IllegalStateException：bean名称“category”的BindingResult和纯目标对象都不能作为请求属性使用

Question

我在web上查找了几乎所有与此问题相关的答案，但无法在代码中找出问题所在。

这是我的JSP页面。

<form:form method="POST" commandName="category" modelAttribute="category" action="search_category">
    <form:input path="category_name" /> 
    <input type="submit" value="Submit">  
</form:form>

当我删除

<form:input path="category_name" /> 

很好用。我可以和我的控制器沟通。所以问题与这条线有关。

@Controller
public class SearchCategory {

    @Autowired      
    private CategoryService categoryService;

    @RequestMapping(value = "/search_category",  method = RequestMethod.POST)
    public @ResponseBody String searchCategoryFromDatabase(@ModelAttribute("category") Category category, BindingResult result){        

        return "something";
    }
}

<?xml version="1.0" encoding="UTF-8"?>
<web-app version="2.5" xmlns="http://java.sun.com/xml/ns/javaee"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_2_5.xsd">

    <!-- Processes application requests -->
    <servlet>
        <servlet-name>appServlet</servlet-name>
        <servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
        <init-param>
            <param-name>contextConfigLocation</param-name>
            <param-value>/WEB-INF/servlet-context.xml</param-value>
        </init-param>
        <load-on-startup>1</load-on-startup>
    </servlet>

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

     <!-- The definition of the Root Spring Container shared by all Servlets and Filters -->  
    <context-param>  
        <param-name>contextConfigLocation</param-name>  
        <param-value>/WEB-INF/applicationContext.xml</param-value>  
    </context-param>  

    <filter>  
        <filter-name>hibernateFilter</filter-name>  
        <filter-class>org.springframework.orm.hibernate4.support.OpenSessionInViewFilter</filter-class>  
    </filter>  
    <filter-mapping>  
        <filter-name>hibernateFilter</filter-name>  
        <url-pattern>/*</url-pattern>  
    </filter-mapping>      

    <listener>
    <listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>

</web-app>

<!--  Set the default page as index.jsp -->
<mvc:view-controller path="/" view-name="index"/>

<!-- Map resources --> 
<mvc:resources mapping="/resources/**" location="/, classpath:/META-INF/web-resources/" /> 

<!-- Map simple view name such as "test" into /WEB-INF/views/test.jsp -->
<bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
    <property name="prefix" value="/WEB-INF/" />
    <property name="suffix" value=".jsp" />
</bean>

<!-- Enable @Controller annotation support -->
    <mvc:annotation-driven />

    <context:annotation-config/>    

    <!--  Set the default page as index.jsp -->
    <mvc:view-controller path="/" view-name="index"/>

     <!-- Map resources --> 
    <mvc:resources mapping="/resources/**" location="/, classpath:/META-INF/web-resources/" /> 

    <!-- Map simple view name such as "test" into /WEB-INF/views/test.jsp -->
    <bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="prefix" value="/WEB-INF/" />
        <property name="suffix" value=".jsp" />
    </bean>

    <!-- Scan classpath for annotations (eg: @Service, @Repository etc) -->
    <context:component-scan base-package="com.XXXX"/>

    <!-- JDBC Data Source. It is assumed you have MySQL running on localhost port 3306 with 
         username root and blank password. Change below if it's not the case -->
    <bean id="dataSource" class="org.apache.commons.dbcp.BasicDataSource" destroy-method="close">
        <property name="driverClassName" value="com.mysql.jdbc.Driver"/>
        <property name="url" value="jdbc:mysql://localhost:3306/XXXX"/>
        <property name="username" value="XXXX"/>
        <property name="password" value="XXXX"/>
        <property name="validationQuery" value="SELECT 1"/>
    </bean>

    <!-- Hibernate Session Factory -->
    <bean id="sessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean">
        <property name="dataSource" ref="dataSource"/>
        <property name="configLocation">
            <value>classpath:hibernate.cfg.xml</value>
        </property>
        <property name="packagesToScan">
            <array>
                <value>com.XXXX</value>
            </array>
        </property>
        <property name="hibernateProperties">
            <value>
                hibernate.dialect=org.hibernate.dialect.MySQLDialect
            </value>
        </property>     
    </bean>

    <!-- Hibernate Transaction Manager -->
    <bean id="transactionManager" class="org.springframework.orm.hibernate4.HibernateTransactionManager">
        <property name="sessionFactory" ref="sessionFactory"/>
    </bean>

    <!-- Activates annotation based transaction management -->
    <tx:annotation-driven transaction-manager="transactionManager"/>  

我可能在XML文件中做错了什么。我是新来的这个春暖花开的员工，所以等待您的帮助。谢谢。

这是引发的异常

Stacktrace:] with root cause
java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name 'category' 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:168)
    at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getPropertyPath(AbstractDataBoundFormElementTag.java:188)
    at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.getName(AbstractDataBoundFormElementTag.java:154)
    at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.autogenerateId(AbstractDataBoundFormElementTag.java:141)
    at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.resolveId(AbstractDataBoundFormElementTag.java:132)
    at org.springframework.web.servlet.tags.form.AbstractDataBoundFormElementTag.writeDefaultAttributes(AbstractDataBoundFormElementTag.java:116)
    at org.springframework.web.servlet.tags.form.AbstractHtmlElementTag.writeDefaultAttributes(AbstractHtmlElementTag.java:422)
    at org.springframework.web.servlet.tags.form.InputTag.writeTagContent(InputTag.java:142)
    at org.springframework.web.servlet.tags.form.AbstractFormTag.doStartTagInternal(AbstractFormTag.java:84)
    at org.springframework.web.servlet.tags.RequestContextAwareTag.doStartTag(RequestContextAwareTag.java:80)
    at org.apache.jsp.index_jsp._jspx_meth_form_005finput_005f0(index_jsp.java:208)
    at org.apache.jsp.index_jsp._jspx_meth_form_005fform_005f0(index_jsp.java:168)
    at org.apache.jsp.index_jsp._jspService(index_jsp.java:100)
    at org.apache.jasper.runtime.HttpJspBase.service(HttpJspBase.java:70)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.jasper.servlet.JspServletWrapper.service(JspServletWrapper.java:432)
    at org.apache.jasper.servlet.JspServlet.serviceJspFile(JspServlet.java:390)
    at org.apache.jasper.servlet.JspServlet.service(JspServlet.java:334)
    at javax.servlet.http.HttpServlet.service(HttpServlet.java:728)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:305)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.springframework.orm.hibernate4.support.OpenSessionInViewFilter.doFilterInternal(OpenSessionInViewFilter.java:149)
    at org.springframework.web.filter.OncePerRequestFilter.doFilter(OncePerRequestFilter.java:108)
    at org.apache.catalina.core.ApplicationFilterChain.internalDoFilter(ApplicationFilterChain.java:243)
    at org.apache.catalina.core.ApplicationFilterChain.doFilter(ApplicationFilterChain.java:210)
    at org.apache.catalina.core.StandardWrapperValve.invoke(StandardWrapperValve.java:222)
    at org.apache.catalina.core.StandardContextValve.invoke(StandardContextValve.java:123)
    at org.apache.catalina.authenticator.AuthenticatorBase.invoke(AuthenticatorBase.java:502)
    at org.apache.catalina.core.StandardHostValve.invoke(StandardHostValve.java:171)
    at org.apache.catalina.valves.ErrorReportValve.invoke(ErrorReportValve.java:99)
    at org.apache.catalina.valves.AccessLogValve.invoke(AccessLogValve.java:953)
    at org.apache.catalina.core.StandardEngineValve.invoke(StandardEngineValve.java:118)
    at org.apache.catalina.connector.CoyoteAdapter.service(CoyoteAdapter.java:408)
    at org.apache.coyote.http11.AbstractHttp11Processor.process(AbstractHttp11Processor.java:1023)
    at org.apache.coyote.AbstractProtocol$AbstractConnectionHandler.process(AbstractProtocol.java:589)
    at org.apache.tomcat.util.net.JIoEndpoint$SocketProcessor.run(JIoEndpoint.java:310)
    at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
    at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
    at java.lang.Thread.run(Thread.java:722)

Answer 1

如果您要通过http://localhost:8080/yourapp这样的方式访问index.jsp，我假设您有一个 。

这意味着index.jsp生成HTML时，无需Spring进行任何预处理。你想把这个

<form:form method="POST" commandName="category" modelAttribute="category" action="search_category">
    <form:input path="category_name" /> 
    <input type="submit" value="Submit">  
</form:form>

其中 来自Spring的标记库。首先，请注意您同时使用commandname和modelattribute。这是多余的。使用其中一个或另一个，而不是两者兼而有之。其次，当您指定其中任何一个时，标记实现将查找具有指定名称的HttpServletRequest属性。在您的示例中，没有向HttpServletRequest属性添加这样的属性。这是因为Servlet容器直接转发到index.jsp。

与其这样做，不如创建一个新的@controller处理程序方法，该方法将向模型添加一个属性并转发到index.jsp视图。

@RequestMapping(value = "/", method = RequestMethod.GET)
public String welcomePage(Model model) {
    model.addAttribute("category", new Category()); // the Category object is used as a template to generate the form
    return "index";
}

你可以把这个处理掉

<!--  Set the default page as index.jsp -->
<mvc:view-controller path="/" view-name="index"/>

此外，将任何MVC配置从applicationcontext.xml文件移动到servlet-context.xml文件。那是属于它的地方。原因如下。