【转载】JSP的静态化

什么是静态化？静态化就是将动态的jsp转换为静态的html;

为什么要静态化？提高性能加快访问速度，静态化的页面html不需要访问数据库等操作所以要比动态的jsp快很多。

怎样实现静态化？

实现静态化的方法很多，本文章要说明的是通过过滤器实现jsp的静态化。

1、我们先了解下jsp页面的请求流程

 

通过上图我们可以知道servlet对象的响应是html，如果我们在servlet对象之后增加个拦截htm响应的功能将html响应保存到服务器，下次访问时直接返回这个静态页面，也就实现了静态化功能。

2、新的请求流程如下图：

 

 实现上图拦截servlet响应、判断是否已经静态化功能最好的方法就是拦截器filter。

 

3、具体实现包括，两个类一个配置，两个类分别是FileCaptureFilter(过滤器)和FileCaptureResponseWrapper(静态化)。

FileCaptureFilter(过滤器)：负责判断是否已经静态化，调用FileCaptureResponseWrapper(静态化)实现静态化，加载静态化html生成html响应。

FileCaptureResponseWrapper(静态化)：继承 HttpServletResponseWrapper，覆写PrintWriter getWriter()方法获得servlet响应内容，负责生成静态化的html、负责将响应返回给客户。

FileCaptureFilter 具体代码如下：

package cn.ce.sale.customer.filter;

 

import java.io.File;

import java.io.IOException;

 

import javax.servlet.Filter;

import javax.servlet.FilterChain;

import javax.servlet.FilterConfig;

import javax.servlet.ServletException;

import javax.servlet.ServletRequest;

import javax.servlet.ServletResponse;

import javax.servlet.http.HttpServletRequest;

import javax.servlet.http.HttpServletResponse;

 

import cn.ce.framework.exception.api.NoLoginException;

import cn.ce.framework.security.api.LoginConstant;

import cn.ce.framework.security.api.LoginUser;

 

public class FileCaptureFilter implements Filter{

 

private String protDirPath;

private FilterConfig filterConfig;

@Override

public void destroy() {

// TODO Auto-generated method stub

 

}

 

@Override

public void doFilter(ServletRequest request,ServletResponse response,FilterChain

chain) throws IOException, ServletException {

//

LoginUser loginUser = (LoginUser) ((HttpServletRequest)request).getSession().getAttribute(LoginConstant.USER);

        if (loginUser == null)

            throw new NoLoginException();

String fileName = "/forum/userId_"+loginUser.getUserId()+".html";

File file = new File(filterConfig.getServletContext().getRealPath(fileName));

// 判断缓存文件是否存在或者是否重新设置了缓存内容

if (!file.exists()) {// 如果缓存文件不存在

fileName=protDirPath+fileName;

FileCaptureResponseWrapper responseWrapper = new

FileCaptureResponseWrapper((HttpServletResponse)response);

chain.doFilter(request, responseWrapper);

//得到的html 页面结果字符串

//String html = responseWrapper.toString();

// 写成html 文件

responseWrapper.writeFile(fileName);

// back to browser

responseWrapper.writeResponse();

}else{

// 转发至缓存文件

request.getRequestDispatcher(fileName).forward(request, response);

 

}

}

 

@Override

public void init(FilterConfig arg0) throws ServletException {

this.filterConfig=arg0;

protDirPath = arg0.getServletContext().getRealPath("/");

}

}

 

  FileCaptureResponseWrapper  具体代码如下：

package cn.ce.sale.customer.filter;

 

import java.io.CharArrayWriter;

import java.io.FileOutputStream;

import java.io.IOException;

import java.io.OutputStreamWriter;

import java.io.PrintWriter;

 

import javax.servlet.http.HttpServletResponse;

import javax.servlet.http.HttpServletResponseWrapper;

 

public class FileCaptureResponseWrapper extends HttpServletResponseWrapper {

private CharArrayWriter output;

private HttpServletResponse response;

public String toString()

{

return output.toString();

}

public FileCaptureResponseWrapper(HttpServletResponse response)

{

super(response);

this.response=response;

output =new CharArrayWriter();

}

//覆写getWriter()

public PrintWriter getWriter()

{

return new PrintWriter(output);

}

public void writeFile(String fileName)throws IOException

{

//FileWriter fw = new FileWriter(fileName,"utf-8");

//fw.write( output.toCharArray(),"utf-8" );

//PrintWriter writer = new PrintWriter(new OutputStreamWriter(new FileOutputStream(fileName),"utf-8"));

FileOutputStream fos=new FileOutputStream(fileName);

OutputStreamWriter osw=new OutputStreamWriter(fos,"UTF-8");

osw.write(output.toCharArray());

osw.close();

}

public void writeResponse() throws IOException

{

PrintWriter out = response.getWriter();

// 重置响应输出的内容长度

response.setContentLength(-1);

out.print( output.toCharArray() );

out.flush();

out.close();

}

}

 

web.xml过滤器配置如下：

<filter>

<filter-name>FileCaptureFilter</filter-name>

<filter-class>

cn.ce.sale.customer.filter.FileCaptureFilter

</filter-class>

</filter>

    <filter-mapping>

<filter-name>FileCaptureFilter</filter-name>

<url-pattern>/order/customer/addCust/*</url-pattern>

</filter-mapping>