1.编写一个实现Tag接口的标签处理器类
1 package cn.itcast.web.tag; 2 3 import java.io.IOException; 4 5 import javax.servlet.http.HttpServletRequest; 6 import javax.servlet.jsp.JspException; 7 import javax.servlet.jsp.JspWriter; 8 import javax.servlet.jsp.PageContext; 9 import javax.servlet.jsp.tagext.Tag; 10 11 public class ViewIPTag implements Tag { 12 13 private PageContext pageContext; 14 15 public int doEndTag() throws JspException { 16 // TODO Auto-generated method stub 17 return 0; 18 } 19 20 public int doStartTag() throws JspException { 21 // TODO Auto-generated method stub 22 23 HttpServletRequest request = (HttpServletRequest) pageContext.getRequest(); 24 JspWriter out = pageContext.getOut(); 25 26 String ip = request.getRemoteAddr(); 27 try { 28 out.write(ip); 29 } catch (IOException e) { 30 // TODO Auto-generated catch block 31 32 throw new RuntimeException(e); 33 } 34 35 return 0; 36 } 37 38 public Tag getParent() { 39 // TODO Auto-generated method stub 40 return null; 41 } 42 43 public void release() { 44 // TODO Auto-generated method stub 45 46 } 47 48 public void setPageContext(PageContext arg0) { 49 // TODO Auto-generated method stub 50 51 this.pageContext = arg0; 52 } 53 54 public void setParent(Tag arg0) { 55 // TODO Auto-generated method stub 56 57 } 58 59 }
2.在/WEB-INF/目录下新建tld文件，在tld文件中对标签处理器进行描述
tld文件中的3种标签体类型
empty
JSP
scriptless
1 <?xml version="1.0" encoding="UTF-8"?> 2 3 <taglib xmlns="http://java.sun.com/xml/ns/j2ee" 4 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 5 xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd" 6 version="2.0"> 7 <description>A tag library exercising SimpleTag handlers.</description> 8 <tlib-version>1.0</tlib-version> 9 <short-name>SimpleTagLibrary</short-name> 10 <uri>/itcast</uri> 11 12 <tag> 13 <name>viewIP</name> 14 <tag-class>cn.itcast.web.tag.ViewIPTag</tag-class> 15 <body-content>empty</body-content> 16 </tag> 17 18 </taglib>
3.在JSP页面中导入并使用自定义标签
1 <%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> 2 <%@ taglib uri="/itcast" prefix="itcast"%> 3 4 <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> 5 <html> 6 <head> 7 <title>My JSP '1.jsp' starting page</title> 8 </head> 9 10 <body> 11 12 你的IP地址是： 13 <itcast:viewIP /> 14 15 </body> 16 </html>