Filter的常见应用
2018-11-12 06:53:30来源:博客园 阅读 ()
1.字符编码过滤器
实现功能,在a.jsp中填写用户名提交到b.jsp,在b.jsp中读取参数名。
a.jsp
<body> <form action="encoding/b.jsp" method="post"> name:<input type="text" name="username"/> <input type="submit" value="Submit"/> </form> </body>
b.jsp
<body> <% request.setCharacterEncoding("UTF-8");%> hello:${param.username} </body>
若需要读取参数的页面太多,需要在每一个页面都添加<% request.setCharacterEncoding("UTF-8");%>,该方法行不通。字符编码过滤器通过配置参数encoding指明使用何种字符编码,以处理Html Form请求参数的中文问题。
HttpFilter.java
package com.javaweb.Filter; import java.io.IOException; import javax.servlet.Filter; import javax.servlet.FilterChain; import javax.servlet.FilterConfig; import javax.servlet.ServletException; import javax.servlet.ServletRequest; import javax.servlet.ServletResponse; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public abstract class HttpFilter implements Filter { @Override public void destroy() { } /* * 原生的doFilter方法,在方法内部把ServletRequest和ServletResponse转为了HttpServletRequest和HttpServletResponse, * 并调用了doFilter(HttpServletRequest request,HttpServletResponse response,FilterChain filterchain)方法。 * 若编写Filter的过滤方法不建议直接继承该方法,而建议继承doFilter(HttpServletRequest request,HttpServletResponse response, * FilterChain filterchain)方法。 * */ @Override public void doFilter(ServletRequest req, ServletResponse resp, FilterChain filterchain) throws IOException, ServletException { HttpServletRequest request=(HttpServletRequest) req; HttpServletResponse response=(HttpServletResponse) resp; doFilter(request,response,filterchain); } //抽象方法,为Http请求定制必须实现的方法。 public abstract void doFilter(HttpServletRequest request,HttpServletResponse response,FilterChain filterchain) throws IOException, ServletException; private FilterConfig filterconfig; //不建议子类直接覆盖,若直接覆盖,将可能会导致filterConfig成员变量初始化失败。 @Override public void init(FilterConfig filterconfig) throws ServletException { this.filterconfig =filterconfig; init(); } //供子类继承的初始化方法,可以通过getFilterConfig()获取FilterConfig对象。 public void init(){} //直接返回init(ServletConfig)的ServletConfig对象。 public FilterConfig getFilterConfig(){ return filterconfig; } }
encodingFilter.java
package com.javaweb.Filter; import java.io.IOException; import javax.servlet.FilterChain; import javax.servlet.ServletException; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.javaweb.Filter.HttpFilter; public class encodingFilter extends HttpFilter { @Override public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain filterchain) throws IOException, ServletException { //2.指定请求的字符编码为1中读取的字符编码 request.setCharacterEncoding(encoding); //3.调用chain.doFile()方法放行请求 filterchain.doFilter(request,response); } private String encoding; public void init(){ //1.读取配置文件web.xml中的字符编码方式 encoding=getFilterConfig().getServletContext().getInitParameter("encoding"); } }
在web.xml中进行配置,首先指定当前页的字符编码:
<context-param> <param-name>encoding</param-name> <param-value>UTF-8</param-value> </context-param>
配置encodingFilter,
<filter> <filter-name>encodingFilter</filter-name> <filter-class>com.javaweb.Filter.encodingFilter</filter-class> </filter> <filter-mapping> <filter-name>encodingFilter</filter-name> <url-pattern>/encoding/*</url-pattern> </filter-mapping>
这样,不用在b.jsp页面指定<% request.setCharacterEncoding("UTF-8");%>也不会出现输入中文的乱码问题。
2.检测用户是否登录过的过滤器
系统中的某些页面只有在正常登录后才可以使用,用户请求这些页面时要检查session中有无该用户的信息,但在所有的页面加上session的判断相当麻烦。因此需要重新编写一个用于检测用户是否登录的过滤器,如果用户未登录,则重定向到指定的登录页面。
示例代码:
a.jsp
<body> <h4>AAA page</h4> <a href="login/list.jsp">return list...</a> </body>
b.jsp
<body> <h4>BBB page</h4> <a href="login/list.jsp">return list...</a> </body>
c.jsp
<body> <h4>CCC page</h4> <a href="login/list.jsp">return list...</a> </body>
d.jsp
<body> <h4>DDD page</h4> <a href="login/list.jsp">return list...</a> </body>
e.jsp
<body> <h4>EEE page</h4> <a href="login/list.jsp">return list...</a> </body>
list.jsp
<body> <a href="login/a.jsp">AAA</a> <br><br> <a href="login/b.jsp">BBB</a> <br><br> <a href="login/c.jsp">CCC</a> <br><br> <a href="login/d.jsp">DDD</a> <br><br> <a href="login/e.jsp">EEE</a> <br><br> </body>
login.jsp
<body> <form action="login/doLogin.jsp" method="post"> username:<input type="text" name="username"/> <input type="submit" value="Submit"/> </form> </body>
doLogin.jsp
<body> <% String username=request.getParameter("username"); if(username!=null){ session.setAttribute(application.getInitParameter("sessionKey"),username); response.sendRedirect("list.jsp"); }else{ response.sendRedirect("login.jsp"); } %> </body>
loginFilter.java
package com.javaweb.Filter; import java.io.IOException; import java.util.Arrays; import java.util.List; import javax.servlet.FilterChain; import javax.servlet.ServletContext; import javax.servlet.ServletException; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.javaweb.Filter.HttpFilter; public class loginFilter extends HttpFilter { String sessionKey; String redirectUrl; String uncheckedUrls; @Override public void init() { ServletContext servletcontext=getFilterConfig().getServletContext(); sessionKey=servletcontext.getInitParameter("sessionKey"); redirectUrl=servletcontext.getInitParameter("redirectPage"); uncheckedUrls=servletcontext.getInitParameter("uncheckedPage"); } @Override public void doFilter(HttpServletRequest request, HttpServletResponse response, FilterChain filterchain) throws IOException, ServletException { //b.jsp c.jsp d.jsp ... String servletPath=request.getServletPath(); //检查uncheckedUrls是否包含请求的URL,若包含,放行 List<String> Urls=Arrays.asList(uncheckedUrls.split(",")); if (Urls.contains(servletPath)){ filterchain.doFilter(request, response); return; } //从sessionKey中检查是否包含sessionKey对应的值,若值不存在,则重定向到redirectUrl Object user=request.getSession().getAttribute(sessionKey); if (user==null){ response.sendRedirect(request.getContextPath()+redirectUrl); return; } //若存在,则放行 filterchain.doFilter(request, response); } }
在web.xml中进行配置:
<context-param> <param-name>redirectPage</param-name> <param-value>/login/login.jsp</param-value> </context-param> <context-param> <param-name>uncheckedPage</param-name> <param-value>/login/a.jsp,/login/doLogin.jsp,/login/list.jsp,/login/login.jsp</param-value> </context-param> <context-param> <param-name>sessionKey</param-name> <param-value>sessionValue</param-value> </context-param>
<filter>
<filter-name>loginFilter</filter-name>
<filter-class>com.javaweb.Filter.loginFilter</filter-class>
</filter>
<filter-mapping>
<filter-name>loginFilter</filter-name>
<url-pattern>/login/*</url-pattern>
</filter-mapping>
AAA页面不需要登录即可访问,
点击BBB(及之后的)超链接时,跳转到登录页面:
填写登录名之后再访问BBB,可以跳转到BBB页面:
标签:
版权申明:本站文章部分自网络,如有侵权,请联系:west999com@outlook.com
特别注意:本站所有转载文章言论不代表本站观点,本站所提供的摄影照片,插画,设计作品,如需使用,请与原作者联系,版权归原作者所有
- JVM常见面试题解析 2020-06-11
- 如何优雅地停止 Spring Boot 应用? 2020-06-08
- 详解SpringBoot(2.3)应用制作Docker镜像(官方方案) 2020-06-08
- 体验SpringBoot(2.3)应用制作Docker镜像(官方方案) 2020-06-07
- 如何在Spring Boot应用启动之后立刻执行一段逻辑?本文详解 2020-06-05
IDC资讯: 主机资讯 注册资讯 托管资讯 vps资讯 网站建设
网站运营: 建站经验 策划盈利 搜索优化 网站推广 免费资源
网络编程: Asp.Net编程 Asp编程 Php编程 Xml编程 Access Mssql Mysql 其它
服务器技术: Web服务器 Ftp服务器 Mail服务器 Dns服务器 安全防护
软件技巧: 其它软件 Word Excel Powerpoint Ghost Vista QQ空间 QQ FlashGet 迅雷
网页制作: FrontPages Dreamweaver Javascript css photoshop fireworks Flash