jdbc 编程

概念先参考：https://www.cnblogs.com/wuziyue/p/4827295.html

不要问为什么，直接代码搞起

1. com.domain 包 User 实体类

package com.domain;

public class User {
	private String u_name;
	private int u_age;
	public String getU_name() {
		return u_name;
	}
	public void setU_name(String u_name) {
		this.u_name = u_name;
	}
	public int getU_age() {
		return u_age;
	}
	public void setU_age(int u_age) {
		this.u_age = u_age;
	}
	
	public User() {
	}
	public User(String u_name, int u_age) {
		super();
		this.u_name = u_name;
		this.u_age = u_age;
	}
	@Override
	public String toString() {
		return "User [u_name=" + u_name + ", u_age=" + u_age + "]";
	}
}

2. com.dao 包下的 IUserDao 接口

package com.dao;

import java.util.List;
import com.domain.User;

public interface IUserDao {
	void addUserInfo(User user);
	void deleteUserInfo(User user);
	void updateUserAgeInfo(User user,int age);
	User selectUserInfoByName(String name);
	List<User> selectAllUserInfo();
}

3. com.dao.impl 包 UserDaoImpl 类

package com.dao.impl;

import org.junit.Test;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.ArrayList;
import java.util.List;

import com.Util.JDBCUtil;
import com.dao.IUserDao;
import com.domain.User;

public class UserDaoImpl implements IUserDao{
	
	ResultSet rs = null;
	Statement st = null;
	User user = null;
	
/*常见的异常错误：No operations allowed after connection closed.
	因为 当 数据库的连接Connection是一个Static的，程序共享这一个Connection。
	那么第一次对数据库操作没问题，当把Connection关闭后，第二次还想操作数据库时Connection肯定不存在了。
所以为了解决这个问题：我们最好把  创建Connection的实例写到每个操作的方法中。
*/
	
/* 1. 增加用户信息*/ 
	@Test
	public void addUserInfo(User user){
		Connection conn = JDBCUtil.getInstance().getConnection();
			try {
				st = conn.createStatement();
				int row = st.executeUpdate("insert into tb_user (id,`name`,age)values(null,'"+user.getU_name()+"',"+user.getU_age()+")");
				if(row > 0){
					System.out.println("添加用户成功");
				}
			} catch (SQLException e) {
				e.printStackTrace();
			}
			JDBCUtil.getInstance().closeAll(rs,st,conn);
	}
	
/*2. 删除用户信息*/
	@Test
	public void deleteUserInfo(User user) {
		Connection conn = JDBCUtil.getInstance().getConnection();
		try{
			st = conn.createStatement();
			int row = st.executeUpdate("delete from tb_user where name = '"+user.getU_name()+"'");
			if(row > 0){
				System.out.println("删除用户成功");
			}
		}catch (Exception e) {
			e.printStackTrace();
		}
		JDBCUtil.getInstance().closeAll(rs,st,conn);
	}
	
	
/*3. 修改用户信息*/
	@Test
	public void updateUserAgeInfo(User user,int age) {
		Connection conn = JDBCUtil.getInstance().getConnection();
		try{
			st = conn.createStatement();
			int row = st.executeUpdate("update tb_user set age = "+age+" where name = '"+user.getU_name()+"'");
			if(row > 0){
				System.out.println("修改用户信息成功");
			}
		}catch (Exception e) {
			e.printStackTrace();
		}
		JDBCUtil.getInstance().closeAll(rs,st,conn);
	}
	
	
/*4. 通过name查询一个用户信息*/
	@Test
	public User selectUserInfoByName(String name) {
		Connection conn = JDBCUtil.getInstance().getConnection();
//这里如果不写，当方法3中调用次方法时，就会因为 Connection 关闭而报错。
		try{
			st = conn.createStatement();
			rs = st.executeQuery("select * from tb_user where `name` = '"+name+"'");
			while(rs.next()){
				user = new User();
				user.setU_name(rs.getString("name"));
				user.setU_age(rs.getInt("age"));
			}
		}catch (Exception e) {
			e.printStackTrace();
		}
		JDBCUtil.getInstance().closeAll(rs,st,conn);
		return user;
	}
	
/*5. 查询所有用户信息*/
	@Override
	public List<User> selectAllUserInfo() {
		Connection conn = JDBCUtil.getInstance().getConnection();
		List<User> userlist = new ArrayList();
		try{
			st = conn.createStatement();
			rs = st.executeQuery("select * from tb_user");
			while(rs.next()){
				User user = new User();
				user.setU_name(rs.getString("name"));
				user.setU_age(rs.getInt("age"));
				userlist.add(user);
			}
		}catch (Exception e) {
			e.printStackTrace();
		}
		JDBCUtil.getInstance().closeAll(rs,st,conn);
		return userlist;
	}
}

4. com.Util 包 JDBCUtil 类封装共用的代码

package com.Util;

import java.io.FileInputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;
import java.util.Properties;

public class JDBCUtil {
	
/*//	1. 参数是硬编码在代码中
	private static String driverName = "com.mysql.jdbc.Driver";
	private static String url = "jdbc:mysql://localhost:3306/mysql001";
	private static String userName = "root";
	private static String passWorld = "root";
	private static JDBCUtil instance = null;
	Connection conn;
	static{
		try {
			Class.forName(driverName);
			instance = new JDBCUtil();
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
	}
//获得链接对象
	public Connection getConn(){
		try {
			return DriverManager.getConnection(url,userName,passWorld);
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return null;
	}
//关闭链接资源
	public void close(ResultSet rs, Statement st, Connection conn){
		try {
			if(rs!=null) rs.close();
		} catch (SQLException e) {
			e.printStackTrace();
		}finally {
			try {
				if(st!=null) st.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}finally {
				try {
					if(conn!=null) conn.close();
				} catch (SQLException e) {
					e.printStackTrace();
				}
			}
		}
	}
*/
	
//2.把参数放到资源文件中	
	static Properties prop = new Properties();
	//懒汉模式获取 JDBCUtil类的一个实例
	private JDBCUtil(){}
	private static JDBCUtil instance = null;
	public static JDBCUtil getInstance(){
		if(instance == null){
			instance = new JDBCUtil();
		}
		return instance;
	}
	
	static{
		try {
			prop.load(new FileInputStream("jdbc.properties"));
			Class.forName(prop.getProperty("driverName"));
		} catch (Exception e) {
			e.printStackTrace();
		}
	}
//获得链接对象
	public Connection getConnection(){
		Connection conn = null;
		try {
			conn = DriverManager.getConnection(prop.getProperty("url"),prop.getProperty("userName"),prop.getProperty("password"));
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return  conn;
	}
	
//关闭所有链接资源	
	public void closeAll(ResultSet rs, Statement st, Connection conn){
		try {
			if(rs!=null) rs.close();
		} catch (SQLException e) {
			e.printStackTrace();
		}finally {
			try {
				if(st!=null) st.close();
			} catch (SQLException e) {
				e.printStackTrace();
			}finally {
				try {
					if(conn!=null) conn.close();
				} catch (SQLException e) {
					e.printStackTrace();
				}
			}
		}
	}
}

5. com.test 包 TestDao 测试类

package com.test;
import java.util.List;
import java.util.Scanner;
import org.junit.Test;

import com.dao.IUserDao;
import com.dao.impl.UserDaoImpl;
import com.domain.User;

public class TestDao {
	IUserDao userdao = new UserDaoImpl();
	
	@Test
	public void addUserInfo(){
		User user = new User("赵本本",75); //获取数据
		userdao.addUserInfo(user);  //将数据传到Dao层进行数据库操作
	}
	
	@Test
	public void deleteUserInfo(){
		User user = new User("赵本本",75);
		userdao.deleteUserInfo(user);;
	}
	
	/*修改用户信息*/
	@Test
	public void updateUserAgeInfo(){
		System.out.println("请输入要修改的用户姓名:");
		String name = new Scanner(System.in).nextLine();
		//将name传到dao层验证该用户是否存在
		User user = userdao.selectUserInfoByName(name);
		if(user != null){
			System.out.println("请输入修改后的用户年龄:");
			int age = new Scanner(System.in).nextInt();
			//将user对象和age传到dao层进行修改数据操作
			userdao.updateUserAgeInfo(user,age);;
		}else{
			System.out.println("不存在该用户,gameover!!");
		}
	}
	
	@Test
	public void selectUserInfoByName(){
		System.out.println("请输入查询的学生姓名");
		String name = "李四";
		System.out.println(userdao.selectUserInfoByName(name));
	}
	
	@Test
	public void selectAllUserInfo(){
		List<User> userlist = userdao.selectAllUserInfo();
		for (User user : userlist) {
			System.out.println(user);
		}
	}
}

6. 数据库表：

CREATE TABLE `tb_user` (
  `id` int(10) NOT NULL AUTO_INCREMENT,
  `name` varchar(20) DEFAULT NULL,
  `age` int(10) DEFAULT NULL,
  PRIMARY KEY (`id`)
) ENGINE=InnoDB AUTO_INCREMENT=11 DEFAULT CHARSET=utf8;

7. jdbc.properties 配置文件

driverName = com.mysql.jdbc.Driver
url = jdbc:mysql://localhost:3306/mysql001
userName = root
password = root

待补充。。。。。。　

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