javaweb中Filter(过滤器)的常见应用

2019-11-26 14:43:54

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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 me.gacl.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*/ 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>me.gacl.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 me.gacl.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: 孤傲苍狼* @date: 2014-8-31 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>me.gacl.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 me.gacl.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*/ 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>me.gacl.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 me.gacl.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 me.gacl.dao.UserDao;import me.gacl.domain.User;import me.gacl.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  * @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 me.gacl.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 me.gacl.dao.UserDao;import me.gacl.domain.User;import me.gacl.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 me.gacl.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  * @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);  }}

以上就是过滤器的几个常见应用场景，希望对大家的学习有所帮助。

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