缓存JSP显示的内容

来源：JR 作者：未知 时间：2006-07-25 Tag： 点击：

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
  <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 */

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