学点Java_Day12

学点Java_Day12_JDBC

1 JDBC

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面向接口编程
在JDBC里面Java这个公司只是提供了一套接口Connection、Statement、ResultSet，每个数据库厂商实现了这套接口，例如MySql公司实现了：MySql驱动程序里面实现了这套接口，Java程序员只要调用实现了这些方法就可以实现对 MySql数据库的增删改查。
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2 JDBC开发步骤

2.1 加载驱动Class.forName(“”)

2.2 获得连接对象Connection

2.3 写sql语句

2.4 创建Statement(一艘船)

2.5 执行sql语句

 (1) 更新类（更改了表里面数据）：delete/update/insert      executeUpdate()返回值：int，表示你影响的行数(2)查询（没有改变表里面数据）:  select                              executeQuery()返回值：结果集ResultSet

2.6 关闭连接

    @Testpublic void test1() {Connection connection = null;Statement statement = null;ResultSet resultSet = null;try {//1、加载驱动Class.forName("");Class.forName("com.mysql.cj.jdbc.Driver");//2、获得连接对象Connection//Connection connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/study", "root", "xiangjie");//jdbc:mysql:协议 localhost 127.0.0.1connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/study?useSSL=false&useUnicode=true&characterEncoding=utf8&serverTimezone=GMT%2b8", "root", "xiangjie");//3、写sql语句String sql = "select id,name,age,gender from student";//4、创建Statement(一艘船)statement = connection.createStatement();//5、执行sql语句//  (1) 更新类（更改了表里面数据）：delete/update/insert     executeUpdate()//    返回值：int，表示你影响的行数//  (2)查询（没有改变表里面数据）:  select                  executeQuery()//    返回值：结果集ResultSetresultSet = statement.executeQuery(sql);List<Student> studentList = new ArrayList<>();while (resultSet.next()) {//判断下一行有没有，如果没有返回FALSE，如果有返回true并且指向这一行。既判断也指向，没有指向自己//当前resultSet指向第一行//while循环每遍历一次，把这一行每个字段的值拿出来，就可以封装一个Student对象int id = resultSet.getInt("id");String name = resultSet.getString("name");int age = resultSet.getInt("age");String gender = resultSet.getString("gender");//以后有框架给干  但是自己也要过一遍流程Student student = new Student(id, name, age, gender);System.out.println(student);studentList.add(student);}//6、关闭连接  见finally} catch (ClassNotFoundException e) {throw new RuntimeException(e);} catch (SQLException e) {throw new RuntimeException(e);} finally {//6、关闭连接if (resultSet != null) {try {resultSet.close();} catch (SQLException e) {throw new RuntimeException(e);}}if (statement != null) {try {statement.close();} catch (SQLException e) {throw new RuntimeException(e);}}if (connection != null) {try {connection.close();} catch (SQLException e) {throw new RuntimeException(e);}}}}

3 JDBC接口核心的API

    @Testpublic void test2() {Connection connection = null;Statement statement = null;ResultSet resultSet = null;try {Class.forName("com.mysql.cj.jdbc.Driver");connection = DriverManager.getConnection("jdbc:mysql://localhost:3306/study?useSSL=false&useUnicode=true&characterEncoding=utf8&serverTimezone=GMT%2b8", "root", "xiangjie");String sql = "select id,name,age,gender from student";statement = connection.createStatement();resultSet = statement.executeQuery(sql);List<Student> studentList = new ArrayList<>();while (resultSet.next()) {int id = resultSet.getInt("id");String name = resultSet.getString("name");int age = resultSet.getInt("age");String gender = resultSet.getString("gender");Student student = new Student(id, name, age, gender);System.out.println(student);studentList.add(student);}} catch (ClassNotFoundException e) {throw new RuntimeException(e);} catch (SQLException e) {throw new RuntimeException(e);} finally {JDBCUtil.close(connection, statement, resultSet);}}

4 PreparedStatement（预编译)和Statement区别

1、语法不同：
PreparedStatement可以使用预编译的sql，只需要发送一次sql语句，后面只要发送参数即可，公用一个sql语句。
Statement只能使用静态的sql。
2、效率不同：PreparedStatement使用了sql缓冲区，效率要比Statement高。
3、安全性不同：PreparedStatement可以有效的防止sql注入，而Statement不能防止sql注入。

    @Testpublic void test3() {//预编译的statementConnection connection = null;//Statement statement = null;PreparedStatement statement = null;ResultSet resultSet = null;try {connection = JDBCUtil.getConnection();String sql = "select id,name,age,gender from student";//预编译的statementstatement = connection.prepareStatement(sql);resultSet = statement.executeQuery();List<Student> studentList = new ArrayList<>();while (resultSet.next()) {int id = resultSet.getInt("id");String name = resultSet.getString("name");int age = resultSet.getInt("age");String gender = resultSet.getString("gender");Student student = new Student(id, name, age, gender);System.out.println(student);studentList.add(student);}} catch (SQLException e) {throw new RuntimeException(e);} finally {JDBCUtil.close(connection, statement, resultSet);}}

5 SQL注入

-- 演示Sql注入问题
CREATE TABLE users(id INT PRIMARY KEY AUTO_INCREMENT,`name` VARCHAR(10),`password` VARCHAR(10)
);
INSERT INTO users(`name`, `password`) VALUES('lisi',123);
SELECT * FROM users WHERE 1=1;  -- 1=1   true
SELECT * FROM users WHERE `name`='lisi' AND `password`='123';
--  zhangsan' OR 1=1 -- y 
SELECT * FROM users WHERE `name`='zhangsan' OR 1=1 -- y' AND `password`='343';