【有道云笔记】十二 3.28 JDBC
https://note.youdao.com/s/HsgmqRMw
一、JDBC简介
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。
ConnectIon connection= 获得连接；
二、JDBC开发步骤
1、加载驱动Class.forName("");
2、获得连接对象Connection
3、写sql语句
4、创建Statement(一艘船)
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
6、关闭连接
//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/java230701?useSSL=false&useUnicode=true&characterEncoding=utf8&serverTimezone=GMT%2b8", "root", "1234");
@Test public void test1() { 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/java230701?useSSL=false&useUnicode=true&characterEncoding=utf8&serverTimezone=GMT%2b8", "root", "1234"); //3、写sql语句 String sql = "SELECT id,name,age,gender FROM student"; //4、创建Statement(一艘船) Statement 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ResultSet ResultSet resultSet = statement.executeQuery(sql); List<Student> list = new ArrayList<>(); while (resultSet.next()) {//判断下一个有没有，如果返回true而且指向下一个，没有返回false //每遍历一行，就封装一个学生对象 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); list.add(student); } for (Student student : list) { System.out.println(student); } } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (SQLException throwables) { throwables.printStackTrace(); } finally { //6、关闭连接 } } @Test public 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/java230701?useSSL=false&useUnicode=true&characterEncoding=utf8&serverTimezone=GMT%2b8", "root", "1234"); String sql = "SELECT id,name,age,gender FROM student"; statement = connection.createStatement(); resultSet = statement.executeQuery(sql); List<Student> list = new ArrayList<>(); while (resultSet.next()) {//判断下一个有没有，如果返回true而且指向下一个，没有返回false 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); list.add(student); } for (Student student : list) { System.out.println(student); } } catch (ClassNotFoundException e) { e.printStackTrace(); } catch (SQLException throwables) { throwables.printStackTrace(); } finally { if (resultSet != null) { try { resultSet.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } } if (statement != null) { try { statement.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } } if (connection != null) { try { connection.close(); } catch (SQLException throwables) { throwables.printStackTrace(); } } } } @Test public void testPreparedStatement() { Connection connection = null; PreparedStatement preparedStatement = null; ResultSet resultSet = null; try { connection = JDBCUtil.getConnection(); String sql = "SELECT id,name,age,gender FROM student"; //预编译 preparedStatement = connection.prepareStatement(sql); resultSet = preparedStatement.executeQuery(); List<Student> list = new ArrayList<>(); while (resultSet.next()) {//判断下一个有没有，如果返回true而且指向下一个，没有返回false 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); list.add(student); } for (Student student : list) { System.out.println(student); } } catch (SQLException throwables) { throwables.printStackTrace(); } finally { JDBCUtil.close(connection, preparedStatement, resultSet); } } @Test public void testInsert() { Connection connection = null; PreparedStatement preparedStatement = null; try { connection = JDBCUtil.getConnection(); //? 占位符 String sql = "insert into student(name,age,gender) values(?,?,?)"; preparedStatement = connection.prepareStatement(sql); preparedStatement.setString(1, "张三"); preparedStatement.setInt(2, 23); preparedStatement.setString(3, "女"); System.out.println(preparedStatement); int count = preparedStatement.executeUpdate(); System.out.println("count: " + count); } catch (SQLException throwables) { throwables.printStackTrace(); } finally { JDBCUtil.close(connection, preparedStatement, null); } } @Test public void testDelete() { Connection connection = null; PreparedStatement preparedStatement = null; try { connection = JDBCUtil.getConnection(); String sql = "delete from student where id=?"; preparedStatement = connection.prepareStatement(sql); preparedStatement.setInt(1, 10); System.out.println(preparedStatement); int count = preparedStatement.executeUpdate(); System.out.println("count: " + count); } catch (SQLException throwables) { throwables.printStackTrace(); } finally { JDBCUtil.close(connection, preparedStatement, null); } } @Test public void testUpdate() { Connection connection = null; PreparedStatement preparedStatement = null; try { connection = JDBCUtil.getConnection(); String sql = "update student set name=?,age=?,gender=? where id=?"; preparedStatement = connection.prepareStatement(sql); preparedStatement.setString(1, "小张"); preparedStatement.setInt(2, 23); preparedStatement.setString(3, "男"); preparedStatement.setInt(4, 9); System.out.println(preparedStatement); int count = preparedStatement.executeUpdate(); System.out.println("count: " + count); } catch (SQLException throwables) { throwables.printStackTrace(); } } @Test public void testLike() { Connection connection = null; PreparedStatement preparedStatement = null; ResultSet resultSet = null; try { connection = JDBCUtil.getConnection(); String sql = "select id,name,age,gender from student where name like ?"; preparedStatement = connection.prepareStatement(sql); preparedStatement.setString(1, "%张%"); System.out.println(preparedStatement); resultSet = preparedStatement.executeQuery(); List<Student> list = 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); list.add(student); } for (Student student : list) { System.out.println(student); } } catch (SQLException throwables) { throwables.printStackTrace(); } } @Test public void test122() { Connection connection = null; PreparedStatement preparedStatement = null; String sql1 = "UPDATE account SET money=money-1000 WHERE name='张三'"; String sql2 = "UPDATE account SET money=money+1000 WHERE name='李四'"; try { connection = JDBCUtil.getConnection(); // 为false，表示禁用自动提交（默认情况是true） connection.setAutoCommit(false); preparedStatement = connection.prepareStatement(sql1); System.out.println(preparedStatement); preparedStatement.executeUpdate(); // ArithmeticException: / by zero int i = 3 / 0; preparedStatement = connection.prepareStatement(sql2); System.out.println(preparedStatement); preparedStatement.executeUpdate(); // setAutoCommit(false)改成false之后，不会提交数据库，只有调用connection.commit()才提交 connection.commit(); } catch (Exception e) { e.printStackTrace(); try { connection.rollback(); } catch (SQLException throwables) { throwables.printStackTrace(); } } finally { JDBCUtil.close(connection, preparedStatement, null); } }
三、JDBC接口核心的API
|- DriverManager类： 驱动管理器类，用于管理所有注册的驱动程序
|-registerDriver(driver) : 注册驱动类对象
|-Connection getConnection(url,user,password); 获取连接对象
|- Connection接口： 表示java程序和数据库的连接对象。
|- Statement createStatement() ： 创建Statement对象
|- PreparedStatement prepareStatement(String sql) 创建PreparedStatement对象
|- CallableStatement prepareCall(String sql) 创建CallableStatement对象(调用写好的存储过程)
|- Statement接口： 用于执行静态的sql语句
|- int executeUpdate(String sql) ： 执行静态的更新sql语句
|- ResultSet executeQuery(String sql) ：执行的静态的查询sql语句
|-PreparedStatement接口：用于执行预编译sql语句
|- int executeUpdate() ： 执行预编译的更新sql语句
|-ResultSet executeQuery() ： 执行预编译的查询sql语句
|- ResultSet接口：用于封装查询出来的数据
|- boolean next() ： 将光标移动到下一行
|-getXX() : 获取列的值
四、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。
delete from student where id=1;
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。
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';