Seam是如何启动的

开发Seam应用，需要了解JSF生命周期、Seam生命周期和它（Seam）通过phase listener在JSF生命周期上扩展了哪些东西。
(这里省略一些无关紧要的...)

“web应用，启动代码可以写在ServletContextListener里。这些代码、是一系列的事件监听器，在应用初始化之后（在处理请求之前）和销毁之前被调用”

Seam 2.1.2的org.jboss.seam.servlet.SeamListener代码如下：

import javax.servlet.ServletContextEvent;
import javax.servlet.ServletContextListener;
import javax.servlet.http.HttpSessionEvent;
import javax.servlet.http.HttpSessionListener;

import org.jboss.seam.Seam;
import org.jboss.seam.contexts.ServletLifecycle;
import org.jboss.seam.init.Initialization;
import org.jboss.seam.jmx.JBossClusterMonitor;
import org.jboss.seam.log.LogProvider;
import org.jboss.seam.log.Logging;

/**
 * Drives certain Seam functionality such as initialization and cleanup
 * of application and session contexts from the web application lifecycle.
 * 
 * @author Gavin King
 */
public class SeamListener implements ServletContextListener, HttpSessionListener
{
   private static final LogProvider log = Logging.getLogProvider(ServletContextListener.class);
   
   public void contextInitialized(ServletContextEvent event) 
   {
      log.info( "Welcome to Seam " + Seam.getVersion() );
      event.getServletContext().setAttribute( Seam.VERSION, Seam.getVersion() );
      ServletLifecycle.beginApplication( event.getServletContext() );
      new Initialization( event.getServletContext() ).create().init();
   }
   
   public void contextDestroyed(ServletContextEvent event) 
   {
      ServletLifecycle.endApplication();
   }
   
   public void sessionCreated(HttpSessionEvent event) 
   {
      ServletLifecycle.beginSession( event.getSession() );
   }
   
   public void sessionDestroyed(HttpSessionEvent event) 
   {
      JBossClusterMonitor monitor = JBossClusterMonitor.getInstance(event.getSession().getServletContext());
      if (monitor != null && monitor.failover())
      {
         // If application is unfarmed or all nodes shutdown simultaneously, cluster cache may still fail to retrieve SFSBs to destroy
         log.debug("Detected fail-over, not destroying session context");
      }
      else
      {
         ServletLifecycle.endSession( event.getSession() );
      }
   }
   
}

SeamListener实现了ServletContextListener接口.

ServletContextListener参考：
http://java.sun.com/javaee/5/docs/api/javax/servlet/ServletContextListener.html

所以你只需要实现ServletContextListener并把作如下配置：

<listener>
        <listener-class>org.jboss.seam.servlet.SeamListener</listener-class>
</listener>

当应用程序初始化时，contextInitialized()方法会被servlet容器调用，这就是seam如何做到，每次当你部署seam应用到servlet或JEE服务器的时候启动。

下面是一篇相关的关于JSF生命周期和phase listener的实现的文章（高度推荐）。

http://balusc.blogspot.com/2006/09/debug-jsf-lifecycle.html