自定义一个很简单的JSP标签

web 工程，新建java类：

[java]  package leon.webtest.tags; 
 
import java.text.simpledateformat; 
import java.util.date; 
 
import javax.servlet..jspexception; 
import javax.servlet.jsp.jspwriter; 
import javax.servlet.jsp.tagext.tagsupport; 
 
 
public class datetime extends tagsupport { 
 
    private static final long serialversionuid = 1l; 
 
    public int dostarttag() throws jspexception { 
        try { 
            jspwriter out = this.pagecontext.getout(); 
             
            simpledateformat sdf = new simpledateformat("yyyy-mm-dd hh:mm:ss"); 
             
            out.println("<span>"); 
            out.println(sdf.format(new date())); 
            out.println("</span>"); 
 
        } catch (exception e) { 
            throw new jspexception(e.getmessage()); 
        } 
        return skip_body; 
    } 
} 

package leon.webtest.tags;

import java.text.simpledateformat;
import java.util.date;

import javax.servlet.jsp.jspexception;
import javax.servlet.jsp.jspwriter;
import javax.servlet.jsp.tagext.tagsupport;

public class datetime extends tagsupport {

 private static final long serialversionuid = 1l;

 public int dostarttag() throws jspexception {
  try {
   jspwriter out = this.pagecontext.getout();
   
   simpledateformat sdf = new simpledateformat("yyyy-mm-dd hh:mm:ss");
   
   out.println("<span>");
   out.println(sdf.format(new date()));
   out.println("</span>");

  } catch (exception e) {
   throw new jspexception(e.getmessage());
  }
  return skip_body;
 }
}
新建tld文件：web-inf/tld/webtest-tags.tld

[html]  <?xml version="1.0" encoding="utf-8" ?> 
<taglib xmlns="https://java.sun.com/xml/ns/j2ee"  
    xmlns:xsi="https://www.w3.org/2001/xmlschema-instance" 
    xsi:schemallocation="https://java.sun.com/xml/ns/j2ee web-jsptaglibrary_2_0.xsd" 
    version="2.0"> 
 
    <description>a tag library exercising simpletag handlers.</description> 
    <tlib-version>1.0</tlib-version> 
    <short-name>examples</short-name> 
    <uri>/mytags</uri> 
    <description>jsp self-define tag library.</description> 
 
    <tag> 
        <description>this is an date time tag</description> 
        <name>datetime</name> 
        <tag-class>leon.webtest.tags.datetime</tag-class> 
        <body-content>empty</body-content> 
    </tag> 
</taglib> 

<?xml version="1.0" encoding="utf-8" ?>
<taglib xmlns="https://java.sun.com/xml/ns/j2ee"
 xmlns:xsi="https://www.w3.org/2001/xmlschema-instance"
 xsi:schemallocation="https://java.sun.com/xml/ns/j2ee web-jsptaglibrary_2_0.xsd"
 version="2.0">

 <description>a tag library exercising simpletag handlers.</description>
 <tlib-version>1.0</tlib-version>
 <short-name>examples</short-name>
 <uri>/mytags</uri>
 <description>jsp self-define tag library.</description>

 <tag>
  <description>this is an date time tag</description>
  <name>datetime</name>
  <tag-class>leon.webtest.tags.datetime</tag-class>
  <body-content>empty</body-content>
 </tag>
</taglib>
web.xml中的配置：

[html] <?xml version="1.0" encoding="utf-8"?> 
<web-app id="webapp_id" version="2.4"  
    xmlns="https://java.sun.com/xml/ns/j2ee"  
    xmlns:xsi="https://www.w3.org/2001/xmlschema-instance"  
    xsi:schemalocation="https://java.sun.com/xml/ns/j2ee https://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd"> 
     
    <display-name>webtest</display-name> 
     
    <welcome-file-list> 
        <welcome-file>index.html</welcome-file> 
        <welcome-file>index.jsp</welcome-file> 
    </welcome-file-list> 
     
    <jsp-config> 
        <taglib> 
            <taglib-uri>/mytags</taglib-uri> 
            <taglib-location>/web-inf/tld/webtest-tag.tld 
            </taglib-location> 
        </taglib> 
    </jsp-config> 
</web-app> 

<?xml version="1.0" encoding="utf-8"?>
<web-app id="webapp_id" version="2.4"
 xmlns="https://java.sun.com/xml/ns/j2ee"
 xmlns:xsi="https://www.w3.org/2001/xmlschema-instance"
 xsi:schemalocation="https://java.sun.com/xml/ns/j2ee https://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
 
 <display-name>webtest</display-name>
 
 <welcome-file-list>
  <welcome-file>index.html</welcome-file>
  <welcome-file>index.jsp</welcome-file>
 </welcome-file-list>
 
 <jsp-config>
  <taglib>
   <taglib-uri>/mytags</taglib-uri>
   <taglib-location>/web-inf/tld/webtest-tag.tld
   </taglib-location>
  </taglib>
 </jsp-config>
</web-app>
jsp中的使用：

首先是导入：

<%@ taglib uri="/mytags" prefix="leon" %>

 

使用标签：

<leon:datetime />

 

加强版：需要显示出来的时间是动态的，像时钟一样会跳秒的。