1. Concept understanding
Recently, I was learning the javaweb video of Kuangshen. His JDBC is very good. I wrote a technical blog to share with everyone, and at the same time, it is convenient for myself to review and use. To the point:
What is JDBC (Java DataBase Connectivity): Java connects to the database
Need jar package support:
- java.sql
- javax.sql
- The mysql-connector-java connection driver must be imported!
2. Setting up the environment before writing JDBC code:
- Database code:
CREATE TABLE users(
id INT PRIMARY KEY,
`name` VARCHAR(40),
`password` VARCHAR(40),
email VARCHAR(60),
birthday DATE
);
INSERT INTO users(id,`name`,`password`,email,birthday)
VALUES(1,'张三','123456','[email protected]','2000-01-01');
INSERT INTO users(id,`name`,`password`,email,birthday)
VALUES(2,'李四','123456','[email protected]','2000-01-01');
INSERT INTO users(id,`name`,`password`,email,birthday)
VALUES(3,'王五','123456','[email protected]','2000-01-01');
SELECT * FROM users;
- Import database dependencies
<!--mysql驱动-->
<dependency>
<groupId>mysql</groupId>
<artifactId>mysql-connector-java</artifactId>
<version>5.1.47</version>
</dependency>
- Connect to the database in IDEA
Three, JDBC code steps
- Load the driver
- Connect to the database, the object represents the database
- Send SQL object statement to the database: CRUD
- Write sql (different sql according to business)
- Execute sql
- Close the connection
code show as below:
package com.xu.test;
import jdk.nashorn.internal.runtime.OptimisticReturnFilters;
import java.sql.*;
public class TestJdbc {
public static void main(String[] args) throws ClassNotFoundException, SQLException {
//配置信息
//useUnicode=true&characterEncoding=utf-8 解决中文乱码
String url = "jdbc:mysql://localhost:3306/jdbc?useUnicode=true&characterEncoding=utf-8";
String username = "root";
String password = "root";
//1.加载驱动
Class.forName("com.mysql.jdbc.Driver");
//2.连接数据库,该对象代表数据库
Connection connection = DriverManager.getConnection(url, username, password);
//3.向数据库发送sql对象 statement,PreparedStatement ： CRUD
Statement statement = connection.createStatement();
//4.编写sql
String sql = "select * from users";
//5.执行查询sql，返回一个结果集
ResultSet rs = statement.executeQuery(sql);
while (rs.next()){
System.out.println("id = " + rs.getObject("name"));
System.out.println("name = " + rs.getObject("name"));
System.out.println("password = " + rs.getObject("password"));
System.out.println("email = " + rs.getObject("email"));
System.out.println("birthday = " + rs.getObject("birthday"));
}
//6.关闭连接，释放资源，一定要做，先开后关
rs.close();
statement.close();
connection.close();
}
}
In the above code, the code used in the query is:
ResultSet rs = statement.executeQuery(sql);
However, all additions , deletions and changes are used, and the return value is the number of affected rows :
int i = statement.executeUpdate(sql);
Pre-compiled sql code:
package com.xu.test;
import java.sql.*;
public class TestJdbc2 {
public static void main(String[] args) throws Exception {
//配置信息
//useUnicode=true&characterEncoding=utf-8 解决中文乱码
String url = "jdbc:mysql://localhost:3306/jdbc";
String username = "root";
String password = "root";
//1.加载驱动
Class.forName("com.mysql.jdbc.Driver");
//2.连接数据库,该对象代表数据库
Connection connection = DriverManager.getConnection(url, username, password);
//3.编写sql
String sql = "insert into users(id,name,password,email,birthday) values(?,?,?,?,?)";
//4.预编译
PreparedStatement preparedStatement = connection.prepareStatement(sql);
preparedStatement.setInt(1,4); //给第一个占位符？ 的值赋值为4
preparedStatement.setString(2,"徐志斌"); //给第二个占位符？ 的值赋值为徐志斌
preparedStatement.setString(3,"123456"); //给第三个占位符？ 的值赋值为123456
preparedStatement.setString(4,"[email protected]"); //给第四个占位符？ 的值赋值为4
preparedStatement.setDate(5,new Date(new java.util.Date().getTime())); //给第五个占位符？ 的值赋值为5
//5.执行sql
int i = preparedStatement.executeUpdate();
if (i > 0){
System.out.println("插入成功");
}
//6.关闭连接，释放资源，一定要做，先开后关
preparedStatement.close();
connection.close();
}
}
Four, affairs
Either all succeed or all fail.
ACID principle: to ensure data security (for example, transfer issues)
开启事务
关闭事务 commit()
事务回滚 rollback()
关闭事务
If A has transferred money, in case the system crashes, A transfers money, B does not receive. In order to prevent this from happening, the role of the transaction is proposed at this time
The code is shown below:
package com.xu.test;
import org.junit.Test;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.SQLException;
public class TestJdbc3 {
@Test
public void test(){
//配置信息
//useUnicode=true&characterEncoding=utf-8 解决中文乱码
String url = "jdbc:mysql://localhost:3306/jdbc?useUnicode=true&characterEncoding=utf-8";
String username = "root";
String password = "root";
Connection connection = null;
try {
//1.加载驱动
Class.forName("com.mysql.jdbc.Driver");
//2.连接数据库,该对象代表数据库
connection = DriverManager.getConnection(url, username, password);
//3.通知数据库开启事务，false代表开启
connection.setAutoCommit(false);
String sql = "update account set money = money - 100 where name = 'A'";
connection.prepareStatement(sql).executeUpdate();
//4.制造错误，体现事务作用
//int i = 1 / 0;
String sql2 = "update account set money = money + 100 where name = 'B'";
connection.prepareStatement(sql2).executeUpdate();
connection.commit(); //以上两条sql都执行成功，就提交事务！
System.out.println("success");
}catch (Exception e){
try {
//如果出现异常，就通知数据库回滚事务
connection.rollback();
} catch (SQLException e1) {
e1.printStackTrace();
}
e.printStackTrace();
}finally {
try {
connection.close();
} catch (SQLException e) {
e.printStackTrace();
}
}
}
}