Java上机实验报告（4）

一、任务简要描述

 数据库编程：练习数据库编程。用MySQL数据库，建立一个数据库表，通过JDBC连接MySQL数据库，并对数据库进行增删改查等操作。

我做了数据库连接，插入数据、删除数据、修改数据、数据查询功能，通过输入密码查询，并解决了sql的注入问题。

Java数据库连接体系结构是用于Java应用程序连接数据库的标准方法。JDBC对Java程序员而言是API，对实现与数据库连接的服务提供商而言是接口模型。作为API，JDBC为程序开发提供标准的接口，并为数据库厂商及第三方中间件厂商实现与数据库的连接提供了标准方法。JDBC使用已有的SQL标准并支持与其它数据库连接标准，如ODBC之间的桥接。JDBC实现了所有这些面向标准的目标并且具有简单、严格类型定义且高性能实现的接口。

Java 具有坚固、安全、易于使用、易于理解和可从网络上自动下载等特性，是编写数据库应用程序的杰出语言。所需要的只是 Java应用程序与各种不同数据库之间进行对话的方法。而 JDBC 正是作为此种用途的机制。   

二、问题及解决

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



public class JDBCDemo01 {
    public static void main(String[] args) {
        selectAll();
        //登录校验
        selectByUsernamePassword("Micheal", "123");
        selectByUP2("Micheal", "123");
        //分页查询
        selectUserByPage(3, 4);
        insert("ky", "123456");
        delete(3);
        update(2, "123456");
        
    }
    
    public static void selectAll() {

        Connection con = null;
        Statement stmt = null;
        ResultSet rs = null;
        
        try {    
            con = JDBCUtils.getConnection();
                
            stmt = con.createStatement();
            rs = stmt.executeQuery("select * from user");
                
            while(rs.next()) {
                System.out.println(rs.getInt("id") + "," + rs.getString(rs.getString("username")) + "," + rs.getString("password"));
                    
            }
                
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    }
    
public static boolean selectByUsernamePassword(String username, String password) {
        Statement stmt = null;
        Connection con = null;
        ResultSet rs = null;
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            
            String url = "jdbc:mysql://localhost:3306/web01?useUnicode = true & characterEncoding = UTF8 & useSSL = false";
            con = DriverManager.getConnection(url, "root", "root");
            
            stmt = con.createStatement();
            
            String sql = "select * from user where username = '"+username+"' and password = '"+password+"'";
            rs = stmt.executeQuery(sql);
            
            if(rs.next()) {
                return true;
            } else {
                return false;
            }
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            try {
                if(rs != null) rs.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        
            try {
                if(stmt != null) stmt.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        
            try {
                if(con != null) con.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return false;
    }
    //解决sql注入问题
    public static boolean selectByUP2(String username, String password) {
        Statement stmt = null;
        Connection con = null;
        ResultSet rs = null;
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            
            String url = "jdbc:mysql://localhost:3306/web01?useUnicode = true & characterEncoding = UTF8 & useSSL = false";
            con = DriverManager.getConnection(url, "root", "root");
            
            String sql = "select * from user where username = ? and password = ?";
            PreparedStatement pstmt = con.prepareStatement(sql);
            
            pstmt.setString(1, username);
            pstmt.setString(2, password);
            
            rs = pstmt.executeQuery();
            if(rs.next()) return true;
            else return false;
            
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            try {
                if(rs != null) rs.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        
            try {
                if(stmt != null) stmt.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        
            try {
                if(con != null) con.close();
            } catch (SQLException e) {
                // TODO Auto-generated catch block
                e.printStackTrace();
            }
        }
        return false;
    }
    //pageNumber是页数，第几页pageCount是每页显示多少条数据
    public static void selectUserByPage(int pageNumber, int pageCount) {
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        
        try {
                Class.forName("com.mysql.cj.jdbc.Driver");
            
                //String url = "jdbc:mysql://localhost:3306/web01";
                String url = "jdbc:mysql://localhost:3306/web01?useUnicode=true&characterEncoding=UTF8&useSSL=false&allowPublicKeyRetrieval=true";
                String user = "root";
                String password = "root";
                
                con = DriverManager.getConnection(url, user, password);
                
                stmt = con.prepareStatement("select * from user limit ?, ?");
                stmt.setInt(1, (pageNumber - 1) * pageCount);
                stmt.setInt(2, pageCount);
                
                rs = stmt.executeQuery();
                
                while(rs.next()) {
                    System.out.println(rs.getInt("id") + "," + rs.getString(rs.getString("username")) + "," + rs.getString("password"));
                    
                }
                
                
                
        } catch (ClassNotFoundException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }//使用什么驱动连接数据库
          catch (SQLException e) {
            // TODO Auto-generated catch block
          e.printStackTrace();
        } finally {
                try {
                    if(rs != null) rs.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            
                try {
                    if(stmt != null) stmt.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
            
                try {
                    if(con != null) con.close();
                } catch (SQLException e) {
                    // TODO Auto-generated catch block
                    e.printStackTrace();
                }
        }
    }
    
    public static void insert(String username, String password) {
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {    
            con = JDBCUtils.getConnection();
            
            String sql = "insert into user(username, password) valuse(?, ?)";
            stmt = con.prepareStatement(sql);
            stmt.setString(1, username);
            stmt.setString(2, password);
            
            int result = stmt.executeUpdate();   //返回值代表受到影响的行数
            
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    
    }

    public static void delete(int id) {
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {    
            con = JDBCUtils.getConnection();
            
            String sql = "delete from user where id = ?";
            stmt = con.prepareStatement(sql);
            stmt.setInt(1, id);
            
            int result = stmt.executeUpdate();   //返回值代表受到影响的行数
            if(result > 0) {
                System.out.println("删除成功");
            }else {
                System.out.println("删除失败");
            }
            
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    
    }
    

    public static void update(int id, String newPassword) {
        Connection con = null;
        PreparedStatement stmt = null;
        ResultSet rs = null;
        try {    
            con = JDBCUtils.getConnection();
            
            String sql = "update user set password = ? where id = ?";
            stmt = con.prepareStatement(sql);
            stmt.setString(1, newPassword);
            stmt.setInt(2, id);
            
            int result = stmt.executeUpdate();   //返回值代表受到影响的行数
            if(result > 0) {
                System.out.println("修改成功");
            }else {
                System.out.println("修改失败");
            }
            
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        } finally {
            JDBCUtils.close(rs, stmt, con);
        }
    
    }
}

工具类用做数据库连接和关闭

package com.kuyan.jdbc01;

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

public class JDBCUtils {
    private static final String connectionURL = "jdbc:mysql://localhost:3306/web01?useUnicode = true & characterEncoding = UTF8 & useSSL = false";
    private static final String username = "root";
    private static final String password = "root";
    
    public static Connection getConnection() {
        try {
            Class.forName("com.mysql.cj.jdbc.Driver");
            
        return DriverManager.getConnection(connectionURL, username, password);
        
        } catch (Exception e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
        
        return null;
    }
    
    public static void close(ResultSet rs, Statement stmt, Connection con) {
        try {
            if(rs != null) rs.close();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    
        try {
            if(stmt != null) stmt.close();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    
        try {
            if(con != null) con.close();
        } catch (SQLException e) {
            // TODO Auto-generated catch block
            e.printStackTrace();
        }
    }

    
}

总结：在数据库连接时报错了好几次，首先我下载的jdbc驱动jar文件与MySQL数据库版本不适用，我又重新下载。

另外，我使用的mysql版本是8.0.x，mysql-connector版本8.0.x

应该改为Class.forName("com.mysql.cj.jdbc.Driver");新版本，系统可以自动加载，不用书写也可以

老版本

url="jdbc:mysql://localhost:3306/databaseName"

新版本

url="jdbc:mysql://localhost:3306/databaseName?serverTimezone=GMT"

这是对时区的设置，不设置就抛错，同时这种写法会有警告，是要求你主动设置是否进行加密校验，即useSSL=false或者useSSL=true  //url中的？之后的是属性设置

我先用sql语句在数据库中建数据库web01、建表user

但在用Java操作数据库时，由于权限设置问题一直报错，上网查找相关资料又询问同学，可能由于版本问题一直得不到解决办法。