1、编写一个实现tag接口的标签处理器类
package cn.itcast.web.tag; import java.io.IOException; import javax.servlet.http.HttpServletRequest; import javax.servlet.jsp.JspException; import javax.servlet.jsp.JspWriter; import javax.servlet.jsp.PageContext; import javax.servlet.jsp.tagext.Tag; public class ViewIPTag implements Tag { private PageContext pageContext; public int doStartTag() throws JspException { HttpServletRequest request = (HttpServletRequest) pageContext.getRequest();//获取页面Servlet中 request 和out 对象 JspWriter out = pageContext.getOut(); String ip = request.getRemoteAddr(); //获取用户IP地址 try { out.write(ip); } catch (IOException e) { throw new RuntimeException(e); } return 0; } public int doEndTag() throws JspException { return 0; } public Tag getParent() { return null; } public void release() { } public void setPageContext(PageContext arg0) { this.pageContext = arg0;//PageContext获取用户request out 等对象 } public void setParent(Tag arg0) { } }
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
<?xml version="1.0" encoding="UTF-8" ?> <taglib xmlns="http://java.sun.com/xml/ns/j2ee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee http://java.sun.com/xml/ns/j2ee/web-jsptaglibrary_2_0.xsd" version="2.0"> <description>A tag library exercising SimpleTag handlers.</description> <tlib-version>1.0</tlib-version> <short-name>SimpleTagLibrary</short-name> <uri>/itcast</uri> <tag> <name>viewIP</name> <!-- 为标签处理器类配一个标签名 --> <tag-class>cn.itcast.web.tag.ViewIPTag</tag-class> <body-content>empty</body-content> </tag> </taglib>
3、在jsp页面中导入并使用自定义标签
<%@ page language="java" import="java.util.*" pageEncoding="UTF-8"%> <%@taglib uri="/itcast" prefix="itcast" %> <!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN"> <html> <head> <title>输出客户机的IP</title> </head> <body> 您的IP是：<itcast:viewIP/> </body> </html>