Servlet 过滤器

• web.xml

  • <filter>
        <filter-name>testFilter
        <filter-class>cn.itcast.filter.text.TestFilter
        <init-param>
            <param-name>encoding</param-name>
            <param-value>GB2312</param-value>
        </init-param>
    </filter>
    <filter-mapping>
        <filter-name>testFilter
        <url-pattern>/*
    </filter-mapping>

• API
  • Filter接口
    • 多个过滤器, 按web.xml中注册的顺序映射调用。servlet执行完后, 从后向前返回执行chain.doFilter之后的方法
    • init
    • destroy
    • doFilter(ServletRequest request, ServletResponse response, FilterChain chain)
  • FilterChain接口
    • doFilter(ServletRequest request, ServletResponse response)
  • FilterConfig接口
    • private FilterConfig config = null;
    • init()
      • this.config = config;
    • doFilter()
      • String ip = this.config.getInitParameter(“ip”);
• 映射
  • 1.映射的url
  • 2.servlet的名字
    • 通配servlet /servlet/*
  • 3.为了映射servlet中的转发, 映射一个过滤器到某种传递方式

    • <filter-mapping>
          <dispatcher>FORWARD
              # FORWARD 转发方式
              # REQUEST  请求方式
              # INCLUDE  包含方式
              # ERROR  错误页面
          </dispatcher>
      </filter-mapping>

• 设置编码

  • doFilter()
        HttpServletRequest httpRequest = (HttpServletRequest) request;
        HttpServletResponse httpResponse = (HttpServletResponse) response;
        httpRequest.setCharacterEncoding("utf-8")
        String method = httpRequest.getMethod();
        if("get".equalsIgnoreCase(method)){
            chain.doFilter(new MyWapperRequest(httpRequest),response);
        }else{
            request.setCharacterEncoding("utf-8");
        }
     
    class MyWapperRequest extends HttpServletRequestWrapper{
        private HttpServletRequest request = null;
     
        public MyWapperRequest (HttpServletRequest request){
            super(request);
            this.request = request;
        }
     
        @Override
        public String getParameter(String name){
            String value = request.getParameter(name);
            String method = request.getMethod();
            if(value != null &&"get".equalsIgnoreCase(method)){
                value = new String(value.getBytes("iso8859-1"),request.getCharacterEncoding())
            }
            return value;
        }
    }

• 设置缓存
  • Expires:-1
  • Cache-Control:no-cache
  • Pragma:no-cache

  • NoCacheFilter implements Filter # 设置不缓存
        doFilter()
            HttpServletResponse httpResponse = response;
            httpResponse.setHeader("Expires",-1 + "");
            //  setDataHeader("expires",-1);
            httpResponse.setHeader("cache-control","no-cache");
            httpResponse.setHeader("pragma","no-cache");
            chain.doFilter(request,httpResponse);
     
     
     
    CacheFilter
        # 缓存静态资源
        # web.xml中url-pattern 可以映射多个 param-name=jpg param-value=2
        private FilterConfig config = null;
     
        doFilter()
            HttpServletResponse httpResponse = (HttpServletResponse) response;
            HttpServletResponse httpRequest = (HttpServletRequest) request;
     
        String resource = request.getRequestURI();
        String date  = null;
        if(resource.endsWith("jpg")){
            date =  config.getInitParameter("jpg");
            httpResponse.setDateHeader("expires",System.currentTimeMillis() + longDate * 60 * 60 * 1000);    // 换算成秒
        } else if(resource.endsWith("js")){
            String date  = config.getInitParameter("js");
            config.getInitParameter("js");
            httpResponse.setDateHeader("expires",System.currentTimeMillis() + longDate * 60 * 60 * 1000);
        }
     
        chain.doFilter(httpRequest,httpResponse);

• 修改编码

  • EncodingFilter implements Filter{
        doFilter(request,response){
            HttpServletResponse httpResponse = (HttpServletResponse) response;
            HttpServletResponse httpRequest = (HttpServletRequest) request;
            httpRequest.setCharacterEncoding("utf-8");
            chain.doFilter(httpRequest,httpResponse);
        }
    }
    class EncodingRequest extends HttpServletRequestWrapper{
        private HttpServletRequest request;
        public EncodingRequest (HttpServletRequest request){
            super(request);
            this.request = request;
        }
     
        @Override
        public String getParameter(String name){
            String value = request.getParameter(name)
            if(value != null && "get".equalsIgnoreCase(request.getMethod)){
                value = new String(value.getBytes("iso8859"),"utf-8");
            }
            return value;
        }
    }

• 登录
  • LoginFilter

    • init(){
          this.config  = config;
      }
      private FilterConfig config = null;
      doFilter(){
          String path = this.config.getInitParameter("loginPage");
          HttpSession session = httpRequest.getSession(false);
       
          // 判断用户请求的是否是UserServlet
          String servletName = httpRequest.getServletPath();
          servletName = substring(servletName.lastIndexOf("/")+1);
          if("UsersServlet".equals(servletName)){
          }else{ // 一般的servlet
              if(session != null){
                  // 获取登录标记
                  User user = null;
                  user = (User)session.getAttribute("user");
       
                  // 判断
                  if(user != null){
                      // 放行资源
                      chain.doFilter(httpRequest,httpResponse);
                  }else{
                      // 页面重定向到登录页面
                      httpResponse.sendRedirect(httpRequest.getContextPath() + "/" + path);
                  }
              }
          }
      }

  • web.xml