JavaWeb的Filter過濾器應用
過濾器應用案例
分ip統計網站的訪問次數
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ip |
count |
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192.168.1.111 |
2 |
|
192.168.1.112 |
59 |
統計工作需要在所有資源執行前，那麼就可以放到Filter中了。
我們這個過濾器不打算做攔截操作！因為我們只是用來做統計的。
用什麼東西來裝載統計的資料。Map<String,Integer>
Map什麼時候建立（使用ServletContextListener，在伺服器啟動時完成建立，並只在到ServletContext中），Map儲存到哪裡！（Map儲存到ServletContext中！！！）
Ø Map需要在Filter中用來儲存資料
Ø Map需要在頁面使用，列印Map中的資料
思路分析
因為一個網站可能有多個頁面，無論哪個頁面被訪問，都要統計訪問次數，所以使用過濾器最為方便。
因為需要分IP統計，所以可以在過濾器中建立一個Map，使用IP為key，訪問次數為value。當有使用者訪問時，獲取請求的IP，如果IP在Map中存在，說明以前訪問過，那麼在訪問次數上加1，即可；IP在Map中不存在，那麼設定次數為1。
把這個Map存放到ServletContext中！
程式碼描述
index.jsp
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<body> <h1>分IP統計訪問次數</h1> <table
align="center" <tr> <th>IP地址</th> <th>次數</th> </tr> <c:forEach items="${applicationScope.ipCountMap }" var="entry"> <tr> <td>${entry.key }</td> <td>${entry.value }</td> </tr> </c:forEach> </table> </body> |
IPFilter
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public class IPFilter implements Filter { private ServletContext context; public void init(FilterConfig fConfig) throws ServletException { context = fConfig.getServletContext(); Map<String, Integer> ipCountMap = Collections .synchronizedMap(new LinkedHashMap<String, Integer>()); context.setAttribute("ipCountMap", ipCountMap); } @SuppressWarnings("unchecked") public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { HttpServletRequest req = (HttpServletRequest) request; String ip = req.getRemoteAddr(); Map<String, Integer> ipCountMap = (Map<String, Integer>) context .getAttribute("ipCountMap"); Integer count = ipCountMap.get(ip); if (count == null) { count = 1; } else { count += 1; } ipCountMap.put(ip, count); context.setAttribute("ipCountMap", ipCountMap); chain.doFilter(request, response); } public void destroy() {} } |
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<filter> <display-name>IPFilter</display-name> <filter-name>IPFilter</filter-name> <filter-class>cn.cloud.filter.ip.IPFilter</filter-class> </filter> <filter-mapping> <filter-name>IPFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> |
使用者許可權控制
RBAC à 基於角色的許可權控制
l tb_user
l tb_role
l tb_userrole
l tb_menu(增、刪、改、查)
l tb_rolemenu
需求說明
我們給出三個頁面：index.jsp、user.jsp、admin.jsp。
l index.jsp：誰都可以訪問，沒有限制；
l user.jsp：只有登入使用者才能訪問；
l admin.jsp：只有管理員才能訪問。
思路分析
設計User類：username、password、grade，其中grade表示使用者等級，1表示普通使用者，2表示管理員使用者。
當用戶登入成功後，把user儲存到session中。
建立LoginFilter，它有兩種過濾方式：
l 如果訪問的是user.jsp，檢視session中是否存在user；
l 如果訪問的是admin.jsp，檢視session中是否存在user，並且user的grade等於2。
程式碼描述
User.java
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public class User { private String username; private String password; private int grade; //get…set方法 } |
在UserService中建立一個Map，用來儲存所有使用者。Map中的key中使用者名稱，value為User物件。
UserService.java
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public class UserService { private static Map<String,User> users = new HashMap<String,User>(); static { users.put("zhangSan", new User("zhangSan", "123", 1)); users.put("liSi", new User("liSi", "123", 2)); } public User login(String username, String password) { User user = users.get(username); if(user == null) return null; return user.getPassword().equals(password) ? user : null; } } |
login.jsp
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<body> <h1>登入</h1> <p style="font-weight: 900; color: red">${msg }</p> <form action="<c:url value='/LoginServlet'/>" method="post"> 使用者名稱：<input type="text" name="username"/><br/> 密 碼：<input type="password" name="password"/><br/> <input type="submit" value="登入"/> </form> </body> |
index.jsp
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<body> <h1>主頁</h1> <h3>${user.username }</h3> <hr/> <a href="<c:url value='/login.jsp'/>">登入</a><br/> <a href="<c:url value='/user/user.jsp'/>">使用者頁面</a><br/> <a href="<c:url value='/admin/admin.jsp'/>">管理員頁面</a> </body> |
/user/user.jsp
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<body> <h1>使用者頁面</h1> <h3>${user.username }</h3> <hr/> </body> |
/admin/admin.jsp
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<body> <h1>管理員頁面</h1> <h3>${user.username }</h3> <hr/> </body> |
LoginServlet
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public class LoginServlet extends HttpServlet { public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { request.setCharacterEncoding("utf-8"); response.setContentType("text/html;charset=utf-8"); String username = request.getParameter("username"); String password = request.getParameter("password"); UserService userService = new UserService(); User user = userService.login(username, password); if(user == null) { request.setAttribute("msg", "使用者名稱或密碼錯誤"); request.getRequestDispatcher("/login.jsp").forward(request, response); } else { request.getSession().setAttribute("user", user); request.getRequestDispatcher("/index.jsp").forward(request, response); } } } |
LoginUserFilter.java
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<filter> <display-name>LoginUserFilter</display-name> <filter-name>LoginUserFilter</filter-name> <filter-class>cn.cloud.filter.LoginUserFilter</filter-class> </filter> <filter-mapping> <filter-name>LoginUserFilter</filter-name> <url-pattern>/user/*</url-pattern> </filter-mapping> |
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public class LoginUserFilter implements Filter { public void destroy() {} public void init(FilterConfig fConfig) throws ServletException {} public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { response.setContentType("text/html;charset=utf-8"); HttpServletRequest req = (HttpServletRequest) request; User user = (User) req.getSession().getAttribute("user"); if(user == null) { response.getWriter().print("您還沒有登入"); return; } chain.doFilter(request, response); } } |
LoginAdminFilter.java
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<filter> <display-name>LoginAdminFilter</display-name> <filter-name>LoginAdminFilter</filter-name> <filter-class>cn.itcast.filter.LoginAdminFilter</filter-class> </filter> <filter-mapping> <filter-name>LoginAdminFilter</filter-name> <url-pattern>/admin/*</url-pattern> </filter-mapping> |
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public class LoginAdminFilter implements Filter { public void destroy() {} public void init(FilterConfig fConfig) throws ServletException {} public void doFilter(ServletRequest request, ServletResponse response, FilterChain chain) throws IOException, ServletException { response.setContentType("text/html;charset=utf-8"); HttpServletRequest req = (HttpServletRequest) request; User user = (User) req.getSession().getAttribute("user"); if(user == null) { response.getWriter().print("您還沒有登入!"); return; } if(user.getGrade() < 2) { response.getWriter().print("您的等級不夠！"); return; } chain.doFilter(request, response); } } |
禁止資源快取
瀏覽器只是要快取頁面，這對我們在開發時測試很不方便，所以我們可以過濾所有資源，然後新增去除所有快取！
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public class NoCacheFilter extends HttpFilter { public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain) throws IOException, ServletException { response.setHeader("cache-control", "no-cache"); response.setHeader("pragma", "no-cache"); response.setHeader("expires", "0"); chain.doFilter(request, response); } } |
POST和GET中文編碼
servlet：
l POST：request.setCharacterEncoding(“utf-8”);
l GET：
Ø String username = request.getParameter(“username”);
Ø username = new String(username.getBytes(“ISO-8859-1”), “utf-8”);
需求說明
亂碼問題：
l 獲取請求引數中的亂碼問題；
Ø POST請求：request.setCharacterEncoding(“utf-8”)；
Ø GET請求：newString(request.getParameter(“xxx”).getBytes(“iso-8859-1”), “utf-8”)；
l 響應的亂碼問題：response.setContextType(“text/html;charset=utf-8”)。
思路分析
全站亂碼問題的難點：處理GET請求引數的問題。
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public class EncodingFilter extends HttpFilter { public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain) throws IOException, ServletException { String charset = this.getInitParameter("charset"); if(charset == null || charset.isEmpty()) { charset = "UTF-8"; } request.setCharacterEncoding(charset); response.setContentType("text/html;charset=" + charset); chain.doFilter(request, response); } } |
如果是POST請求，當執行目標Servlet時，Servlet中呼叫request.getParameter()方法時，就會根據request.setCharacterEncoding()設定的編碼來轉碼！這說明在過濾器中呼叫request.setCharacterEncoding()方法會影響在目標Servlet中的request.getParameter()方法的行為！
但是如果是GET請求， request只有getParameter()，而沒有setParameter()方法。
下面是三種對a物件進行增強的手段：
程式碼描述
EncodingRequest
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public class EncodingRequest extends HttpServletRequestWrapper { private String charset; public EncodingRequest(HttpServletRequest request, String charset) { super(request); this.charset = charset; } public String getParameter(String name) { HttpServletRequest request = (HttpServletRequest) getRequest(); String method = request.getMethod(); if(method.equalsIgnoreCase("post")) { try { request.setCharacterEncoding(charset); } catch (UnsupportedEncodingException e) {} } else if(method.equalsIgnoreCase("get")) { String value = request.getParameter(name); try { value = new String(name.getBytes("ISO-8859-1"), charset); } catch (UnsupportedEncodingException e) { } return value; } return request.getParameter(name); } } |
EncodingFilter
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public class EncodingFilter extends HttpFilter { public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain chain) throws IOException, ServletException { String charset = this.getInitParameter("charset"); if(charset == null || charset.isEmpty()) { charset = "UTF-8"; } response.setCharacterEncoding(charset); response.setContentType("text/html;charset=" + charset); EncodingRequest res = new EncodingRequest(request, charset); chain.doFilter(res, response); } } |
web.xml
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<filter> <filter-name>EncodingFilter</filter-name> <filter-class>cn.itcast.filter.EncodingFilter</filter-class> <init-param> <param-name>charset</param-name> <param-value>UTF-8</param-value> </init-param> </filter> <filter-mapping> <filter-name>EncodingFilter</filter-name> <url-pattern>/*</url-pattern> </filter-mapping> |