jstl标签基础开发步骤(详解)

<?xml version="1.0" encoding="UTF-8" ?>

<taglib xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-jsptaglibrary_2_1.xsd"
  version="2.1">

  <tlib-version>1.1</tlib-version>
  <short-name>d1</short-name>
  <uri>http://aliyun.com</uri>

  <tag>
    <!-- name:表示自定义标签 <c1:date名字相同 -->
    <name>date</name>
    <tag-class>tag.DateTag</tag-class>
    <body-content>empty</body-content>
    <attribute>
      <!-- name:表示自定义标签 <c1:date datetag名字相同 -->
      <name>datetag</name>
      <!-- true,表示可以使用el表达式来赋值 -->
      <required>true</required>
      <rtexprvalue>false</rtexprvalue>
    </attribute>
  </tag>
</taglib>

package tag;
/**
 * 自定义日期标签
 */
import java.io.IOException;
import java.text.SimpleDateFormat;
import java.util.Date;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.SimpleTagSupport;

public class DateTag extends SimpleTagSupport {
  private String datetag;

  public String getDatetag() {
    return datetag;
  }

  public void setDatetag(String datetag) {
    this.datetag = datetag;
  }

  @Override
  public void doTag() throws JspException, IOException {
    PageContext pc = (PageContext) getJspContext();
    SimpleDateFormat sdf = new SimpleDateFormat(datetag);
    String date = sdf.format(new Date());
    JspWriter out = pc.getOut();
    out.println(date);
  }
}