JDBC预编译机制解决SQL注入问题

SQL注入

在SQL语句采用字符串拼接传递参数的情况，会出现因为参数值得改变导致SQL语义发生改变的情况。

预编译

1.SQL指令中需要参数一律用?表示

2.如果语句中有?，则使用” PreparedStatement ps = conn.prepareStatement(sql);”加载SQL指令，不再使用“Statement stmt = conn.createStatement();”

代码：

StudentDAO.java

package com.joker.jdbc.dao;

import java.util.*;
import java.util.List;
import java.awt.*;
import java.awt.datatransfer.StringSelection;
import java.sql.*;

import com.joker.jdbc.dto.Student;
import com.joker.jdbc.utils.DBManager;

public class StudentDAO {
	//1.添加操作
	public boolean insertStudent(Student s) {
		boolean flag = false;
		try {
			Connection conn = DBManager.getConn();//1.创建对象实现类的方法--连接数据库
			
			String sql = "insert into tb_students(stu_num,stu_name,stu_sex,stu_age,stu_tel) values(?,?,?,?,?)";//2.准备SQL语句
			
			PreparedStatement ps = conn.prepareStatement(sql);//3.对SQL语句预处理
			ps.setString(1, s.getStuNum());
			ps.setString(2, s.getStuName());
			ps.setString(3, s.getStuSex());
			ps.setInt(4, s.getStuAge());
			ps.setString(5, s.getStuTel());//4.对?赋值
			
			int i = ps.executeUpdate();//5.执行更新返回整型的结果表示数据库几行受影响
			
			flag = i>0?true:false;//6.处理结果
			
			conn.close();//7.关闭连接
			
		} catch (Exception e) {
			e.printStackTrace();
		}
		return flag;
	}
	
	//2.删除操作:根据学号删除学生信息
	public boolean deleteStudent(String stuNum) {
		boolean flag=false;
		
		try {
			Connection conn = DBManager.getConn();
			String sql = "delete from tb_students where stu_num=?";
			PreparedStatement ps = conn.prepareStatement(sql);
			ps.setString(1, stuNum);
			int i = ps.executeUpdate();
			flag = i>0?true:false;
			conn.close();	
		} catch (Exception e) {
			e.printStackTrace();
		}
		
		return flag;
	}
	
	//3.修改操作：根据学号修改姓名、性别、年龄、电话
	public boolean updateStudent(Student s) {
		boolean flag = false;
		
		try {
			Connection conn = DBManager.getConn();
			String sql = "update tb_students set stu_name=?,stu_sex=?,stu_age=?,stu_tel=? where stu_num=?";
			PreparedStatement ps = conn.prepareStatement(sql);
			ps.setString(1, s.getStuName());
			ps.setString(2, s.getStuSex());
			ps.setInt(3, s.getStuAge());
			ps.setString(4, s.getStuTel());
			ps.setString(5, s.getStuNum());
			int i = ps.executeUpdate();
			flag = i>0?true:false;
			conn.close();
			
		} catch (Exception e) {
			e.printStackTrace();
		}
		
		return flag;
	}
	
	//4.查询1：根据学号查询学生信息
	public Student queryStudent(String stuNum) {
		Student s = null;
		
		try {
			Connection conn = DBManager.getConn();
			String sql = "select * from tb_students where stu_num=?";
			PreparedStatement ps = conn.prepareStatement(sql);
			ps.setString(1, stuNum);
			ResultSet rs = ps.executeQuery();//结果集存参
			if(rs.next()) {
				String stuName = rs.getString("stu_name");//把结果暂存
				String stuSex = rs.getString("stu_sex");
				int stuAge = rs.getInt("stu_age");
				String stuTel = rs.getString("stu_tel");
				s = new Student(stuNum, stuName, stuSex, stuAge, stuTel);
			}
			conn.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
		
		return s;
	}
	
	//5.查询2：查询所有学生（只装Student的集合）
	public List allStudent() {
		List stus = new ArrayList();
		
		try {
			Connection conn = DBManager.getConn();
			String sql = "select * from tb_students";
			PreparedStatement ps = conn.prepareStatement(sql);
			ResultSet rs = ps.executeQuery();
			while(rs.next()) {
				String stuNum = rs.getString("stu_num");
				String stuName =rs.getString("stu_name");
				String stuSex = rs.getString("stu_sex");
				int stuAge = rs.getInt("stu_age");
				String stuTel = rs.getString("stu_tel");
				
				Student stu = new Student(stuNum, stuName, stuSex, stuAge, stuTel);
				stus.add(stu);
			}
			conn.close();
			
		} catch (Exception e) {
			e.printStackTrace();
		}
		
		return stus;
	}
	
	//6.查询3：根据性别查询学生信息
	public List allStudent(String stuSexx) {
		List stus = new ArrayList();
		
		try {
			Connection conn = DBManager.getConn();
			String sql = "select * from tb_students where stu_sex=?";
			PreparedStatement ps = conn.prepareStatement(sql);
			ps.setString(1, stuSexx);
			ResultSet rs = ps.executeQuery();
			while(rs.next()) {
				String stuNum = rs.getString("stu_num");
				String stuName = rs.getString("stu_name");
				String stuSex = rs.getString("stu_sex");
				int stuAge = rs.getInt("stu_age");
				String stuTel = rs.getString("stu_tel");
				Student s6 = new Student(stuNum, stuName, stuSex, stuAge, stuTel);
				stus.add(s6);
			}
			conn.close();
		} catch (Exception e) {
			e.printStackTrace();
		}
		
		return stus;
	}

	//7.查询4：根据年龄区间查询学生信息
	public List allStudent(int minn,int maxx) {
		List stus = new ArrayList();
		
		try {
			
			Connection conn = DBManager.getConn();
			String sql = "select * from tb_students where stu_age between ? and ?";
			PreparedStatement ps = conn.prepareStatement(sql);
			ps.setInt(1, minn);
			ps.setInt(2, maxx);
			ResultSet rs = ps.executeQuery();
			while(rs.next()) {
				String stuNum = rs.getString("stu_num");
				String stuName = rs.getString("stu_name");
				String stuSex = rs.getString("stu_sex");
				int stuAge = rs.getInt("stu_age");
				String stuTel = rs.getString("stu_tel");
				Student s7 =new Student(stuNum, stuName, stuSex, stuAge, stuTel);
				stus.add(s7);
			}
			conn.close();
			
		} catch (Exception e) {
			e.printStackTrace();
		}
		
		return stus;
	}
}

DAManager.java

package com.joker.jdbc.utils;

import java.sql.Connection;
import java.sql.DriverManager;

public class DBManager {

	private static final String DRIVER="com.mysql.cj.jdbc.Driver";
	private static final String URL="jdbc:mysql://localhost:3306/db_sims";
	private static final String USERNAME="root";
	private static final String PASSWORD="123456";
	
	static {
		try {
			Class.forName(DRIVER);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	public static Connection getConn() {
		Connection conn = null;
		try {
			conn = DriverManager.getConnection(URL, USERNAME, PASSWORD);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return conn;
	}
}

测试代码 Test.java

package com.joker.jdbc.dao;

import java.util.*;

import com.joker.jdbc.dto.Student;

public class Test {
	public static void main(String[] args) {
		StudentDAO sdao = new StudentDAO();

//		测试插入		
//		Student s1 = new Student("stu9","qoker","MM",18,"12123232233");//有参构造
//		boolean flag1 = sdao.insertStudent(s1);
//		System.out.println(flag1);

//		测试删除：根据学号删除学生信息
//		boolean flag2 = sdao.deleteStudent("stu9");
//		System.out.println(flag2);
		
//		测试修改：根据学号修改姓名、性别、年龄、电话		
//		Student s3 = new Student("stu2","zoker","MM",17,"16868686688");
//		boolean flag3 = sdao.updateStudent(s3);
//		System.out.println(flag3);

//		测试查询：根据学号查询学生信息
//		Student s4 = sdao.queryStudent("stu1");
//		System.out.println(s4);
		
//		测试查询2：查询所有学生（只装Student的集合）
//		List stus2 = sdao.allStudent();
//		for (Student s5 : stus2) {//foreach遍历
//			System.out.println(s5);
//		}

//		测试查询3：输入性别查询学生信息
//		List stus3 = sdao.allStudent("MM");
//		for (Student s6 : stus3) {
//			System.out.println(s6);
//		}
		
//		测试查询4：输入年龄范围查询学生信息
//		List stus4 = sdao.allStudent(20, 30);
//		for (Student s7 : stus4) {
//			System.out.println(s7);
//		}
		
	}
	
}

其中遇到的一些问题以及解决方法：

mysql的时区错误问题： The server time zone value 'ÖÐ¹ú±ê×¼Ê±¼ä' is unrecognized or represents more than one

Loading class `com.mysql.jdbc.Driver'. This is deprecated警告处理，jdbc更新处

如何在MySQL官网下载jar包附8.0jar包百度云地址

一些知识点：

数据库操作中 pstmt.setString(1,id) ; 是什么意思那个“1”指什么详解

ResultSet类的基本解读

Java的常见术语（PO/POJO/VO/BO/DAO/DTO）

Java中三种for循环之间的对比

以下代码加了些注释，以备将来温习所用，代码和上面是一样的，可忽略~

DBManager.java

package com.joker.jdbc.utils;

import java.sql.*;

public class DBManager {

	//设置成常量避免被修改
	private static final String DRIVER = "com.mysql.cj.jdbc.Driver";
	private static final String URL = "jdbc:mysql://localhost:3306/db_qzone";
	private static final String USERNAME = "root";
	private static final String PASSWORD = "123456";
	
	
	//驱动只需加载一次,静态块只执行一次
	static {
		try {
			Class.forName(DRIVER);
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
	
	
	//创建连接
	public static Connection getConn() {
		Connection conn = null;
		try {
			conn = DriverManager.getConnection(URL, USERNAME, PASSWORD);
		} catch (Exception e) {
			e.printStackTrace();
		}
		return conn;
	}
	
}

Student.java

package com.joker.jdbc.dto;

import java.io.Serializable;

/**
 * 1.类中属性的个数和类型要与对应的数据表保持一致
 * 2.提供无参构造器 和 带有参数的构造器
 * 3.提供所有属性的get和set方法
 * 4.重写toString方法：右键--source--Generate toString--OK
 * 
 * 5.实现序列化接口
 * 6.重写equals方法
 * 7.重写hashcode方法
 * @author 25213
 *
 */

public class Student {
	
	private String stuNum;
	private String stuName;
	private String stuSex;
	private int stuAge;
	private String stuTel;
	
	@Override
	public String toString() {
		return "Student [stuNum=" + stuNum + ", stuName=" + stuName + ", stuSex=" + stuSex + ", stuAge=" + stuAge
				+ ", stuTel=" + stuTel + "]";
	}

	public Student() {
	}

	public Student(String stuNum, String stuName, String stuSex, int stuAge, String stuTel) {
		super();
		this.stuNum = stuNum;
		this.stuName = stuName;
		this.stuSex = stuSex;
		this.stuAge = stuAge;
		this.stuTel = stuTel;
	}

	public String getStuNum() {
		return stuNum;
	}

	public void setStuNum(String stuNum) {
		this.stuNum = stuNum;
	}

	public String getStuName() {
		return stuName;
	}

	public void setStuName(String stuName) {
		this.stuName = stuName;
	}

	public String getStuSex() {
		return stuSex;
	}

	public void setStuSex(String stuSex) {
		this.stuSex = stuSex;
	}

	public int getStuAge() {
		return stuAge;
	}

	public void setStuAge(int stuAge) {
		this.stuAge = stuAge;
	}

	public String getStuTel() {
		return stuTel;
	}

	public void setStuTel(String stuTel) {
		this.stuTel = stuTel;
	}
	
	
	
}