JSP自定義標(biāo)簽簡單入門教程

public interface SimpleTag
extends JspTag
Interface for defining Simple Tag Handlers.
Simple Tag Handlers differ from Classic Tag Handlers in that instead of supporting doStartTag() and doEndTag(), the SimpleTag interface provides a simple doTag() method, which is called once and only once for any given tag invocation. All tag logic, iteration, body evaluations, etc. are to be performed in this single method. Thus, simple tag handlers have the equivalent power of BodyTag, but with a much simpler lifecycle and interface.

To support body content, the setJspBody() method is provided. The container invokes the setJspBody() method with a JspFragment object encapsulating the body of the tag. The tag handler implementation can call invoke() on that fragment to evaluate the body as many times as it needs.

A SimpleTag handler must have a public no-args constructor. Most SimpleTag handlers should extend SimpleTagSupport.

package web.simpletag;
import java.io.IOException;
import java.io.StringWriter;

import javax.servlet.jsp.JspException;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.SkipPageException;
import javax.servlet.jsp.tagext.JspFragment;
import javax.servlet.jsp.tagext.SimpleTagSupport;


/**
 * 控制標(biāo)簽體是否執(zhí)行
 * @author Summer
 *
 */
public class BodyController extends SimpleTagSupport {
  static{
    /*
     * 簡單標(biāo)簽整體的執(zhí)行流程如下：
     * 1.瀏覽器向web服務(wù)器發(fā)送請求，然后web服務(wù)器調(diào)用servlet（jsp）
     * 2.complier解釋器進行初始化工作，先是調(diào)用setJspContext方法，將pageContext對象傳遞進去
     * 3.然后是看看此標(biāo)簽的父標(biāo)簽，即setParent方法
     * 4.再就是調(diào)用doTag方法了吧？但是要知道doTag內(nèi)部會使用JspFragment對象，所以就必須先得到它，因此應(yīng)該是調(diào)用setJspBody(JspFragment jspBody)方法
     * 5.最后是調(diào)用doTag 方法，執(zhí)行相關(guān)的代碼邏輯
     */
  }

  /**
   * 簡單標(biāo)簽可以使用這一個方法實現(xiàn)所有的業(yè)務(wù)邏輯
   */
  @Override
  public void doTag() throws JspException, IOException {
    //代表標(biāo)簽體的對象
    JspFragment fragment = this.getJspBody();
    //fragment.invoke(null);是指將標(biāo)簽中的內(nèi)容寫給誰，null代表瀏覽器


    //1.修改標(biāo)簽體的內(nèi)容
//   fragment.invoke(null);


    //2.控制標(biāo)簽體內(nèi)容的重復(fù)輸出
//   for(int i=1;i=5;i++){
//     fragment.invoke(null);//設(shè)置為null，默認為向瀏覽器輸出
//   }


    //3.修改標(biāo)簽體的內(nèi)容
    PageContext context = (PageContext) fragment.getJspContext();
    StringWriter writer = new StringWriter();
    fragment.invoke(writer);
    String content = writer.getBuffer().toString();

    this.getJspContext().getOut().write(content.toUpperCase());

    //4.控制jsp頁面的執(zhí)行與否，只需要掌握一個原理即可
    /*
     * SkipPageException - If the page that (either directly or indirectly) invoked this 
     * tag is to cease evaluation. A Simple Tag Handler generated from a tag
     * file must throw this exception if an invoked Classic Tag Handler
     *  returned SKIP_PAGE or if an invoked Simple Tag Handler threw
     *  SkipPageException or if an invoked Jsp Fragment threw a 
     *  SkipPageException.
     */
//   throw new SkipPageException();
  }


}

?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>JSTL 1.1 XML library/description>
  display-name>JSTL XML/display-name>
  tlib-version>1.1/tlib-version>
  short-name>x/short-name>
  uri>/simplesummer/uri>


  !-- 控制標(biāo)簽體內(nèi)容的的簡單標(biāo)簽的自定義標(biāo)簽 -->
  tag>
    name>BodyController/name>
    tag-class>web.simpletag.BodyController/tag-class>
    body-content>scriptless/body-content>
  /tag>
/taglib>

%@ page language="java" contentType="text/html; charset=UTF-8"
  pageEncoding="UTF-8"%>
%@taglib uri="/simplesummer" prefix="summer"%>
!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
html>
head>
meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
title>用SimpleTag接口實現(xiàn)的控制標(biāo)簽體內(nèi)容是否執(zhí)行的測試頁面/title>
/head>
body>
  summer:BodyController>Summer/summer:BodyController>


/body>
/html>