JSP学习笔记（六）：自定义标签-JSP2.x

一、SimpleTag 接口 和 SimpleTagSupport 类

SimpleTag 接口只有一个 doTag()方法，同时支持参数与标签体。一般实现 SimpleTagSupport 类即可。

二、简单实现

<span style="font-family:Arial;">package taglib.jsp_two;import java.io.IOException;import javax.servlet.jsp.JspException;import javax.servlet.jsp.tagext.SimpleTagSupport;/** * * @Title: 继承 SimpleTagSupport Jsp2.0标签 * @Description: * @Copyright: Copyright (c) 2015 * @Company: * * @author: SAM-SHO * @version: 1.0 * @CreateDate：Feb 16, 2015 */public class MultiTag extends SimpleTagSupport { private int num1; private int num2; @Override public void doTag() throws JspException, IOException {  this.getJspContext().getOut().write("" + num1 + " * " + num2 + " = " + (num1 * num2)); } public int getNum1() {  return num1; } public void setNum1(int num1) {  this.num1 = num1; } public int getNum2() {  return num2; } public void setNum2(int num2) {  this.num2 = num2; }}// end</span>

<span style="font-family:Arial;"><tag>  <name>multi</name>  <tagclass>taglib.jsp_two.MultiTag</tagclass>  <bodycontent>empty</bodycontent>  <info>multi tag with parameters.</info>  <attribute>   <name>num1</name>   <required>true</required>   <rtexprvalue>true</rtexprvalue>  </attribute>  <attribute>   <name>num2</name>   <required>true</required>   <rtexprvalue>true</rtexprvalue>  </attribute> </tag></span>

三、带标签体

1、实现方式不同： 

1）JSP1.x 标签将标签体通过 setBodyContent()方法注入 在 bodyTag 中，通过 getBodyContent()即可得到标签体。

2）SimpleTag 是通过 jspFragment 的对象实现的。

2、实现代码：

<span style="font-family:Arial;">package taglib.jsp_two;import java.io.IOException;import java.io.StringWriter;import javax.servlet.jsp.JspException;import javax.servlet.jsp.tagext.JspFragment;import javax.servlet.jsp.tagext.SimpleTagSupport;/** * * @Title: 带标签体的jsp2.x实现 * @Description: * @Copyright: Copyright (c) 2015 * @Company: * * @author: SAM-SHO * @version: 1.0 * @CreateDate：Feb 16, 2015 */public class ToUpperCaseTag extends SimpleTagSupport { @Override public void doTag() throws JspException, IOException {  // 将 标签体内容读入该 writer  StringWriter writer = new StringWriter();  // 标签体 为 JspFragment 的形式  JspFragment jspFragment = this.getJspBody();  // 通过 invoke 输出到指定的 writer 中。  // 如果参数为 null，将输出到默认的 writer 中，即 getJspContext().getOut() 输出到HTML中  jspFragment.invoke(writer);  String content = writer.getBuffer().toString();  this.getJspContext().getOut().print(content.toUpperCase()); }}// end</span>

<span style="font-family:Arial;"> <tag>  <name>toUpperCase</name>  <tagclass>taglib.jsp_two.ToUpperCaseTag</tagclass>  <bodycontent>tagdependent</bodycontent>  <info>body tag</info> </tag></span>

1）ToUpperCaseTag 中，标签体的内容被封装为 JspFragment 对象，通过 getJspBody 方法可以得到该对象。代码通过invoke() 方法输出到了指定的 StringWriter对象中，然后通过StringWriter 对象获取字符串。若果要直接输出，可以使用JspFragment.invoke(null) 。

2）tld注意：bodycontent为 tagdependent。

四、多个标签体

<span style="font-family:Arial;">package taglib.jsp_two;import java.io.IOException;import java.io.StringWriter;import javax.servlet.jsp.JspException;import javax.servlet.jsp.tagext.JspFragment;import javax.servlet.jsp.tagext.SimpleTagSupport;/** * * @Title: 带标多个标签体的jsp2.x实现 * @Description: * @Copyright: Copyright (c) 2015 * @Company: * * @author: SAM-SHO * @version: 1.0 * @CreateDate：Feb 16, 2015 */public class MultiAttributeTag extends SimpleTagSupport { private JspFragment body1;//一个标签体 private JspFragment body2;//第二个标签体 public void setBody1(JspFragment body1) {  this.body1 = body1; } public void setBody2(JspFragment body2) {  this.body2 = body2; } @Override public void doTag() throws JspException, IOException {  StringWriter writer1 = new StringWriter();  StringWriter writer2 = new StringWriter();  for (int i = 0; i < 5; i++) {   // body1 调用 5 次   body1.invoke(writer1);  }  for (int i = 0; i < 3; i++) {   // body2 调用 3 次   body2.invoke(writer2);  }  this.getJspContext().getOut().print("3 次调用 body2 后的结果：" + writer2.getBuffer().toString() + "<br/><br/>");  this.getJspContext().getOut().print("5 次调用 body1 后的结果：" + writer1.getBuffer().toString() + "<br/><br/>"); }}// end</span>

<span style="font-family:Arial;"><tag>  <name>multiAttribute</name>  <tagclass>taglib.jsp_two.MultiAttributeTag</tagclass>  <bodycontent>tagdependent</bodycontent>  <info>multi attribute tag with parameters.</info>  <attribute>   <name>body1</name>   <required>false</required>   <fragment>true</fragment>  </attribute>  <attribute>   <name>body2</name>   <required>false</required>   <fragment>true</fragment>  </attribute> </tag></span>

五、调用标签的JSP代码

<span style="font-family:Arial;"><%@ page language="java" contentType="text/html; charset=UTF-8"%><%@ taglib uri="http://java.sun.com/jsp/jstl/core" prefix="c"%><%@ taglib uri="http://www.mayTaglib.com/tags" prefix="myTaglib"%><c:set var="base" value="${pageContext.request.contextPath}" /><html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>Insert title here</title></head><body><myTaglib:multi num1="3" num2="4" /><myTaglib:toUpperCase>abcdefg</myTaglib:toUpperCase><br/><myTaglib:multiAttribute> <jsp:attribute name="body1">标签体一, </jsp:attribute> <jsp:attribute name="body2">标签体二, </jsp:attribute></myTaglib:multiAttribute></body></html></span>

1、借助JSP的 <jsp：attribute/>行为。

2、两个标签体实际上就是标签类的两个属性。这两个属性必须是 JspFragment 类型。也必须通过 <jsp：attribute/>行为设定。而且tld 配置必须配置为 fragment类型。