1.前言
為了能深入淺出的理解這個框架的由來，我們首先來了解一下
JSP
解析器將我們寫的
JSP
代碼轉換成的
JAVA
文件的內容。
下面是一個
JSP
文件
test.jsp
<%@ page language="java"? contentType="text/html;charset=GB2312" %>
<%
out.write("<!--
文件開始
-->");
%>
<html>
<head>
<body>
<%= "
輸出
"%>
</body>
</head>
</html>
經過
TOMCAT
轉換出的
JAVA
文件
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，我刪除了解釋器添加的注釋
???????????????
out.write("\r\n");
//
上一句是由于
<%@ page language="java"? contentType="text/html;charset=GB2312" %>
后面的換行產生的
???????????????
out.write("<!--
文件開始
-->");
???????????????
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
）是怎么產生的，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，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() ;
}
我相信當我寫到這里你可能已經知道我想怎么做了。是的，來個偷天換日，繼承
JspWriter
類，然后實現其定義的虛函數，然后把
out
變量替換成你自己實現的類的實例就
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/根據參數生成文件名_" + arg1 + ".html";
//首先判斷文件是否已經存在，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("<!--文件開始-->");
%>
<html>
<head>
<body>
<%= "看吧，這就是輸出被重定向到文件的實現，很簡單吧^_^"%>
</body>
</head>
</html>
<%
??out.close();//關閉生成的靜態文件
? out_bak.clear();
? pageContext.forward(filePath);
? System.out.println("執行本頁面后再轉到靜態頁面");
? return;
%>
3.更新問題
下面就討論一下如何更新生成靜態文件，其實從上面實現中你可以看到，很簡單的就是將生成的靜態文件刪除即可，至于什么時候刪除，要看你的需求了。我能想到的幾種情況如下
-
當用來生成頁面的數據更新時
-
如果不需要很提供時時的數據可以定時更新
-
永遠不更新
待更新……
code source:http://www.zahui.com/html/6/11558.htm
posted on 2006-06-22 10:26
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