web启动加载资源

1.struts1 plugin
创建类实现接口org.apache.struts.action.PlugIn;
创建一个空构造函数
实现接口方法
配置struts-config.xml添加<plug-in/>元素
例：
public class WileyPlugin implements PlugIn {
  public static final String PROPERTIES = "PROPERTIES";
  public WileyPlugin() { }
  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: LDAP " + rProperties.getProperty("LDAP"));
    }
    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：
LDAP=some ldap server name
struts-config.xml：
<plug-in className="wiley.WileyPlugin"/>

2.通过servlet来实现
   新建一个类继承javax.servlet.http.HttpServlet，然后将加载数据的代码放到   init方法就可以了。具体代码如下：
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("public void init");  
        setdata();  
    }   

    protected void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException   
    {  
    }     
      
    protected void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException   
    {  
    }  
      
    public void setdata()  
    {  
        try 
        {  
            Properties props = new Properties();  
            props.setProperty("java.naming.factory.initial",  
                    "org.jnp.interfaces.NamingContextFactory");  
            props.setProperty("java.naming.provider.url", "192.168.1.17:1099");  
            props.setProperty("java.naming.factory.url.pkgs",  
                    "org.jboss.naming:org.jnp.interfaces");           
            InitialContext remotectx = new InitialContext(props);  
              
            DeptTempMgr deptTempMgr = (DeptTempMgr)remotectx.lookup("Business/DeptTempMgrBean/remote");  
            InetAddress inetAddress= deptTempMgr.getLocalIp();  
            String ipName = inetAddress.getHostAddress();  
            String homeName = inetAddress.getHostName();  
           System.out.println("远程调用的主机内网ip是："+ipName);  
            System.out.println("远程调用的主机名是："+homeName);  
        }  
        catch (Exception e)  
        {  
            System.out.println(e);  
        }  
          
    }  
      
} 
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Struts、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>