原⽣jdbc与预处理对象PreparedStatment 1

JDBC（Java DataBase Connectivity,java数据库连接）是⼀种⽤于执⾏SQL语句的Java API。JDBC是Java访问数据库的标准规范，可以为不同的关系型数据库提供统⼀访问，它由⼀组⽤Java语⾔编写的接⼝和类组成。
JDBC需要连接驱动，驱动是两个设备要进⾏通信，满⾜⼀定通信数据格式，数据格式由设备提供商规定，设备提供商为设备提供驱动软件，通过软件可以与该设备进⾏通信。mysql的驱动mysql-connector-java-5.1.37-bin.jar
 

JDBC规范（掌握四个核⼼对象）：

• DriverManager:用于注册驱动

• Connection: 表示与数据库创建的连接

• Statement: 操作数据库sql语句的对象

• ResultSet: 结果集或⼀张虚拟表

JDBC原理

Java提供访问数据库规范称为JDBC，⽽⽣产⼚商提供规范的实现类称为驱动。

JDBC是接⼝，驱动是接⼝的实现，没有驱动将⽆法完成数据库连接，从⽽不能操作数据库！每个数据库⼚商都需要提供⾃⼰的驱动，⽤来连接⾃⼰公司的数据库，也就是说驱动⼀般都由数据库⽣成⼚商提供。

JDBC入门案例

准备数据：

/*==============================================================*/
/* DBMS name:     MySQL 5.0                                   */
/*==============================================================*/


drop table if exists tb_course;

drop table if exists tb_score;

drop table if exists tb_student;

drop table if exists tb_teacher;

/*==============================================================*/
/* Table: tb_course                                             */
/*==============================================================*/
create table tb_course
(
  id                   int not null auto_increment,
  name                 varchar(20),
  description         varchar(200),
  primary key (id)
);

/*==============================================================*/
/* Table: tb_score                                             */
/*==============================================================*/
create table tb_score
(
  id                   int not null auto_increment,
  stu_id               int,
  course_id           int,
  teacher_id           int,
  score               int,
  primary key (id)
);

/*==============================================================*/
/* Table: tb_student                                           */
/*==============================================================*/
create table tb_student
(
  id                   int not null auto_increment,
  name                 varchar(20),
  sex                 char(6),
  stu_num             varchar(20),
  age                 int,
  primary key (id)
);

/*==============================================================*/
/* Table: tb_teacher                                           */
/*==============================================================*/
create table tb_teacher
(
  id                   int not null auto_increment,
  name                 varchar(20),
  sex                 varchar(6),
  primary key (id)
);

alter table tb_score add constraint FK_COURSE_SCORE foreign key (course_id)
    references tb_course (id) on delete restrict on update restrict;

alter table tb_score add constraint FK_STU_SCORE foreign key (stu_id)
    references tb_student (id) on delete restrict on update restrict;

alter table tb_score add constraint FK_Teacher_SCORE foreign key (teacher_id)
    references tb_teacher (id) on delete restrict on update restrict;


下面sql语句可以添加数据

insert into tb_course 
values
(null, "数学","数学"),
(null, "英语","英语"),
(null, "语文","语文"),
(null, "物理","物理"),
(null, "化学","化学"),
(null, "生物","生物");



insert into tb_teacher VALUES
(null, "石老师", "男"),
(null, "田老师", "女"),
(null, "杨老师", "男"),
(null, "张老师", "女"),
(null, "李老师", "男"),
(null, "马老师", "男");


insert into tb_student VALUES
(null, "刘备","男",1, 50),
(null, "关羽","男",2, 48),
(null, "张飞","男",3, 46),
(null, "貂蝉","女",4, 20),
(null, "杨玉环","女",5,24),
(null, "西施","女",6, 22),
(null, "如花","女",7, 18);

insert into tb_score VALUE
(null, 1, 1, 1 ,80),
(null, 1, 2, 3 ,60),
(null, 2, 1, 3 ,40),
(null, 3, 2, 2 ,70),
(null, 4, 5, 4 ,90),
(null, 3, 1, 1 ,100),
(null, 4, 1, 1 ,89),
(null, 1, 3, 3 ,99),
(null, 1, 4, 3 ,47),
(null, 5, 5, 5 ,90),
(null, 5, 2, 2 ,38),
(null, 6, 1, 4 ,100),
(null, 6, 4, 3 ,89),
(null, 6, 2, 3 ,88),
(null, 6, 4, 1 ,77);

导⼊驱动jar包
创建lib⽬录，存放mysql的驱动mysql-connector-java-5.1.37-bin.jar
选中mysql的jar包，右键选择“ Add as Library...” 完成jar导⼊

链接：https://pan.baidu.com/s/1QQyVFB5bzGnfSlpuC5bB4Q 提取码：r70v
开发步骤
1. 注册驱动.
2. 获得连接.
3. 获得执⾏sql语句的对象
4. 执⾏sql语句，并返回结果
5. 处理结果
6. 释放资源.

案例实现

package JDBCTest;

import org.junit.Test;

import java.sql.*;

public class JDBCOldTest {
    @Test
    public void JDBCTest() throws ClassNotFoundException, SQLException {
        //注册驱动 就是把Driver.class 文件加载到内存
        Class.forName("com.mysql.jdbc.Driver");
        /**
         * 获取连接
         * 参数url：需要连接数据库的地址 jdbc:mysql://IP地址:端口号/要连接的数据库名称
         * 参数user：连接数据库使用的 用户名
         * 参数password：连接数据库使用的 密码
         */
        String url = "jdbc:mysql://localhost:3306/test_wensong";
        Connection conn = DriverManager.getConnection(url,"root","root");
        System.out.println("conn="+conn);
        //获取执行sql语句的对象
        Statement stat = conn.createStatement();
        //执行查询sql语句，并返回结果
        String sql = "select * from tb_student";
        ResultSet rs = stat.executeQuery(sql);
        System.out.println("rs = " + rs);
        //处理结果
        while(rs.next()){
            int age = rs.getInt(5);//通过列的位置获取值,从1开始
            String name= rs.getString(2);//通过列的位置获取值，从1开始
            System.out.println("name = " + name +" age = " + age);
        }
        rs.close();
        //执行增删改sql语句
        //增加一条数据
        String sql1 = "INSERT INTO tb_student(name,age,sex,stu_num) values('wensong',27,'男',8)";
        stat.executeUpdate(sql1);
        //删除数据
        String sql2 = "DELETE FROM tb_student WHERE name='如花'";
        stat.executeUpdate(sql2);
        //修改数据
        String sql3 = "UPDATE tb_student SET age=18 where name='杨玉环' ";
        stat.executeUpdate(sql3);
        //再次查询数据对比操作效果
        String sql4 = "select * from tb_student";
        ResultSet rs1 = stat.executeQuery(sql4);
        System.out.println("rs1 = " + rs1);
        //处理结果
        while(rs1.next()){
            int age = rs1.getInt("age");//通过字段名查询
            String name= rs1.getString("name");//通过字段名查询
            System.out.println("name = " + name +" age = " + age);
        }
        //释放资源，不然其他线程无法获取

        rs1.close();
        stat.close();
        conn.close();

    }
}