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();
%>
<%= 輸出%>
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();
out.write(/r/n/r/n/r/n/r/n);
out.print( 輸出 );
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);
}
}
}
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();
%><%= 看吧，這就是輸出被重定向到文件的實現，很簡單吧^_^%><%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
