XP开发模式：第一个最简单的Web Servlet应用演示例子

package com.jb.arklis.web.mytag; import javax.servlet.*; import javax.servlet.jsp.*; import javax.servlet.jsp.tagext.*; import java.io.*; /** 功能：书写一个自定义标签处理程序，用来演示web工程的书写 作者：Arklis zeng 时间：2008-5-16 地点：雅安Home 版本：ver 1.0.0 @jsp.tag name="happy" body-content="empty" */ public class HappyTag extends TagSupport{ //声明一个boolean变量，用来说明测试值 private boolean verbose = false; private boolean fail = false; /** @jsp.attribute required="false" */ public void setVerbose(boolean verbose){ this.verbose = verbose; } /** @jsp.attribute required="false" */ public void setFail(boolean fail){ this.fail = fail; } /*重写doStartTag()方法*/ public int toStartTag()throws JspException{ //呼叫测试方法 testServletVersion(); testFailureBehavior(); return SKIP_BODY; } /*测试servlet的版本*/ public void testServletVersion()throws JspException{ //取得servlet上下文 ServletContext context = pageContext.getServletContext(); //得到servlet的版本号 int major = context.getMajorVersion(); int minor = context.getMinorVersion(); if(major < 2 || (major == 2 && minor < 3)){ String text = "Servlet version (" + major + "." + minor + ") too old; 2.3+ required"; throw new JspException(text); } //日志版本 log("version = " + major + "." + minor); } /*测试解析错误*/ public void testFailureBehavior()throws JspException{ //如果有错误 if(fail){ //抛出错误信息 throw new JspException("Failure requested...."); } } private void log(String message)throws JspException{ if(verbose){ try{ pageContext.getOut().println(message); }catch(IOException ioe){ throw new JspException(ioe); } } } }