Web启动加载资源的几种方式

1、struts1 plugin

例：

//实现接口org.apache.struts.action.PlugInpublic class WileyPlugin implements PlugIn {public static final String PROPERTIES = "PROPERTIES";public WileyPlugin() { }     //创建一个空构造函数//实现接口方法public void init(ActionServlet servlet, ApplicationConfig applicationConfig) throws javax.servlet.ServletException {System.err.println("---->The Plugin is starting<----");Properties properties = new Properties();try {  File file = new File("/WEB-INF/props.txt");  FileInputStream fis =new FileInputStream(file);  properties.load(fis);  ServletContext context = servlet.getServletContext();  context.setAttribute(PROPERTIES, properties);  Properties rProperties =   (Properties)context.getAttribute (PROPERTIES);  System.err.println("---->Prop: LOAD " +   rProperties.getProperty("LOAD"));}catch (FileNotFoundException fnfe) {  throw new ServletException(fnfe.getMessage());}catch (IOException ioe) {  throw new ServletException(ioe.getMessage());}}public void destroy() {System.err.println("---->The Plugin is stopping<----");}}//props文件内容：LOAD=some load //配置struts-config.xml添加<plug-in/>元素<plug-in className="wiley.WileyPlugin"/>

2、通过servlet来实现

例：

public class StaticClass extends javax.servlet.http.HttpServlet implements javax.servlet.Servlet  {      private static final long serialVersionUID = 1L;      private static String title =" StaticClass ";            public void init(ServletConfig config)       {           System.out.println("init");          ........     }       protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException       {      }               protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException       {      }        } 

然后在web.xml配置一下：

<servlet>     <servlet-name> staticclass</servlet-name>       <servlet-class>           action.util.StaticClass      </servlet-class>       <load-on-startup> 1</load-on-startup>     </servlet>   <servlet-mapping>       <servlet-name> staticclass</servlet-name>      <url-pattern> /servlet/staticclass.jsp</url-pattern>  </servlet-mapping> 

其中load-on-startup的含义是：容器启动时加载这个servlet的顺序，正常的取值范围是：负数，0-5，如果是负数或者没有这个标签，则容器在启动时不自动加载 这个servlet，如果是0-5，则按照顺序加载这个servlet，执行初始化方法init()。数字是0-5，加载顺序也是0-5。

3、不管是Struts1、Struts2还是其他的web层框架，它们目前基于的技术都是Servlet，只要根据web.xml找到那个启动类，我们就能通过覆盖该类的的init()方法来实现系统的初始化工作。可以写一个listener让它实现 ServletContextListener接口，在contextInitialized()方法中做想做的事情。将此listener配置到 web.xml中，Servlet容器如tomcat会在启动该web应用程序时调用此方法。

 public class InitListener implements ServletContextListener {       public void contextDestroyed(ServletContextEvent sce) {          System.out.println("web exit ... ");      }       public void contextInitialized(ServletContextEvent sce) {          System.out.println("web init ... ");          //系统的初始化工作          // ...      }   } 

<?xml version="1.0" encoding="UTF-8"?><web-app>   <listener>     <listener-class>fangwei.listener.InitListener</listener-class>  </listener>  <filter>     <filter-name>struts2</filter-name>    <filter-class>org.apache.struts2.dispatcher.FilterDispatcher</filter-class>   </filter>   <filter-mapping>    <filter-name>struts2</filter-name>    <url-pattern>/*</url-pattern>   </filter-mapping></web-app>