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缓存JSP显示的html

摘要: jsp 缓存

前段时间做自己社区的论坛，在jive的基础上做一个页面显示所有论坛的帖子,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

FileCaptureFilter
class>com.junjing.filter.FileCaptureFilterclass>



FileCaptureFilter
/latest.jsp

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("lastThread.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 */