为什么我的电脑运行部了带javabean的jsp文件，配置绝对正确，因为之前的简单代码都可以运行，

出现
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: /4/useBean.jsp(4,3) The value for the useBean class attribute tom.jiafei.Circle is invalid.
	org.apache.jasper.compiler.DefaultErrorHandler.jspError(DefaultErrorHandler.java:40)
	org.apache.jasper.compiler.ErrorDispatcher.dispatch(ErrorDispatcher.java:407)
	org.apache.jasper.compiler.ErrorDispatcher.jspError(ErrorDispatcher.java:148)
	org.apache.jasper.compiler.Generator$GenerateVisitor.visit(Generator.java:1272)
	org.apache.jasper.compiler.Node$UseBean.accept(Node.java:1178)
	org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2361)
	org.apache.jasper.compiler.Node$Visitor.visitBody(Node.java:2411)
	org.apache.jasper.compiler.Node$Visitor.visit(Node.java:2417)
	org.apache.jasper.compiler.Node$Root.accept(Node.java:495)
	org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2361)
	org.apache.jasper.compiler.Generator.generate(Generator.java:3426)
	org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:216)
	org.apache.jasper.compiler.Compiler.compile(Compiler.java:332)
	org.apache.jasper.compiler.Compiler.compile(Compiler.java:312)
	org.apache.jasper.compiler.Compiler.compile(Compiler.java:299)
	org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:586)
	org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:317)
	org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:342)
	org.apache.jasper.servlet.JspServlet.service(JspServlet.java:267)
	javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
note The full stack trace of the root cause is available in the Apache Tomcat/6.0.20 logs.

Apache Tomcat/6.0.20