根据id查询数据库中的一个内容:
1.连接数据库
2.编写带?的sql语句
3.预编译
4.填充占位符
5.执行操作
6.if判断是否有值,打印输出
7.关闭驱动
示例:
package cn.kgc.crud;
import cn.kgc.entity.User;
import cn.kgc.util.JDBCUtil;
import java.sql.*;
/**
* Created by helloworld on 2020/6/24.
* 根据id查询一个数据
*/
public class SelectUserById {
public static void main(String[] args){
Connection connection=null;
PreparedStatement pstm=null;
ResultSet rs=null;
try {
//1连接数据库
Class.forName("com.mysql.jdbc.Driver");
// 使用的技术:数据库名://ip:mysql端口/数据库名字
connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/xxx", "rxxx", "xxxxx")
//2.编写?sql
String sql ="select * from user where id=?";
//3.预编译
pstm = connection.prepareStatement(sql);
//4.填充占位符
pstm.setObject(1,"1");
//5.执行
rs = pstm.executeQuery();
//6判断是否有值,然后打印
if(rs.next()){
/*int id = rs.getInt(1);
String name = rs.getString(2);
int age = rs.getInt(3);
*/
int id = rs.getInt("id");
String name = rs.getString("name");
int age = rs.getInt("age");
User user = new User(id,name,age);
System.out.println(user.toString());
// System.out.println("id:"+id+",name:"+name+",age"+age);
}
} catch (SQLException e) {
e.printStackTrace();
}finally {
//7.关闭
JDBCUtil.closeResource2(rs,pstm,connection);
}
}
}