Java_常瑞鹏 Filter常见的应用

• Z时代
• 2024-01-10
• 分类：综合

一、Filter常见的应用（2）------不缓存页面

1、禁止浏览器缓存所有动态页面的过滤器：

（1）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中的实例代码如下：response.setDateHeader("Expires",-1);

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

response.setHeader("Pragma","no-cache");

（2）、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。

（3）Expires数据头：值为GMT时间值，为-1指浏览器不要缓存页面。

2、Cache-Control响应头有两个常用值：

（1）no-cache指浏览器不要缓存当前页面

（2）max-age:xxx指浏览器缓存页面xxx秒。

实例：

[java]

view plaincopyprint?

1. package com.hbsi.filter;

3. import java.io.IOException;

5. import javax.servlet.Filter;

7. import javax.servlet.FilterChain;

9. import javax.servlet.FilterConfig;

11. import javax.servlet.ServletException;

13. import javax.servlet.ServletRequest;

15. import javax.servlet.ServletResponse;

17. import javax.servlet.http.HttpServletRequest;

19. import javax.servlet.http.HttpServletResponse;

21. public class NoCatchFilter

    implements Filter {

23. public void destroy() {

25. // TODO Auto-generated method stub

27. }

29. public void doFilter(ServletRequest request, ServletResponse response,

31. FilterChain chain) throws IOException, ServletException {

33. HttpServletRequest req=(HttpServletRequest) request;

35. HttpServletResponse resp=(HttpServletResponse) response;

37. resp.setDateHeader("expires",-1);

39. resp.setHeader("Cache-Control","no-cache");

41. resp.setHeader("Pragma","no-cache");

43. chain.doFilter(req, resp);
45. }

48. public void init(FilterConfig filterConfig)

    throws ServletException {

50. // TODO Auto-generated method stub

52. }
54. }

package com.hbsi.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;
public class NoCatchFilter implements Filter {
public void destroy() {
// TODO Auto-generated method stub
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest req=(HttpServletRequest) request;
HttpServletResponse resp=(HttpServletResponse) response;
resp.setDateHeader("expires",-1);
resp.setHeader("Cache-Control","no-cache");
resp.setHeader("Pragma","no-cache");
chain.doFilter(req, resp);
}
public void init(FilterConfig filterConfig) throws ServletException {
// TODO Auto-generated method stub 
}
}

二、Filter常见的应用（3）------控制浏览器缓存页面中的静态资源的过滤器

1、场景：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。

实例：

[java]

view plaincopyprint?

1. package com.hbsi.filter;

4. import java.io.IOException;

7. import javax.servlet.Filter;

9. import javax.servlet.FilterChain;

11. import javax.servlet.FilterConfig;

13. import javax.servlet.ServletException;

15. import javax.servlet.ServletRequest;

17. import javax.servlet.ServletResponse;

19. import javax.servlet.http.HttpServletRequest;

21. import javax.servlet.http.HttpServletResponse;

23. public class ExpiresFilter

    implements Filter {

25. private FilterConfig config;

27. public void destroy() {

29. // TODO Auto-generated method stub

31. }

33. public void doFilter(ServletRequest request, ServletResponse response,

35. FilterChain chain) throws IOException, ServletException {

37. HttpServletRequest req=(HttpServletRequest) request;

39. HttpServletResponse resp=(HttpServletResponse) response;

41. String uri=req.getRequestURI();

43. if(uri.endsWith(".css")){

45. long time=Integer.parseInt(config.getInitParameter("css"))*1000;

47. resp.setDateHeader("expries", System.currentTimeMillis()+time);

49. }else if(uri.endsWith(".jpg")){

51. long time=Integer.parseInt(config.getInitParameter("jpg"))*1000;

53. resp.setDateHeader("expries",System.currentTimeMillis()+time);

55. }else if(uri.endsWith(".js")){

57. long time=Integer.parseInt(config.getInitParameter("js"))*1000;

59. resp.setDateHeader("expries",System.currentTimeMillis()+time);

61. }
63. chain.doFilter(req, resp);
65. }

67. public void init(FilterConfig filterConfig)

    throws ServletException {

69. this.config=filterConfig;

71. }
73. }

package com.hbsi.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;
public class ExpiresFilter implements Filter {
private FilterConfig config;
public void destroy() {
// TODO Auto-generated method stub
}
public void doFilter(ServletRequest request, ServletResponse response,
FilterChain chain) throws IOException, ServletException {
HttpServletRequest req=(HttpServletRequest) request;
HttpServletResponse resp=(HttpServletResponse) response;
String uri=req.getRequestURI();
if(uri.endsWith(".css")){
long time=Integer.parseInt(config.getInitParameter("css"))*1000;
resp.setDateHeader("expries", System.currentTimeMillis()+time);
}else if(uri.endsWith(".jpg")){
long time=Integer.parseInt(config.getInitParameter("jpg"))*1000;
resp.setDateHeader("expries",System.currentTimeMillis()+time);
}else if(uri.endsWith(".js")){
long time=Integer.parseInt(config.getInitParameter("js"))*1000;
resp.setDateHeader("expries",System.currentTimeMillis()+time);
}
chain.doFilter(req, resp);
}
public void init(FilterConfig filterConfig) throws ServletException {
this.config=filterConfig;
}
}

Web.xml中的过滤器配置：

[html]

view plaincopyprint?

1. <filter>

3. <filter-name>ExpiresFilter</filter-name>

5. <filter-class>com.hbsi.filter.ExpiresFilter</filter-class>

7. <init-param>

9. <param-name>css</param-name>

11. <param-value>120</param-value>

13. </init-param>

15. <init-param>

17. <param-name>jpg</param-name>

19. <param-value>120</param-value>

21. </init-param>

23. <init-param>

25. <param-name>js</param-name>

27. <param-value>120</param-value>

29. </init-param>

31. </filter>

33. <filter-mapping>

35. <filter-name>ExpiresFilter</filter-name>

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

39. </filter-mapping>

43. <filter-mapping>

45. <filter-name>ExpiresFilter</filter-name>

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

49. </filter-mapping>

53. <filter-mapping>

55. <filter-name>ExpiresFilter</filter-name>

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

59. </filter-mapping>

<filter>
 <filter-name>ExpiresFilter</filter-name>
 <filter-class>com.hbsi.filter.ExpiresFilter</filter-class>
 <init-param>
 <param-name>css</param-name>
 <param-value>120</param-value>
 </init-param>
 <init-param>
 <param-name>jpg</param-name>
 <param-value>120</param-value>
 </init-param>
 <init-param>
 <param-name>js</param-name>
 <param-value>120</param-value>
 </init-param>
 </filter>
 <filter-mapping>
 <filter-name>ExpiresFilter</filter-name>
 <url-pattern>*.css</url-pattern>
 </filter-mapping>
 <filter-mapping>
 <filter-name>ExpiresFilter</filter-name>
 <url-pattern>*.jpg</url-pattern>
 </filter-mapping>
 <filter-mapping>
 <filter-name>ExpiresFilter</filter-name>
 <url-pattern>*.js</url-pattern>
 </filter-mapping>

三、Filter常见的应用（4）------使用Filter实现URL级别的权限认证

情景：在实际开发中我们经常把一些执行敏感操作的servlet映射到一些特殊目录中，并用filter把这些特殊目录保护起来，限制只能拥有相应访问权限的用户才能访问这些目录下的资源。从而在我们系统中实现一种URL级别的权限功能。

要求：为使Filter具有通用性，Filter保护的资源和相应的访问权限通过filter参数的形式予以配置。

四、Filter常见的应用（5）------实现自动登录

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。

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。

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