jsp实用两例：用filter解决汉字编码及禁止页面缓存和用listener实现在线人数统计

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JSP XSL JBuilder XML Servlet

1.用filter解决汉字编码及禁止页面缓存 (不用再在每个页面里去加那几行代码了):
package beanservlettest;

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;

public class servfilter extends HttpServlet implements Filter {
private FilterConfig filterConfig;
//Handle the passed-in FilterConfig
public void init(FilterConfig filterConfig) {
  this.filterConfig = filterConfig;
}
//Process the request/response pair
public void doFilter(ServletRequest request, ServletResponse response, FilterChain filterChain) {
  try {
     request.setCharacterEncoding("GB2312");//设置编码
     ((HttpServletResponse)response).setHeader("Pragma","No-cache");
     ((HttpServletResponse)response).setHeader("Cache-Control","no-cache");
     ((HttpServletResponse)response).setHeader("Expires","0");//禁止缓存
   //自己添加的代码就这上面四行，其它的都是Jbuilder自动生成的：）
   filterChain.doFilter(request, response);
  }
  catch(ServletException sx) {
   filterConfig.getServletContext().log(sx.getMessage());
  }
  catch(IOException iox) {
   filterConfig.getServletContext().log(iox.getMessage());
  }
}
//Clean up resources
public void destroy() {
}
}

下面是在web.xml里的配置：
（我的是Jbuilder自动生成的）
<filter>
  <filter-name>servfilter</filter-name>
  <filter-class>beanservlettest.servfilter</filter-class>
</filter>
<filter-mapping>
  <filter-name>servfilter</filter-name>
  <url-pattern>/*</url-pattern>   ///这里表示对整个网站都有效
</filter-mapping>

2.用listener实现在线人数统计.

package beanservlettest;//除了其中三行代码，其余均由Jbuilder自动生成

import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
import java.util.*;

public class sessioncount extends HttpServlet implements ServletContextListener, ServletContextAttributeListener, HttpSessionListener, HttpSessionAttributeListener {
private static int activeSessions = 0;
public void contextInitialized(ServletContextEvent sce) {

}

public void contextDestroyed(ServletContextEvent sce) {

}
  public void attributeAdded(ServletContextAttributeEvent scab) {

}
public void attributeRemoved(ServletContextAttributeEvent scab) {

}
public void attributeReplaced(ServletContextAttributeEvent scab) {

}
public void sessionCreated(HttpSessionEvent se) {
activeSessions++;//每创建一个新的session就加1
}
public void sessionDestroyed(HttpSessionEvent se) {
  if(activeSessions > 0) //每销毁一个新的session就减1
  activeSessions--;
}
public void attributeAdded(HttpSessionBindingEvent se) {

}
public void attributeRemoved(HttpSessionBindingEvent se) {
  }

public void attributeReplaced(HttpSessionBindingEvent se) {
}
public static int getActiveSessions() {
return activeSessions;
}

}

web.xml里的配置如下：

<listener>
  <listener-class>beanservlettest.sessioncount</listener-class>
</listener>

jsp测试页面：

<%@ page contentType="text/html; charset=GBK" %>
<%@ page import="beanservlettest.sessioncount" %>

<html>
<head>
<title>
sc
</title>
</head>
<body bgcolor="#ffffff">
<h1>
JBuilder Generated JSP
</h1>
当前在线人数有<%=sessioncount.getActiveSessions()%>人。
</body>
</html>
<a href= "logout.jsp">注销</a>

网页连接：

http://expert.csdn.net/Expert/topic/1788/1788525.xml?temp=.2403833
http://www.chinaunix.net/bbsjh/14/397.html

2003-7-23 12:44:00
查看评语 ?

2003-7-23 16:45:15  刚才找到了其它程序的一个错误，总算解决了。在xslt文件里：
把<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/1999/XSL/Transform">

写成了：

<xsl:stylesheet version="1.0" xmlns:xsl="http://www.w3.org/TR/WD-xsl">
//这是当时从 http://expert.csdn.net/expert/Xsl/2.xsl里copy的，
//我晕：（

IE6里能够正常解析，
而java的JAXP却老是出错：

"javax.xml.transform.TransformerException: stylesheet 要求属性：version"
幸好我突然想到找另外个xsl文件来对照了一下。

把这句话一修改，程序马上执行就成功了。

程序代码：
import java.io.*;
import javax.xml.transform.*;
import javax.xml.transform.stream.*;

第一种：
/*
try{
   File xmlFile = new File("C:\\xmltest\\tiezi.xml");
   File xsltFile = new File("C:\\xmltest\\tiezi.xsl");
   javax.xml.transform.Source xmlSource =
     new javax.xml.transform.stream.StreamSource(xmlFile);
   javax.xml.transform.Source xsltSource =
     new javax.xml.transform.stream.StreamSource(xsltFile);
   javax.xml.transform.Result result =
     new javax.xml.transform.stream.StreamResult(System.out);

   //创建一个TransformerFactory 实例
   javax.xml.transform.TransformerFactory transFact =
     javax.xml.transform.TransformerFactory.newInstance();
   javax.xml.transform.Transformer trans =
     transFact.newTransformer(xsltSource);
   trans.transform(xmlSource, result);

   return "转换成功了！！！";
  }
catch(Exception e){
  System.out.println("出错");
  return e.toString()+"出错了：（";
}
*/
第二种：
/* try {
TransformerFactory transformerFactory =
             TransformerFactory.newInstance();

    StreamSource source = new StreamSource("C:\\xmltest\\tiezi.xml");
    StreamResult result = new StreamResult("C:\\xmltest\\result.xml");
    StreamSource style = new StreamSource("C:\\xmltest\\tiezi.xsl");

    Transformer transformer =
           transformerFactory.newTransformer(style);

    transformer.transform(source, result);
return "OK";
   } catch (Exception e) {
       e.printStackTrace();
       return "Failed";
   }
*/

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