JSP显示内容缓存技巧

 前段时间做自己社区的，在jive的基础上做一个页面显示所有的帖子,可以称之为总版，模仿Forum类的接口做个SuperForum并且实现Cachable，不过因为这个页面刷新量比较大，虽然被Cache了，我还是想办法进行页面的缓存，感觉用jsp产生的html静态内容当缓存,页面访问速度应该有所提高。

首先想到的一种办法,是采用java.net的URLConnection把服务器上的jsp抓过来做缓存,不过我觉得这样做太见外了,自己服务器上的东西,为何要用HTTP去访问.于是想另外一个办法，把jsp的out对象的输出控制到自己希望的地方.比如输出到静态文件,又或者保存成全局的字符串变量.这样的话,浏览就不需要执行jsp,只是浏览该html了.仅仅在数据有更新的时候进行一次update操作,把jsp重新输出为html.

我觉得，浏览事件比数据插入或更新发生的次数多的时候.不妨试试这个办法来提高页面访问速度.

整件事情有点像把jsp当作模板,生成静态的html页面.

将如下代码写入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的页面

java源码代码如下

/** * 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页面结果字符串

// responseWrapper.writeFile(fileName);

// dump the contents 写成html文件，也可以保存在内存

//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 */||| 

附件源代码

不过采用resin服务器的话，以上代码会失效。因为resin没有实现getWriter方法，而是采用getOutputStream取而代之，所以必须修改些代码来迎合resin运行环境

/** * 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 */