一個在JSP下實現將動態頁面轉為靜態的方案

2024-09-05 00:20:15

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來源：轉載

供稿：網友

　　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("");
%>
<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("");
                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("");
%>
<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;
%>