Article Directory
surroundings
- MySQL 8.0.16
1 Mybatis
1.1 Database configuration file
jdbc.driver=com.mysql.cj.jdbc.Driver
# 如果使用mysql 6+，增加一个时区的配置
jdbc.url=jdbc:mysql://localhost:3306/ssmbuild?useUnicode=true&characterEncoding=utf8&serverTimezone=UTC&useSSL=false
jdbc.username=root
jdbc.password=123456
com.mysql.jdbc.Driver 与 com.mysql.cj.jdbc.Driver ?
- com.mysql.jdbc.Driver is in mysql-connector-java 5
- com.mysql.cj.jdbc.Driver is in mysql-connector-java 6
JDBC connect to mysql 5:
url=jdbc:mysql://localhost:3306/test?useUnicode=true&characterEncoding=utf8&useSSL=false
JDBC connect to mysql 6:
url=jdbc:mysql://localhost:3306/test?serverTimezone=UTC&?useUnicode=true&characterEncoding=utf8&useSSL=false
1.2 Configure Mybatis
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration
PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<!--配置数据源，交给 spring 去做-->
<typeAliases>
<package name="com.fyy.pojo"/>
</typeAliases>
<mappers>
<mapper class="com.fyy.dao.BookMapper"/>
</mappers>
</configuration>
What does the typeAiases tag do?
Among them, the function of the <typeAiases> tag is only to specify a short name for the Java type. It is only related to the xml configuration, and its significance is only to reduce the redundancy of the fully qualified name of the class.
Specify a package name, Mybatis will search for the required Java Bean under this package name, and each Java Bean under this package will use the unqualified class name of the first letter of the Bean as its lowercase if there is no comment. Alias, such as: com.fyy.pojo.User's alias is: user, if there is an annotation, the alias is the annotation value. The following example:
@Alias("hello")
public class Hello(){
}
What does the mappers tag do?
Mybatis is a framework based on Sql mapping configuration. Sql statements are in the Mapper configuration file. After the SqlSession class is built, you need to read the sql configuration in the Mapper configuration file.
mappers: The mapper, which tells Mybatis where to find the mapping file in the best way, is used to configure the SQL mapping configuration file path that needs to be loaded.
Each mapper under mappers is a mapper, which is configured with the path of an independent mapping configuration file. The configuration methods are as follows.
1. The package where the interface is located
<mappers>
<!-- mapper接口所在的包名 -->
<package name="com.fyy.mapper"/>
</mappers>
# package标签，通过 name 属性指定 mapper 接口所在的包名，此时对应的映射文件必须
与接口位于同一路径下，并且名称相同。
2. Relative path configuration
<mappers>
<mapper resource="com/fyy/mapper/FlowerMapper.xml"/>
</mappers>
# mapper标签，通过 resource 属性引入 classpath 路径的相对资源
3. Class registration introduction
<mappers>
<mapper class="com.fyy.mapper.FlowerMapper"/>
</mappers>
# mapper 标签，通过 class 属性指定 mapper 接口名称，此时对应的映射文件必须与接口位于同一路径
下，并且名称相同
4. Use url absolute path to import (not recommended)
<mappers>
<mapper url="file:///var/mappers/UserMapper.xml"/>
</mappers>
# mapper 标签，通过 url 引入网络资源或者本地磁盘资源
to sum up
Only when the mappers information is configured, Mybatis knows where to load the Mapper configuration file. During development, select the configuration method of the integrated configuration file according to the configuration preference of the Mapper in the project.
2 Spring integrates Mybatis
2.1 Spring integrates dao layer
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
https://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context https://www.springframework.org/schema/context/spring-context.xsd">
<!-- 配置整合Mybatis-->
<!--1、关联数据库配置文件-->
<context:property-placeholder location="classpath:database.properties"/>
<!--2、连接池-->
<!--数据库连接池
dbcp 半自动化操作 不能自动连接
c3p0 自动化操作（自动的加载配置文件 并且设置到对象里面）-->
<bean id="dataSource" class="com.mchange.v2.c3p0.ComboPooledDataSource">
<!-- 配置连接池属性 -->
<property name="driverClass" value="${jdbc.driver}"/>
<property name="jdbcUrl" value="${jdbc.url}"/>
<property name="user" value="${jdbc.username}"/>
<property name="password" value="${jdbc.password}"/>
<!-- c3p0连接池的私有属性 -->
<property name="maxPoolSize" value="30"/>
<property name="minPoolSize" value="10"/>
<!-- 关闭连接后不自动commit -->
<property name="autoCommitOnClose" value="false"/>
<!-- 获取连接超时时间 -->
<property name="checkoutTimeout" value="10000"/>
<!-- 当获取连接失败重试次数 -->
<property name="acquireRetryAttempts" value="2"/>
</bean>
<!-- 3.配置SqlSessionFactory对象 -->
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<!-- 注入数据库连接池 -->
<property name="dataSource" ref="dataSource"/>
<!-- 配置MyBaties全局配置文件:mybatis-config.xml -->
<property name="configLocation" value="classpath:mybatis-config.xml"/>
</bean>
<!-- 4.配置扫描Dao接口包，动态实现Dao接口注入到spring容器中 -->
<bean class="org.mybatis.spring.mapper.MapperScannerConfigurer">
<!-- 注入sqlSessionFactory -->
<property name="sqlSessionFactoryBeanName" value="sqlSessionFactory"/>
<!-- 给出需要扫描Dao接口包 -->
<property name="basePackage" value="com.fyy.dao"/>
</bean>
</beans>
2.1.1 What does context:property-placeholder tag do?
In development, some parameters are constants, such as: url, password, username and other information to connect to the database, which do not need to be changed frequently, but they need to be changed at different stages. Is there a solution that facilitates us not to write one frequently in a stage The value of the parameter, but the configuration information of the parameter can be conveniently switched between different stages.
Solution: Spring 3 provides an easy way to solve the above problems, which is the content:property-placeholder element.
Use the attribute localtion in the content:property-placeholder tag, the value is the file path, you can use classpath: to specify the file name. Here we associate the database configuration information.
Only one context:property-placeholder is allowed to be defined in the Spring container, and the rest will be ignored.
2.1.2 Database connection pool
Every time a database connection is created is a huge resource consumption, so connection reuse, through the establishment of a database connection pool and a set of connection management strategies, a database connection can be reused efficiently and safely, which can avoid This reduces the overhead of frequent establishment and closure of database connection pools.
连接池的本质：介于 Java 和 JDBC 之间的 Java jar 包！
In the first step, we associate the database configuration information, and use the bean tag to obtain the configuration information.
According to the actual development of the project, you can configure the maximum and minimum number of connection pools, whether to automatically commit after closing the connection, get the connection timeout, get the connection failure retry times, etc., many attributes, I will not repeat them here.
2.1.3 Configure SqlSessionFactory object
The role of SqlSessionFacoty is to create SqlSession. SqlSession is a session, which is equivalent to the Connection object in JDBC. Every time an application accesses a database, a SqlSession must be created through SqlSessionFactory, so SqlSessionFacoty should be in the entire life cycle of Mybatis, and each database should only correspond to one SqlSessionFacoty.The role of SqlSessionFacoty in the entire Mybatis running process is as follows.
When configuring the SqlSessionFactory object, inject the database connection pool into it, and then configure the mybatis global configuration file.
My understanding is: When creating a SqlSession to connect to a database in SqlSessionFactory, you need to know the information of the database connection pool and the data source.
2.1.4 Configure scan dao interface package
MapperScannerConfigurer automatically scans and injects the Mapper interface generation proxy into the Spring container. Mybatis configures the MapperFactoryBean to generate the Mapper interface proxy when integrating with Spring. The basePackage attribute allows you to set the basic package path for the mapper interface file. You can use a semicolon or comma as a separator to set more than one package path. Each mapper will be searched recursively in the specified package path . Note that there is no need to specify SqlSessionFactory or SqlSessionTemplate, because MapperScannerConfigurer will create MapperFactoryBean and then auto-assemble, but if more than one DataSource is used, auto-assembly may fail. In this case, you can use the sqlSessionFactoryBeanName or sqlSessionTemplateBeanName properties to set the correct bean name to use.Big vernacular understanding: Scan the dao layer interface, MapperScannerConfigurer will automatically generate an interface proxy for each interface, this interface proxy is the implementation class of the interface, and injected into the Spring container.
2.2 Spring integrates service layer
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd">
<!-- 扫描service相关的bean -->
<context:component-scan base-package="com.fyy.service" />
<!--BookServiceImpl注入到IOC容器中-->
<bean id="BookServiceImpl" class="com.fyy.service.BookServiceImpl">
<property name="bookMapper" ref="bookMapper"/>
</bean>
<!-- 配置事务管理器 -->
<bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
<!-- 注入数据库连接池 -->
<property name="dataSource" ref="dataSource" />
</bean>
</beans>
事务管理器：DataSourceTransactionManager
事务管理是应用系统开发中必不可少的一部分。Spring 为事务管理提供了丰富的功能支持。Spring 事务管理分为编码式和声明式的两种方式。编程式事务指的是通过编码方式实现事务；声明式事务基于 AOP,将具体业务逻辑与事务处理解耦。声明式事务管理使业务代码逻辑不受污染, 因此在实际使用中声明式事务用的比较多。声明式事务有两种方式，一种是在配置文件（xml）中做相关的事务规则声明，另一种是基于 @Transactional 注解的方式。
其中 配置文件声明事务，是将数据库连接池注入到 事务管理器中。关于注解方式声明事务，就不在这里做过多介绍，后期会单独拿出来分享Spring事务。
3 整合 SpringMVC
web.xml 配置文件
3.1 web.xml 文件是如何执行的？
3.1.1 执行顺序
访问顺序为：1->2->3->4，其中 2 和 3 的值必须相同。url-pattern标签代表当一个请求发送到 servlet 容器时，容器会先将请求的 url 减去 当前应用上下文的路径作为 servlet 的映射 url，比如我访问的是 http://localhost/test/aaa.html，我的应用上下文是 test，容器会将 http://localhost/test 去掉，剩下的 /aaa.html 部分拿来做 servlet 映射匹配。如果与 设置的 url-pattern 映射匹配成功，请求才会被 DispatcherServlet 处理。图中的 <url-pattern> 中的值为：/，代表所有请求都会被处理。
而被DispatcherServlet 处理前，还会经过 2 ，3 步骤，url 匹配成功后，这个 url 访问名为 servlet-name 中值的 servlet，两个 servlet-name 值必须相同，因为 servlet 标签中的 servlet-name 标签映射到 servlet-class 标签中的值，最终访问 servlet-class 标签中的 DispatcherServlet 类，此时，请求才会被 DispatcherServlet 处理。
3.1.2 init-param标签
图中 \标签中的 \标签作用是，设置 springmvc 配置文件位置以及名称，springmvc配置文件不设置默认位置是：webapp，可以使用 classpath 设置文件的名称为：spring-mvc.xml ，代表 springmvc 配置文件名必须为 spring-mvc.xml，如不使用 classpath 设置其路径及名称，默认在 webapp下，名称为：\标签中的值 + "-servlet.xml"，例如：如 标签中值为：springmvc，则默认的 springmvc 配置文件名为：springmvc-servlet.xml3.1.3 load-on-startup标签
图中 \标签作用是，设置 servlet加载时间，如不设置默认在第一次请求访问时加载 servlet，若设置此标签值为正整数，会将 servlet 的加载时间提前到项目启动时，此标签中可以写整数，但写负整数和0和没有设置是一样的效果，只有设置为正整数才会将 servlet 的加载时间提前到项目启动时，也就是 tomcat 启动时，值越小，代表优先级越高。3.2 springmvc 配置文件是如何执行的？
spring-mvc.xml 配置文件
3.2.1 mvc:annotation-driven作用？
springmvc注解驱动会自动注册：DefaultAnnotationHandlerMapping 与 AnnotationMethodHandlerAdapter 两个bean，这两个 bean 是 SpringMVC 为 @Controller 分发请求所必须的，解决了使用 @Controller 注解的前提配置。在 Spring MVC 3.1 以上：
- DefaultAnnotationHandlerMapping 变更为：RequestMappingHandlerMapping
- AnnotationMethodHandlerAdapter 变更为：RequestMappingHandlerAdapter
我们来看看这个类主要做了什么工作？
AnnotationDrivenBeanDefinitionParser类向工厂中注册了几个 bean 实例，其中包括：
- RequestMappingHandlerMapping
- BeanNameUrlHandlerMapping
- RequestMappingHandlerAdapter
- HttpRequestHandlerAdapter
- SimpleControllerHandlerAdapter
- ExceptionHandlerExceptionResolver
- ResponseStatusExceptionResolver
- DefaultHandlerExceptionResolver
上面的bean实例都是做什么的呢？
前两个 bean 是 HandlerMapping 接口的实现类，用来处理请求映射的。其中第一个处理是 @RequestMapping 注解的，第二个是将 controller 类的名字映射为 请求 url，中间三个 adpter 是用来处理请求的，具体说就是确定调用哪个 controller 的哪个方法来处理当前请求，第一个处理 @Controller 注解的处理器，支持自定义方法参数和返回值，第二个是处理继承 HttpRequestHandler 的处理器，第三个处理继承自 Controller 接口的处理器，后面三个是用来处理异常的解析器。
结论
如果使用@Controller 注解，没有配置注解驱动： <mvc:annotation-driven> 的话，那么所有的请求都无法找到 DispatcherServlet ,并无法把请求分发至控制器。添加注解驱动后，才会扫描所有带有 @Controller 注解的类，由 spring 管理并维护。
3.2.2 mvc:default-servlet-handler作用？
还记得我们在 web.xml 中配置了 url-pattern，用来过滤请求，SpringMVC 将接收到的所有请求都看做是一个普通请求，包括对于静态资源的请求，这样一来，所有对于静态资源的请求都会被看做是一个普通的后台控制器请求，而静态资源的请求会因为找不到资源而报404异常。查看 tomcat 日志就可以看到会有警告。
对于此问题 SpringMVC 在全局配置文件中提供了一个 <mvc:default-servlet-handler>标签，在 web 容器启动的时候会在上下文中定义一个 DefaultServletHttpRequestHandler ，它会对 DispatcherServlet 请求进行处理，如果该请求已经做了映射，那么会接着交给后台对应的处理程序，如果没有映射，就交给 web 应用服务器默认的 servlet 处理，从而找到对应的静态资源，只有找不到静态资源时会报错。
如果默认的 Servlet 容器不用默认的 default ，用不同名称进行自定义配置，或者在缺省 Servlet 名称未知的情况下使用了不同的 Servlet 容器，则必须显示提供默认 Servlet 的名称。
<mvc:default-servlet-handler default-servlet-name="myCustomDefaultServlet"/>
3.2.3 context:component-scan 作用？
扫描组件，将所有使用 @Controller 注解的类作为 SpringMVC 的控制层。其中 base-package 属性是指定扫描的包。3.2.4 视图解析器 作用？
视图解析器，是将 prefix + 视图名称 + suffix = 确定最终要跳转的页面，其中视图名称是什么？？ 处理请求的方法会返回一个字符串，这个字符串即视图名称，最终会通过配置文件中配置的视图解析器实现页面的跳转。例如：@Controller
public class TestController {
@RequestMapping("hello")
public String hello() {
System.out.println("success");
return "success";
}
}
# 其中返回字符串为：success，所以处理此请求最终要跳转的页面为：/WEB-INF/view/success.jsp
For an explanation of SpringMVC, you can view another article by Xiaobian. SpringMVC from basic to source code
4 Spring configuration integration file
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd">
<import resource="classpath:spirng/spring-dao.xml"/>
<import resource="classpath:spirng/spring-service.xml"/>
<import resource="classpath:spirng/spring-mvc.xml"/>
</beans>
- ClassPathXmlApplicationContext
- ClassPathResource
- XmlWebApplicationContext
- FileSystemXmlApplicationContext
- …
End
The above is the summary of my study of the ssm framework configuration. Some places are not deep enough, but for beginners, it should also be quite rewarding. If there are errors, please correct me!