tag 編寫一個Tag涉及三個步驟，
（1）編寫JSP
（2）編寫Tag的java程式
（3）編寫tag庫的描述檔案tld（實際是一個XML檔案）
這三個步驟之間沒有順序約束，下面是一個簡單的例子：
1 編寫HelloTag.jsp
<%@page contentType="text/html"%>
<html>
<head><title>Hello Tags Page</title></head>
<body>
<%@ taglib uri="/WEB-INF/classes/tags/helloTag.tld" prefix="hello" %>
<hello:helloTag />
</body>
</html>
2 編寫tag
HelloTag.java
package tags; //注意:必須放在一個包中
import java.io.*;
import javax.servlet.jsp.*;
import javax.servlet.jsp.tagext.*;
public class HelloTag extends TagSupport {
public int doStartTag() {
try {
//使用JspWriter獲得JSP的輸出對象
JspWriter jspWriterOutput = pageContext.getOut();
jspWriterOutput.print("Hello Tag!");
} catch (IOException ioEx) {
System .out.println("IOException in HelloTag " + ioEx);
}
return (SKIP_BODY);
}
}
3 編寫helloTag.tld
這是Tag庫的描述部分：
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE taglib
PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.2//EN"
"http://java.sun.com/dtd/web-jsptaglibrary_1_2.dtd">
<taglib>
<tlib-version>1.0</tlib-version>
<jsp-version>1.2</jsp-version>
<shorttag -name>helloTag</short -name>
<uri>/WEB-INFtagshelloTag</uri>
<display-name>helloTag</display-name>
<small-icon></small-icon>
<large-icon></large-icon>
<description>simple hello tags tag
</description>
<tag>
<name>helloTag</name>
<tag-class >tags.HelloTag</tag-class >
<body-content>empty</body-content>
<small-icon></small-icon>
<large-icon></large-icon>
<description></description>
<example></example>
</tag>
</taglib>
4 注意:
通常手工編寫XML檔案,但是Sun的教程建議使用IDE工具編寫自訂tag，比如NetBeans
一般，直接把tld檔案放到WEB-INF目錄中。
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