JSP的自定义标签其实是挺好用的，比如在一个比较复杂的页面中，简单地插入几句
，就可以避免大量的冗余的代码，比如在一个新闻网站中，可以做一个播放幻灯的自定义标签。下面总结下，大概做自定义标签的套路如下：
public class SlidenewsTag extends SimpleTagSupport {
/** 标签体处理 */
public void doTag() throws JspException, IOException{
。。。。。。。
//使用WebApplicationContextUtils工具类获取Spring IOC容器中的dao实例
dao = (BaseDAOImpl)WebApplicationContextUtils.getRequiredWebApplicationContext(((PageContext)getJspContext()).getServletContext()).getBean("dao");
StringBuffer sb=new StringBuffer();
List list=dao.query(hql,1,number);
if(list==null||list.size()==0){
//输出处理结果到页面上
getJspContext().getOut().println("");
return;
}
Iterator it=list.iterator();
sb.append(" <script language=javascript>\n");
sb.append(" var focus_width"+slideno+"="+width+"; /*幻灯片新闻图片宽度*/\n");
sb.append(" var focus_height"+slideno+"="+height+"; /*幻灯片新闻图片高度*/\n");
sb.append(" var text_height"+slideno+"=20; /*幻灯片新闻文字标题高度*/\n");
sb.append(" var swf_height"+slideno+" = focus_height"+slideno+"+text_height"+slideno+";\n");
sb.append(" var pics"+slideno+" = '';\n");
sb.append(" var links"+slideno+" = '';\n");
sb.append(" var texts"+slideno+" = '';\n");
sb.append(" function ati"+slideno+"(url, img, title)\n");
sb.append(" {\n");
sb.append(" if(pics"+slideno+" != '')\n");
sb.append(" {\n");
sb.append(" pics"+slideno+" = \"|\" + pics"+slideno+";\n");
sb.append(" links"+slideno+" = \"|\" + links"+slideno+";\n");
sb.append(" texts"+slideno+" = \"|\" + texts"+slideno+";\n");
sb.append(" }");
sb.append(" pics"+slideno+" = escape(img) + pics"+slideno+";\n");
sb.append(" links"+slideno+" = escape(url) + links"+slideno+";\n");
sb.append(" texts"+slideno+" = title + texts"+slideno+";\n");
sb.append(" }\n");
sb.append(" </script>\n");
sb.append(" <script language=javascript> \n");
while(it.hasNext()){
obj=(News)it.next();
if (obj.getTitle().length()>titlelen){
sb.append(" ati"+slideno+"('"+baseurl+obj.getHtmlPath()+"', '"+baseurl+"/"+obj.getPicture().trim()+"', '"+Tools.cutString(obj.getTitle(), titlelen*2)+"');\n");
}else{
sb.append(" ati"+slideno+"('"+baseurl+obj.getHtmlPath()+"', '"+baseurl+"/"+obj.getPicture().trim()+"', '"+obj.getTitle()+"');\n");
}
}
sb.append(" document.write('<embed src=\""+baseurl+"/js/pixviewer.swf\" wmode=\"opaque\" FlashVars=\"pics='+pics"+slideno+"+'&links='+links"+slideno+"+'&texts='+texts"+slideno+"+'&borderwidth='+focus_width"+slideno+"+'&borderheight='+focus_height"+slideno+"+'&textheight='+text_height"+slideno+"+'\" menu=\"false\" bgcolor=\"#DADADA\" quality=\"high\" width=\"'+ focus_width"+slideno+"+'\" height=\"'+ swf_height"+slideno+" +'\" allowScriptAccess=\"sameDomain\" type=\"application/x-shockwave-flash\"/>'); \n");
sb.append("</script>\n");
//输出处理结果到页面上
getJspContext().getOut().println(sb);
}
可以看到，其实就是不断组装HTML而已，没什么复杂和特别的
2 建立xxx.tld文件
<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">
<!-- 标签库的版本号 -->
<tlib-version>1.0</tlib-version>
<!-- 标签库的默认前缀 -->
<short-name>eportal</short-name>
<!-- 标签库的默认URI -->
<uri>/eportal</uri>
<tag>
<description>幻灯片新闻列表标签</description>
<name>slidenews</name>
<tag-class>com.eportal.tld.SlidenewsTag</tag-class>
<!-- 标签体为空 -->
<body-content>empty</body-content>
<attribute>
<description>栏目编号,多个栏目编号中间用号码分隔,如:I_001,I_002</description>
<name>section</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>新闻类型:0-最新新闻 1-头条新闻 2-热点新闻 3-精彩推荐 4-所有类型</description>
<name>newstype</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>显示新闻的条数</description>
<name>number</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>幻灯片宽度</description>
<name>width</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>幻灯片高度</description>
<name>height</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>标题字数</description>
<name>titlelen</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>基本URL</description>
<name>baseurl</name>
<required>false</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
<attribute>
<description>在本页中当前幻灯片的序号</description>
<name>slideno</name>
<required>true</required>
<rtexprvalue>true</rtexprvalue>
</attribute>
</tag>
注意，其中的所有<attribute>,都要在JAVA里设置getter和setter
3 调用
<%@ taglib prefix="e" uri="/eportal"%>
<!-- 使用自定义幻灯新闻标签 -->
<e:slidenews section="001" number="5" titlelen="30" width="440" height="260" baseurl="<%=basepath%>" slideno="1"/>
注意不TLD放在web-inf下就可以了