JAVA笔记-JDBC开发

JDBC开发

  1. 注册驱动

  1. 使用Class.forName("com.mysql.jdbc.Driver");手动加载字节码文件到JVM

  2. Class.forName("com.mysql.jdbc.Driver");//加载驱动类

  1. 链接数据库
  1. 通过DriverManager.etConnection(url,user,password)获取数据库连接对象
  2. URL：jdbc:mysql://localhost:3306/database
  3. username:root
  4. password:123456
  1. 获取发送sql的对象
Statement statement = connection.createStatement();//创建对象
  1. 编写sql语句
int result = statement.executeUpdate("");
  1. 处理接收结果
  2. 释放资源

example：

package com.study.day1;

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

public class TestJDBC {
    public static void main(String[] args) throws Exception{
        //1.注册驱动 加载驱动
        Class.forName("com.mysql.jdbc.Driver");

        //2.获得连接
        String url = "jdbc:mysql://localhost:3306/companydb";
        String user="root";
        String password = "123456";

        Connection connection = DriverManager.getConnection(url,user,password);

        if(connection!=null){
            System.out.println("succerss");
        }else {
            System.out.println("error!!!");
        }
        //3. 获得sql执行语句的对象 statement对象
        Statement statement = connection.createStatement();//创建对象

        //4. 编写sql语句，执行sql语句
//        String sql = "";
//
//        int result = statement.executeUpdate(sql);//dml操作调用的方法

        int result = statement.executeUpdate("");
        System.out.println(result);

        //5. 处理接受结果 先开后关
        if(result=1){
            System.out.println("success");

        }else {
            System.out.println("error");
        }
        //释放资源 先开后关
        statement.close();
        connection.close();
    }

}

resultSet结果集

案例：

package com.study.day1;

import com.sun.org.apache.bcel.internal.generic.DREM;

import java.sql.*;

public class QueryJDBC {
    public static void main(String[] args) throws ClassNotFoundException, SQLException {

        Class.forName("com.mysql.jdbc.Driver");

        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost/companydb","root", "123456");

        Statement statement = connection.createStatement();
        ResultSet resultSet = statement.executeQuery("select * from jdbctest");
        while (resultSet.next()){
            String job_id = resultSet.getString(1);
            String job_password = resultSet.getString(2);
            String job_phone = resultSet.getString(3);
            String job_address = resultSet.getString(4);
            System.out.println(job_id+"	"+job_password+"	"+job_phone+"	"+job_address);


        }
        resultSet.close();
        statement.close();
        connection.close();
    }
}

package com.study.day1;

import com.sun.org.apache.bcel.internal.generic.DREM;

import java.sql.*;

public class QueryJDBC2 {
    public static void main(String[] args) throws ClassNotFoundException, SQLException {

        Class.forName("com.mysql.jdbc.Driver");

        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost/companydb","root", "123456");

        Statement statement = connection.createStatement();
        ResultSet resultSet = statement.executeQuery("select * from jdbctest");
        while (resultSet.next()){
            String job_id = resultSet.getString("username");
            String job_password = resultSet.getString("password");
            String job_phone = resultSet.getString("phone");
            String job_address = resultSet.getString("address");
            System.out.println(job_id+"	"+job_password+"	"+job_phone+"	"+job_address);


        }
        resultSet.close();
        statement.close();
        connection.close();
    }
}

这两个案例的区别在于在便利resultset结果集的时候前者是通过列名，后者是通过表名查询，比较推荐的是后者。

image-20210928153146761

image-20210928153138728

登录jdbc

案例：

package com.study.day1.LoginJdbc;

import java.sql.*;
import java.util.Scanner;

public class LoginJDBC {
    public static void main(String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入用户名：");
        String username = scanner.next();
        System.out.println("请输入密码：");
        String password = scanner.next();

        Class.forName("com.mysql.jdbc.Driver");
        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/companydb", "root", "123456");

        Statement statement = connection.createStatement();
        ResultSet resultSet = statement.executeQuery("select * from jdbctest where username = '"+username+"' and password = '"+password+"'");

        if (resultSet.next()){
            System.out.println("登录成功！");
        }else {
            System.out.println("登陆失败");
        }
        resultSet.close();
        statement.close();
        connection.close();

    }
}

image-20210928153234201

登录是造成sql注入的问题

scanner.next()与scanner.nextLine()的区别：

next：不能读取空格 相当于结束

nextLine: 把空格当作字符，可以读取空格

当程序使用scanner.nextLine()时会造成以下情况：

image-20210928153658769

在输入用户名时输入了恶意的sql语句，or判定成永真式可以得到正确结果。

避免sql注入

由于编写的sql语句是在用户输入数据，整合后在进行编译的，所以我们要在用户输入数据前进行编译好完整的sql语句在进行填充查询即可(预编译！！)

PreparedStatement：继承statement接口，预编译使用的方法

  1. 参数标记

PreparedStatement pstmt = conn.preparedstatement("select * from user where username=? and password = ?");

在JDBC中，所有参数都是由?符号占位，即为占位符。

  1. 动态参数绑定

在完成sql预编译语句后，我们需要对预编译占位符进行动态参数绑定

preparedStatement.setString(1,username);

preparedStatement.setString(2.password);

package com.study.day1.LoginJdbc;

import java.sql.*;
import java.util.Scanner;

public class LoginJDBC {
    public static void main(String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入用户名：");
        String username = scanner.nextLine();
        System.out.println("请输入密码：");
        String password = scanner.nextLine();

        Class.forName("com.mysql.jdbc.Driver");
        Connection conn = DriverManager.getConnection("jdbc:mysql://localhost:3306/companydb", "root", "123456");


        PreparedStatement pstmt = conn.prepareStatement("select * from jdbctest where username=? and password = ?");

        pstmt.setString(1,username);
        pstmt.setString(2,password);

        System.out.println(pstmt);


    }
}

image-20210928155414663

DBUtils(封装工具类)

对于jdbc而言，模板就是这个样子

package com.study.day1.LoginJdbc2;


import java.sql.*;
import java.util.Scanner;

public class LoginJDBC2 {
    public static void main(String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入用户名:");
        String username = scanner.nextLine();
        System.out.println("请输入密码：");
        String password = scanner.nextLine();

        //1. 加载驱动类 Class.forName()
        Class.forName("com.mysql.jdbc.Driver");
        //2. 获取数据库对象 通过DriverManger加载getConnection
        Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/companydb", "root","123456");
        //3. 预编译加载statedment子类preparedStatement
        PreparedStatement preparedStatement = connection.prepareStatement("select * from jdbctest where username=? and password = ?");
        //占位符
        preparedStatement.setString(1,username);
        preparedStatement.setString(2.password);
        //设置resultset对象接收数据集
        ResultSet resultSet = preparedStatement.executeQuery();
        //4.处理结果
        if (resultSet.next()){
            System.out.println("登录成功");
        }else {
            System.out.println("登录失败！！！");
        }

    }

}

之所以封装工具类，是因为有很多代码可以重复利用，我们只需要调用这个类就可以减少很多代码量。

对于jdbc来说，加载驱动类，获取数据库对象，释放资源都是重复的代码，我们可以把它们封装到一个java模块中随时调用。

DBUtils.java

package com.study.day1.LoginJdbc2;

import java.sql.*;

/*
1. 获取链接方法
2. 释放资源方法
 */

//1. 获取连接，用getConnection命名，其中可能会产生异常的地方try_catch以下
public class DBUtils {
    public static Connection getConnection(){
        Connection connection = null;
        try {
            Class.forName("com.mysql.jdbc.Driver");
            connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/companydb","root","123456");
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }
        return connection;

        //释放资源， 用closeAll命名

    }
    public static void closeAll(Connection connection, Statement statement, ResultSet resultSet){

        try {
            if (connection!=null){
                connection.close();
            }
            if (statement!=null){
                statement.close();

            }
            if (resultSet!=null){
                resultSet.close();

            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }

    }
}

DBUtils写好后，在上述LoginJDBC2.java中可以将部分删除换成调用函数。

package com.study.day1.LoginJdbc2;


import java.sql.*;
import java.util.Scanner;

public class LoginJDBC2 {
    public static void main(String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入用户名:");
        String username = scanner.nextLine();
        System.out.println("请输入密码：");
        String password = scanner.nextLine();


        Connection connection = DBUtils.getConnection();

        //3. 预编译加载statedment子类preparedStatement
        PreparedStatement preparedStatement = connection.prepareStatement("select * from jdbctest where username=? and password = ?");
        //占位符
        preparedStatement.setString(1,username);
        preparedStatement.setString(2,password);
        //设置resultset对象接收数据集
        ResultSet resultSet = preparedStatement.executeQuery();

        //4.处理结果

        if (resultSet.next()){
            System.out.println("success");
        }else{
            System.out.println("error!");
        }
        //释放资源

        DBUtils.closeAll(connection,preparedStatement,resultSet);
    }

}

image-20210928201448897

跨平台方案(可以更便捷操作)

  • 定义public static finall Properties prop = new Properties();//读取配置文件的Map

  • 定义 static{

​ //首次使用工具类时，需要加载驱动类

​ InputStream is = JDBCUtil.class.getResourceAsStream("路径");//通过服用本类自带的流，读取jdbc.properties配置文件

​ prop.load(is);

​ String driverName = prop.getProperty("driver");//通过driverName的键获取对应的值

​ Class.forName(driverName);//加载驱动

}

DBUtils.java

package com.study.day1.LoginJdbc3;

import com.study.day1.LoginJdbc2.DBUtils;

import java.io.IOException;
import java.io.InputStream;
import java.sql.*;
import java.util.Properties;

public class DBUtils_prop {

    //1.加载静态资源
    private static final Properties PROPERTIES = new Properties(); //给一个私有的静态的常量->存储配置文件的map集合
    static {

        //2. 拿java里面一个字节输入流is，不用new，可以用自带的
        InputStream is = DBUtils.class.getResourceAsStream("/DB.properies");
        //3. 通过properties中的一个方法load()把文件里的东西读取进来
        try {
            PROPERTIES.load(is);//通过流将文件内容加载到properties集合

            Class.forName(PROPERTIES.getProperty("driver"));
        } catch (IOException e) {
            e.printStackTrace();
        } catch (ClassNotFoundException e) {
            e.printStackTrace();
        }

    }

    public static Connection getConnection(){
        try {
            Connection connection = null;
            connection = DriverManager.getConnection(PROPERTIES.getProperty("url"),PROPERTIES.getProperty("username"),PROPERTIES.getProperty("password"));
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }

    }

    public static void closeAll(Connection connection, Statement statement, ResultSet resultSet){
        try {
            if (resultSet!=null){

                resultSet.close();
            }
            if (statement!=null){

                statement.close();
            }
            if (connection!=null){
                connection.close();
            }
        } catch (SQLException throwables) {
            throwables.printStackTrace();
        }


    }
}

image-20210928205641761

loginJDBC3.java

package com.study.day1.LoginJdbc3;



import com.study.day1.LoginJdbc2.DBUtils;

import java.sql.*;
import java.util.Scanner;

public class loginJDBC3 {
    public static void main(String[] args) throws Exception {
        Scanner scanner = new Scanner(System.in);
        System.out.println("请输入用户名:");
        String username = scanner.nextLine();
        System.out.println("请输入密码：");
        String password = scanner.nextLine();


        Connection connection = DBUtils.getConnection();

        //3. 预编译加载statedment子类preparedStatement
        PreparedStatement preparedStatement = connection.prepareStatement("select * from jdbctest where username=? and password = ?");
        //占位符
        preparedStatement.setString(1,username);
        preparedStatement.setString(2,password);
        //设置resultset对象接收数据集
        ResultSet resultSet = preparedStatement.executeQuery();

        //4.处理结果

        if (resultSet.next()){
            System.out.println("success");
        }else{
            System.out.println("error!");
        }
        //释放资源

        DBUtils.closeAll(connection,preparedStatement,resultSet);
    }

}

DB.properties

image-20210928210229381

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原文地址：https://www.cnblogs.com/zjhzjhhh/p/15364866.html