Java笔记Spring（六）

web.xml各节点加载顺序

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">

  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>/WEB-INF/applicationContext.xml</param-value>
  </context-param>
  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
  <!--<servlet>-->
    <!--<servlet-name>dispatcher</servlet-name>-->
    <!--<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>-->
    <!--<init-param>-->
      <!--<param-name>contextConfigLocation</param-name>-->
      <!--<param-value>/WEB-INF/dispatcher-servlet2.xml</param-value>-->
    <!--</init-param>-->
    <!--<load-on-startup>1</load-on-startup>-->
  <!--</servlet>-->
  <!--<servlet-mapping>-->
    <!--<servlet-name>dispatcher</servlet-name>-->
    <!--<url-pattern>/</url-pattern>-->
  <!--</servlet-mapping>-->
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>

  <filter>
    <filter-name>CharacterEncodingFilter</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>
  </filter>
  <filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
</web-app>

加载顺序：context-param -> listener -> filter -> servlet

Servlet不配置的话，并不会在Web启动的时候加载，而且即使配置了Servlet，没有load-on-startup节点或者配置的load-on-startup节点不是正整数，同样不会在启动的时候生效，而是在第一次访问（无论是否匹配相应的pattern）生效

自定义一个PersonServlet

package com.example.demo.controller;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;

import javax.servlet.ServletException;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;
import java.io.IOException;

public class PersonServlet extends HttpServlet {

    private Log logger = LogFactory.getLog(PersonServlet.class);

    @Override
    public void init() throws ServletException {
        logger.info("personServlet被初始化了");
    }

    @Override
    protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
//        super.doGet(req, resp);

        System.out.println("personServlet被访问了");
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns="http://xmlns.jcp.org/xml/ns/javaee"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://xmlns.jcp.org/xml/ns/javaee http://xmlns.jcp.org/xml/ns/javaee/web-app_3_1.xsd"
         version="3.1">

  <context-param>
    <param-name>contextConfigLocation</param-name>
    <param-value>/WEB-INF/applicationContext.xml</param-value>
  </context-param>
  <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
  </listener>
  <!--<servlet>-->
    <!--<servlet-name>dispatcher</servlet-name>-->
    <!--<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>-->
    <!--<init-param>-->
      <!--<param-name>contextConfigLocation</param-name>-->
      <!--<param-value>/WEB-INF/dispatcher-servlet2.xml</param-value>-->
    <!--</init-param>-->
    <!--<load-on-startup>1</load-on-startup>-->
  <!--</servlet>-->
  <!--<servlet-mapping>-->
    <!--<servlet-name>dispatcher</servlet-name>-->
    <!--<url-pattern>/</url-pattern>-->
  <!--</servlet-mapping>-->

  <servlet>
    <servlet-name>dispatcher</servlet-name>
    <servlet-class>com.example.demo.controller.PersonServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>dispatcher</servlet-name>
    <url-pattern>/</url-pattern>
  </servlet-mapping>

  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>

  <filter>
    <filter-name>CharacterEncodingFilter</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>
  </filter>
  <filter-mapping>
    <filter-name>CharacterEncodingFilter</filter-name>
    <url-pattern>/*</url-pattern>
  </filter-mapping>
</web-app>

与实际所想一致，PersonServlet在Web启动的时候进行了初始化。