Filter
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1)过滤器概念
过滤器,在执行request前或者response后进行过滤处理。
request前过滤举例:在要求登录的网站,在未登录的状态下,除了登录界面,访问其他然都会自动转到登录界面。2)执行顺序
假设有2个Filter,那么在显示网页和过滤器的执行顺序如下:doFilter1{
System.out.println("1:Filter1");
chain.doFilter(request, response); //"下一个Filter执行"
System.out.println("5:Filter1 response"); //在chain.doFilter后面的过滤是倒叙执行的,即此处将在Filter2后面执行。
}
Filter2{
System.out.println("2:Filter2");
chain.doFilter(request, response); //最后一个Filter执行后会显示网页,然后在执行doFilter之后的内容
System.out.println("4:Filter2 response");
}
filtertest.jsp
<%
System.out.println("3:display page");
%>
3)Filter->Dispatcher
★Filter默认被触发的动作为request,也就是说通过<jsp:forward page="filtertest.jsp">转到页面是不会触发filter的。可以通过dispatcher来设置的触发方式有:request(默认),include,forward,error。
<filter>
<filter-name>Filter1</filter-name>
<filter-class>xmlweb.Filter1</filter-class>
</filter>
<filter-mapping>
<filter-name>Filter1</filter-name>
<url-pattern>/*</url-pattern>
<dispatcher>REQUEST</dispatcher>
<dispatcher>FORWARD</dispatcher>
<dispatcher>ERROR</dispatcher> //参加下面ErrorPage的两种设置方法
<dispatcher>INCLUDE</dispatcher>
</filter-mapping>
4)ErrorPage的两种配置方法:
1.<%@page errorPage="error.jsp"%>2.通过web.xml配置
<error-page>
<exception-type>java.lang.ArithemticException</exception-type>
<location>error.jsp</location>
</error-page>
5)可以设置某些页面自动刷新等等。下面是禁用缓存举例:
doFilter(...){response.setDateHeader("Expires", -1); //注意response要强转为HttpServletResponse
response.setheader("Cache-Control", "no-cache");
response.setHeader("Pragma", "no-cache");
chain.doFilter(request, response);
}
6)重新设置编码过滤器(Spring框架会提供这样的过滤器)
doFilter(...){request.setCharacterEncoding("UTF-8");
chain.doFilter(request, response);
}
登录可以访问控制例子:
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {HttpServletRequest req = (HttpServletRequest)request;if(req.getServletPath().equals("/login.jsp") || req.getServletPath().equals("/doLogin.jsp")) {chain.doFilter(request, response); //这两个页面不进行过滤,跳到下一个过滤器执行return;}//request.getSeesion可以获取当前的Sessionif(req.getSession().getAttribute("isLogin") != null && (boolean)req.getSession().getAttribute("isLogin")){chain.doFilter(request, response);//如果满足条件,则继续执行,否则报错。return;}else{request.setAttribute("errorMessage", "You did not login!");request.getRequestDispatcher("NewFile.jsp").forward(request, response);return;}}
7)使用Filter来进行权限管理
权限管理和业务逻辑很容易分开,在Filter中实现是非常好的选择。
8)HttpServletRequestWrapper HttpServletResponseWrapper
这两个分别是HttpServletReqest和HttpServletResponse的装饰这类。
如果想对原有的类进行改写,则只需要继承这两个类即可。
举例:过滤文字(abcd 替换为 ****)
class RequestDecorator extends HttpServletRequestWrapper {public RequestDecorator(ServletRequest request){super((HttpServletRequest)request);}@Overridepublic String getParameter(String param){String tmp = super.getParameter(param);return tmp.replace(" abcd ", " **** ");}}只需要在过滤器的实现时替换request对象即可。
public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException {RequestDecorator req = new RequestDecorator(request);chain.doFilter(req, response);}
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