J2EE设计模式浅谈(二)之Filter
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<script type="text/javascript">google_ad_client = "pub-8800625213955058";/* 336x280, 创建于 07-11-21 */google_ad_slot = "0989131976";google_ad_width = 336;google_ad_height = 280;//</script><script type="text/javascript"src="http://pagead2.googlesyndication.com/pagead/show_ads.js"></script>J2EE设计模式浅谈(二)之Filter zhaum@studyjava.com其实J2EE中太多的定义是很烦人的,设计模式也很抽象的,今天我就以Servlet2.3中新增的Filter在Web Application中的应用,来进一步的说明设计模式。首先假设我们现在想做一个Web Application(例如BBS)。要求具备下列功能:1、 在用户发帖子之前,要进行身份认证,以确认该用户是已登陆用户。2、 其次是要对删除帖子,修改帖子,进行权限检查。3、 访问特定资源(Web 页、JSP 页)时的身份认证那么对待这些要求我们该怎么去做,如果在每个页面中都写检查权限的代码,不是一个好想法,且使的程序的可重用性降低,对比设计模式Intercepting Filter(截获过滤)正好符合我们的要求,且在Servlet2.3中通过使用过滤器(Filter)能够使得Web Application开发者能够在请求到达Web资源之前截取请求,在处理请求之后修改应答。一个执行过滤器的Java 类必须实现javax.servlet.Filter 接口。这一接口含有三个方法:· init(FilterConfig):这是容器所调用的初始化方法。它保证了在第一次 doFilter() 调用前由容器调用。它能获取在 web.xml 文件中指定的filter初始化参数(文章的后面有lightningboard 的web.xml文件)。 · doFilter(ServletRequest, ServletResponse, FilterChain):这是一个完成过滤行为的方法。它同样是上一个过滤器调用的方法。引入的 FilterChain 对象提供了后续过滤器所要调用的信息,Filter中因为有了 FilterChain,就使的几个FILTER 成了一个链条。 · destroy():容器在销毁过滤器实例前,doFilter()中的所有活动都被该实例终止后,调用该方法在开源的lightningboard BBS中实现了两个Filter,如下1、ControllerFilter在这里起到的是Front Controller(前端控制器)的作用,是MVC模式中的控制器,是该BBS的入口点。package lightningboard;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.Filter;import javax.servlet.FilterConfig;import javax.servlet.FilterChain;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import lightningboard.action.*;/** * Control all *.do. * @version 0.3.5 * @author Xiaobo Liu */public class ControllerFilter implements Filter { /** * Action dispatch
* example: homde.do will be create HomeAction and call its excute() method. */ protected FilterConfig filterConfig; public void init(FilterConfig config) { this.filterConfig = config; } public void destroy() { this.filterConfig = null; } public void doFilter(ServletRequest srequest, ServletResponse sresponse, FilterChain filterChain) throws IOException, ServletException{ HttpServletRequest request = (HttpServletRequest)srequest; HttpServletResponse response = (HttpServletResponse)sresponse; long timeStart=System.currentTimeMillis(); Configuration cfg=Configuration.getInstance(); String encoding=cfg.getValue("SYS.ENCODING"); request.setCharacterEncoding(encoding); String path = (String) request.getRequestURI(); String actionString = path.substring(path.lastIndexOf("/") 1,path.lastIndexOf(".")); String forwardPage=null; try { if(actionString.equals("forum")) forwardPage=new ForumAction().excute(request,response); else if(actionString.equals("topic")) forwardPage=new TopicAction().excute(request,response); else if(actionString.equals("user")) forwardPage=new UserAction().excute(request,response); else if(actionString.equals("userList")) forwardPage=new UserListAction().excute(request,response); else if(actionString.equals("login")) forwardPage=new LoginAction().excute(request,response); else if(actionString.equals("register")) forwardPage=new RegisterAction().excute(request,response); else if(actionString.equals("post")) forwardPage=new PostAction().excute(request,response); else if(actionString.equals("postP")) forwardPage=new PostPAction().excute(request,response); else if(actionString.equals("userEdit")) forwardPage=new UserEditAction().excute(request,response); else if(actionString.equals("userEditP")) forwardPage=new UserEditPAction().excute(request,response); else if(actionString.equals("logout")) forwardPage=new LogoutAction().excute(request,response); else //default: home forwardPage=new HomeAction().excute(request,response); }catch (ActionException ex) { Debug.out(ex); request.setAttribute("actionMessage",new ActionMessage("system_error")); forwardPage="/actionMessage.jsp"; } // forward page if (forwardPage!=null){ String processTime="" (System.currentTimeMillis()-timeStart); request.setAttribute("processTime",processTime); filterConfig.getServletContext().getRequestDispatcher(forwardPage).forward(request,response); } }}2、此FILTER起的是Intercepting Filter(截获过滤)的作用。package lightningboard.filter;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.Filter;import javax.servlet.FilterConfig;import javax.servlet.FilterChain;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class SessionAuthorizationFilter implements Filter { protected FilterConfig filterConfig; public void init(FilterConfig config) { this.filterConfig = config; } public void destroy() { this.filterConfig = null; } private boolean passed(ServletRequest request, ServletResponse response) throws IOException, ServletException { boolean result=false; String objectName=this.filterConfig.getInitParameter("OBJECT_NAME"); HttpServletRequest req = (HttpServletRequest)request; HttpSession session =req.getSession(false); if(session!=null){ Object object=session.getAttribute(objectName); if(object!=null) result= true; } return result; } public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException{ if (passed(request,response)) filterChain.doFilter(request, response); else{ HttpServletResponse res = (HttpServletResponse)response; String errorPage=this.filterConfig.getInitParameter("ERROR_PAGE"); res.sendRedirect(errorPage); } }}容器通过 Web 应用程序中的配置描述符 web.xml 文件解析过滤器配置信息。有两个新的标记与过滤器相关: 和 。 标记是一个过滤器定义,它必定有一个 和 子元素。 子元素给出了一个与过滤器实例相关的名字。 指定了由容器载入的实现类。您能随意地包含一个 子元素为过滤器实例提供初始化参数。 标记代表了一个过滤器的映射,指定了过滤器会对其产生作用的 URL 的子集。lightningboard 项目中的web.xml文件如下: controllerFilter lightningboard.ControllerFilter sessionAuthorizationFilter lightningboard.filter.SessionAuthorizationFilter ERROR_PAGE login.jsp OBJECT_NAME loginBean sessionAuthorizationFilter /post.do sessionAuthorizationFilter /postP.do sessionAuthorizationFilter /post.jsp sessionAuthorizationFilter /userEdit.do sessionAuthorizationFilter /userEditP.do sessionAuthorizationFilter /userEdit.jsp sessionAuthorizationFilter /userList.do controllerFilter *.do index.html 由于本人水平有限,不当之处还请指正,谢谢!!!
* example: homde.do will be create HomeAction and call its excute() method. */ protected FilterConfig filterConfig; public void init(FilterConfig config) { this.filterConfig = config; } public void destroy() { this.filterConfig = null; } public void doFilter(ServletRequest srequest, ServletResponse sresponse, FilterChain filterChain) throws IOException, ServletException{ HttpServletRequest request = (HttpServletRequest)srequest; HttpServletResponse response = (HttpServletResponse)sresponse; long timeStart=System.currentTimeMillis(); Configuration cfg=Configuration.getInstance(); String encoding=cfg.getValue("SYS.ENCODING"); request.setCharacterEncoding(encoding); String path = (String) request.getRequestURI(); String actionString = path.substring(path.lastIndexOf("/") 1,path.lastIndexOf(".")); String forwardPage=null; try { if(actionString.equals("forum")) forwardPage=new ForumAction().excute(request,response); else if(actionString.equals("topic")) forwardPage=new TopicAction().excute(request,response); else if(actionString.equals("user")) forwardPage=new UserAction().excute(request,response); else if(actionString.equals("userList")) forwardPage=new UserListAction().excute(request,response); else if(actionString.equals("login")) forwardPage=new LoginAction().excute(request,response); else if(actionString.equals("register")) forwardPage=new RegisterAction().excute(request,response); else if(actionString.equals("post")) forwardPage=new PostAction().excute(request,response); else if(actionString.equals("postP")) forwardPage=new PostPAction().excute(request,response); else if(actionString.equals("userEdit")) forwardPage=new UserEditAction().excute(request,response); else if(actionString.equals("userEditP")) forwardPage=new UserEditPAction().excute(request,response); else if(actionString.equals("logout")) forwardPage=new LogoutAction().excute(request,response); else //default: home forwardPage=new HomeAction().excute(request,response); }catch (ActionException ex) { Debug.out(ex); request.setAttribute("actionMessage",new ActionMessage("system_error")); forwardPage="/actionMessage.jsp"; } // forward page if (forwardPage!=null){ String processTime="" (System.currentTimeMillis()-timeStart); request.setAttribute("processTime",processTime); filterConfig.getServletContext().getRequestDispatcher(forwardPage).forward(request,response); } }}2、此FILTER起的是Intercepting Filter(截获过滤)的作用。package lightningboard.filter;import java.io.IOException;import javax.servlet.ServletException;import javax.servlet.ServletRequest;import javax.servlet.ServletResponse;import javax.servlet.Filter;import javax.servlet.FilterConfig;import javax.servlet.FilterChain;import javax.servlet.http.HttpServletRequest;import javax.servlet.http.HttpServletResponse;import javax.servlet.http.HttpSession;public class SessionAuthorizationFilter implements Filter { protected FilterConfig filterConfig; public void init(FilterConfig config) { this.filterConfig = config; } public void destroy() { this.filterConfig = null; } private boolean passed(ServletRequest request, ServletResponse response) throws IOException, ServletException { boolean result=false; String objectName=this.filterConfig.getInitParameter("OBJECT_NAME"); HttpServletRequest req = (HttpServletRequest)request; HttpSession session =req.getSession(false); if(session!=null){ Object object=session.getAttribute(objectName); if(object!=null) result= true; } return result; } public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) throws IOException, ServletException{ if (passed(request,response)) filterChain.doFilter(request, response); else{ HttpServletResponse res = (HttpServletResponse)response; String errorPage=this.filterConfig.getInitParameter("ERROR_PAGE"); res.sendRedirect(errorPage); } }}容器通过 Web 应用程序中的配置描述符 web.xml 文件解析过滤器配置信息。有两个新的标记与过滤器相关: