Spring入门之spring:bind

最近在学习spring，按照一个spring的例子，结果出错拉。错误是：
Neither BindingResult nor plain target object for bean name 'command' available as request attribute

使用的是jdk1.5 + tomcat5.5 +Spring2.1

下面说说我的代码：
spring.login.LoginAction.java
spring.login.LoginForm.java
web.xml
login-serlvet.xml
form.jsp
success.jsp
这些是主要的文件，部署的话是普通的web部署，当然，jsp文件在WEB-INF/jsp/内。
1、 LoginAction.java:

packagespring.login;

importorg.springframework.validation.BindException;
importorg.springframework.web.servlet.ModelAndView;
importorg.springframework.web.servlet.mvc.SimpleFormController;

publicclassLoginActionextendsSimpleFormController...{

protectedModelAndViewonSubmit(Objectcommand,BindExceptionerrors)
throwsException...{
LoginFormform=(LoginForm)command;
if("madic".equals(form.getUsername())
&&"123".equals(form.getPassword()))...{
returnnewModelAndView(this.getSuccessView(),"user",form.getUsername());
}else...{
errors.reject("loginfail","用户名或密码错");
returnnewModelAndView(this.getFormView(),errors.getModel());
}

}

}

LoginForm.java：

packagespring.login;

publicclassLoginForm...{
privateStringusername;
privateStringpassword;
publicStringgetUsername()...{
returnusername;
}
publicvoidsetUsername(Stringusername)...{
this.username=username;
}
publicStringgetPassword()...{
returnpassword;
}
publicvoidsetPassword(Stringpassword)...{
this.password=password;
}
}

loginValidator.java

packagespring.login;

importorg.springframework.validation.Errors;
importorg.springframework.validation.Validator;

publicclassLoginValidatorimplementsValidator...{
publicbooleansupports(Classclazz)...{
returnclazz.equals(LoginForm.class);
}

publicvoidvalidate(Objectobj,Errorserrors)...{
LoginFormform=(LoginForm)obj;
if(form.getPassword().length()<2)...{
errors.rejectValue("password","less-than-two",null,"密码不得小于2个字符");
}
}
}

web.xml

<?xmlversion="1.0"encoding="UTF-8"?>
<web-appid="WebApp_ID"version="2.4"xmlns="http://java.sun.com/xml/ns/j2ee"xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"xsi:schemaLocation="http://java.sun.com/xml/ns/j2eehttp://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
<display-name>
login</display-name>
<description>
SpringLoginExamples.
</description>
<display-name>SpringLogin2Examples</display-name>

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


<context-param>
<param-name>contextConfigLocation</param-name>
<param-value>WEB-INF/login-servlet.xml</param-value>
</context-param>

<servlet>
<servlet-name>login</servlet-name>
<servlet-class>org.springframework.web.servlet.DispatcherServlet</servlet-class>
<init-param>
<param-name>contextConfigLocation</param-name>
<param-value>/WEB-INF/login-servlet.xml</param-value>
</init-param>
</servlet>

<servlet-mapping>
<servlet-name>login</servlet-name>
<url-pattern>*.htm</url-pattern>
</servlet-mapping>

<taglib>
<taglib-uri>/spring</taglib-uri>
<taglib-location>/WEB-INF/spring.tld</taglib-location>
</taglib>
</web-app>

login-servlet.xml

<?xmlversion="1.0"encoding="UTF-8"?>
<!DOCTYPEbeansPUBLIC"-//SPRING/DTDBEAN/EN""http://www.springframework.org/dtd/spring-beans.dtd">
<beans>
<beanid="loginValidator"class="spring.login.LoginValidator"/>

<beanid="urlMapping"class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
<propertyname="mappings">
<props>
<propkey="login.htm">loginAction</prop>
</props>
</property>

</bean>

<beanid="viewResolver"class="org.springframework.web.servlet.view.InternalResourceViewResolver">
<propertyname="viewClass">
<value>org.springframework.web.servlet.view.InternalResourceView</value>
</property>

<propertyname="prefix">
<value>/WEB-INF/jsp/</value>
</property>

<propertyname="suffix">
<value>.jsp</value>
</property>
</bean>

<beanid="loginAction"class="spring.login.LoginAction">
<propertyname="sessionForm">
<value>true</value>
</property>
<propertyname="commandClass">
<value>spring.login.LoginForm</value>
</property>
<propertyname="successView">
<value>success</value>
</property>
<propertyname="formView">
<value>form</value>
</property>
<propertyname="commandName">
<value>loginForm</value>
</property>

<propertyname="validator">
<refbean="loginValidator"/>
</property>
</bean>


</beans>

form.jsp

<%...@tagliburi="/spring"prefix="spring"%>
<%...@pagelanguage="java"contentType="text/html;charset=UTF-8"
pageEncoding="UTF-8"%>
<html>
<head><title>Login</title></head>
<body>

<spring:bindpath="command.*">
<fontcolor="red"><b>${status.errorMessage}</b></font><br>
</spring:bind>

请输入使用者
的名称与密码:<p>
<formname="loginForm"action="login.htm"method="post">

<spring:bindpath="command.username">
名称<br>
<inputtype="text"name="${status.expression}"value="${status.value}"/>
</spring:bind>
<br>
<spring:bindpath="command.password">
密码<br>
<inputtype="password"name="${status.expression}"value="${status.value}"/><br>
</spring:bind>

<inputtype="submit"value="确定"/>

</form>
</body>
</html>

success.jsp就不用说了。很简单。
大家看到什么错误了没有？

<propertyname="commandName">
<value>loginForm</value>
</property>
看看这里，这个commandName就是在login-servlet.xml里的 controller bean loginAction的属性之一。
我们要改为： command
这样在<Spring:bind path="command.*">就不会找不到了。

此外，这里还要注意：

<input>的name属性值必须与<spring:bind>的path属性的匹配，否则就绑定不了！

例如下面的代码就绑定不了

<spring:bind path="user.age">
<input type="text" name="theAge" value="${status.value}">
<font color="red">${status.errorMessage}</font>
</spring:bind>

为了避免手误，强烈推荐下列方法来绑定：

<spring:bind path="user.age">
<input type="text" name="${status.expression}" value="${status.value}">
<font color="red">${status.errorMessage}</font>
</spring:bind>

这个倒是没有注意，看来只有错误，才能更深理解阿。