【SpringMVC】配置<context:component-scan>

   当我们启动一个web项目时，容器（tomcat）会先读取项目web.xml配置文件的配置，这一步骤完成后项目才正常启动。
   在web.xml文件中的节点加载是有顺序，

     <context-param>-> <listener> -> <filter> -> <servlet>相同元素按照先后顺序加载。

     我们首先在在web.xml中通过contextConfigLocation配置spring，contextConfigLocation定义spring配置文件的位置，
在applicationContext.xml中可以配置Bean，添加springMVC的Servlet节点，将springMVC的配置独立出来。

这样在springmvc.xml中只对@Controller进行扫描就可，作为一个控制器，其他的事情不做。

在applicationContext.xml中只对一些事务逻辑的注解扫描。

web.xml配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" id="WebApp_ID" version="2.5">
  <display-name>mes</display-name>
  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>classpath:applicationContext.xml</param-value>
  </context-param>
  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
  <listener>
    <listener-class>org.springframework.web.context.request.RequestContextListener</listener-class>
  </listener>
  <filter>
    <filter-name>encodingFilter</filter-name>
    <filter-class>org.springframework.web.filter.CharacterEncodingFilter</filter-class>
    <init-param>
      <param-name>encoding</param-name>
      <param-value>UTF-8</param-value>
    </init-param>
    <init-param>
      <param-name>forceEncoding</param-name>
      <param-value>true</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>encodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <filter>
    <filter-name>shiroFilter</filter-name>
    <filter-class>org.springframework.web.filter.DelegatingFilterProxy</filter-class>
    <init-param>
      <param-name>targetFilterLifecycle</param-name>
      <param-value>true</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>shiroFilter</filter-name>
    <url-pattern>/*</url-pattern>
    <dispatcher>REQUEST</dispatcher>
    <dispatcher>FORWARD</dispatcher>
  </filter-mapping>
  <servlet>
    <servlet-name>springmvc</servlet-name>
    <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
    <init-param>
      <param-name>contextConfigLocation</param-name>
      <param-value>classpath:spring/springmvc.xml</param-value>
    </init-param>
    <load-on-startup>1</load-on-startup>
    <async-supported>true</async-supported>
  </servlet>
  <servlet-mapping>
    <servlet-name>springmvc</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>
  <filter>
    <filter-name>DruidWebStatFilter</filter-name>
    <filter-class>com.alibaba.druid.support.http.WebStatFilter</filter-class>
    <init-param>
      <param-name>exclusions</param-name>
      <param-value>/static/*,*.js,*.gif,*.jpg,*.png,*.css,*.ico,/druid/*</param-value>
    </init-param>
    <init-param>
      <param-name>sessionStatEnable</param-name>
      <param-value>false</param-value>
    </init-param>
  </filter>
  <filter-mapping>
    <filter-name>DruidWebStatFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
  <servlet>
    <servlet-name>DruidStatView</servlet-name>
    <servlet-class>com.alibaba.druid.support.http.StatViewServlet</servlet-class>
    <init-param>
      <param-name>loginUsername</param-name>
      <param-value>druid</param-value>
    </init-param>
    <init-param>
      <param-name>loginPassword</param-name>
      <param-value>dream</param-value>
    </init-param>
  </servlet>
  <servlet-mapping>
    <servlet-name>DruidStatView</servlet-name>
    <url-pattern>/druid/*</url-pattern>
  </servlet-mapping>
  <session-config>
    <session-timeout>30</session-timeout>
  </session-config>
  <error-page>
    <error-code>404</error-code>
    <location>/WEB-INF/views/error/404.jsp</location>
  </error-page>
  <error-page>
    <error-code>500</error-code>
    <location>/WEB-INF/views/error/500.jsp</location>
  </error-page>
  
   <error-page>
    <error-code>403</error-code>
    <location>/WEB-INF/jsp/403.jsp</location>
  </error-page>
  
  <welcome-file-list>
    <welcome-file>index.html</welcome-file>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

springmvc.xml配置
在springmvc.xml配置中，我们需要配置<context:component-scan>，这样spring就可以自动去扫描base-pack下面或者子包下面的Java文件，
如果扫描到有@Component @Controller@Service等这些注解的类，则把这些类注册为bean。
由于我们把spring的配置分开了，在这里只要配置Control的扫描就可以了

 <context:component-scan base-package="test.*.controller" use-default-filters="false">
        <context:include-filter type="annotation" expression="org.springframework.stereotype.Controller"/>
        <context:include-filter type="annotation" expression="org.springframework.web.bind.annotation.ControllerAdvice"/>
 </context:component-scan>

需要注意的是，在<context:component-scan>的参数中，use-default-filters默认为true，这时候他会对指定包下面全部带@注解标签的类注册为bean。

<context:component-scan>有两个子标签，<context:include-filter>和<context:exclude-filter>

        <context:component-scan base-package="test.*">
        <context:exclude-filter type="annotation" expression="org.springframework.stereotype.Controller"/>
        <context:exclude-filter type="annotation" expression="org.springframework.web.bind.annotation.ControllerAdvice"/>
      </context:component-scan> 

如果你只想扫描指定包下面的Controller时，需要设置use-default-filters为false，这时候使用<include-filter>才起效，
如果use-default-filters不设置为false，那你就需要把base-package精确到只含有control的包，不然他会扫描所有注解内容；
如果使用<exclude-filter>则不扫描该类注释，如果这里也设置了use-default-filters为false，则会导致不扫描，所以使用该标签时不需要设置false。