一個實現將動態網頁面轉為靜態方案

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動態|靜態|頁面 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();%><%= 輸出%>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();                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();%><%= 看吧,這就是輸出被重新導向到檔案的實現,很簡單吧^_^%><%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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