JSF頁面跳轉時清除Session

用JSF開發時，難以避免地常會有些Session Scope的MBean，對於這些Bean，我們希望它在同一頁面操作時保留，在頁面跳轉時清除，本文介紹一種自動清除Session的方法。

1.首先在頁面中添加一個Session，用來記錄原頁面的URI，代碼如下：

<%

session.setAttribute("pageFrom", request.getRequestURI());

%>

2.添加一個Filter，攔截所有的JSF，進行Session處理，需在web.xml中添加如下代碼：

 <filter>
  <display-name>sessionGuard</display-name>
  <filter-name>sessionGuard</filter-name>
  <filter-class>net.moon.filter.SessionGuardFilter</filter-class>
  <init-param>
   <description>the key of sessions want to keep to next page, others
    will be delete</description>
   <param-name>keepSessionKeys</param-name>
   <param-value>userID;pageId;com.sun.faces.logicalViewMap;com.sun.faces.application.StateManagerImpl.SerialId;javax.faces.request.charset<param-value>
  </init-param>
 </filter>
 <filter-mapping>
  <filter-name>sessionGuard</filter-name>
  <url-pattern>*.jsf</url-pattern>
 </filter-mapping>

其中，com.sun.faces.logicalViewMap;com.sun.faces.application.StateManagerImpl.SerialId;javax.faces.request.charset為JSF儲存狀態的一些Session，必須保留。

3.編寫SessionGuardFilter類，判斷請求頁面是否為當前頁面，如不是，進行Session處理，代碼如下：

package net.moon.filter;

import java.io.IOException;
import java.util.ArrayList;
import java.util.Enumeration;
import java.util.List;
import java.util.StringTokenizer;

import javax.servlet.Filter;
import javax.servlet.FilterChain;
import javax.servlet.FilterConfig;
import javax.servlet.ServletException;
import javax.servlet.ServletRequest;
import javax.servlet.ServletResponse;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;

public class SessionGuardFilter implements Filter {
 private List<String> keepSessionKeys = new ArrayList<String>();

 public void destroy() {
  // TODO Auto-generated method stub

 }

 @SuppressWarnings("unchecked")
 public void doFilter(ServletRequest request, ServletResponse response,
   FilterChain filterChain) throws IOException, ServletException {
  // TODO Auto-generated method stub
  HttpServletRequest hRequest = (HttpServletRequest) request;
  HttpSession session = hRequest.getSession();
  
  // delete useless sessions when change page
  if (!(hRequest.getRequestURI().replace(".jsf", ".jsp").equals(session
    .getAttribute("pageFrom")))) {
   Enumeration<String> en = session.getAttributeNames();
   while (en.hasMoreElements()) {
    String key = en.nextElement();
    if (!keepSessionKeys.contains(key)) {
     session.removeAttribute(key);
    }
   }
  }
 }

 public void init(FilterConfig filterConfig) throws ServletException {
  // TODO Auto-generated method stub
  StringTokenizer st = new StringTokenizer(filterConfig
    .getInitParameter("keepSessionKeys"), ";");
  while (st.hasMoreTokens()) {
   keepSessionKeys.add(st.nextToken());
  }
 }
}