自定义JSP标签：（必须扩展javax.servlet.jsp.TagSupport或javax.servlet.jsp.BodyTagSupport）

1。步骤：

**创建标签的处理类
**创建标签的描述文件
**在JSP文件中引入标签

2。创建标签处理类

(1)JSP Tag API

方法：doStartTag()：在JSP容器遇到标签的起始标志时调用，返回一个整数：Tag.SKIP_BODY,Tag.EVAL_BODY_INCLUDE
doEndTag():返回一个整数：Tag.SKIP_PAGE,Tag.EVAL_PAGE
setValue(String k,Object o)
getValue(String k)
removeValue(String k)
setPageContext(PageContext pc):设置PageContext对象，在doStartTag()和doEndTag()之前调用
setParent(Tag t):设置了该标签的上层标签的处理类，在doStartTag()和doEndTag()之前调用
getParent()：返回上层标签的处理类

PageContext类提供了保存和访问web应用的共乡数据的方法setAttribute(String name,Object o,int scope)和getAttribute(String name,int scope) (scope的值类似PageContext.PAGE_SCOPE)

(2)<prefix:Mytag attribute="value">
  ...
  </prefix:Mytag>

标签处理类就应该把这个属性作为成员变量，如：
private int attribute;

public void setAttribute(int value)
{
this.attribute=value;
}

public void getAttribute()
{
return attribute;
}

(3)
**创建静态文本文件(以key/value形式存放)：
message.properties 文件：
hello.title = helloapp
hello.hello = Hello
login.title = helloapp
login.user = User Name
login.password = Password
login.submit = Submit

**在web应用启动时装载静态文本：

public void init(ServletConfig config)
  throws ServletException {
  super.init(config);

  Properties ps=new Properties();
  Properties ps_ch=new Properties();
  try{
    ServletContext context=config.getServletContext();
    InputStream in=context.getResourceAsStream("/WEB-INF/messageresource.properties");
    ps.load(in);
    InputStream in_ch=context.getResourceAsStream("/WEB-INF/messageresource_ch.properties");
    ps_ch.load(in_ch);

    in.close();
    in_ch.close();

    context.setAttribute("ps",ps);
    context.setAttribute("ps_ch",ps_ch);
  }catch(Exception e){
    e.printStackTrace();
  }

}

*web.xml


<servlet>
    <servlet-name>dispatcher</servlet-name>
    <servlet-class>mypack.DispatcherServlet</servlet-class>
    <load-on-startup>1</load-on-startup>
  </servlet>

  <servlet-mapping>
    <servlet-name>dispatcher</servlet-name>
    <url-pattern>/dispatcher</url-pattern>
  </servlet-mapping>

**创建MessageTag.java

package mypack;
import javax.servlet.jsp.JspException;
import javax.servlet.jsp.JspTagException;
import javax.servlet.jsp.tagext.TagSupport;
import javax.servlet.http.HttpSession;
import java.util.*;
import java.io.*;

public class MessageTag extends TagSupport
{
  private String key=null;

  public MessageTag() {
  }
  public String getKey(){
    return this.key;
  }

  public void setKey(String key){
    this.key=key;
  }

  // Method called when the closing hello tag is encountered
  public int doEndTag() throws JspException {

    try {
      Properties ps=(Properties)pageContext.getAttribute("ps",pageContext.APPLICATION_SCOPE);
        Properties ps_ch=(Properties)pageContext.getAttribute("ps_ch",pageContext.APPLICATION_SCOPE);

        HttpSession session=pageContext.getSession();
        String language=(String)session.getAttribute("language");
        String message=null;
        if(language!=null && language.equals("Chinese")){
        message=(String)ps_ch.get(key);
       message=new String(message.getBytes("ISO-8859-1"),"GB2312");
        }    
        else
        message=(String)ps.get(key);
        pageContext.getOut().print(message);
    }
    catch (Exception e) {
        throw new JspTagException(e.getMessage());
    }
    // We want to return SKIP_BODY because this Tag does not support
    // a Tag Body
    return SKIP_BODY;
  }

  public void release() {
    super.release();
  }

}

3.创建标签库描述文件：(mytaglib.tld)
<?xml version="1.0" encoding="ISO-8859-1" ?>
<!DOCTYPE taglib
    PUBLIC "-//Sun Microsystems, Inc.//DTD JSP Tag Library 1.1//EN"
   "http://java.sun.com/j2ee/dtds/web-jsptaglibrary_1_1.dtd">

<!-- a tag library descriptor -->

<taglib>
<tlibversion>1.0</tlibversion>
<jspversion>1.1</jspversion>
<shortname>mytaglib</shortname>
<uri>/mytaglib</uri>



<tag>
  <name>message</name>
  <tagclass>mypack.MessageTag</tagclass>
  <bodycontent>empty</bodycontent>
  <info>produce message by key</info>
  <attribute>
   <name>key</name>
   <required>true</required>    
  </attribute>
</tag>


</taglib>

在web.xml加入：
<taglib>
  <taglib-uri>/mytaglib</taglib-uri>
  <taglib-location>/WEB-INF/mytaglib.tld</taglib-location>
</taglib>

4. 应用标签

<%@ taglib uri="/mytaglib" prefix="mm"%>

<mm:message key="hello.title"/>