缓存JSP显示的html
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("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
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 */