一个实现将动态页面转为静态的方案

1.前言

为了能深入浅出的理解这个框架的由来，我们首先来了解一下JSP解析器将我们写的JSP代码转换成的JAVA文件的内容。

下面是一个JSP文件test.jsp

<!--page language=java contentType=text/html;charset=GB2312-->

<!--输-->

经过TOMCAT转换出的JAVA文件test$jsp.java内容如下：

package org.apache.jsp;

import javax.servlet.*;

import javax.servlet.http.*;

import javax.servlet.jsp.*;

import org.apache.jasper.runtime.*;

public class test$jsp extends HttpJspBase {

static {

}

public testOutRedir$jsp( ) {

}

private static boolean _jspx_inited = false;

public final void _jspx_init() throws org.apache.jasper.runtime.JspException {

}

public void _jspService(HttpServletRequest request, HttpServletResponse response)

throws java.io.IOException, ServletException {

JspFactory _jspxFactory = null;

PageContext pageContext = null;

HttpSession session = null;

ServletContext application = null;

ServletConfig config = null;

JspWriter out = null;

Object page = this;

String _value = null;

try {

if (_jspx_inited == false) {

synchronized (this) {

if (_jspx_inited == false) {

_jspx_init();

_jspx_inited = true;

}

}

}

_jspxFactory = JspFactory.getDefaultFactory();

response.setContentType(text/html;charset=GB2312);

pageContext = _jspxFactory.getPageContext(this, request, response,

, true, 8192, true);

application = pageContext.getServletContext();

config = pageContext.getServletConfig();

session = pageContext.getSession();

out = pageContext.getOut();

//为了节省篇幅，我删除了解释器添加的注释

out.write(\r\n);

//上一句是由于<!--page language=java&nbsp; contentType=text/html;charset=GB2312-->后面的换行产生的

out.write(<!--文件开始-->);

out.write(\r\n\r\n\r\n\r\n);

out.print( 输出 );

out.write(\r\n\r\n\r\n\r\n);

} catch (Throwable t) {

if (out != null && out.getBufferSize() != 0)

out.clearBuffer();

if (pageContext != null) pageContext.handlePageException(t);

} finally {

if (_jspxFactory != null) _jspxFactory.releasePageContext(pageContext);

}

}

}

从上面的代码中可以清晰的看到JSP内建的几个对象（out、request、response、session、pageContext、application、config、page）是怎么产生的，懂servlet的朋友一看就能明白。

下面重点理解一下out对象，它被声明为JspWriter类型，JspWriter是一个抽象类，在包javax.servlet.jsp中可以找到它的定义。

abstract public class javax.servlet.jsp.JspWriter extends java.io.Writer{

final public static int NO_BUFFER = 0;

final public static int DEFAULT_BUFFER = -1;

final public static int UNBOUNDED_BUFFER = -2;

protected int bufferSize;

protected Boolean autoFlush;

protected javax.servlet.jsp.JspWriter(int arg1, boolean arg2);

abstract public void newLine() throws IOException ;

abstract public void print(boolean arg0) throws IOException ;

abstract public void print(char arg0) throws IOException ;

abstract public void print(int arg0) throws IOException ;

abstract public void print(long arg0) throws IOException ;

abstract public void print(float arg0) throws IOException ;

abstract public void print(double arg0) throws IOException ;

abstract public void print(char[] arg0) throws IOException ;

abstract public void print(String arg0) throws IOException ;

abstract public void print(Object arg0) throws IOException ;

abstract public void println() throws IOException ;

abstract public void println(boolean arg0) throws IOException ;

abstract public void println(char arg0) throws IOException ;

abstract public void println(int arg0) throws IOException ;

abstract public void println(long arg0) throws IOException ;

abstract public void println(float arg0) throws IOException ;

abstract public void println(double arg0) throws IOException ;

abstract public void println(char[] arg0) throws IOException ;

abstract public void println(String arg0) throws IOException ;

abtract public void println(Object arg0) throws IOException ;

abstract public void clear() throws IOException ;

abstract public void clearBuffer() throws IOException ;

abstract public void flush() throws IOException ;

abstract public void close() throws IOException ;

public int getBufferSize() ;

abstract public int getRemaining() ;

public boolean isAutoFlush() ;

}

我相信当我写到这里你可能已经知道我想怎么做了。是的，来个偷天换日，继承JspWriter类，然后实现其定义的虚函数，然后把out变量替换成你自己实现的类的实例就ok了。

2.实现替换

假设

<!--page language=java&nbsp; contentType=text/html;charset=GB2312 import=jwb.util.HtmlIntoFile,jwb.util.TempSinglet,java.io.Fil--><!--看吧，这就是输出被重定向到文件的实现，很简单吧^_--><!--ONT color=#ff0000>out</FONT>.close<FONT color=#008000>();//关闭生成的静态文件</FONT>out_bak.clear();pageContext.forward(filePath);</FONT></DIV> <DIV 0cm 0pt><FONT size=2>System.out.println(执行本页面后再转到静态页面);return-->

3.更新问题

下面就讨论一下如何更新生成静态文件，其实从上面实现中你可以看到，很简单的就是将生成的静态文件删除即可，至于什么时候删除，要看你的需求了。我能想到的几种情况如下

• 当用来生成页面的数据更新时
• 如果不需要很提供时时的数据可以定时更新
• 永远不更新