二十七、JDBC连接数据库与预编译登录（及用预编译的原因）

导入驱动包：
链接：https://pan.baidu.com/s/1RGvpXLW7ZvcDX1DpoqLuIg
提取码：t2ee
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1.连接数据库

package com.conn;

import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.sql.Statement;

public class JDBC {
	//驱动
	final static String driver = "com.mysql.jdbc.Driver";
    //连接数据库的地址
	final static String url = "jdbc:mysql://127.0.0.1:3306/db_test?useUnicode=true&characterEncoding=utf-8";
	//数据库用户名
	final static String username = "root";
	//数据库密码
	final static String password = "123456";
	//建立数据库连接
	static{
		try {
			//加载驱动
			Class.forName(driver);
		} catch (ClassNotFoundException e) {
			e.printStackTrace();
		}
	}
	//建立连接
	public static Connection getConnection() {
		Connection conn = null;
		try {
			//通过DriverManager获取到数据库连接
		    conn = DriverManager.getConnection(url, username, password);
		} catch (SQLException e) {
			e.printStackTrace();
		}
		return conn;
	}
	//释放资源
	public static void close(Connection conn,Statement st,ResultSet rs) throws SQLException {
		if (conn != null) {
			conn.close();
		}
		if (st != null) {
			st.close();
		}
		if (rs != null) {
			rs.close();
		}
	}
	//测试连接数据库是否成功
	public static void main(String[] args) {
		System.out.println(JDBC.getConnection());
	}
}

2.创建表

CREATE TABLE user (
  id int(11) NOT NULL AUTO_INCREMENT,
  usernam` varchar(64) DEFAULT NULL,
  password varchar(64) DEFAULT NULL,
  PRIMARY KEY (id)
) ENGINE=InnoDB AUTO_INCREMENT=7 DEFAULT CHARSET=utf8;

/*Data for the table `user` */

insert  into `user`(`id`,`username`,`password`) values (1,'张三','123'),(2,'李四','456'),(3,'王五','789');

3.建立实体类

package com.entity;

public class User {
	private Integer id;
	private String username;
	private String password;
	public User() {
		
	}
	public User(Integer id, String username, String password) {
		this.id = id;
		this.username = username;
		this.password = password;
	}
	public Integer getId() {
		return id;
	}
	public void setId(Integer id) {
		this.id = id;
	}
	public String getUsername() {
		return username;
	}
	public void setUsername(String username) {
		this.username = username;
	}
	public String getPassword() {
		return password;
	}
	public void setPassword(String password) {
		this.password = password;
	}
	@Override
	public String toString() {
		return "用户信息 [编号=" + id + ", 姓名=" + username + ", 密码=" + password + "]";
	}
}

4.增删改查

package com.baseDao;

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

import com.conn.JDBC;
import com.entity.User;

public class DB {
	// 查询所有数据
	public static List<User> seleteAll() {
		// 创建一个User对象的集合
		List<User> user = new ArrayList<User>();
		// sql语句
		String sql = "select * from user";
		Connection conn = null;
		Statement st = null;
		ResultSet rs = null;
		try {
			conn = JDBC.getConnection();
			st = conn.createStatement();
			// 将sql语句发送到数据库
			rs = st.executeQuery(sql);
			while (rs.next()) {
				// 通过表头获取
				Integer id = rs.getInt("id");
				String usename = rs.getString("username");
				String password = rs.getString("password");
				// 将每一条数据存放到User对象的集合中
				user.add(new User(id, usename, password));
			}
		} catch (SQLException e) {
			e.printStackTrace();
		} finally {
			// 关闭连接
			try {
				JDBC.close(conn, st, rs);
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
		return user;
	}

	// 增删改
	public static int update(String sql) {
		Connection conn = null;
		Statement st = null;
		int i = 0;
		try {
			conn = JDBC.getConnection();
			st = conn.createStatement();
			i = st.executeUpdate(sql);
		} catch (SQLException e) {
			e.printStackTrace();
		} finally {
			try {
				JDBC.close(conn, st, null);
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
		return i;
	}

	// 登录
	public static User login(String name, String password) {
		// 创建一个User对象的集合
		User user = null;
		String sql = "select * from user where username='" + name + "'and password = '" + password + "'";// （不安全）
		Connection conn = null;
		Statement st = null;
		ResultSet rs = null;
		try {
			// 建立数据库连接
			conn = JDBC.getConnection();
			st = conn.createStatement();
			rs = st.executeQuery(sql);
			while (rs.next()) {
				user = new User(rs.getInt("id"), rs.getString("username"), rs.getString("password"));
			}
		} catch (SQLException e) {
			e.printStackTrace();
		} finally {
			try {
				JDBC.close(conn, st, rs);
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}

		return user;

	}

	// 预编译登录
	public static User preLogin(String name, String password) {
		String sql = "select * from user where username= ? and password = ?";
		User user = null;
		Connection conn = null;
		PreparedStatement pst = null;
		ResultSet rs = null;
		try {
			conn = JDBC.getConnection();
			pst = conn.prepareStatement(sql);
			pst.setString(1, name);
			pst.setString(2, password);
			rs = pst.executeQuery();
			while (rs.next()) {
				user = new User(rs.getInt("id"), rs.getString("username"), rs.getString("password"));
			}
		} catch (Exception e) {
			e.printStackTrace();
		} finally {
			try {
				JDBC.close(conn, pst, rs);
			} catch (SQLException e) {
				e.printStackTrace();
			}
		}
		return user;
	}

	// 预编增删该查
	public static int Preupdate(String sql, Object... prams) {
		Connection conn = null;
		PreparedStatement pst = null;
		int i = 0;
		try {
			conn = JDBC.getConnection();
			pst = conn.prepareStatement(sql);
			for (int j = 0; j < prams.length; j++) {
				pst.setObject(j + 1, prams[j]);
			}
			i = pst.executeUpdate();
		} catch (Exception e) {
			e.printStackTrace();
		}

		return i;
	}

	public static void main(String[] args) {
		List<User> user = DB.seleteAll();
		for (User users : user) {
			System.out.println(users);
		}

//		System.out.println("增加数据===========");
//		System.out.println(DB.update("insert into user values(4,'赵六','4321');"));
		
//		System.out.println("删除一条数据=======");
//		System.out.println(DB.update("delete from user where id="+4));
		
//		System.out.println("修改一条数据======");
//		System.out.println(DB.update("update user set username='西西'  where id=3"));
		
		System.out.println("普通登录=======不安全");
		System.out.println(DB.login("' or 1=1 -- ", " "));
		
		System.out.println("预编译登录======");
		System.out.println(DB.preLogin("张三", "123"));
		System.out.println(DB.preLogin("' or 1=1 -- ", " "));
		
//		System.out.println("预编译增");
//		System.out.println(DB.Preupdate("insert into user values(?,?,?)", 4,"赵六","432"));
//		System.out.println("预编译删");
//		System.out.println(DB.Preupdate("delete from user where id=?", 4));
		System.out.println("预编译改");
		System.out.println(DB.Preupdate("update user set username=? where id=?", "王五",3));
		
	}
}

运行截图