标签入门

1、编写一个实现tag接口的java类,并覆盖其doStarttag方法

public class ViewIpTag implements Tag {
 private PageContext pagecontext;
 public void setPageContext(PageContext arg0) {
  this.pagecontext = arg0;
 }
 public int doStartTag() throws JspException {
  HttpServletRequest request = (HttpServletRequest) this.pagecontext.getRequest();
  JspWriter out = this.pagecontext.getOut();
  String ip = request.getRemoteAddr();
  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 setParent(Tag arg0) {

 }

}

2、在web-inf\目录中新建一个tld文件,在tld文件中对标签处理器类进行描述(为标签处理器类配一个标签名)

<?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>
  <tag-class>cn.itcast.web.tag.ViewIpTag</tag-class>
  <body-content>empty</body-content>
    </tag>
</taglib>

3、在jsp页面中就可以导入并使用开发的自定义标签
<%@ 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>My JSP '1.jsp' starting page</title>
  </head>
 
  <body>
 
 您的IP是:<itcast:viewIp/>

  </body>
</html>

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