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：
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。
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。