自定义标签库

<?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 web-jsptaglibrary_2_0.xsd"
    version="2.0">
    
  <description>JSTL 1.1 core library</description>
  <display-name>JSTL core</display-name>
  <tlib-version>1.1</tlib-version>
  <short-name>zhb</short-name>
  <uri>http://www.zhb.cn/mytag</uri>

  <!-- 显示IP地址 -->
  <tag>
    <description>
        Catches any Throwable that occurs in its body and optionally
        exposes it.
    </description>
    <name>viewIP</name>
    <tag-class>MyTag</tag-class>
    <body-content>empty</body-content>
  </tag>
</taglib>

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.TagSupport;

import com.sun.org.apache.xml.internal.resolver.helpers.PublicId;

public class MyTag extends TagSupport{
    private static final long serialVersionUID = 1L;

    @Override
    public int doStartTag() throws JspException {
        //内置一个pageContext对象，我们之前说到pageContext对象，它里面是封装了9个隐式对象
        HttpServletRequest request = (HttpServletRequest)this.pageContext.getRequest();
        JspWriter out = this.pageContext.getOut();
        String ip = request.getRemoteAddr();
        try {
            out.print(ip);
        } catch (IOException e) {
            throw new RuntimeException(e);
        }
        return TagSupport.EVAL_PAGE;
    }

    @Override
    public int doEndTag() throws JspException {
        return TagSupport.EVAL_PAGE;
    }
}