java - BindingResult 和 bean 名称 'userBean' 的普通目标对象都不能作为请求属性

Question

我正在尝试使用 Spring 表单，但是遇到异常，我在代码中找不到任何错误，并卡在了很长一段时间:

May 16, 2014 11:51:08 PM org.springframework.web.servlet.tags.RequestContextAwareTag doStartTag
SEVERE: Neither BindingResult nor plain target object for bean name 'userBean' available as request attribute
java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name 'userBean' available as request attribute
at org.springframework.web.servlet.support.BindStatus.<init>(BindStatus.java:141)
at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getBindStatus(AbstractDataBoundFormElementTag.java:174)
at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getPropertyPath(AbstractDataBoundFormElementTag.java:194)
at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getName(AbstractDataBoundFormElementTag.java:160)
at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.autogenerateId(AbstractDataBoundFormElementTag.java:147)
at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.resolveId(AbstractDataBoundFormElementTag.java:138)
at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.writeDefaultAttributes(AbstractDataBoundFormElementTag.java:122)
at org.springframework.web.servlet.tags.form.AbstractHtmlElementTag.writeDefaultAttributes(AbstractHtmlElementTag.java:408)
at org.springframework.web.servlet.tags.form.InputTag.writeTagContent(InputTag.java:140)
at org.springframework.web.servlet.tags.form.AbstractFormTag.doStartTagInternal(AbstractFormTag.java:102)
at org.springframework.web.servlet.tags.RequestContextAwareTag.doStartTag(RequestContextAwareTag.java:79)
at org.apache.jsp.login_jsp._jspx_meth_form_005finput_005f0(login_jsp.java:156)
at org.apache.jsp.login_jsp._jspx_meth_form_005fform_005f0(login_jsp.java:111)
at org.apache.jsp.login_jsp._jspService(login_jsp.java:70)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:857)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Thread.java:619)
May 16, 2014 11:51:08 PM org.apache.catalina.core.StandardWrapperValve invoke
SEVERE: Servlet.service() for servlet jsp threw exception
java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name 'userBean' available as request attribute
at org.springframework.web.servlet.support.BindStatus.<init>(BindStatus.java:141)
at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getBindStatus(AbstractDataBoundFormElementTag.java:174)
at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getPropertyPath(AbstractDataBoundFormElementTag.java:194)
at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getName(AbstractDataBoundFormElementTag.java:160)
at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.autogenerateId(AbstractDataBoundFormElementTag.java:147)
at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.resolveId(AbstractDataBoundFormElementTag.java:138)
at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.writeDefaultAttributes(AbstractDataBoundFormElementTag.java:122)
at org.springframework.web.servlet.tags.form.AbstractHtmlElementTag.writeDefaultAttributes(AbstractHtmlElementTag.java:408)
at org.springframework.web.servlet.tags.form.InputTag.writeTagContent(InputTag.java:140)
at org.springframework.web.servlet.tags.form.AbstractFormTag.doStartTagInternal(AbstractFormTag.java:102)
at org.springframework.web.servlet.tags.RequestContextAwareTag.doStartTag(RequestContextAwareTag.java:79)
at org.apache.jsp.login_jsp._jspx_meth_form_005finput_005f0(login_jsp.java:156)
at org.apache.jsp.login_jsp._jspx_meth_form_005fform_005f0(login_jsp.java:111)
at org.apache.jsp.login_jsp._jspService(login_jsp.java:70)
at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:377)
at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:313)
at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:260)
at javax.servlet.http.HttpServlet.service(HttpServlet.java:717)
at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:290)
at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:206)
at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:233)
at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:191)
at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:127)
at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:102)
at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:109)
at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:298)
at org.apache.coyote.http11.Http11Processor.process(Http11Processor.java:857)
at org.apache.coyote.http11.Http11Protocol$Http11ConnectionHandler.process(Http11Protocol.java:588)
at org.apache.tomcat.util.net.JIoEndpoint$Worker.run(JIoEndpoint.java:489)
at java.lang.Thread.run(Thread.java:619)

下面是我的login.jsp页面:

<%@ page language="java" contentType="text/html; charset=ISO-8859-1"
pageEncoding="ISO-8859-1"%>
<%@taglib prefix="form" uri="http://www.springframework.org/tags/form"%>
<!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=ISO-8859-1">
<title>Insert title here</title>
</head>
<body>
<center>
<form:form action="/login" commandName="userBean" method="post"  >
<table>
<tr>
<td>Username:</td><td><form:input path="username"/></td>
</tr>
<tr>
<td>Password:</td><td><form:input path="password"/></td>
</tr>
<tr>
<td><input type="submit"/></td>
</tr>
</table>
</form:form> 
</center>
</body>
</html>

Controller 类SampleController.java

package com.infy.controller;

import org.springframework.stereotype.Controller;
import org.springframework.ui.ModelMap;
import org.springframework.web.bind.annotation.ModelAttribute;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;

@Controller
public class SampleController {

@RequestMapping(value="/login", method=RequestMethod.GET)
public String showForm(ModelMap m){
    System.out.println("viewing the login page.");
    UserBean userBean=new UserBean();
    m.addAttribute("userBean",userBean);
    return "login";
}
@RequestMapping(value="/login",method=RequestMethod.POST)
public String onSubmit(@ModelAttribute("userBean")UserBean userBean){

    System.out.println("Submitting the form");
    return "loginSuccess";
}
}

UserBean.java

package com.infy.controller;

public class UserBean {

private String username;
private String password;
public String getUsername() {
    return username;
}
public void setUsername(String username) {
    this.username = username;
}
public String getPassword() {
    return password;
}
public void setPassword(String password) {
    this.password = password;
}

}

Web.xml

    <?xml version="1.0" encoding="UTF-8"?>
    <web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    id="WebApp_ID" version="2.5">
    <display-name>Spring3MVC</display-name>
   <context-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/dispatcherServlet-servlet.xml</param-value>
    </context-param>
  <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener> 
    <servlet id="dispatcherServlet">
        <servlet-name>dispatcherServlet</servlet-name>
        <servlet-class>
            org.springframework.web.servlet.DispatcherServlet
        </servlet-class>

        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>dispatcherServlet</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>

和dispatcherServlet-servlet.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xmlns:p="http://www.springframework.org/schema/p"
       xmlns:mvc="http://www.springframework.org/schema/mvc"
       xsi:schemaLocation="http://www.springframework.org/schema/beans 
       http://www.springframework.org/schema/beans/spring-beans-3.2.xsd 
       http://www.springframework.org/schema/context  
       http://www.springframework.org/schema/context/spring-context-3.2.xsd
       http://www.springframework.org/schema/mvc
       http://www.springframework.org/schema/mvc/spring-mvc-3.2.xsd
       ">


    <context:component-scan base-package="com.infy"/>
    <mvc:annotation-driven />       
    <bean id="jspViewResolver"
          class="org.springframework.web.servlet.view.InternalResourceViewResolver"
          p:prefix="/WEB-INF/jsp/"
          p:suffix=".jsp" />

</beans>
<welcome-file-list>
    <welcome-file>login.jsp</welcome-file>
</welcome-file-list> 

如果我不在 login.jsp 中使用表单标记，则页面将正确呈现。所以我不认为配置有什么问题。我在表单中使用“userBean”作为 commandName，并在我的 Controller 中添加同名的命令，我不明白为什么它会抛出此异常。请帮忙!

编辑:添加了welcome-file-list的新web.xml

<?xml version="1.0" encoding="UTF-8"?>
<web-app xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:web="http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd"
    id="WebApp_ID" version="2.5">
    <display-name>Spring3MVC</display-name>
    <welcome-file-list>
        <welcome-file>login</welcome-file>
    </welcome-file-list> 
   <context-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>WEB-INF/dispatcherServlet-servlet.xml</param-value>
    </context-param>
  <listener>
        <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
    </listener> 
    <servlet id="dispatcherServlet">
        <servlet-name>dispatcherServlet</servlet-name>
        <servlet-class>
            org.springframework.web.servlet.DispatcherServlet
        </servlet-class>

        <load-on-startup>1</load-on-startup>
    </servlet>
    <servlet-mapping>
        <servlet-name>dispatcherServlet</servlet-name>
        <url-pattern>/</url-pattern>
    </servlet-mapping>



</web-app>

Answer 1

我理解您的问题，这是您两个问题的答案

1) 在 SpringMVC 中，流程从 Controller 开始到 Jsp，而不是 JSP 到 Controller 。在浏览器中，无论您输入什么请求，它都只会指向 Controller 类。在您的 Controller 中，@RequestMapping 属性路径是“/login”，它等于您在浏览器中键入的内容，这就是它起作用的原因。

2) 在 SpringMVC 中，为了访问 WEB-INF 内的任何 View (JSP 文件)只能通过 Controller 来完成。也就是说，您无法直接从浏览器调用 WEB-INF 内的 jsp 文件，这就是为什么即使您在欢迎列表中的 login.jsp 中指定它也不起作用

希望能解答您的疑惑