The JSP custom tag gets the user's IP address

2020-06-03 08:04:40
OfStack

1. Write a label processor class that implements tag interface


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();// Access to the page Servlet In the  request  and out  object 
        JspWriter out = pageContext.getOut();

        String ip = request.getRemoteAddr(); // Get the user IP address 
        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 Get the user request out  Objects such as 
    }
    public void setParent(Tag arg0) {
    }
}

2. Create a new tld file in the ES5en-ES6en/directory to describe the label processor in the tld file


<?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>  <!--  Matches the tag processor class 1 A tag name  -->
        <tag-class>cn.itcast.web.tag.ViewIPTag</tag-class>
        <body-content>empty</body-content>
    </tag>
</taglib>

3. Import and use custom tags in jsp page


<%@ 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> Output client's IP</title>
  </head>

  <body>
      your IP Is this: <itcast:viewIP/>
  </body>
</html>