Servlet-初始化

好记性不如烂笔头

所有的百度谷歌不如自己敲一遍来得真实

学web开发，后面一直用到一些框架，开发速率大大提升，但是也不能忘本  Servlet

现在讲一下Servlet是如何初始化的

一般写完Servlet后得在WEB.xml里配置，以下是摘抄一段web.xml的配置

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="3.0" 
	xmlns="http://java.sun.com/xml/ns/javaee" 
	xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 
	xsi:schemaLocation="http://java.sun.com/xml/ns/javaee 
	http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd">
  <display-name></display-name>
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>firstServlet</servlet-name>
    <servlet-class>Main.firstServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>secondServlet</servlet-name>
    <servlet-class>Main.secondServlet</servlet-class>
    <load-on-startup>0</load-on-startup>
  </servlet>
  <servlet>
    <description>This is the description of my J2EE component</description>
    <display-name>This is the display name of my J2EE component</display-name>
    <servlet-name>thirdServlet</servlet-name>
    <servlet-class>Main.thirdServlet</servlet-class>
    <load-on-startup>-1</load-on-startup>
  </servlet>
  <servlet-mapping>
    <servlet-name>firstServlet</servlet-name>
    <url-pattern>/servlet/firstServlet</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>secondServlet</servlet-name>
    <url-pattern>/servlet/secondServlet</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
    <servlet-name>thirdServlet</servlet-name>
    <url-pattern>/servlet/thirdServlet</url-pattern>
  </servlet-mapping>	
  <welcome-file-list>
    <welcome-file>index.jsp</welcome-file>
  </welcome-file-list>
</web-app>

<load-on-startup>-1</load-on-startup> 就是这一行属性，决定了servlet什么时候初始化

数字只要大于0，那么在web容器开始的时候就对servlet进行初始化实例化了，并且数字越大，初始化的顺序越后，数字小于0的时候，那么只有在访问servlet的时候才会去初始化