java-day24

JDBC控制事务：

　1.事务：一个包含多个步骤的业务操作，如果这个业务操作被事务管理，则这个步骤要么同时成功，要么同时失败。

2. 操作：
        1. 开启事务
        2. 提交事务
        3. 回滚事务
    3. 使用Connection对象来管理事务
        * 开启事务：setAutoCommit(boolean autoCommit) ：调用该方法设置参数为false，即开启事务
            * 在执行sql之前开启事务
        * 提交事务：commit() 
            * 当所有sql都执行完提交事务
        * 回滚事务：rollback() 
            * 在catch中回滚事务

4. 代码：
        public class JDBCDemo10 {

public static void main(String[] args) {
                Connection conn = null;
                PreparedStatement pstmt1 = null;
                PreparedStatement pstmt2 = null;
        
                try {
                    //1.获取连接
                    conn = JDBCUtils.getConnection();
                    //开启事务
                    conn.setAutoCommit(false);
        
                    //2.定义sql
                    //2.1 张三 - 500
                    String sql1 = "update account set balance = balance - ? where id = ?";
                    //2.2 李四 + 500
                    String sql2 = "update account set balance = balance + ? where id = ?";
                    //3.获取执行sql对象
                    pstmt1 = conn.prepareStatement(sql1);
                    pstmt2 = conn.prepareStatement(sql2);
                    //4. 设置参数
                    pstmt1.setDouble(1,500);
                    pstmt1.setInt(2,1);
        
                    pstmt2.setDouble(1,500);
                    pstmt2.setInt(2,2);
                    //5.执行sql
                    pstmt1.executeUpdate();
                    // 手动制造异常
                    int i = 3/0;
        
                    pstmt2.executeUpdate();
                    //提交事务
                    conn.commit();
                } catch (Exception e) {
                    //事务回滚
                    try {
                        if(conn != null) {
                            conn.rollback();
                        }
                    } catch (SQLException e1) {
                        e1.printStackTrace();
                    }
                    e.printStackTrace();
                }finally {
                    JDBCUtils.close(pstmt1,conn);
                    JDBCUtils.close(pstmt2,null);
                }
        
        
            }
        
        }

## 数据库连接池
    1. 概念：其实就是一个容器(集合)，存放数据库连接的容器。
            当系统初始化好后，容器被创建，容器中会申请一些连接对象，当用户来访问数据库时，从容器中获取连接对象，用户访问完之后，会将连接对象归还给容器。

2. 好处：
        1. 节约资源
        2. 用户访问高效

3. 实现：
        1. 标准接口：DataSource   javax.sql包下的
            1. 方法：
                * 获取连接：getConnection()
                * 归还连接：Connection.close()。如果连接对象Connection是从连接池中获取的，那么调用Connection.close()方法，则不会再关闭连接了。而是归还连接

2. 一般我们不去实现它，有数据库厂商来实现
            1. C3P0：数据库连接池技术
            2. Druid：数据库连接池实现技术，由阿里巴巴提供的

4. C3P0：数据库连接池技术
        * 步骤：
            1. 导入jar包 (两个) c3p0-0.9.5.2.jar mchange-commons-java-0.2.12.jar ，
                * 不要忘记导入数据库驱动jar包
            2. 定义配置文件：
                * 名称： c3p0.properties 或者 c3p0-config.xml
                * 路径：直接将文件放在src目录下即可。

3. 创建核心对象 数据库连接池对象 ComboPooledDataSource
            4. 获取连接： getConnection
        * 代码：
             //1.创建数据库连接池对象
            DataSource ds  = new ComboPooledDataSource();
            //2. 获取连接对象
            Connection conn = ds.getConnection();
    5. Druid：数据库连接池实现技术，由阿里巴巴提供的
        1. 步骤：
            1. 导入jar包 druid-1.0.9.jar
            2. 定义配置文件：
                * 是properties形式的
                * 可以叫任意名称，可以放在任意目录下
            3. 加载配置文件。Properties
            4. 获取数据库连接池对象：通过工厂来来获取  DruidDataSourceFactory
            5. 获取连接：getConnection
        * 代码：
             //3.加载配置文件
            Properties pro = new Properties();
            InputStream is = DruidDemo.class.getClassLoader().getResourceAsStream("druid.properties");
            pro.load(is);
            //4.获取连接池对象
            DataSource ds = DruidDataSourceFactory.createDataSource(pro);
            //5.获取连接
            Connection conn = ds.getConnection();
        2. 定义工具类
            1. 定义一个类 JDBCUtils
            2. 提供静态代码块加载配置文件，初始化连接池对象
            3. 提供方法
                1. 获取连接方法：通过数据库连接池获取连接
                2. 释放资源
                3. 获取连接池的方法

* 代码：
            public class JDBCUtils {

//1.定义成员变量 DataSource
                private static DataSource ds ;
            
                static{
                    try {
                        //1.加载配置文件
                        Properties pro = new Properties();
                        pro.load(JDBCUtils.class.getClassLoader().getResourceAsStream("druid.properties"));
                        //2.获取DataSource
                        ds = DruidDataSourceFactory.createDataSource(pro);
                    } catch (IOException e) {
                        e.printStackTrace();
                    } catch (Exception e) {
                        e.printStackTrace();
                    }
                }
            
                /**
                 * 获取连接
                 */
                public static Connection getConnection() throws SQLException {
                    return ds.getConnection();
                }
            
                /**
                 * 释放资源
                 */
                public static void close(Statement stmt,Connection conn){
                   /* if(stmt != null){
                        try {
                            stmt.close();
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }
                    }
            
                    if(conn != null){
                        try {
                            conn.close();//归还连接
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }
                    }*/
            
                   close(null,stmt,conn);
                }
            
            
                public static void close(ResultSet rs , Statement stmt, Connection conn){
            
            
                    if(rs != null){
                        try {
                            rs.close();
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }
                    }
            
            
                    if(stmt != null){
                        try {
                            stmt.close();
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }
                    }
            
                    if(conn != null){
                        try {
                            conn.close();//归还连接
                        } catch (SQLException e) {
                            e.printStackTrace();
                        }
                    }
                }
            
                /**
                 * 获取连接池方法
                 */
            
                public static DataSource getDataSource(){
                    return  ds;
                }
            
            }

## Spring JDBC
    * Spring框架对JDBC的简单封装。提供了一个JDBCTemplate对象简化JDBC的开发
    * 步骤：
        1. 导入jar包
        2. 创建JdbcTemplate对象。依赖于数据源DataSource
            * JdbcTemplate template = new JdbcTemplate(ds);

3. 调用JdbcTemplate的方法来完成CRUD的操作
            * update():执行DML语句。增、删、改语句
            * queryForMap():查询结果将结果集封装为map集合，将列名作为key，将值作为value 将这条记录封装为一个map集合
                * 注意：这个方法查询的结果集长度只能是1
            * queryForList():查询结果将结果集封装为list集合
                * 注意：将每一条记录封装为一个Map集合，再将Map集合装载到List集合中
            * query():查询结果，将结果封装为JavaBean对象
                * query的参数：RowMapper
                    * 一般我们使用BeanPropertyRowMapper实现类。可以完成数据到JavaBean的自动封装
                    * new BeanPropertyRowMapper<类型>(类型.class)
            * queryForObject：查询结果，将结果封装为对象
                * 一般用于聚合函数的查询

4. 练习：
            * 需求：
                1. 修改1号数据的 salary 为 10000
                2. 添加一条记录
                3. 删除刚才添加的记录
                4. 查询id为1的记录，将其封装为Map集合
                5. 查询所有记录，将其封装为List
                6. 查询所有记录，将其封装为Emp对象的List集合
                7. 查询总记录数

* 代码：
                
                import cn.itcast.domain.Emp;
                import cn.itcast.utils.JDBCUtils;
                import org.junit.Test;
                import org.springframework.jdbc.core.BeanPropertyRowMapper;
                import org.springframework.jdbc.core.JdbcTemplate;
                import org.springframework.jdbc.core.RowMapper;
                
                import java.sql.Date;
                import java.sql.ResultSet;
                import java.sql.SQLException;
                import java.util.List;
                import java.util.Map;
                
                public class JdbcTemplateDemo2 {
                
                    //Junit单元测试，可以让方法独立执行
                
                
                    //1. 获取JDBCTemplate对象
                    private JdbcTemplate template = new JdbcTemplate(JDBCUtils.getDataSource());
                    /**
                     * 1. 修改1号数据的 salary 为 10000
                     */
                    @Test
                    public void test1(){
                
                        //2. 定义sql
                        String sql = "update emp set salary = 10000 where id = 1001";
                        //3. 执行sql
                        int count = template.update(sql);
                        System.out.println(count);
                    }
                
                    /**
                     * 2. 添加一条记录
                     */
                    @Test
                    public void test2(){
                        String sql = "insert into emp(id,ename,dept_id) values(?,?,?)";
                        int count = template.update(sql, 1015, "郭靖", 10);
                        System.out.println(count);
                
                    }
                
                    /**
                     * 3.删除刚才添加的记录
                     */
                    @Test
                    public void test3(){
                        String sql = "delete from emp where id = ?";
                        int count = template.update(sql, 1015);
                        System.out.println(count);
                    }
                
                    /**
                     * 4.查询id为1001的记录，将其封装为Map集合
                     * 注意：这个方法查询的结果集长度只能是1
                     */
                    @Test
                    public void test4(){
                        String sql = "select * from emp where id = ? or id = ?";
                        Map<String, Object> map = template.queryForMap(sql, 1001,1002);
                        System.out.println(map);
                        //{id=1001, ename=孙悟空, job_id=4, mgr=1004, joindate=2000-12-17, salary=10000.00, bonus=null, dept_id=20}
                
                    }
                
                    /**
                     * 5. 查询所有记录，将其封装为List
                     */
                    @Test
                    public void test5(){
                        String sql = "select * from emp";
                        List<Map<String, Object>> list = template.queryForList(sql);
                
                        for (Map<String, Object> stringObjectMap : list) {
                            System.out.println(stringObjectMap);
                        }
                    }
                
                    /**
                     * 6. 查询所有记录，将其封装为Emp对象的List集合
                     */
                
                    @Test
                    public void test6(){
                        String sql = "select * from emp";
                        List<Emp> list = template.query(sql, new RowMapper<Emp>() {
                
                            @Override
                            public Emp mapRow(ResultSet rs, int i) throws SQLException {
                                Emp emp = new Emp();
                                int id = rs.getInt("id");
                                String ename = rs.getString("ename");
                                int job_id = rs.getInt("job_id");
                                int mgr = rs.getInt("mgr");
                                Date joindate = rs.getDate("joindate");
                                double salary = rs.getDouble("salary");
                                double bonus = rs.getDouble("bonus");
                                int dept_id = rs.getInt("dept_id");
                
                                emp.setId(id);
                                emp.setEname(ename);
                                emp.setJob_id(job_id);
                                emp.setMgr(mgr);
                                emp.setJoindate(joindate);
                                emp.setSalary(salary);
                                emp.setBonus(bonus);
                                emp.setDept_id(dept_id);
                
                                return emp;
                            }
                        });
                
                
                        for (Emp emp : list) {
                            System.out.println(emp);
                        }
                    }
                
                    /**
                     * 6. 查询所有记录，将其封装为Emp对象的List集合
                     */
                
                    @Test
                    public void test6_2(){
                        String sql = "select * from emp";
                        List<Emp> list = template.query(sql, new BeanPropertyRowMapper<Emp>(Emp.class));
                        for (Emp emp : list) {
                            System.out.println(emp);
                        }
                    }
                
                    /**
                     * 7. 查询总记录数
                     */
                
                    @Test
                    public void test7(){
                        String sql = "select count(id) from emp";
                        Long total = template.queryForObject(sql, Long.class);
                        System.out.println(total);
                    }
                
                }

## web概念概述
    * JavaWeb：
        * 使用Java语言开发基于互联网的项目

* 软件架构：
        1. C/S: Client/Server 客户端/服务器端
            * 在用户本地有一个客户端程序，在远程有一个服务器端程序
            * 如：QQ，迅雷...
            * 优点：
                1. 用户体验好
            * 缺点：
                1. 开发、安装，部署，维护 麻烦
        2. B/S: Browser/Server 浏览器/服务器端
            * 只需要一个浏览器，用户通过不同的网址(URL)，客户访问不同的服务器端程序
            * 优点：
                1. 开发、安装，部署，维护 简单
            * 缺点：
                1. 如果应用过大，用户的体验可能会受到影响
                2. 对硬件要求过高

* B/S架构详解
        * 资源分类：
            1. 静态资源：
                * 使用静态网页开发技术发布的资源。
                * 特点：
                    * 所有用户访问，得到的结果是一样的。
                    * 如：文本，图片，音频、视频, HTML,CSS,JavaScript
                    * 如果用户请求的是静态资源，那么服务器会直接将静态资源发送给浏览器。浏览器中内置了静态资源的解析引擎，可以展示静态资源
            2. 动态资源：
                * 使用动态网页及时发布的资源。
                * 特点：
                    * 所有用户访问，得到的结果可能不一样。
                    * 如：jsp/servlet,php,asp...
                    * 如果用户请求的是动态资源，那么服务器会执行动态资源，转换为静态资源，再发送给浏览器

* 我们要学习动态资源，必须先学习静态资源！

* 静态资源：
            * HTML：用于搭建基础网页，展示页面的内容
            * CSS：用于美化页面，布局页面
            * JavaScript：控制页面的元素，让页面有一些动态的效果

## HTML
    1. 概念：是最基础的网页开发语言
        * Hyper Text Markup Language 超文本标记语言
            * 超文本:
                * 超文本是用超链接的方法，将各种不同空间的文字信息组织在一起的网状文本.
            * 标记语言:
                * 由标签构成的语言。<标签名称> 如 html，xml
                * 标记语言不是编程语言

2. 快速入门：
        * 语法：
            1. html文档后缀名 .html 或者 .htm
            2. 标签分为
                1. 围堵标签：有开始标签和结束标签。如 <html> </html>
                2. 自闭和标签：开始标签和结束标签在一起。如 <br/>

3. 标签可以嵌套：
                需要正确嵌套，不能你中有我，我中有你
                错误：<a><b></a></b>
                正确：<a><b></b></a>

4. 在开始标签中可以定义属性。属性是由键值对构成，值需要用引号(单双都可)引起来
            5. html的标签不区分大小写，但是建议使用小写。