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2. Spring JDBC : JDBC Template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 ...</div></div></div><div class="recent-post-item"><div class="post_cover right_radius"><a href="/2020/07/25/ckd1l6zch0000y4ndh8csb75o/" title="Java-JDBC">     <img class="post_bg" data-src="https://i.loli.net/2020/05/01/gkihqEjXxJ5UZ1C.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="Java-JDBC"></a></div><div class="recent-post-info"><a class="article-title" href="/2020/07/25/ckd1l6zch0000y4ndh8csb75o/" title="Java-JDBC">Java-JDBC</a><div class="article-meta-wrap"><time class="post-meta__date" title="发表于 2020-07-25 19:40:18"><i class="far fa-calendar-alt"></i>2020-07-25</time></div><div class="content">
title: Java-JDBCdata: 2020-07-25 11:30:00tags: [Java,JDBC]id: 1category: Java

2. 1. JDBC基本概念
2. 快速入门
3. 对JDBC中各个接口和类详解JDBC：1. 概念：Java DataBase Connectivity  Java 数据库连接， Java语言操作数据库
    * JDBC本质：其实是官方（sun公司）定义的一套操作所有关系型数据库的规则，即接口。各个数据库厂商去实现这套接口，提供数据库驱动jar包。我们可以使用这套接口（JDBC）编程，真正执行的代码是驱动jar包中的实现类。

2. 快速入门：
    * 步骤：
        1. 导入驱动jar包 mysql-connector-java-5.1.37-bin.jar
            1.复制mysql-connector-java-5.1.37-bin.jar到项目的libs目录下
            2.右键--&gt;Add As Library
        2. 注册驱动
        3. ...</div></div></div><div class="recent-post-item"><div class="post_cover left_radius"><a href="/2020/07/23/2/" title="MySQL-约束">     <img class="post_bg" data-src="https://i.loli.net/2020/05/01/gkihqEjXxJ5UZ1C.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="MySQL-约束"></a></div><div class="recent-post-info"><a class="article-title" href="/2020/07/23/2/" title="MySQL-约束">MySQL-约束</a><div class="article-meta-wrap"><time class="post-meta__date" title="发表于 2020-07-23 16:54:40"><i class="far fa-calendar-alt"></i>2020-07-23</time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/MySQL/">MySQL</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/MySQL/">MySQL</a></span></div><div class="content">1. DQL:查询语句
    1. 排序查询
    2. 聚合函数
    3. 分组查询
    4. 分页查询

2. 约束
3. 多表之间的关系
4. 范式
5. 数据库的备份和还原DQL:查询语句1. 排序查询
    * 语法：order by 子句
        * order by 排序字段1 排序方式1 ，  排序字段2 排序方式2...

    * 排序方式：
        * ASC：升序，默认的。
        * DESC：降序。

    * 注意：
        * 如果有多个排序条件，则当前边的条件值一样时，才会判断第二条件。


2. 聚合函数：将一列数据作为一个整体，进行纵向的计算。
    1. count：计算个数
        1. 一般选择非空的列：主键
        2. count(*)
    2. max：计算最大值
    3. min：计算最小值
    4. sum：计算和
    5. avg：计算平均值


    * 注意：聚合函数的计算，排除null值。
        解决方案：
            ...</div></div></div><div class="recent-post-item"><div class="post_cover right_radius"><a href="/2020/07/23/1/" title="MySQL-基础">     <img class="post_bg" data-src="https://i.loli.net/2020/05/01/gkihqEjXxJ5UZ1C.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="MySQL-基础"></a></div><div class="recent-post-info"><a class="article-title" href="/2020/07/23/1/" title="MySQL-基础">MySQL-基础</a><div class="article-meta-wrap"><time class="post-meta__date" title="发表于 2020-07-23 11:22:21"><i class="far fa-calendar-alt"></i>2020-07-23</time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/MySQL/">MySQL</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/MySQL/">MySQL</a></span></div><div class="content">数据库
数据库的基本概念


MySQL数据库软件

安装
卸载
配置


SQL


数据库的基本概念1. 数据库的英文单词： DataBase 简称 ： DB
2. 什么数据库？
    * 用于存储和管理数据的仓库。

3. 数据库的特点：
    1. 持久化存储数据的。其实数据库就是一个文件系统
    2. 方便存储和管理数据
    3. 使用了统一的方式操作数据库 -- SQL    4. 常见的数据库软件        * 参见《MySQL基础.pdf》
MySQL数据库软件1. 安装
    * 参见《MySQL基础.pdf》
2. 卸载
    1. 去mysql的安装目录找到my.ini文件
        * 复制 datadir=&quot;C:/ProgramData/MySQL/MySQL Server 5.5/Data/&quot;
    2. 卸载MySQL
    3. 删除C:/ProgramData目录下的MySQL文件夹。

3. 配置
    * MySQL服务启动
        1. 手动。
        2. cmd--&g ...</div></div></div><div class="recent-post-item"><div class="post_cover left_radius"><a href="/2020/07/22/1/" title="Java-反射、注解">     <img class="post_bg" data-src="https://i.loli.net/2020/05/01/gkihqEjXxJ5UZ1C.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="Java-反射、注解"></a></div><div class="recent-post-info"><a class="article-title" href="/2020/07/22/1/" title="Java-反射、注解">Java-反射、注解</a><div class="article-meta-wrap"><time class="post-meta__date" title="发表于 2020-07-22 20:08:41"><i class="far fa-calendar-alt"></i>2020-07-22</time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/Java/">Java</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/Java/">Java</a><span class="article-meta__link">•</span><a class="article-meta__tags" href="/tags/%E6%B3%A8%E8%A7%A3/">注解</a><span class="article-meta__link">•</span><a class="article-meta__tags" href="/tags/%E5%8F%8D%E5%B0%84/">反射</a></span></div><div class="content">Junit测试:

测试分类
黑盒测试:不需要写代码,给输入值,看程序是否能够输出期望的值
白盒测试:需要写代码.关注程序具体的执行流程


Junit使用: 白盒测试
步骤
定义一个测试类(测试用例)
建议:
测试类名使用被测试类+Test
包名:xxx.xxx.xxx.test


定义测试方法: 可以独立运行
建议:
方法名: test+测试方法名
返回值: void
参数列表: 空参


给方法加注解@Test
点击小灯泡导入Jnuit环境依赖


判定结果
红色: 失败
绿色: 成功
一般使用断言操作处理结果,Assert类中的assertXXX方法  assertEquals(期望的结果,程序运算的结果),若两个数不同显示红色


注解@Before 被修饰的方法会在测试方法之前被自动执行,常用于初始化资源
注解@After  被修饰的方法会在测试方法之后被自动执行,常用于释放资源


反射框架设计的灵魂
反射:将类的各个部分封装成其他对象,这就是反射机制

好处:

可以在程序的运行过程中,操作这些对象
可以解耦,提高程序的可扩展性


获取class类对象的三种方式
 ...</div></div></div><div class="recent-post-item"><div class="post_cover right_radius"><a href="/2020/07/20/2/" title="Java-Stream流">     <img class="post_bg" data-src="https://i.loli.net/2020/05/01/gkihqEjXxJ5UZ1C.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="Java-Stream流"></a></div><div class="recent-post-info"><a class="article-title" href="/2020/07/20/2/" title="Java-Stream流">Java-Stream流</a><div class="article-meta-wrap"><time class="post-meta__date" title="发表于 2020-07-20 15:50:13"><i class="far fa-calendar-alt"></i>2020-07-20</time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/Java/">Java</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/Java/">Java</a><span class="article-meta__link">•</span><a class="article-meta__tags" href="/tags/Stream/">Stream</a></span></div><div class="content">Stream流用于解决已有集合类库既有的弊端,用来对集合和数组进行简化操作
当使用一个流的时候,通常包含三个基本步骤:获取一个数据源(source)-&gt;数据转换-&gt;执行操作获取想要的结果-&gt;每次转换原有Stream对象不改变,返回一个新的Stream对象(可以有多次转换),这就允许对其操作可以像链条一样排列,变成一个管道
12345678910111213141516171819202122/* * Stream是1.8之后出现的,关注的是做什么,而不是怎么做 * 过滤集合,只要张开头,长度为3的 * */public class TestStream &#123;    public static void main(String[] args) &#123;        ArrayList&lt;String&gt; list = new ArrayList&lt;&gt;();        list.add("张无忌");        list.add("周芷若");        list.add("赵敏");        list.add("张强") ...</div></div></div><div class="recent-post-item"><div class="post_cover left_radius"><a href="/2020/07/19/2/" title="Java-函数式接口">     <img class="post_bg" data-src="https://i.loli.net/2020/05/01/gkihqEjXxJ5UZ1C.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="Java-函数式接口"></a></div><div class="recent-post-info"><a class="article-title" href="/2020/07/19/2/" title="Java-函数式接口">Java-函数式接口</a><div class="article-meta-wrap"><time class="post-meta__date" title="发表于 2020-07-19 21:30:17"><i class="far fa-calendar-alt"></i>2020-07-19</time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/Java/">Java</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/Java/">Java</a><span class="article-meta__link">•</span><a class="article-meta__tags" href="/tags/Lambda/">Lambda</a><span class="article-meta__link">•</span><a class="article-meta__tags" href="/tags/%E5%87%BD%E6%95%B0%E5%BC%8F%E6%8E%A5%E5%8F%A3/">函数式接口</a></span></div><div class="content">函数式接口有且仅有一个抽象方法的接口,叫做函数式接口即适用于函数式编程场景的接口,也就是使用Lambda编程
12345格式:	修饰符 interface 接口名称&#123;        public abstract 返回值类型 方法名称(可选参数信息);        //其他非抽象方法内容,默认方法,静态方法,私有方法    &#125;


语法糖:指使用更加方便,但是原理不变的代码语法,例如使用for-each语法,其实底层实现的原理仍然使迭代器,这便是”语法糖”,从应用层面来讲,Java的Lambda可以被当作使匿名内部类的”语法糖”,但使二者在原理上是不同的,匿名内部类会创建一个.class文件,而使用Lambda表达式就不会
12345678910/** 注解:检测所写代码是否符合要求,若不符合,则编译报错* @FunctionalInterface:检测接口是否为一个函数式接口*   是:编译成功*   否:编译失败(抽象方法的个数不为一个)* */@FunctionalInterfacepublic interface Function &#123;    pu ...</div></div></div><div class="recent-post-item"><div class="post_cover right_radius"><a href="/2020/07/19/1/" title="Java-网络编程">     <img class="post_bg" data-src="https://i.loli.net/2020/05/01/gkihqEjXxJ5UZ1C.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="Java-网络编程"></a></div><div class="recent-post-info"><a class="article-title" href="/2020/07/19/1/" title="Java-网络编程">Java-网络编程</a><div class="article-meta-wrap"><time class="post-meta__date" title="发表于 2020-07-19 12:30:17"><i class="far fa-calendar-alt"></i>2020-07-19</time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/Java/">Java</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/Java/">Java</a><span class="article-meta__link">•</span><a class="article-meta__tags" href="/tags/Socket/">Socket</a></span></div><div class="content">网络编程UDP

用户数据报协议(User Datagram Protocol),UDP是无连接协议,即在数据传输时,数据的发送端和接收端不建立逻辑连接
耗资小,通信效率高,通常用于音频,视频,和普通数据的传输,因为这种情况偶尔丢失一两个数据包,也不会对接收结果产生太大的影响,但是使用UDP不保证数据的完整性.
特点:数据被限制在64KB以内,超出这个范围就不能发送了

TCP

传输控制协议(Transmission Control Protocol) TCP是面向连接的通信协议,传输数据之前.在发送端和接收端会建立逻辑连接,可靠无差错的数据传输

三次握手

第一次握手 客户端向服务器端发出连接请求,等待服务器确认
第二次握手 服务器端向客户端回送一个响应,通知客户端接收到了连接请求
第三次握手 客户端再次向服务器端发送确认信息,确认连接


服务器端
12345678910111213141516171819202122232425262728293031323334/**TCP通信的服务器端:接收客户端的请求,读取客户端发送的数据,给客户端回写数据* 表示服务器的类:*   j ...</div></div></div><div class="recent-post-item"><div class="post_cover left_radius"><a href="/2020/07/18/1/" title="Java-File、IO流">     <img class="post_bg" data-src="https://i.loli.net/2020/05/01/gkihqEjXxJ5UZ1C.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="Java-File、IO流"></a></div><div class="recent-post-info"><a class="article-title" href="/2020/07/18/1/" title="Java-File、IO流">Java-File、IO流</a><div class="article-meta-wrap"><time class="post-meta__date" title="发表于 2020-07-18 10:30:50"><i class="far fa-calendar-alt"></i>2020-07-18</time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/Java/">Java</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/Java/">Java</a><span class="article-meta__link">•</span><a class="article-meta__tags" href="/tags/FIle/">FIle</a><span class="article-meta__link">•</span><a class="article-meta__tags" href="/tags/IO/">IO</a></span></div><div class="content">File类java.io.File类是文件和目录路径名的抽象表示,主要用于文件和目录的创建、查找和删除等操作,File是一个与系统无关的类,任何的操作系统都可以使用类中的方法,

记住三个词:  file:文件  directory :文件夹/目录   path :路径

静态变量

static String pathSeparator  与系统有关的路径分隔符，为了方便，它被表示为一个字符串。
windows  为”;”
Linux   为”:”


static String separator    与系统有关的默认名称分隔符，为了方便，它被表示为一个字符串。 文件名称分隔符
windows  为”\“
Linux  为”/“


构造方法

File(File parent, String child)    根据 parent 抽象路径名和 child 路径名字符串创建一个新 File 实例。
File(String pathname)      通过将给定路径名字符串转换为抽象路径名来创建一个新 File 实例。
File(String parent, Str ...</div></div></div><div class="recent-post-item"><div class="post_cover right_radius"><a href="/2020/07/15/3/" title="Java-Lambda表达式">     <img class="post_bg" data-src="https://i.loli.net/2020/05/01/gkihqEjXxJ5UZ1C.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" alt="Java-Lambda表达式"></a></div><div class="recent-post-info"><a class="article-title" href="/2020/07/15/3/" title="Java-Lambda表达式">Java-Lambda表达式</a><div class="article-meta-wrap"><time class="post-meta__date" title="发表于 2020-07-15 19:53:08"><i class="far fa-calendar-alt"></i>2020-07-15</time><span class="article-meta"><span class="article-meta__separator">|</span><i class="fas fa-inbox article-meta__icon"></i><a class="article-meta__categories" href="/categories/Java/">Java</a></span><span class="article-meta tags"><span class="article-meta__separator">|</span><i class="fas fa-tag article-meta__icon"></i><a class="article-meta__tags" href="/tags/Java/">Java</a><span class="article-meta__link">•</span><a class="article-meta__tags" href="/tags/Lambda/">Lambda</a></span></div><div class="content">lambda表达式
jdk8发布
12345678910111213141516171819202122232425262728293031/*lambda的标准格式    由三部分组成    	一些参数    	一个箭头    	一段代码    (参数列表) -&gt; &#123;一些重写方法的代码&#125;;*/public static void main(String[] args) &#123;    //普通多线程方式    new Thread(new Runnable() &#123;        @Override        public void run() &#123;            System.out.println("线程创建");        &#125;    &#125;).start();    //使用Lambda表达式实现多线程    //大括号就是重写run方法的大括号    new Thread(() -&gt; &#123;        System.out.println("lambda实现多线程");        ...</div></div></div><nav id="pagination"><div class="pagination"><span class="page-number current">1</span><a class="page-number" href="/page/2/">2</a><a class="extend next" rel="next" href="/page/2/"><i class="fas fa-chevron-right fa-fw"></i></a></div></nav></div><div class="aside_content" id="aside_content"><div class="card-widget card-info"><div class="card-content"><div class="card-info-avatar is-center"><img class="avatar-img" src="https://gitee.com/lqhao/img-bed/raw/master/img-page/04232036663275.jpg" onerror="this.onerror=null;this.src='/img/friend_404.gif'" alt="avatar"/><div class="author-info__name">laden</div><div class="author-info__description">万丈高楼平地起,一切承担靠地基</div></div><div class="card-info-data"><div class="card-info-data-item is-center"><a href="/archives"><div class="headline">文章</div><div class="length_num">16</div></a></div><div class="card-info-data-item is-center">      <a href="/tags"><div class="headline">标签</div><div class="length_num">20</div></a></div><div class="card-info-data-item is-center">     <a href="/categories"><div class="headline">分类</div><div class="length_num">4</div></a></div></div><div class="card-info-bookmark is-center"><button class="button--animated" id="bookmark-it" title="加入书签"><i class="fas fa-bookmark"></i><span>加入书签</span></button></div><div class="card-info-social-icons is-center"><a class="social-icon" href="https://mail.qq.com/cgi-bin/qm_share?t=qm_mailme&amp;email=949132421@qq.com" target="_blank" title="Email"><i class="fas fa-envelope"></i></a></div></div></div><div class="card-widget card-recent-post"><div class="card-content"><div class="item-headline"><i class="fas fa-history"></i><span>最新文章</span></div><div class="aside-recent-item"><div class="aside-recent-post"><a href="/2020/07/25/2/"><div class="aside-post-cover"><img class="aside-post-bg" data-src="https://i.loli.net/2020/05/01/gkihqEjXxJ5UZ1C.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" title="Java-JDBC连接池、JDBCTemplate" alt="Java-JDBC连接池、JDBCTemplate"/></div><div class="aside-post-title"><div class="aside-post_title" href="/2020/07/25/2/" title="Java-JDBC连接池、JDBCTemplate">Java-JDBC连接池、JDBCTemplate</div><time class="aside-post_meta post-meta__date" title="发表于 2020-07-25 19:41:52">2020-07-25</time></div></a></div><div class="aside-recent-post"><a href="/2020/07/25/ckd1l6zch0000y4ndh8csb75o/"><div class="aside-post-cover"><img class="aside-post-bg" data-src="https://i.loli.net/2020/05/01/gkihqEjXxJ5UZ1C.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" title="Java-JDBC" alt="Java-JDBC"/></div><div class="aside-post-title"><div class="aside-post_title" href="/2020/07/25/ckd1l6zch0000y4ndh8csb75o/" title="Java-JDBC">Java-JDBC</div><time class="aside-post_meta post-meta__date" title="发表于 2020-07-25 19:40:18">2020-07-25</time></div></a></div><div class="aside-recent-post"><a href="/2020/07/23/2/"><div class="aside-post-cover"><img class="aside-post-bg" data-src="https://i.loli.net/2020/05/01/gkihqEjXxJ5UZ1C.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" title="MySQL-约束" alt="MySQL-约束"/></div><div class="aside-post-title"><div class="aside-post_title" href="/2020/07/23/2/" title="MySQL-约束">MySQL-约束</div><time class="aside-post_meta post-meta__date" title="发表于 2020-07-23 16:54:40">2020-07-23</time></div></a></div><div class="aside-recent-post"><a href="/2020/07/23/1/"><div class="aside-post-cover"><img class="aside-post-bg" data-src="https://i.loli.net/2020/05/01/gkihqEjXxJ5UZ1C.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" title="MySQL-基础" alt="MySQL-基础"/></div><div class="aside-post-title"><div class="aside-post_title" href="/2020/07/23/1/" title="MySQL-基础">MySQL-基础</div><time class="aside-post_meta post-meta__date" title="发表于 2020-07-23 11:22:21">2020-07-23</time></div></a></div><div class="aside-recent-post"><a href="/2020/07/22/1/"><div class="aside-post-cover"><img class="aside-post-bg" data-src="https://i.loli.net/2020/05/01/gkihqEjXxJ5UZ1C.jpg" onerror="this.onerror=null;this.src='/img/404.jpg'" title="Java-反射、注解" alt="Java-反射、注解"/></div><div class="aside-post-title"><div class="aside-post_title" href="/2020/07/22/1/" title="Java-反射、注解">Java-反射、注解</div><time class="aside-post_meta post-meta__date" title="发表于 2020-07-22 20:08:41">2020-07-22</time></div></a></div></div></div></div><div class="card-widget card-categories"><div class="card-content"><div class="item-headline"><i class="fas fa-folder-open"></i><span>分类</span></div><ul class="card-category-list">
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