继承SimpleTagSupport 类实现 DynamicAttributes接口 主要步骤 1.java类 package MyTag; import java.io.IOException;
import java.util.HashMap;
import java.util.List;
import java.util.Map; import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspWriter;
import javax.servlet.jsp.PageContext;
import javax.servlet.jsp.tagext.DynamicAttributes;
import javax.servlet.jsp.tagext.SimpleTagSupport; public class Tag2 extends SimpleTagSupport implements DynamicAttributes {
private static final String ATTR_TEMPLATE = "%s='%s'";
private static final String OPTION_TEMPLATE = "<option value='%1$s'>%1$s</option>";
private List optionsList;
private String name;
private String size;
private Map<String, Object> tagAttrs = new HashMap<String, Object>(); public void setName(String name) {
this.name = name;
} public void setSize(String size) {
this.size = size;
} public void setOptionsList(List optionsList) {
this.optionsList = optionsList;
} @Override
public void doTag() throws JspException, IOException {
PageContext pageContext = (PageContext) getJspContext();
JspWriter out = pageContext.getOut();
out.print("<select ");
out.print(String.format(ATTR_TEMPLATE, "name", this.name));
out.print(String.format(ATTR_TEMPLATE, "size", this.size));
for (String attrName : tagAttrs.keySet()) {
String attrDefinition = String.format(ATTR_TEMPLATE, attrName, tagAttrs.get(attrName));
out.print(attrDefinition);
}
out.print(">"); for (Object option : this.optionsList) { String optionTag = String.format(OPTION_TEMPLATE, option.toString());
out.println(optionTag);
}
out.println("</select>");
} @Override
public void setDynamicAttribute(String uri, String name, Object value) throws JspException { //动态加载标签的其他属性（tld文件未定义属性） 例如 style="width:140px" name 为style value 为 width:140px 若存在过个其他属性时 //循环此方法
tagAttrs.put(name, value);
}
} 2.jsp文件 <%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@ page import="java.util.*" %>
<%@ taglib uri="/mytag2" prefix="formTags" %>
<!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=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<%
List<String> colorList = new ArrayList<String>();
colorList.add("red");
colorList.add("blue");
colorList.add("white");
request.setAttribute("colorList",colorList);
%>
<form action="" method="post">
<formTags:select name="color" size="1" optionsList="${requestScope.colorList}" style="width:140px"/>
</form>
</body>
</html> 3.tld文件 <?xml version="1.0" encoding="UTF-8" ?> <taglib xmlns="http://java.sun.com/xml/ns/j2ee"
xmlns:xsi="http://www.w3g.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://java.sun.com/xml/ns/j2ee web-jsptaglibrary_2_0.xsd"
version="2.0">
<tlib-version>1.2</tlib-version>
<jsp-version>1.2</jsp-version>
<short-name>Forms Taglib</short-name>
<uri>MyTagLib2</uri>
<description>
An example tab library of replacements for the html form tags.
</description>
<tag>
<name>select</name>
<tag-class>MyTag.Tag2</tag-class>
<body-content>empty</body-content>
<attribute>
<name>optionsList</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
<type>java.util.List</type>
</attribute>
<attribute>
<name>name</name>
<required>true</required>
</attribute>
<attribute>
<name>size</name>
<required>true</required>
</attribute>
<dynamic-attributes>true</dynamic-attributes> //动态加载其他属性 例如 style="width:140px
</tag>
</taglib>
4.web.xml <?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://java.sun.com/xml/ns/javaee" xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd" xsi:schemaLocation="http://java.sun.com/xml/ns/javaeehttp://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" >
<display-name>MyProject</display-name>
<welcome-file-list>
<welcome-file>index.jsp</welcome-file>
</welcome-file-list>
<jsp-config>
<taglib>
<taglib-uri>/mytag2</taglib-uri>
<taglib-location>/WEB-INF/tlds/tagLib2.tld</taglib-location>
</taglib>
</jsp-config>
</web-app> 5.效果 | 
