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jsp显示内容缓存技巧
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 */
