• 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。

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  • 原文地址:https://www.cnblogs.com/324fch/p/11806708.html
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