JSP自定义标签获取用户IP地址的方法

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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

复制代码代码如下:

<?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页面中导入并使用自定义标签

复制代码代码如下:

<%@ 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>