JavaWeb的Filter过滤器应用

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过滤器应用案例

分ip统计网站的访问次数

count

192.168.1.111

192.168.1.112

统计工作需要在所有资源执行前，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>

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！！！）

Ø Map需要在Filter中用来保存数据

Ø Map需要在页面使用，打印Map中的数据

思路分析

因为一个网站可能有多个页面，无论哪个页面被访问，都要统计访问次数，所以使用过滤器最为方便。

因为需要分IP统计，所以可以在过滤器中创建一个Map，使用IP为key，访问次数为value。当有用户访问时，获取请求的IP，如果IP在Map中存在，说明以前访问过，那么在访问次数上加1，即可；IP在Map中不存在，那么设置次数为1。

把这个Map存放到ServletContext中！

代码描述

index.jsp

<body>

<h1>分IP统计访问次数</h1>

<tablealign="center"width="50%"border="1">

<tr>

</tr>

<c:forEachitems="${applicationScope.ipCountMap }" var="entry">

<tr>

<td>${entry.key }</td>

<td>${entry.value }</td>

</tr>

</c:forEach>

</table>

</body>

IPFilter

publicclass IPFilter implements Filter {

private ServletContextcontext;

publicvoid init(FilterConfig fConfig) throws ServletException {

context = fConfig.getServletContext();

Map<String, Integer> ipCountMap = Collections

.synchronizedMap(new LinkedHashMap<String, Integer>());

context.setAttribute("ipCountMap", ipCountMap);

}

@SuppressWarnings("unchecked")

publicvoid 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);

}

publicvoid destroy() {}

}

<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>

用户权限控制

RBAC à 基于角色的权限控制

l tb_user

l tb_role

l tb_userrole

l tb_menu(增、删、改、查)

l tb_rolemenu

需求说明

我们给出三个页面：index.jsp、user.jsp、admin.jsp。

l index.jsp：谁都可以访问，没有限制；

l user.jsp：只有登录用户才能访问；

l admin.jsp：只有管理员才能访问。

思路分析

设计User类：username、password、grade，其中grade表示用户等级，1表示普通用户，2表示管理员用户。

当用户登录成功后，把user保存到session中。

创建LoginFilter，它有两种过滤方式：

l 如果访问的是user.jsp，查看session中是否存在user；

l 如果访问的是admin.jsp，查看session中是否存在user，并且user的grade等于2。

代码描述

User.java

publicclass User {

private Stringusername;

private Stringpassword;

privateint grade;

//get…set方法

}

在UserService中创建一个Map，用来保存所有用户。Map中的key中用户名，value为User对象。

UserService.java

publicclass UserService {

privatestatic 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) returnnull;

return user.getPassword().equals(password) ? user :null;

}

<body>

<pstyle="font-weight:900; color:red">${msg }</p>

<formaction="<c:urlvalue='/LoginServlet'/>"method="post">

用户名：<inputtype="text"name="username"/><br/>

密　码：<inputtype="password"name="password"/><br/>

<inputtype="submit"value="登录"/>

</form>

</body>

index.jsp

<body>

<h3>${user.username }</h3>

<hr/>

<ahref="<c:urlvalue='/login.jsp'/>">登录</a><br/>

<ahref="<c:urlvalue='/user/user.jsp'/>">用户页面</a><br/>

<ahref="<c:urlvalue='/admin/admin.jsp'/>">管理员页面</a>

</body>

/user/user.jsp

<body>

<h3>${user.username }</h3>

<hr/>

</body>

/admin/admin.jsp

<body>

<h1>管理员页面</h1>

<h3>${user.username }</h3>

<hr/>

</body>

LoginServlet

publicclass LoginServlet extends HttpServlet {

publicvoid 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","用户名或密码错误");

request.getRequestDispatcher("/login.jsp").forward(request, response);

} else {

request.getSession().setAttribute("user", user);

request.getRequestDispatcher("/index.jsp").forward(request, response);

}

LoginUserFilter.java

<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>

publicclass LoginUserFilter implements Filter {

publicvoid destroy() {}

publicvoid init(FilterConfig fConfig) throws ServletException {}

publicvoid 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("您还没有登录");

return;

}

chain.doFilter(request, response);

}

LoginAdminFilter.java

<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>

publicclass LoginAdminFilter implements Filter {

publicvoid destroy() {}

publicvoid init(FilterConfig fConfig) throws ServletException {}

publicvoid 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("您还没有登录!");

return;

}

if(user.getGrade() < 2) {

response.getWriter().print("您的等级不够！");

return;

}

chain.doFilter(request, response);

}

禁止资源缓存

浏览器只是要缓存页面，这对我们在开发时测试很不方便，所以我们可以过滤所有资源，然后添加去除所有缓存！

publicclass NoCacheFilter extends HttpFilter {

publicvoid 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中文编码

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”);

需求说明

乱码问题：

l 获取请求参数中的乱码问题；

Ø POST请求：request.setCharacterEncoding(“utf-8”)；

Ø GET请求：newString(request.getParameter(“xxx”).getBytes(“iso-8859-1”), “utf-8”)；

l 响应的乱码问题：response.setContextType(“text/html;charset=utf-8”)。

思路分析

全站乱码问题的难点：处理GET请求参数的问题。

publicclass EncodingFilter extends HttpFilter {

publicvoid 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请求，当执行目标Servlet时，Servlet中调用request.getParameter()方法时，就会根据request.setCharacterEncoding()设置的编码来转码！这说明在过滤器中调用request.setCharacterEncoding()方法会影响在目标Servlet中的request.getParameter()方法的行为！

但是如果是GET请求， request只有getParameter()，而没有setParameter()方法。

下面是三种对a对象进行增强的手段：

代码描述

EncodingRequest

publicclass EncodingRequest extends HttpServletRequestWrapper {

private Stringcharset;

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) {}

} elseif(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

publicclass EncodingFilter extends HttpFilter {

publicvoid 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

<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>

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