1樓 jewelsh (
blog.mynetech.com)
回復于
2003-12-11 09:59:48 得分
100
給個例子你看看。
--------------
JSP 顯示內容緩存技巧
前段時間做自己社區(qū)的論壇，在jive 的基礎上做一個頁面顯示所有論壇的帖子,可以稱
之為總版，模仿Forum 類的接口做個SuperForum 并且實現(xiàn)Cachable，不過因為這個頁面
刷新量比較大，雖然被Cache 了，我還是想辦法進行頁面的緩存，感覺用jsp 產生的html
靜態(tài)內容當緩存,頁面訪問速度應該有所提高。
首先想到的一種辦法,是采用java.net 的URLConnection 把服務器上的jsp 抓過來做緩
存,不過我覺得這樣做太見外了,自己服務器上的東西,為何要用HTTP 去訪問.于是想另外一
個辦法，把jsp 的out 對象的輸出控制到自己希望的地方.比如輸出到靜態(tài)文件,又或者保存
成全局的字符串變量.這樣的話,瀏覽就不需要執(zhí)行jsp,只是瀏覽該html 了.僅僅在數(shù)據(jù)有更
新的時候進行一次update 操作,把jsp 重新輸出為html.
我覺得，瀏覽事件比數(shù)據(jù)插入或更新發(fā)生的次數(shù)多的時候.不妨試試這個辦法來提高頁
面訪問速度.
整件事情有點像把jsp 當作模板,生成靜態(tài)的html 頁面.
將如下代碼寫入web-xml
＜filter＞
＜filter-name＞FileCaptureFilter＜/filter-name＞
＜filter-class＞com.junjing.filter.FileCaptureFilter＜/filter-class＞
＜/filter＞
＜filter-mapping＞
＜filter-name＞FileCaptureFilter＜/filter-name＞
＜url-pattern＞/latest.jsp＜/url-pattern＞
＜/filter-mapping＞
latest.jsp 是我要cache 的頁面
java 源碼代碼如下
/** * START File FileCaptureFilter.java */
package com.junjing.filter;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public class FileCaptureFilter implements Filter
{
private String protDirPath;
public void init(FilterConfig filterConfig)
throws ServletException
{
protDirPath = filterConfig.getServletContext().getRealPath("/");
}
public void doFilter(ServletRequest request,ServletResponse response,FilterChain
chain)
throws IOException, ServletException
{
String fileName = protDirPath + "forum/lastest.html";
PrintWriter out = response.getWriter();
FileCaptureResponseWrapper responseWrapper = new
FileCaptureResponseWrapper((HttpServletResponse)response);
chain.doFilter(request, responseWrapper);
// fill responseWrapper up
String html = responseWrapper.toString();
//得到的html 頁面結果字符串
// responseWrapper.writeFile(fileName);
// dump the contents 寫成html 文件，也可以保存在內存
//responseWrapper.writeResponse( out );
// back to browser
//responseWrapper.sendRedirect("lastestThread.jsp");
}
public void destroy() {}
}
/** * END File FileCaptureFilter.java */
/** * START File FileCaptureResponseWrapper.java */
package com.junjing.filter;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public class FileCaptureResponseWrapper
extends HttpServletResponseWrapper
{
private CharArrayWriter output;
public String toString()
{
return output.toString();
}
public FileCaptureResponseWrapper(HttpServletResponse response)
{
super(response);
output = new CharArrayWriter();
}
public PrintWriter getWriter()
{
return new PrintWriter(output);
}
public void writeFile(String fileName)
throws IOException
{
FileWriter fw = new FileWriter(fileName);
fw.write( output.toCharArray() );
fw.close();
}
public void writeResponse(PrintWriter out)
{
out.print( output.toCharArray() );
}
}
/** * END File FileCaptureResponseWrapper.java */
附件源代碼
不過采用resin 服務器的話，以上代碼會失效。因為resin 沒有實現(xiàn)getWriter 方法，而
是采用getOutputStream 取而代之，所以必須修改些代碼來迎合resin 運行環(huán)境：
/** * START File FileCaptureResponseWrapper.java */
package com.junjing.filter;
import javax.servlet.*;
import javax.servlet.http.*;
import java.io.*;
public class FileCaptureResponseWrapper
extends HttpServletResponseWrapper
{
private CharArrayWriter output;
public String toString()
{
return output.toString();
}
public FileCaptureResponseWrapper(HttpServletResponse response)
{
super(response);
output = new CharArrayWriter();
}
public PrintWriter getWriter()
{
return new PrintWriter(output);
}
public void writeFile(String fileName)
throws IOException
{
FileWriter fw = new FileWriter(fileName);
fw.write( output.toString());
fw.close();
}
public ServletOutputStream getOutputStream()
throws java.io.IOException
{
return new ServletOutputStream();
}
public void write(int b)
throws IOException
{
output.write(b);
}
public void write(byte b[])
throws IOException
{
output.write(new String(b,"GBK"));
}
public void write(byte b[], int off, int len)
throws IOException
{
output.write(new String(b, off, len));
}
};
}
public void writeResponse(PrintWriter out)
{
out.print(output.toCharArray());
}
}
/** * END File FileCaptureResponseWrapper.java */
