Filter学习（三）Filter(过滤器)常见应用-白红宇

Filter学习（三）Filter(过滤器)常见应用

阅读量：5967 次

发布时间：2019-06-19

本文共 11833 字，大约阅读时间需要 39 分钟。

一、统一全站字符编码

　　通过配置参数charset指明使用何种字符编码,以处理Html Form请求参数的中文问题：

package com.web.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.HttpServletRequestWrapper;import javax.servlet.http.HttpServletResponse;/*** @ClassName: CharacterEncodingFilter* @Description: 此过滤器用来解决全站中文乱码问题* @author: hdb* @date: 2017-8-31 下午11:09:37**/ public class CharacterEncodingFilter implements Filter {    private FilterConfig filterConfig = null;    //设置默认的字符编码    private String defaultCharset = "UTF-8";    public void doFilter(ServletRequest req, ServletResponse resp,            FilterChain chain) throws IOException, ServletException {                HttpServletRequest request = (HttpServletRequest) req;        HttpServletResponse response = (HttpServletResponse) resp;        String charset = filterConfig.getInitParameter("charset");        if(charset==null){            charset = defaultCharset;        }        request.setCharacterEncoding(charset);        response.setCharacterEncoding(charset);        response.setContentType("text/html;charset="+charset);                MyCharacterEncodingRequest requestWrapper = new MyCharacterEncodingRequest(request);        chain.doFilter(requestWrapper, response);    }    public void init(FilterConfig filterConfig) throws ServletException {        //得到过滤器的初始化配置信息        this.filterConfig = filterConfig;    }        public void destroy() {    }}/*1.实现与被增强对象相同的接口 2、定义一个变量记住被增强对象3、定义一个构造器，接收被增强对象4、覆盖需要增强的方法5、对于不想增强的方法，直接调用被增强对象（目标对象）的方法 */ class MyCharacterEncodingRequest extends HttpServletRequestWrapper{        private HttpServletRequest request;    public MyCharacterEncodingRequest(HttpServletRequest request) {        super(request);        this.request = request;    }    /* 重写getParameter方法     * @see javax.servlet.ServletRequestWrapper#getParameter(java.lang.String)     */    @Override    public String getParameter(String name) {                try{            //获取参数的值            String value= this.request.getParameter(name);            if(value==null){                return null;            }            //如果不是以get方式提交数据的，就直接返回获取到的值            if(!this.request.getMethod().equalsIgnoreCase("get")) {                return value;            }else{                //如果是以get方式提交数据的，就对获取到的值进行转码处理                value = new String(value.getBytes("ISO8859-1"),this.request.getCharacterEncoding());                return value;            }        }catch (Exception e) {            throw new RuntimeException(e);        }    }}

　　web.xml文件中的配置如下：


           
      
       CharacterEncodingFilter
            
      
       com.web.filter.CharacterEncodingFilter
            
                
       
        charset
                 
       
        UTF-8
             
        
         
           
      
       CharacterEncodingFilter
            
      
       /*

二、禁止浏览器缓存所有动态页面

　　有3 个HTTP响应头字段都可以禁止浏览器缓存当前页面，它们在 Servlet 中的示例代码如下：

response.setDateHeader("Expires",-1); response.setHeader("Cache-Control","no-cache"); response.setHeader("Pragma","no-cache");

　　并不是所有的浏览器都能完全支持上面的三个响应头，因此最好是同时使用上面的三个响应头。

Expires数据头：值为GMT时间值，为-1指浏览器不要缓存页面

Cache-Control响应头有两个常用值：

no-cache指浏览器不要缓存当前页面。

max-age:xxx指浏览器缓存页面xxx秒

package com.web.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;/*** @ClassName: NoCacheFilter* @Description: 禁止浏览器缓存所有动态页面* @author: hdb* @date: 2017-8-31 下午11:25:40**/ public class NoCacheFilter implements Filter {    public void doFilter(ServletRequest req, ServletResponse resp,            FilterChain chain) throws IOException, ServletException {        //把ServletRequest强转成HttpServletRequest        HttpServletRequest request = (HttpServletRequest) req;        //把ServletResponse强转成HttpServletResponse        HttpServletResponse response = (HttpServletResponse) resp;        //禁止浏览器缓存所有动态页面        response.setDateHeader("Expires", -1);        response.setHeader("Cache-Control", "no-cache");        response.setHeader("Pragma", "no-cache");                chain.doFilter(request, response);    }    public void init(FilterConfig filterConfig) throws ServletException {    }        public void destroy() {            }}

　　web.xml文件中的配置如下：


           
      
       NoCacheFilter
            
      
       com.web.filter.NoCacheFilter
        
         
           
      
       NoCacheFilter
              
            
      
       *.jsp

三、控制浏览器缓存页面中的静态资源

　　有些动态页面中引用了一些图片或css文件以修饰页面效果，这些图片和css文件经常是不变化的，所以为减轻服务器的压力，可以使用filter控制浏览器缓存这些文件，以提升服务器的性能。

package com.web.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;/*** @ClassName: CacheFilter* @Description: 控制缓存的filter* @author: hdb* @date: 2017-9-1 20:39:38**/ public class CacheFilter implements Filter {    private FilterConfig filterConfig;    public void doFilter(ServletRequest req, ServletResponse resp,            FilterChain chain) throws IOException, ServletException {            HttpServletRequest request = (HttpServletRequest) req;        HttpServletResponse response = (HttpServletResponse) resp;                //1.获取用户想访问的资源        String uri = request.getRequestURI();                 //2.得到用户想访问的资源的后缀名        String ext = uri.substring(uri.lastIndexOf(".")+1);                //得到资源需要缓存的时间        String time = filterConfig.getInitParameter(ext);        if(time!=null){            long t = Long.parseLong(time)*3600*1000;            //设置缓存            response.setDateHeader("expires", System.currentTimeMillis() + t);        }                chain.doFilter(request, response);    }    public void init(FilterConfig filterConfig) throws ServletException {        this.filterConfig = filterConfig;    }        public void destroy() {            }}

　　web.xml文件中的配置如下：


        
           
      
       CacheFilter
            
      
       com.web.filter.CacheFilter
             
            
                
       
        css
                 
       
        4
             
            
                
       
        jpg
                 
       
        1
             
            
                
       
        js
                 
       
        4
             
            
                
       
        png
                 
       
        4
             
        
       
       
           
      
       CacheFilter
            
      
       *.jpg
        
         
           
      
       CacheFilter
            
      
       *.css
        
         
           
      
       CacheFilter
            
      
       *.js
        
        
           
      
       CacheFilter
            
      
       *.png

四、实现用户自动登陆

　　思路是这样的：

　　1、在用户登陆成功后，发送一个名称为user的cookie给客户端，cookie的值为用户名和md5加密后的密码。

　　2、编写一个AutoLoginFilter，这个filter检查用户是否带有名称为user的cookie来，如果有，则调用dao查询cookie的用户名和密码是否和数据库匹配，匹配则向session中存入user对象（即用户登陆标记），以实现程序完成自动登陆。

　　核心代码如下：

　　处理用户登录的控制器：LoginServlet：

package com.web.controller;import java.io.IOException;import javax.servlet.ServletException; import javax.servlet.http.Cookie; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.dao.UserDao; import com.domain.User; import com.util.WebUtils; public class LoginServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { String username = request.getParameter("username"); String password = request.getParameter("password"); UserDao dao = new UserDao(); User user = dao.find(username, password); if(user==null){ request.setAttribute("message", "用户名或密码不对！！"); request.getRequestDispatcher("/message.jsp").forward(request, response); return; } request.getSession().setAttribute("user", user); //发送自动登陆cookie给客户端浏览器进行存储 sendAutoLoginCookie(request,response,user); request.getRequestDispatcher("/index.jsp").forward(request, response); } /** * @Method: sendAutoLoginCookie * @Description: 发送自动登录cookie给客户端浏览器 * @Anthor:hdb * * @param request * @param response * @param user */ private void sendAutoLoginCookie(HttpServletRequest request, HttpServletResponse response, User user) { if (request.getParameter("logintime")!=null) { int logintime = Integer.parseInt(request.getParameter("logintime")); //创建cookie,cookie的名字是autologin，值是用户登录的用户名和密码，用户名和密码之间使用.进行分割，密码经过md5加密处理 Cookie cookie = new Cookie("autologin",user.getUsername() + "." + WebUtils.md5(user.getPassword())); //设置cookie的有效期 cookie.setMaxAge(logintime); //设置cookie的有效路径 cookie.setPath(request.getContextPath()); //将cookie写入到客户端浏览器 response.addCookie(cookie); } } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }

　　处理用户自动登录的过滤器：AutoLoginFilter：

package com.web.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.Cookie; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import com.dao.UserDao; import com.domain.User; import com.util.WebUtils; public class AutoLoginFilter implements Filter { public void doFilter(ServletRequest req, ServletResponse resp, FilterChain chain) throws IOException, ServletException { HttpServletRequest request = (HttpServletRequest) req; HttpServletResponse response = (HttpServletResponse) resp; //如果已经登录了，就直接chain.doFilter(request, response)放行 if(request.getSession().getAttribute("user")!=null){ chain.doFilter(request, response); return; } //1.得到用户带过来的authlogin的cookie String value = null; Cookie cookies[] = request.getCookies(); for(int i=0;cookies!=null && i

　　如果想取消自动登录，那么可以在用户注销时删除自动登录cookie，核心代码如下：

package com.web.controller;import java.io.IOException;import javax.servlet.ServletException; import javax.servlet.http.Cookie; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class CancelAutoLoginServlet extends HttpServlet { public void doGet(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { //移除存储在session中的user request.getSession().removeAttribute("user"); //移除自动登录的cookie removeAutoLoginCookie(request,response); //注销用户后跳转到登录页面 request.getRequestDispatcher("/login.jsp").forward(request, response); } /** * @Method: removeAutoLoginCookie * @Description: 删除自动登录cookie， * JavaWeb中删除cookie的方式就是新创建一个cookie，新创建的cookie与要删除的cookie同名， * 设置新创建的cookie的cookie的有效期设置为0，有效路径与要删除的cookie的有效路径相同 * @Anthor:hdb * * @param request * @param response */ private void removeAutoLoginCookie(HttpServletRequest request, HttpServletResponse response) { //创建一个名字为autologin的cookie Cookie cookie = new Cookie("autologin",""); //将cookie的有效期设置为0，命令浏览器删除该cookie cookie.setMaxAge(0); //设置要删除的cookie的path cookie.setPath(request.getContextPath()); response.addCookie(cookie); } public void doPost(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { doGet(request, response); } }

转载于:https://www.cnblogs.com/huangdabing/p/9217400.html

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