1.前言
為了能深入淺出的理解這個架構的由來，我們首先來瞭解一下JSP解析器將我們寫的JSP代碼轉換成的JAVA檔案的內容。
下面是一個JSP檔案test.jsp
<%@ page language="java" contentType="text/html;charset=GB2312" %>
<%
out.write("<!--檔案開始-->");
%>
<html>
<head>
<body>
<%= "輸出"%>
</body>
</head>
</html>
經過TOMCAT轉換出的JAVA檔案test$jsp.java內容如下：
package org.apache.jsp;
import javax.servlet.*;
import javax.servlet.http.*;
import javax.servlet.jsp.*;
import org.apache.jasper.runtime.*;
public class test$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();
//為了節省篇幅，我刪除瞭解釋器添加的注釋
out.write("\r\n");
//上一句是由於<%@ page language="java" contentType="text/html;charset=GB2312" %>後面的換行產生的
out.write("<!--檔案開始-->");
out.write("\r\n<html>\r\n<head>\r\n<body>\r\n");
out.print( "輸出" );
out.write("\r\n</body>\r\n</head>\r\n</html>\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);
}
}
}
從上面的代碼中可以清晰的看到JSP內建的幾個對象（out、request、response、session、pageContext、application、config、page）是怎麼產生的，懂servlet的朋友一看就能明白。
下面重點理解一下out對象，它被聲明為JspWriter類型，JspWriter是一個抽象類別，在包javax.servlet.jsp中可以找到它的定義。
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() ;
}
我相信當我寫到這裡你可能已經知道我想怎麼做了。是的，來個偷天換日，繼承JspWriter類，然後實現其定義的虛函數，然後把out變數替換成你自己實現的類的執行個體就ok了。
2.實現替換
假設：
<%@ page language="java" contentType="text/html;charset=GB2312"
import="jwb.util.HtmlIntoFile,jwb.util.TempSinglet,java.io.File"%><%
JspWriter out_bak = out;
String arg1="argument1";
String filePath = "/cache/根據參數組建檔案名_" + arg1 + ".html";
//首先判斷檔案是否已經存在，如果不存在則執行本頁面，否則跳轉到靜態頁面就OK了
File f = new File(pageContext.getServletContext().getRealPath(filePath));
if(f.exists())
{
out_bak.clear();
pageContext.forward(filePath);
System.out.println("直接轉到靜態頁面");
return;
}
out = new HtmlIntoFile(pageContext.getServletContext().getRealPath(filePath));
out.write("<!--檔案開始-->");
%>
<html>
<head>
<body>
<%= "看吧，這就是輸出被重新導向到檔案的實現，很簡單吧^_^"%>
</body>
</head>
</html>
<%
out.close();//關閉產生的靜態檔案
out_bak.clear();
pageContext.forward(filePath);
System.out.println("執行本頁面後再轉到靜態頁面");
return;
%>
3.更新問題
下面就討論一下如何更新產生靜態檔案，其實從上面實現中你可以看到，很簡單的就是將產生的靜態檔案刪除即可，至於什麼時候刪除，要看你的需求了。我能想到的幾種情況如下：
當用來產生頁面的資料更新時
如果不需要很提供時時的資料可以定時更新
永遠不更新
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