动态页转为静态页的一个实例 Java版

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Java JSP Servlet HTML Apache

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(\r\n);

//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(\r\n<html>\r\n<head>\r\n<body>\r\n);

out.print(输出);

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);

}

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。

abstractpublicclassjavax.servlet.jsp.JspWriterextends java.io.Writer{

final public static intNO_BUFFER = 0;

final public static intDEFAULT_BUFFER = -1;

final public static intUNBOUNDED_BUFFER = -2;

protected intbufferSize;

protected BooleanautoFlush;

protectedjavax.servlet.jsp.JspWriter(intarg1,booleanarg2);

abstractpublicvoidnewLine()throwsIOException;

abstractpublicvoidprint(booleanarg0)throwsIOException;

abstractpublicvoidprint(chararg0)throwsIOException;

abstractpublicvoidprint(intarg0)throwsIOException;

abstractpublicvoidprint(longarg0)throwsIOException;

abstractpublicvoidprint(floatarg0)throwsIOException;

abstractpublicvoidprint(doublearg0)throwsIOException;

abstractpublicvoidprint(char[]arg0)throwsIOException;

abstractpublicvoidprint(Stringarg0)throwsIOException;

abstractpublicvoidprint(Objectarg0)throwsIOException;

abstractpublicvoidprintln()throwsIOException;

abstractpublicvoidprintln(booleanarg0)throwsIOException;

abstractpublicvoidprintln(chararg0)throwsIOException;

abstractpublicvoidprintln(intarg0)throwsIOException;

abstractpublicvoidprintln(longarg0)throwsIOException;

abstractpublicvoidprintln(floatarg0)throwsIOException;

abstractpublicvoidprintln(doublearg0)throwsIOException;

abstractpublicvoidprintln(char[]arg0)throwsIOException;

abstractpublicvoidprintln(Stringarg0)throwsIOException;

abtractpublicvoidprintln(Objectarg0)throwsIOException;

abstractpublicvoidclear()throwsIOException;

abstractpublicvoidclearBuffer()throwsIOException;

abstractpublicvoidflush()throwsIOException;

abstractpublicvoidclose()throwsIOException;

publicintgetBufferSize() ;

abstractpublicintgetRemaining();

publicbooleanisAutoFlush();

}

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

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java基本语法 5.0后新增 | jsp把动态页面转为静态页面转

2009-05-08 23:51
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