2007-03-16 20:03:02
标签：
Servlet 过滤器 版权声明：原创作品，允许转载，转载时请务必以超链接形式标明文章 原始出处 、作者信息和本声明。否则将追究法律责任。/article/4381680.html
|
本文主要介绍Servlet过滤器的基本原理
author: ZJ 2007-2-21
Blog: http://zhangjunhd.blog.51cto.com/
1．Servlet过滤器
1.1 什么是过滤器
过滤器是一个程序，它先于与之相关的servlet或JSP页面运行在服务器上。过滤器可附加到一个或多个servlet或JSP页面上，并且可以检查进入这些资源的请求信息。在这之后，过滤器可以作如下的选择：
①以常规的方式调用资源（即，调用servlet或JSP页面）。
②利用修改过的请求信息调用资源。
③调用资源，但在发送响应到客户机前对其进行修改。
④阻止该资源调用，代之以转到其他的资源，返回一个特定的状态代码或生成替换输出。
1.2 Servlet过滤器的基本原理
在Servlet作为过滤器使用时，它可以对客户的请求进行处理。处理完成后，它会交给下一个过滤器处理，这样，客户的请求在过滤链里逐个处理，直到请求发送到目标为止。例如，某网站里有提交“修改的注册信息”的网页，当用户填写完修改信息并提交后，服务器在进行处理时需要做两项工作：判断客户端的会话是否有效；对提交的数据进行统一编码。这两项工作可以在由两个过滤器组成的过滤链里进行处理。当过滤器处理成功后，把提交的数据发送到最终目标；如果过滤器处理不成功，将把视图派发到指定的错误页面。
2．Servlet过滤器开发步骤
开发Servlet过滤器的步骤如下：
①编写实现Filter接口的Servlet类。
②在web.xml中配置Filter。
开发一个过滤器需要实现Filter接口，Filter接口定义了以下方法：
①destory（）由Web容器调用，初始化此Filter。
②init（FilterConfig filterConfig）由Web容器调用，初始化此Filter。
③doFilter（ServletRequest request,ServletResponse response,FilterChain chain）具体过滤处理代码。
3．一个过滤器框架实例
SimpleFilter1.java
[align=left]package com.zj.sample;[/align]
[align=left]import java.io.IOException;[/align]
[align=left]import javax.servlet.Filter;[/align]
[align=left]import javax.servlet.FilterChain;[/align]
[align=left]import javax.servlet.FilterConfig;[/align]
[align=left]import javax.servlet.ServletException;[/align]
[align=left]import javax.servlet.ServletRequest;[/align]
[align=left]import javax.servlet.ServletResponse;[/align]
[align=left] [/align]
[align=left]publicclass SimpleFilter1 implements Filter {[/align]
[align=left] @SuppressWarnings("unused")[/align]
[align=left] private FilterConfig filterConfig;[/align]
[align=left] [/align]
[align=left] publicvoid init(FilterConfig config) throws ServletException {[/align]
[align=left] this.filterConfig = config;[/align]
[align=left] }[/align]
[align=left] [/align]
[align=left] publicvoid doFilter(ServletRequest request, ServletResponse response,[/align]
[align=left] FilterChain chain) {[/align]
[align=left] try {[/align]
[align=left] System.out.println("Within SimpleFilter1:Filtering the Request...");[/align]
[align=left] chain.doFilter(request, response);// 把处理发送到下一个过滤器[/align]
[align=left] System.out .println("Within SimpleFilter1:Filtering the Response...");[/align]
[align=left] } catch (IOException ioe) {[/align]
[align=left] ioe.printStackTrace();[/align]
[align=left] } catch (ServletException se) {[/align]
[align=left] se.printStackTrace();[/align]
[align=left] }[/align]
[align=left] }[/align]
[align=left] [/align]
[align=left] publicvoid destroy() {[/align]
[align=left] this.filterConfig = null;[/align]
[align=left] }[/align]
}
|
SimpleFilter2.java
[align=left]package com.zj.sample;[/align]
[align=left]import java.io.IOException;[/align]
[align=left]import javax.servlet.Filter;[/align]
[align=left]import javax.servlet.FilterChain;[/align]
[align=left]import javax.servlet.FilterConfig;[/align]
[align=left]import javax.servlet.ServletException;[/align]
[align=left]import javax.servlet.ServletRequest;[/align]
[align=left]import javax.servlet.ServletResponse;[/align]
[align=left] [/align]
[align=left]publicclass SimpleFilter2 implements Filter {[/align]
[align=left] @SuppressWarnings("unused")[/align]
[align=left] private FilterConfig filterConfig;[/align]
[align=left] [/align]
[align=left] publicvoid init(FilterConfig config) throws ServletException {[/align]
[align=left] this.filterConfig = config;[/align]
[align=left] }[/align]
[align=left] [/align]
[align=left] publicvoid doFilter(ServletRequest request, ServletResponse response,[/align]
[align=left] FilterChain chain) {[/align]
[align=left] try {[/align]
[align=left] System.out.println("Within SimpleFilter2:Filtering the Request...");[/align]
[align=left] chain.doFilter(request, response); // 把处理发送到下一个过滤器[/align]
[align=left] System.out.println("Within SimpleFilter2:Filtering the Response...");[/align]
[align=left] } catch (IOException ioe) {[/align]
[align=left] ioe.printStackTrace();[/align]
[align=left] } catch (ServletException se) {[/align]
[align=left] se.printStackTrace();[/align]
[align=left] }[/align]
[align=left] }[/align]
[align=left] [/align]
[align=left] publicvoid destroy() {[/align]
[align=left] this.filterConfig = null;[/align]
[align=left] }[/align]
}
|
web.xml
[align=left]<filter>[/align]
[align=left] <filter-name>filter1</filter-name>[/align]
[align=left] <filter-class>com.zj.sample.SimpleFilter1</filter-class>[/align]
[align=left]</filter>[/align]
[align=left]<filter-mapping>[/align]
[align=left] <filter-name>filter1</filter-name>[/align]
[align=left] <url-pattern>/*</url-pattern>//为所有的访问做过滤[/align]
[align=left]</filter-mapping>[/align]
[align=left] [/align]
[align=left]<filter>[/align]
[align=left] <filter-name>filter2</filter-name>[/align]
[align=left] <filter-class>com.zj.sample.SimpleFilter2</filter-class>[/align]
[align=left]</filter>[/align]
[align=left]<filter-mapping>[/align]
[align=left] <filter-name>filter2</filter-name>[/align]
[align=left] <url-pattern>/*</url-pattern>//为所有的访问做过滤[/align]
</filter-mapping>
|
打开web容器中任意页面输出结果：（注意过滤器执行的请求/响应顺序）
Within SimpleFilter1:Filtering the Request...
Within SimpleFilter2:Filtering the Request...
Within SimpleFilter2:Filtering the Response...
Within SimpleFilter1:Filtering the Response...
4．报告过滤器
我们来试验一个简单的过滤器，只要调用相关的servlet或JSP页面，它就打印一条消息到标准输出。为实现此功能，在doFilter方法中执行过滤行为。每当调用与这个过滤器相关的servlet或JSP页面时，doFilter方法就生成一个打印输出，此输出列出请求主机和调用的URL。因为getRequestURL方法位于HttpServletRequest而不是ServletRequest中，所以把ServletRequest对象构造为HttpServletRequest类型。我们改动一下章节3的SimpleFilter1.java。
SimpleFilter1.java
[align=left]package com.zj.sample;[/align]
[align=left]import java.io.IOException;[/align]
[align=left]import java.util.Date;[/align]
[align=left]import javax.servlet.Filter;[/align]
[align=left]import javax.servlet.FilterChain;[/align]
[align=left]import javax.servlet.FilterConfig;[/align]
[align=left]import javax.servlet.ServletException;[/align]
[align=left]import javax.servlet.ServletRequest;[/align]
[align=left]import javax.servlet.ServletResponse;[/align]
[align=left]import javax.servlet.http.HttpServletRequest;[/align]
[align=left] [/align]
[align=left]publicclass SimpleFilter1 implements Filter {[/align]
[align=left] @SuppressWarnings("unused")[/align]
[align=left] private FilterConfig filterConfig;[/align]
[align=left] [/align]
[align=left] publicvoid init(FilterConfig config) throws ServletException {[/align]
[align=left] this.filterConfig = config;[/align]
[align=left] }[/align]
[align=left] [/align]
[align=left] publicvoid doFilter(ServletRequest request, ServletResponse response,[/align]
[align=left] FilterChain chain) {[/align]
[align=left] try {[/align]
[align=left] System.out.println("Within SimpleFilter1:Filtering the Request...");[/align]
[align=left] HttpServletRequest req = (HttpServletRequest) request;[/align]
[align=left] System.out.println(req.getRemoteHost() + " tried to access "[/align]
[align=left] + req.getRequestURL() + " on " + new Date() + ".");[/align]
[align=left] chain.doFilter(request, response);[/align]
[align=left] System.out.println("Within SimpleFilter1:Filtering the Response...");[/align]
[align=left] } catch (IOException ioe) {[/align]
[align=left] ioe.printStackTrace();[/align]
[align=left] } catch (ServletException se) {[/align]
[align=left] se.printStackTrace();[/align]
[align=left] }[/align]
[align=left] }[/align]
[align=left] [/align]
[align=left] publicvoid destroy() {[/align]
[align=left] this.filterConfig = null;[/align]
[align=left] }[/align]
}
|
web.xml设置不变，同章节3。
测试：
输入http://localhost:8080/Test4Jsp/login.jsp
结果：
Within SimpleFilter1:Filtering the Request...
0:0:0:0:0:0:0:1 tried to access http://localhost:8080/Test4Jsp/login.jsp on Sun Mar 04 17:01:37 CST 2007.
Within SimpleFilter2:Filtering the Request...
Within SimpleFilter2:Filtering the Response...
Within SimpleFilter1:Filtering the Response...
5．访问时的过滤器（在过滤器中使用servlet初始化参数）
下面利用init设定一个正常访问时间范围，对那些不在此时间段的访问作出记录。我们改动一下章节3的SimpleFilter2.java。
SimpleFilter2.java。
[align=left]package com.zj.sample;[/align]
[align=left]import java.io.IOException;[/align]
[align=left]import java.text.DateFormat;[/align]
[align=left]import java.util.Calendar;[/align]
[align=left]import java.util.GregorianCalendar;[/align]
[align=left]import javax.servlet.Filter;[/align]
[align=left]import javax.servlet.FilterChain;[/align]
[align=left]import javax.servlet.FilterConfig;[/align]
[align=left]import javax.servlet.ServletContext;[/align]
[align=left]import javax.servlet.ServletException;[/align]
[align=left]import javax.servlet.ServletRequest;[/align]
[align=left]import javax.servlet.ServletResponse;[/align]
[align=left]import javax.servlet.http.HttpServletRequest;[/align]
[align=left] [/align]
[align=left]publicclass SimpleFilter2 implements Filter {[/align]
[align=left] @SuppressWarnings("unused")[/align]
[align=left] private FilterConfig config;[/align]
[align=left] private ServletContext context;[/align]
[align=left] privateintstartTime, endTime;[/align]
[align=left] private DateFormat formatter;[/align]
[align=left] [/align]
[align=left] publicvoid init(FilterConfig config) throws ServletException {[/align]
[align=left] this.config = config;[/align]
[align=left] context = config.getServletContext();[/align]
[align=left] formatter = DateFormat.getDateTimeInstance(DateFormat.MEDIUM,[/align]
[align=left] DateFormat.MEDIUM);[/align]
[align=left] try {[/align]
[align=left] startTime = Integer.parseInt(config.getInitParameter("startTime"));// web.xml[/align]
[align=left] endTime = Integer.parseInt(config.getInitParameter("endTime"));// web.xml[/align]
[align=left] } catch (NumberFormatException nfe) { // Malformed or null[/align]
[align=left] // Default: access at or after 10 p.m. but before 6 a.m. is[/align]
[align=left] // considered unusual.[/align]
[align=left] startTime = 22; // 10:00 p.m.[/align]
[align=left] endTime = 6; // 6:00 a.m.[/align]
[align=left] }[/align]
[align=left] }[/align]
[align=left] [/align]
[align=left] publicvoid doFilter(ServletRequest request, ServletResponse response,[/align]
[align=left] FilterChain chain) {[/align]
[align=left] try {[/align]
[align=left] System.out.println("Within SimpleFilter2:Filtering the Request...");[/align]
[align=left] HttpServletRequest req = (HttpServletRequest) request;[/align]
[align=left] GregorianCalendar calendar = new GregorianCalendar();[/align]
[align=left] int currentTime = calendar.get(Calendar.HOUR_OF_DAY);[/align]
[align=left] if (isUnusualTime(currentTime, startTime, endTime)) {[/align]
[align=left] context.log("WARNING: " + req.getRemoteHost() + " accessed "[/align]
[align=left] + req.getRequestURL() + " on "[/align]
[align=left] + formatter.format(calendar.getTime()));[/align]
[align=left] // The log file is under <CATALINA_HOME>/logs.One log per day.[/align]
[align=left] }[/align]
[align=left] chain.doFilter(request, response);[/align]
[align=left] System.out[/align]
[align=left] .println("Within SimpleFilter2:Filtering the Response...");[/align]
[align=left] } catch (IOException ioe) {[/align]
[align=left] ioe.printStackTrace();[/align]
[align=left] } catch (ServletException se) {[/align]
[align=left] se.printStackTrace();[/align]
[align=left] }[/align]
[align=left] }[/align]
[align=left] [/align]
[align=left] publicvoid destroy() {}[/align]
[align=left] [/align]
[align=left] // Is the current time between the start and end[/align]
[align=left] // times that are marked as abnormal access times?[/align]
[align=left] privateboolean isUnusualTime(int currentTime, int startTime, int endTime) {[/align]
[align=left] // If the start time is less than the end time (i.e.,[/align]
[align=left] // they are two times on the same day), then the[/align]
[align=left] // current time is considered unusual if it is[/align]
[align=left] // between the start and end times.[/align]
[align=left] if (startTime < endTime) {[/align]
[align=left] return ((currentTime >= startTime) && (currentTime < endTime));[/align]
[align=left] }[/align]
[align=left] // If the start time is greater than or equal to the[/align]
[align=left] // end time (i.e., the start time is on one day and[/align]
[align=left] // the end time is on the next day), then the current[/align]
[align=left] // time is considered unusual if it is NOT between[/align]
[align=left] // the end and start times.[/align]
[align=left] else {[/align]
[align=left] return (!isUnusualTime(currentTime, endTime, startTime));[/align]
[align=left] }[/align]
[align=left] }[/align]
}
|
web.xml设置不变。
关于Tomcat日志处理，这里补充介绍一下。config.getServletContext().log（"log message"）会将日志信息写入<CATALINA_HOME>/logs文件夹下，文件名应该为localhost_log.2007-03-04.txt这样的形式（按日期每天产生一个，第二天可以看见）。要得到这样一个日志文件，应该在server.xml中有：
<Logger className="org.apache.catalina.logger.FileLogger" prefix="catalina_log." suffix=".txt" timestamp="true"/>
|
参考资料
[1] Marty Halls ，Servlet与JSP权威指南，机械工业出版社
[2] 赵强，精通JSP编程，电子工业出版社
|
内容来自用户分享和网络整理，不保证内容的准确性，如有侵权内容，可联系管理员处理
