Java基础学习数据库之JDBC

一JDBC 的含义:

JDBC是Java提供的一套内和接口

  链接数据哭的一套规范

  链接数据库是你要做什么? 使用这些类和接口

JDBC操作数据库的步骤:

  1.注册驱动(加载驱动类)  registerDriver(Driver driver)   Driver是数据库厂商实现的

  2.获取数据库连接对象 getConnection(String url, String user, String password); 

  ---这里就相当于连接上了数据库

  3.通过连接对象 获取Sql 语句的执行对象  createStatement()  

  创建一个 Statement 对象来将 SQL 语句发送到数据库。 获取 执行SQL语句的对象;

  4.执行SQL语句 通过 Statement 对象 ; 

  executeQuery(String sql)  返回值为resultset  DQL (select)

  executeUpdate(String sql)  返回值为 int  执行 DDL DML

  5.处理执行SQL后得到的结果集

  6.释放资源(调用close()方法)

	public static void main(String[] args) throws SQLException, ClassNotFoundException {
		//注册驱动
		// 如果这么注册相当于注册了两遍 
		//DriverManager.registerDriver(new Driver());
		//Driver类源码中静态代码块
		//并且代码块中已经注册了一次
		//该如何正确注册驱动? 利用反射注册驱动
			Class.forName("com.mysql.jdbc.Driver");
			//获取数据库连接对象
			//url 数据库的连接地址 jdbc:mysql://主机IP地址 :数据库端口号3306/数据库名
			String url = "jdbc:mysql://localhost:3306/mysql01";
			String user = "root";
			String password = "123456";
			Connection connection = DriverManager.getConnection(url, user, password);
			System.out.println(connection);
			//通过连接对象 获取Sql 语句的执行对象
		    Statement statement = connection.createStatement();
		    //执行SQL语句
		    String sql = "insert into goods"
		    		+"(sname,sprice,sdesc)"
		    		+"values('手机',8000,'一塔手机')";
		    int executeUpdate = statement.executeUpdate(sql);
		    System.out.println(executeUpdate);
		    connection.close();
		    statement.close();
		    
	}

处理执行SQL后得到的结果集

	public static void main(String[] args) throws ClassNotFoundException, SQLException {
		Class.forName("com.mysql.jdbc.Driver");
		String url = "jdbc:mysql://localhost:3306/mysql01";
		String user = "root";
		String password = "123456";
		Connection connection = DriverManager.getConnection(url, user, password);
		Statement statement = connection.createStatement();
		//执行SQL语句
		//String sql ="select * from goods";
		String sql ="select sname,sid,sprice,sdesc from goods";
		ResultSet executeQuery = statement.executeQuery(sql);
		//处理结果
		
		while (executeQuery.next()) {
			//打印数据
			//使用索引从1开始
			//如果使用* 查询 索引是数据库表中的顺序;
			//如果不使用 * 直接查询 使用字段
			//那么索引顺序就是你sql 语句中的顺序
			/*int sid = executeQuery.getInt(2);
			String sname = executeQuery.getString(1);
			double sprice = executeQuery.getDouble(3);
			String sdesc = executeQuery.getString(4);
			System.out.println(sid);
			System.out.println(sname);
			System.out.println(sprice);
			System.out.println(sdesc);*/
			//获取数据方法二 直接使用字段名
			String string = executeQuery.getString("sname");
			System.out.println(string);
		}
		//关闭资源
		connection.close();
		statement.close();
		executeQuery.close();
		
	}

 键盘输入 账号 密码

 查询数据库 

 并且打印该账号和密码

 select * from users where usename = 'wanglong'

	public static void main(String[] args) throws ClassNotFoundException, SQLException {
		System.out.println("请输入账号");
		Scanner scanner = new Scanner(System.in);
		String usename = scanner.nextLine();
		System.out.println("请输入密码");
		String passwor = scanner.nextLine();
		
		Class.forName("com.mysql.jdbc.Driver");
		String url = "jdbc:mysql://localhost:3306/mysql01";
		String user = "root";
		String password = "123456";
		Connection connection = DriverManager.getConnection(url, user, password);
		Statement statement = connection.createStatement();
		String sql = "select * from users where username = '"+usename+"'and password ='"+passwor+"'";
		ResultSet resultSet = statement.executeQuery(sql);
		while (resultSet.next()) {
			String string = resultSet.getString("username");
			String string2 = resultSet.getString("password");
			System.out.println(string);
			System.out.println(string2);
		}
		connection.close();
		statement.close();
		resultSet.close();
	}

wang'or'1=1  

通过在sql 语句拼接时键入了一个恒等式 让这条语句一定成立

可以通过这个方式 来改变你SQL语句的原来含义

为了避免出现拼接时发生注入 于是在执行SQL语句时 我们先对SQL语句进行处理.

	public static void main(String[] args) throws ClassNotFoundException, SQLException {
		System.out.println("请输入账号");
		Scanner scanner = new Scanner(System.in);
		String usename = scanner.nextLine();
		System.out.println("请输入密码");
		String passwor = scanner.nextLine();
		
		Class.forName("com.mysql.jdbc.Driver");
		String url = "jdbc:mysql://localhost:3306/mysql01";
		String user = "root";
		String password = "123456";
		Connection connection = DriverManager.getConnection(url, user, password);
		//获取预编译SQL语句的对象
		//使用占位符 ?
		//注意 使用占位 时 不用加'' 单引号
		String sql = "select * from users where "
				+ "username = ?"
				+ "and password = ?";
		PreparedStatement statement = connection.prepareStatement(sql);
		//设置占位符的值
		//参数1 是? 的索引  从1开始
		//参数2 替换问号的值
		statement.setObject(1, usename);
		statement.setObject(2, passwor);
		
		//执行SQL语句
		ResultSet executeQuery = statement.executeQuery();
		//处理结果集
		while (executeQuery.next()) {
			System.out.println(executeQuery.getString("username")+"  "+executeQuery.getString("password"));
		}
		connection.close();
		statement.close();
		executeQuery.close();
		
	}

封装一个jdbc的工具类

package com.lanou3g;

import java.io.IOException;
import java.io.InputStream;
import java.sql.Connection;
import java.sql.DriverManager;
import java.sql.PreparedStatement;
import java.sql.ResultSet;
import java.sql.SQLException;
import java.util.Properties;

/*
 * 利用配置文件
 * 封装连接数据库工具类
 */

public class JDBCUtilX {
	public static String url;
	public static String user;
	public static String password;
	public static String driver;
	//静态注册
	static {
		try {
			Properties properties = new Properties();
			InputStream inputStream = JDBCUtilX.class.getClassLoader().getResourceAsStream("db.properties");
			properties.load(inputStream);
			
			driver = properties.getProperty("driverClass");
			url = properties.getProperty("url");
			user = properties.getProperty("user");
			password = properties.getProperty("password");
			
			Class.forName(driver);
			
		} catch (IOException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		} catch (ClassNotFoundException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
		}
	}
	//获取连接
	public static Connection getConnection() {
		 try {
			Connection connection = DriverManager.getConnection(url, user, password);
			return connection;
			
		} catch (SQLException e) {
			// TODO Auto-generated catch block
			e.printStackTrace();
			throw new RuntimeException("连接数据库失败");
		}
	}
	//关闭资源
		//把需要关闭的资源传进来
		  public static void close( Connection connection,PreparedStatement statement,ResultSet resultSet) {
			  //判断不为空再关
			  if (connection!=null) {
				try {
					connection.close();
				} catch (SQLException e) {
					// TODO Auto-generated catch block
					e.printStackTrace();
				}
			}
			  if (statement!=null) {
					try {
						statement.close();
					} catch (SQLException e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
					}
				} if (resultSet!=null) {
					try {
						resultSet.close();
					} catch (SQLException e) {
						// TODO Auto-generated catch block
						e.printStackTrace();
					}
				}
		  }
	
	

}

properties 文件

driverClass=com.mysql.jdbc.Driver
url=jdbc:mysql://localhost:3306/mysql01
user=root
password=123456

查询goods表

并且将查出来的数据保存到对象中 

并且放入集合中 遍历数据

	public static void main(String[] args) throws SQLException {
		ArrayList<Goods> list = new ArrayList<>();
		Connection connection = JDBCUtilX.getConnection();
		String sql = "select * from goods";
		PreparedStatement statement = connection.prepareStatement(sql);
		ResultSet resultSet = statement.executeQuery();
		while (resultSet.next()) {
			Goods g =  new Goods(resultSet.getInt("sid"), resultSet.getString("sname")
					, resultSet.getDouble("sprice"), resultSet.getString("sdesc"));
			list.add(g);
		}
		JDBCUtilX.close(connection, statement, resultSet);
		for (Goods goods : list) {
			System.out.println(goods);
		}
		
		
	
		
	}