JavaWeb过滤器的应用

￡神魔★判官ぃ 2021-12-03 11:13 336阅读 0赞

# 一:粗粒度权限控制（拦截是否登录、拦截用户名admin权限） #

思路:过滤器能够在Web组件被调用之前检查ServletRequest对象,修改请求头或者请求的正文;过滤器能够在被Web组件调用之后检查ServletResponse对象,修改响应头或者响应的内容,所以判断是否进入那个页面 就应该写在Filter

UserFilter

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1 public class UserFilter implements Filter {
     2     public void destroy() {}
     3     public void doFilter(ServletRequest request, ServletResponse response,
     4             FilterChain chain) throws IOException, ServletException {
     5         /*
     6          * 1. 得到session
     7          * 2. 判断session域中是否存在admin，如果存在，放行
     8          * 3. 判断session域中是否存在username，如果存在，放行，否则打回到login.jsp，并告诉它不要瞎留达
     9          */
    10         HttpServletRequest req = (HttpServletRequest) request;
    11         String name = (String)req.getSession().getAttribute("admin");
    12         if(name != null) {
    13             chain.doFilter(request, response);
    14             return;
    15         }
    16         
    17         name = (String)req.getSession().getAttribute("username");
    18         if(name != null) {
    19             chain.doFilter(request, response);
    20         } else {
    21             req.setAttribute("msg", "您啥都不是，不要瞎溜达！");
    22             req.getRequestDispatcher("/login.jsp").forward(request, response);
    23         }
    24     }
    25     public void init(FilterConfig fConfig) throws ServletException { }
    26 }

AdminFilter.java

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1 public class AdminFilter implements Filter {
     2     public void destroy() {}
     3     public void doFilter(ServletRequest request, ServletResponse response,
     4             FilterChain chain) throws IOException, ServletException {
     5         /*
     6          * 1. 得到session
     7          * 2. 判断session域中是否存在admin，如果存在，放行
     8          * 3. 判断session域中是否存在username，如果存在，放行，否则打回到login.jsp，并告诉它不要瞎留达
     9          */
    10         HttpServletRequest req = (HttpServletRequest) request;
    11         String name = (String)req.getSession().getAttribute("admin");
    12         if(name != null) {
    13             chain.doFilter(request, response);
    14         } else {
    15             req.setAttribute("msg", "您可能是个啥，但肯定不是管理员！");
    16             req.getRequestDispatcher("/login.jsp").forward(request, response);
    17         }
    18     }
    19     
    20 }

LoginServlet

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1 public class LoginServlet extends HttpServlet {
     2     public void doPost(HttpServletRequest request, HttpServletResponse response)
     3             throws ServletException, IOException {
     4         request.setCharacterEncoding("utf-8");
     5         response.setContentType("text/html;charset=utf-8");
     6         
     7         /*
     8          * 1. 获取用户名
     9          * 2. 判断用户名中是否包含itcast
    10          *   3. 如果包含，就是管理员
    11          *   4. 如果不包含，就是普通会员
    12          * 5. 要把登录的用户名称保存到session中
    13          * 6. 转发到index.jsp
    14          */
    15         String username = request.getParameter("username");
    16         if(username.contains("itcast")) {
    17             request.getSession().setAttribute("admin", username);
    18         } else {
    19             request.getSession().setAttribute("username", username);
    20         }
    21         request.getRequestDispatcher("/index.jsp").forward(request, response);
    22     }
    23 }

# 二: 分ip统计网站的访问次数 #

统计工作需要在所有资源之前都执行，那么就可以放到Filter中了。

我们这个过滤器不打算做拦截操作！因为我们只是用来做统计的。

用什么东西来装载统计的数据。Map<String,Integer>

整个网站只需要一个Map即可！

Map什么时候创建（使用ServletContextListener，在服务器启动时完成创建，并只在到ServletContext中），Map保存到哪里！（Map保存到ServletContext中！！！）

*  Map需要在Filter中用来保存数据
 *  Map需要在页面使用，打印Map中的数据

AListener.java

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1 public class AListener implements ServletContextListener {
     2     /**
     3      * 在服务器启动时创建Map，保存到ServletContext
     4      */
     5     public void contextInitialized(ServletContextEvent sce) {
     6         // 创建Map
     7         Map<String,Integer> map = new LinkedHashMap<String,Integer>();
     8         // 得到ServletContext
     9         ServletContext application = sce.getServletContext();
    10         // 把map保存到application中
    11         application.setAttribute("map", map);
    12     }
    13  
    14  
    15     public void contextDestroyed(ServletContextEvent sce) {
    16     }
    17 }

AFilter.java

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1 public class AFilter implements Filter {
     2     private FilterConfig config;
     3     public void destroy() {
     4     }
     5     public void doFilter(ServletRequest request, ServletResponse response,
     6             FilterChain chain) throws IOException, ServletException {
     7         /*
     8          * 1. 得到application中的map
     9          * 2. 从request中获取当前客户端的ip地址
    10          * 3. 查看map中是否存在这个ip对应访问次数，如果存在，把次数+1再保存回去
    11          * 4. 如果不存在这个ip，那么说明是第一次访问本站，设置访问次数为1
    12          */
    13         /*
    14          * 1. 得到appliction
    15          */
    16         ServletContext app = config.getServletContext();
    17         Map<String,Integer> map = (Map<String, Integer>) app.getAttribute("map");
    18         /*
    19          * 2. 获取客户端的ip地址
    20          */
    21         String ip = request.getRemoteAddr();
    22         /*
    23          * 3. 进行判断
    24          */
    25         if(map.containsKey(ip)) {
           //这个ip在map中存在，说明不是第一次访问
    26             int cnt = map.get(ip);
    27             map.put(ip, cnt+1);
    28         } else {
           //这个ip在map中不存在，说明是第一次访问
    29             map.put(ip, 1);
    30         }
    31         app.setAttribute("map", map);//把map再放回到app中
    32         
    33         chain.doFilter(request, response);//肯定放行
    34     }
    35  
    36  
    37     /**
    38      * 在服务器启动时就会执行本方法，而且本方法只执行一次！
    39      */
    40     public void init(FilterConfig fConfig) throws ServletException {
    41         this.config = fConfig;
    42     }
    43 }

show.jsp

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1 <table align="center" border="1" width="50%">
    2   <tr><td>ip</td><td>次数</td></tr>
    3    <c:forEach items="${applicationScope.map}"  var="entry">
    4      <tr>
    5      <td>${entry.key }</td>
    6      <td>${entry.value }</td>
    7      </tr>
    8    </c:forEach>
    9 </table>

# 三:解决全站字符乱码（POST和GET中文编码问题） #

RequestFilter

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1     public void doFilter(ServletRequest request,  ServletResponse response, FilterChain chain) throws  IOException, ServletException {
     2          request.setCharacterEncoding("utf-8");
     3          
     4          HttpServletRequest req =  (HttpServletRequest)request;
     5          if(req.getMethod().equals("GET")){
     6               EncodingRequest er = new  EncodingRequest(req);
     7               chain.doFilter(er, response);
     8          }else if(req.getMethod().equals("POST")){
     9               chain.doFilter(request, response);
    10          }
    11          
    12      }

EncodingServlet

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1     public void doPost(HttpServletRequest request,  HttpServletResponse response)
    2               throws ServletException, IOException {
    3           response.setContentType("text/html;charset=utf-8");
    4          String username=  request.getParameter("username");
    5          response.getWriter().print(username);
    6      }
    7

EncodingRequest

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1 public class EncodingRequest  extends  HttpServletRequestWrapper{
     2      private HttpServletRequest req;
     3      public EncodingRequest(HttpServletRequest request)  {
     4          super(request);
     5          // TODO Auto-generated constructor stub
     6          this.req=request;
     7      }
     8      public String getParameter(String name){
     9          String value = req.getParameter(name);
    10          try {
    11          value =new  String(value.getBytes("iso-8859-1"),"utf-8");
    12               
    13          } catch (UnsupportedEncodingException e) {
    14               // TODO Auto-generated catch block
    15               e.printStackTrace();
    16          }
    17          return value;
    18      }
    19 }

效果图:

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转载于:https://www.cnblogs.com/Yzengxin/p/11204585.html

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[Image 1]: