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javaweb学习总结(四十六)——Filter(过滤器)常见应用详解编程语言

应用学习编程语言 详解 总结 常见 过滤器 filter
2023-06-13 09:20:31 时间
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

 1 package me.gacl.web.filter; 

 3 import java.io.IOException; 

 4 import javax.servlet.Filter; 

 5 import javax.servlet.FilterChain; 

 6 import javax.servlet.FilterConfig; 

 7 import javax.servlet.ServletException; 

 8 import javax.servlet.ServletRequest; 

 9 import javax.servlet.ServletResponse; 

10 import javax.servlet.http.HttpServletRequest; 

11 import javax.servlet.http.HttpServletRequestWrapper; 

12 import javax.servlet.http.HttpServletResponse; 

14 /** 

15 * @ClassName: CharacterEncodingFilter 

16 * @Description: 此过滤器用来解决全站中文乱码问题 

17 * @author: 孤傲苍狼 

18 * @date: 2014-8-31 下午11:09:37 

19 * 

20 */ 

21 public class CharacterEncodingFilter implements Filter { 

23 private FilterConfig filterConfig = null; 

24 //设置默认的字符编码 

25 private String defaultCharset = "UTF-8"; 

27 public void doFilter(ServletRequest req, ServletResponse resp, 

28 FilterChain chain) throws IOException, ServletException { 

30 HttpServletRequest request = (HttpServletRequest) req; 

31 HttpServletResponse response = (HttpServletResponse) resp; 

32 String charset = filterConfig.getInitParameter("charset"); 

33 if(charset==null){ 

34 charset = defaultCharset; 

35 } 

36 request.setCharacterEncoding(charset); 

37 response.setCharacterEncoding(charset); 

38 response.setContentType("text/html;charset="+charset); 

40 MyCharacterEncodingRequest requestWrapper = new MyCharacterEncodingRequest(request); 

41 chain.doFilter(requestWrapper, response); 

42 } 

44 public void init(FilterConfig filterConfig) throws ServletException { 

45 //得到过滤器的初始化配置信息 

46 this.filterConfig = filterConfig; 

47 } 

49 public void destroy() { 

51 } 

52 } 

54 /* 

55 1.实现与被增强对象相同的接口 

56 2、定义一个变量记住被增强对象 

57 3、定义一个构造器，接收被增强对象 

58 4、覆盖需要增强的方法 

59 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 

60 */ 

62 class MyCharacterEncodingRequest extends HttpServletRequestWrapper{ 

64 private HttpServletRequest request; 

65 public MyCharacterEncodingRequest(HttpServletRequest request) { 

66 super(request); 

67 this.request = request; 

68 } 

69 /* 重写getParameter方法 

70 * @see javax.servlet.ServletRequestWrapper#getParameter(java.lang.String) 

71 */ 

72 @Override 

73 public String getParameter(String name) { 

75 try{ 

76 //获取参数的值 

77 String value= this.request.getParameter(name); 

78 if(value==null){ 

79 return null; 

80 } 

81 //如果不是以get方式提交数据的，就直接返回获取到的值 

82 if(!this.request.getMethod().equalsIgnoreCase("get")) { 

83 return value; 

84 }else{ 

85 //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 

86 value = new String(value.getBytes("ISO8859-1"),this.request.getCharacterEncoding()); 

87 return value; 

88 } 

89 }catch (Exception e) { 

90 throw new RuntimeException(e); 

91 } 

92 } 

93 }

web.xml文件中的配置如下：

 1 filter 

 2 filter-name CharacterEncodingFilter /filter-name 

 3 filter-class me.gacl.web.filter.CharacterEncodingFilter /filter-class 

 4 init-param 

 5 param-name charset /param-name 

 6 param-value UTF-8 /param-value 

 7 /init-param 

 8 /filter 

10 filter-mapping 

11 filter-name CharacterEncodingFilter /filter-name 

12 url-pattern /* /url-pattern 

13 /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：

1 response.setDateHeader("Expires",-1); 

2 response.setHeader("Cache-Control","no-cache"); 

3 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。
10 import javax.servlet.ServletResponse; 11 import javax.servlet.http.HttpServletRequest; 12 import javax.servlet.http.HttpServletResponse; 14 /** 15 * @ClassName: NoCacheFilter 16 * @Description: 禁止浏览器缓存所有动态页面 17 * @author: 孤傲苍狼 18 * @date: 2014-8-31 下午11:25:40 19 * 20 */ 21 public class NoCacheFilter implements Filter { 24 public void doFilter(ServletRequest req, ServletResponse resp, 25 FilterChain chain) throws IOException, ServletException { 26 //把ServletRequest强转成HttpServletRequest 27 HttpServletRequest request = (HttpServletRequest) req; 28 //把ServletResponse强转成HttpServletResponse 29 HttpServletResponse response = (HttpServletResponse) resp; 30 //禁止浏览器缓存所有动态页面 31 response.setDateHeader("Expires", -1); 32 response.setHeader("Cache-Control", "no-cache"); 33 response.setHeader("Pragma", "no-cache"); 35 chain.doFilter(request, response); 36 } 38 public void init(FilterConfig filterConfig) throws ServletException { 40 } 42 public void destroy() { 44 } 45 }

web.xml文件中的配置如下：

 1 filter 

 2 filter-name NoCacheFilter /filter-name 

 3 filter-class me.gacl.web.filter.NoCacheFilter /filter-class 

 4 /filter 

 6 filter-mapping 

 7 filter-name NoCacheFilter /filter-name 

 8 !--只拦截Jsp请求-- 

 9 servlet-name *.jsp /servlet-name 

10 /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。

 1 package me.gacl.web.filter; 

 3 import java.io.IOException; 

 5 import javax.servlet.Filter; 

 6 import javax.servlet.FilterChain; 

 7 import javax.servlet.FilterConfig; 

 8 import javax.servlet.ServletException; 

 9 import javax.servlet.ServletRequest; 

10 import javax.servlet.ServletResponse; 

11 import javax.servlet.http.HttpServletRequest; 

12 import javax.servlet.http.HttpServletResponse; 

14 /** 

15 * @ClassName: CacheFilter 

16 * @Description: 控制缓存的filter 

17 * @author: 孤傲苍狼 

18 * @date: 2014-9-1 下午9:39:38 

19 * 

20 */ 

21 public class CacheFilter implements Filter { 

23 private FilterConfig filterConfig; 

25 public void doFilter(ServletRequest req, ServletResponse resp, 

26 FilterChain chain) throws IOException, ServletException { 

28 HttpServletRequest request = (HttpServletRequest) req; 

29 HttpServletResponse response = (HttpServletResponse) resp; 

31 //1.获取用户想访问的资源 

32 String uri = request.getRequestURI(); 

34 //2.得到用户想访问的资源的后缀名 

35 String ext = uri.substring(uri.lastIndexOf(".")+1); 

37 //得到资源需要缓存的时间 

38 String time = filterConfig.getInitParameter(ext); 

39 if(time!=null){ 

40 long t = Long.parseLong(time)*3600*1000; 

41 //设置缓存 

42 response.setDateHeader("expires", System.currentTimeMillis() + t); 

43 } 

45 chain.doFilter(request, response); 

47 } 

49 public void init(FilterConfig filterConfig) throws ServletException { 

50 this.filterConfig = filterConfig; 

51 } 

53 public void destroy() { 

55 } 

56 }

web.xml文件中的配置如下：

 1 !-- 配置缓存过滤器 -- 

 2 filter 

 3 filter-name CacheFilter /filter-name 

 4 filter-class me.gacl.web.filter.CacheFilter /filter-class 

 5 !-- 配置要缓存的web资源以及缓存时间，以小时为单位 -- 

 6 init-param 

 7 param-name css /param-name 

 8 param-value 4 /param-value 

 9 /init-param 

10 init-param 

11 param-name jpg /param-name 

12 param-value 1 /param-value 

13 /init-param 

14 init-param 

15 param-name js /param-name 

16 param-value 4 /param-value 

17 /init-param 

18 init-param 

19 param-name png /param-name 

20 param-value 4 /param-value 

21 /init-param 

22 /filter 

23 !-- 配置要缓存的web资源的后缀-- 

24 filter-mapping 

25 filter-name CacheFilter /filter-name 

26 url-pattern *.jpg /url-pattern 

27 /filter-mapping 

29 filter-mapping 

30 filter-name CacheFilter /filter-name 

31 url-pattern *.css /url-pattern 

32 /filter-mapping 

34 filter-mapping 

35 filter-name CacheFilter /filter-name 

36 url-pattern *.js /url-pattern 

37 /filter-mapping 

38 filter-mapping 

39 filter-name CacheFilter /filter-name 

40 url-pattern *.png /url-pattern 

41 /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

 1 package me.gacl.web.controller; 

 3 import java.io.IOException; 

 5 import javax.servlet.ServletException; 

 6 import javax.servlet.http.Cookie; 

 7 import javax.servlet.http.HttpServlet; 

 8 import javax.servlet.http.HttpServletRequest; 

 9 import javax.servlet.http.HttpServletResponse; 

11 import me.gacl.dao.UserDao; 

12 import me.gacl.domain.User; 

13 import me.gacl.util.WebUtils; 

15 public class LoginServlet extends HttpServlet { 

17 public void doGet(HttpServletRequest request, HttpServletResponse response) 

18 throws ServletException, IOException { 

20 String username = request.getParameter("username"); 

21 String password = request.getParameter("password"); 

23 UserDao dao = new UserDao(); 

24 User user = dao.find(username, password); 

25 if(user==null){ 

26 request.setAttribute("message", "用户名或密码不对！！"); 

27 request.getRequestDispatcher("/message.jsp").forward(request, response); 

28 return; 

29 } 

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

31 //发送自动登陆cookie给客户端浏览器进行存储 

32 sendAutoLoginCookie(request,response,user); 

33 request.getRequestDispatcher("/index.jsp").forward(request, response); 

34 } 

36 /** 

37 * @Method: sendAutoLoginCookie 

38 * @Description: 发送自动登录cookie给客户端浏览器 

39 * @Anthor:孤傲苍狼 

40 * 

41 * @param request 

42 * @param response 

43 * @param user 

44 */ 

45 private void sendAutoLoginCookie(HttpServletRequest request, HttpServletResponse response, User user) { 

46 if (request.getParameter("logintime")!=null) { 

47 int logintime = Integer.parseInt(request.getParameter("logintime")); 

48 //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 

49 Cookie cookie = new Cookie("autologin",user.getUsername() + "." + WebUtils.md5(user.getPassword())); 

50 //设置cookie的有效期 

51 cookie.setMaxAge(logintime); 

52 //设置cookie的有效路径 

53 cookie.setPath(request.getContextPath()); 

54 //将cookie写入到客户端浏览器 

55 response.addCookie(cookie); 

56 } 

57 } 

59 public void doPost(HttpServletRequest request, HttpServletResponse response) 

60 throws ServletException, IOException { 

62 doGet(request, response); 

63 } 

65 }

处理用户自动登录的过滤器：AutoLoginFilter

 1 package me.gacl.web.filter; 

 3 import java.io.IOException; 

 5 import javax.servlet.Filter; 

 6 import javax.servlet.FilterChain; 

 7 import javax.servlet.FilterConfig; 

 8 import javax.servlet.ServletException; 

 9 import javax.servlet.ServletRequest; 

10 import javax.servlet.ServletResponse; 

11 import javax.servlet.http.Cookie; 

12 import javax.servlet.http.HttpServletRequest; 

13 import javax.servlet.http.HttpServletResponse; 

15 import me.gacl.dao.UserDao; 

16 import me.gacl.domain.User; 

17 import me.gacl.util.WebUtils; 

19 public class AutoLoginFilter implements Filter { 

21 public void doFilter(ServletRequest req, ServletResponse resp, 

22 FilterChain chain) throws IOException, ServletException { 

24 HttpServletRequest request = (HttpServletRequest) req; 

25 HttpServletResponse response = (HttpServletResponse) resp; 

26 //如果已经登录了，就直接chain.doFilter(request, response)放行 

27 if(request.getSession().getAttribute("user")!=null){ 

28 chain.doFilter(request, response); 

29 return; 

30 } 

32 //1.得到用户带过来的authlogin的cookie 

33 String value = null; 

34 Cookie cookies[] = request.getCookies(); 

35 for(int i=0;cookies!=null i cookies.length;i++){ 

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

37 value = cookies[i].getValue(); 

38 } 

39 } 

41 //2.得到 cookie中的用户名和密码 

42 if(value!=null){ 

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

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

46 //3.调用dao获取用户对应的密码 

47 UserDao dao = new UserDao(); 

48 User user = dao.find(username); 

49 String dbpassword = user.getPassword(); 

51 //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 

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

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

54 } 

55 } 

57 chain.doFilter(request, response); 

58 } 

60 public void destroy() { 

62 } 

64 public void init(FilterConfig filterConfig) throws ServletException { 

66 } 

67 }

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：

 1 package me.gacl.web.controller; 

 3 import java.io.IOException; 

 5 import javax.servlet.ServletException; 

 6 import javax.servlet.http.Cookie; 

 7 import javax.servlet.http.HttpServlet; 

 8 import javax.servlet.http.HttpServletRequest; 

 9 import javax.servlet.http.HttpServletResponse; 

11 public class CancelAutoLoginServlet extends HttpServlet { 

13 public void doGet(HttpServletRequest request, HttpServletResponse response) 

14 throws ServletException, IOException { 

15 //移除存储在session中的user 

16 request.getSession().removeAttribute("user"); 

17 //移除自动登录的cookie 

18 removeAutoLoginCookie(request,response); 

19 //注销用户后跳转到登录页面 

20 request.getRequestDispatcher("/login.jsp").forward(request, response); 

21 } 

23 /** 

24 * @Method: removeAutoLoginCookie 

25 * @Description: 删除自动登录cookie， 

26 * 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， 

27 * 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 

28 * @Anthor:孤傲苍狼 

29 * 

30 * @param request 

31 * @param response 

32 */ 

33 private void removeAutoLoginCookie(HttpServletRequest request, HttpServletResponse response) { 

34 //创建一个名字为autologin的cookie 

35 Cookie cookie = new Cookie("autologin",""); 

36 //将cookie的有效期设置为0，命令浏览器删除该cookie 

37 cookie.setMaxAge(0); 

38 //设置要删除的cookie的path 

39 cookie.setPath(request.getContextPath()); 

40 response.addCookie(cookie); 

41 } 

43 public void doPost(HttpServletRequest request, HttpServletResponse response) 

44 throws ServletException, IOException { 

45 doGet(request, response); 

46 } 

47 }

以上就是过滤器的几个常见应用场景。

原创文章，作者：Maggie-Hunter，如若转载，请注明出处：https://blog.ytso.com/11367.html

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