JavaWeb-10-Filter(過濾器)

1.概述

Filter:用來過濾網站的資料

• 進行中文亂碼
• 登入驗證
• …

2.編寫過濾器

• 建立Filter(javax.servlet下的接口)的實作類

  

• 過濾器用法(以解決頁面亂碼為例)

  public class CharacterEncodingFilter implements Filter {
      //初始化,在web伺服器啟動就已經初始化了 随時等待監聽
      public void init(FilterConfig filterConfig) throws ServletException {
          System.out.println("進入CharacterEncodingFilter init 方法");
      }
  
      /*
       filterChain 過濾鍊  (不止一個過濾器)
       1.過濾器中的所有代碼,再過濾特定請求時都會執行
       2.必須要讓過濾器繼續轉接,
      */
      public void doFilter(ServletRequest req, ServletResponse resp, FilterChain filterChain) throws IOException, ServletException {
          req.setCharacterEncoding("utf-8");
          resp.setCharacterEncoding("utf-8");
          resp.setContentType("text/html;charset=utf-8");
  
          System.out.println("CharacterEncodingFilter執行前");
          filterChain.doFilter(req,resp);//将請求繼續轉接,不寫,程式将被攔截停止
          System.out.println("CharacterEncodingFilter執行後");
      }
  
      //銷毀 web伺服器關閉時銷毀
      public void destroy() {
          System.out.println("CharacterEncodingFilter 銷毀");
      }
  }
             

• web.xml的配置

  //模拟亂碼的servlet 的注冊資訊,注意給了兩條映射
  // /show    沒有過濾器的路徑     
  // /servlet/show  	經過過濾器的路徑
  <servlet>
      <servlet-name>show</servlet-name>
      <servlet-class>com.cmy.servlet.ShowServlet</servlet-class>
  </servlet>
  <servlet-mapping>
      <servlet-name>show</servlet-name>
      <url-pattern>/show</url-pattern>
  </servlet-mapping>
  <servlet-mapping>
      <servlet-name>show</servlet-name>
      <url-pattern>/servlet/show</url-pattern>
  </servlet-mapping>
  //設定指定路徑/servlet/所有路徑  通過過濾器
  <filter>
      <filter-name>CharacterEncodingFilter</filter-name>
      <filter-class>com.cmy.filter.CharacterEncodingFilter</filter-class>
  </filter>
  <filter-mapping>
      <filter-name>CharacterEncodingFilter</filter-name>
      <url-pattern>/servlet/*</url-pattern>
  </filter-mapping>
             

• 效果示範

  

3.過濾器的應用

在web應用的檔案夾下,隻要知道路徑大多可以直接通路

但是,現在隻想讓登入了的使用者才能通路/sys/content.jsp,其他直接輸入該位址的遊客都重定向到/error/error.jsp界面,就需要過濾器

實作

• 在登入時,為該登入使用者将資訊儲存至session,這裡模拟admin,123456為資料庫中的存在使用者

  //Constant.USER_SESSION 為常量類的USER_SESSION屬性 "USER_SESSION" 為了修改友善
  public class LoginServlet extends HttpServlet {
      @Override
      protected void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          String username = req.getParameter("username");
          String password = req.getParameter("password");
          if (username.equals("admin")&&password.equals("123456")){
              req.getSession().setAttribute(Constant.USER_SESSION,req.getSession().getId());
              resp.sendRedirect("/sys/content.jsp");
          }else {
              resp.sendRedirect("/error/error.jsp");
          }
      }
  
      @Override
      protected void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException {
          doGet(req, resp);
      }
  }
             

• 為/sys/*的通路設定過濾器,保證使用者必須要有Constant.USER_SESSION屬性(登入過才有),否則重定向到錯誤界面

  public class SysFilter implements Filter {
      public void init(FilterConfig filterConfig) throws ServletException {
  
      }
  
      public void doFilter(ServletRequest req, ServletResponse resp, FilterChain filterChain) throws IOException, ServletException {
          HttpServletRequest request = (HttpServletRequest) req;
          HttpServletResponse response = (HttpServletResponse) resp;
          if (request.getSession().getAttribute(Constant.USER_SESSION)==null){
              response.sendRedirect("/error/error.jsp");
          }
          filterChain.doFilter(request,response);
      }
      public void destroy() {
  
      }
  }
             

• 在web.xml注冊過濾器,所有通路/sys/*的請求,都将進入SysFilter.java,精選過濾判斷,遊客将被重定向,登入過擁有session屬性的可以直接通路

  <filter>
      <filter-name>SysFilter</filter-name>
      <filter-class>com.cmy.filter.SysFilter</filter-class>
  </filter>
  <filter-mapping>
      <filter-name>SysFilter</filter-name>
      <url-pattern>/sys/*</url-pattern>
  </filter-mapping>