求助:关于jsp文件无法调用Bean的问题,谢谢!
愚弟百思不得其解，请各位大虾相助!!!

usebean.jsp文件置于D:\Tomcat   5.5\webapps\ROOT\目录下
源程序如下:
<%@   page   import   =   "test.TestBean "   %>
<jsp:useBean   id   = "test "   class   =   "test.TestBean ">
</jsp:useBean>
<%   test.setString1( "Hello ");
      test.setString2( "   world ");
%>
<%=   test.getString1Value()   %>
<br>
<%=   test.getString2Value()   %>


TestBean.java       置于D:\Tomcat   5.5\webapps\ROOT\WEB-INF\classes\test\目录下
源程序如下:
package   test;
public   class   TestBean{
private   String     string1   =   null;
private   String     string2   =   null;
public   TestBean()
{
}
public   void   setString1(String   value)
{
string1   =   value;
}
public   void   setString2(String   value)
{
string2   =   value;
}
public   String   getString1Value()
{
return   string1;
}
public   String   getString2Value()
{
return   string2;
}
}

Jdk环境已经配置好
Tomcat已经启动
在IE地址栏键入http://localhost:8080/usebean.jsp

出现以下错误提示:

HTTP   Status   500   -  
--------------------------------------------
type   Exception   report

message  

description   The   server   encountered   an   internal   error   ()   that   prevented   it   from   fulfilling   this   request.

exception  

org.apache.jasper.JasperException:   /usebean.jsp(4,0)   The   value   for   the   useBean   class   attribute   test.TestBean   is   invalid.
org.apache.jasper.servlet.JspServletWrapper.handleJspException(JspServletWrapper.java:512)
org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377)
org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:314)
org.apache.jasper.servlet.JspServlet.service(JspServlet.java:264)
javax.servlet.http.HttpServlet.service(HttpServlet.java:802)


root   cause  

org.apache.jasper.JasperException:   /usebean.jsp(4,0)   The   value   for   the   useBean   class   attribute   test.TestBean   is   invalid.
org.apache.jasper.compiler.DefaultErrorHandler.jspError(DefaultErrorHandler.java:39)
org.apache.jasper.compiler.ErrorDispatcher.dispatch(ErrorDispatcher.java:405)
org.apache.jasper.compiler.ErrorDispatcher.jspError(ErrorDispatcher.java:146)
org.apache.jasper.compiler.Generator$GenerateVisitor.visit(Generator.java:1174)
org.apache.jasper.compiler.Node$UseBean.accept(Node.java:1116)
org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2163)
org.apache.jasper.compiler.Node$Visitor.visitBody(Node.java:2213)
org.apache.jasper.compiler.Node$Visitor.visit(Node.java:2219)
org.apache.jasper.compiler.Node$Root.accept(Node.java:456)
org.apache.jasper.compi