Filter学习（三）Filter(过滤器)常见应用

2023-08-28 19:23:40

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：

<filter>

      <filter-name>CharacterEncodingFilter</filter-name>

      <filter-class>com.web.filter.CharacterEncodingFilter</filter-class>

      <init-param>

          <param-name>charset</param-name>

          <param-value>UTF-8</param-value>

      </init-param>

  </filter>

  <filter-mapping>

      <filter-name>CharacterEncodingFilter</filter-name>

      <url-pattern>/*</url-pattern>

  </filter-mapping>

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：

<filter>

      <filter-name>NoCacheFilter</filter-name>

      <filter-class>com.web.filter.NoCacheFilter</filter-class>

  </filter>

  <filter-mapping>

      <filter-name>NoCacheFilter</filter-name>

        <!--只拦截Jsp请求-->

      <servlet-name>*.jsp</servlet-name>

  </filter-mapping>

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：

<!-- 配置缓存过滤器 -->

   <filter>

      <filter-name>CacheFilter</filter-name>

      <filter-class>com.web.filter.CacheFilter</filter-class>

       <!-- 配置要缓存的web资源以及缓存时间，以小时为单位 -->

      <init-param>

          <param-name>css</param-name>

          <param-value>4</param-value>

      </init-param>

      <init-param>

          <param-name>jpg</param-name>

          <param-value>1</param-value>

      </init-param>

      <init-param>

          <param-name>js</param-name>

          <param-value>4</param-value>

      </init-param>

      <init-param>

          <param-name>png</param-name>

          <param-value>4</param-value>

      </init-param>

  </filter>

  <!-- 配置要缓存的web资源的后缀-->

  <filter-mapping>

      <filter-name>CacheFilter</filter-name>

      <url-pattern>*.jpg</url-pattern>

  </filter-mapping>

  <filter-mapping>

      <filter-name>CacheFilter</filter-name>

      <url-pattern>*.css</url-pattern>

  </filter-mapping>

  <filter-mapping>

      <filter-name>CacheFilter</filter-name>

      <url-pattern>*.js</url-pattern>

  </filter-mapping>

   <filter-mapping>

      <filter-name>CacheFilter</filter-name>

      <url-pattern>*.png</url-pattern>

  </filter-mapping>

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<cookies.length;i++){

            if(cookies[i].getName().equals("autologin")){

                value = cookies[i].getValue();

            }

        }

        //2.得到 cookie中的用户名和密码

        if(value!=null){

            String username = value.split("\\.")[0];

            String password = value.split("\\.")[1];

            //3.调用dao获取用户对应的密码

            UserDao dao = new UserDao();

            User user = dao.find(username);

            String dbpassword = user.getPassword();

            //4.检查用户带过来的md5的密码和数据库中的密码是否匹配,如匹配则自动登陆

            if(password.equals(WebUtils.md5(dbpassword))){

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

            }

        }

        chain.doFilter(request, response);

    }

    public void destroy() {

    }

    public void init(FilterConfig filterConfig) throws ServletException {

    }

}

　　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);

    }

}

码农公寓

一、统一全站字符编码

二、禁止浏览器缓存所有动态页面

三、控制浏览器缓存页面中的静态资源

四、实现用户自动登陆

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