这个异常是啥情况
错误提示：
org.apache.jasper.JasperException: file:/dologin.jsp(13,4) jsp:getProperty for bean with name 'username'. Name was not previously introduced as per JSP.5.3
at org.apache.jasper.compiler.Generator$GenerateVisitor.visit(Generator.java:1249)
at org.apache.jasper.compiler.Node$GetProperty.accept(Node.java:1131)
at org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2392)
at org.apache.jasper.compiler.Node$Visitor.visitBody(Node.java:2444)
at org.apache.jasper.compiler.Node$Visitor.visit(Node.java:2450)
at org.apache.jasper.compiler.Node$Root.accept(Node.java:471)
at org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2392)
at org.apache.jasper.compiler.Generator.generate(Generator.java:3652)
at org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:252)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:372)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:349)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:333)
at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:600)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:368)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:726)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:469)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:394)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:311)
at servlet.loginServlet.doPost(loginServlet.java:75)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:474)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:783)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:789)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1437)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)
org.apache.jasper.JasperException: file:/dologin.jsp(13,4) jsp:getProperty for bean with name 'username'. Name was not previously introduced as per JSP.5.3
at org.apache.jasper.compiler.Generator$GenerateVisitor.visit(Generator.java:1249)
at org.apache.jasper.compiler.Node$GetProperty.accept(Node.java:1131)
at org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2392)
at org.apache.jasper.compiler.Node$Visitor.visitBody(Node.java:2444)
at org.apache.jasper.compiler.Node$Visitor.visit(Node.java:2450)
at org.apache.jasper.compiler.Node$Root.accept(Node.java:471)
at org.apache.jasper.compiler.Node$Nodes.visit(Node.java:2392)
at org.apache.jasper.compiler.Generator.generate(Generator.java:3652)
at org.apache.jasper.compiler.Compiler.generateJava(Compiler.java:252)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:372)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:349)
at org.apache.jasper.compiler.Compiler.compile(Compiler.java:333)
at org.apache.jasper.JspCompilationContext.compile(JspCompilationContext.java:600)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:368)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:385)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:329)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.catalina.core.ApplicationDispatcher.invoke(ApplicationDispatcher.java:726)
at org.apache.catalina.core.ApplicationDispatcher.processRequest(ApplicationDispatcher.java:469)
at org.apache.catalina.core.ApplicationDispatcher.doForward(ApplicationDispatcher.java:394)
at org.apache.catalina.core.ApplicationDispatcher.forward(ApplicationDispatcher.java:311)
at servlet.loginServlet.doPost(loginServlet.java:75)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:648)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:729)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:230)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.tomcat.websocket.server.WsFilter.doFilter(WsFilter.java:52)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:192)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:165)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:198)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:96)
at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:474)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:140)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:79)
at org.apache.catalina.valves.AbstractAccessLogValve.invoke(AbstractAccessLogValve.java:624)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:87)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:349)
at org.apache.coyote.http11.Http11Processor.service(Http11Processor.java:783)
at org.apache.coyote.AbstractProcessorLight.process(AbstractProcessorLight.java:66)
at org.apache.coyote.AbstractProtocol$ConnectionHandler.process(AbstractProtocol.java:789)
at org.apache.tomcat.util.net.NioEndpoint$SocketProcessor.doRun(NioEndpoint.java:1437)
at org.apache.tomcat.util.net.SocketProcessorBase.run(SocketProcessorBase.java:49)
at java.util.concurrent.ThreadPoolExecutor.runWorker(Unknown Source)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(Unknown Source)
at org.apache.tomcat.util.threads.TaskThread$WrappingRunnable.run(TaskThread.java:61)
at java.lang.Thread.run(Unknown Source)
dologin.jsp代码如下
<%@ page language="java" contentType="text/html; charset=UTF-8"
pageEncoding="UTF-8"%>
<%@ page import="user.Users,java.text.*" %>
<!DOCTYPE html PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
<title>dologin</title>
</head>
<body>
<h1>注册信息</h1>
<jsp:useBean id="regUser" class="user.Users" scope="session"/>
用户名：<jsp:getProperty property="regUser" name="username"/><br>
密码：<jsp:getProperty property="regUser" name="password"/><br>
邮箱：<jsp:getProperty property="regUser" name="email"/><br>
性别：<jsp:getProperty property="regUser" name="gender"/><br>
生日：<%
SimpleDateFormat sdf = new SimpleDateFormat("yyyy年MM月dd日");
String date = sdf.format(regUser.getBirthday());
%>
<%=date %>
自我介绍：<jsp:getProperty property="regUser" name="instroduce"/><br>
是否接受协议：<jsp:getProperty property="regUser" name="flag"/><br>
爱好：<%
String[] hobby = regUser.getHobby();
for(String h : hobby){
%>
<%=h %>
<%
}
%>
</body>
</html>
