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在jsp下，一个实现将动态页面转为静态的方案

2008-04-25 05:12 751 查看

1.前言 为了能深入浅出的理解这个框架的由来，我们首先来了解一下jsp解析器将我们写的jsp代码转换成的JAVA文件的内容。下面是一个jsp文件test.jsp <%@ page language="java" contentType="text/html;charset=GB2312" %> <% out.write(""); %> <html> <head> <body> <%= "输出"%> </body> </head> </html> 经过TOMCAT转换出的JAVA文件test$jsp.java内容如下： package org.apache.jsp; import javax.servlet.*; import javax.servlet.http.*; import javax.servlet.jsp.*; import org.apache.jasper.runtime.*; public class test$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(); //为了节省篇幅，我删除了解释器添加的注释 out.write(""); //上一句是由于<%@ page language="java" contentType="text/html;charset=GB2312" %>后面的换行产生的 out.write(""); out.write("<html><head><body>"); out.print( "输出" ); out.write("</body></head></html>"); } catch (Throwable t) { if (out != null && out.getBufferSize() != 0) out.clearBuffer(); if (pageContext != null) pageContext.handlePageException(t); } finally { if (_jspxFactory != null) _jspxFactory.releasePageContext(pageContext); } } } 从上面的代码中可以清晰的看到jsp内建的几个对象（out、request、response、session、pageContext、application、config、page）是怎么产生的，懂servlet的朋友一看就能明白。下面重点理解一下out对象，它被声明为jspWriter类型，jspWriter是一个抽象类，在包javax.servlet.jsp中可以找到它的定义。 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() ; } 我相信当我写到这里你可能已经知道我想怎么做了。是的，来个偷天换日，继承jspWriter类，然后实现其定义的虚函数，然后把out变量替换成你自己实现的类的实例就ok了。 2.实现替换 假设 <%@ 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/根据参数生成文件名_" + arg1 + ".html";//首先判断文件是否已经存在，如果不存在则执行本页面，否则跳转到静态页面就OK了File f = new File(pageContext.getServletContext().getRealPath(filePath));if(f.exists()){ out_bak.clear(); pageContext.forward(filePath); System.out.println("直接转到静态页面"); return;}out = new HtmlIntoFile(pageContext.getServletContext().getRealPath(filePath));out.write(""); %><html><head><body><%= "看吧，这就是输出被重定向到文件的实现，很简单吧^_^"%></body></head></html><%out.close();//关闭生成的静态文件out_bak.clear();pageContext.forward(filePath); System.out.println("执行本页面后再转到静态页面");return;%> 3.更新问题 下面就讨论一下如何更新生成静态文件，其实从上面实现中你可以看到，很简单的就是将生成的静态文件删除即可，至于什么时候删除，要看你的需求了。我能想到的几种情况如下当用来生成页面的数据更新时
如果不需要很提供时时的数据可以定时更新
永远不更新
待更新……

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