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:

package spring.login;

import org.springframework.validation.BindException;
import org.springframework.web.servlet.ModelAndView;
import org.springframework.web.servlet.mvc.SimpleFormController;

public class LoginAction extends SimpleFormController...{
    
    protected ModelAndView onSubmit(Object command, BindException errors)
    throws Exception...{
                LoginForm form = (LoginForm)command;
                if("madic".equals(form.getUsername())
                        &&"123".equals(form.getPassword()))...{
                    return new ModelAndView(this.getSuccessView(),"user",form.getUsername());
                }else...{ 
                    errors.reject("loginfail","用户名或密码错 ");
                    return new ModelAndView(this.getFormView(),errors.getModel());
                }
        
    }

}

LoginForm.java：

package spring.login;

public class LoginForm ...{
    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;
    }
}

loginValidator.java

package spring.login;

import org.springframework.validation.Errors;
import org.springframework.validation.Validator;

public class LoginValidator implements Validator ...{
    public boolean supports(Class clazz) ...{
        return clazz.equals(LoginForm.class);
    }
    
    public void validate(Object obj, Errors errors)...{
        LoginForm form = (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

<?xml version="1.0" encoding="UTF-8"?>
<web-app id="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/j2ee http://java.sun.com/xml/ns/j2ee/web-app_2_4.xsd">
    <display-name>
    login</display-name>
<description>
    Spring Login Examples.
</description>
    <display-name>Spring Login2 Examples</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

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE beans PUBLIC "-//SPRING/DTD BEAN/EN" "http://www.springframework.org/dtd/spring-beans.dtd">
<beans>
    <bean id="loginValidator" class="spring.login.LoginValidator"/>

    <bean id="urlMapping" class="org.springframework.web.servlet.handler.SimpleUrlHandlerMapping">
        <property name="mappings">
            <props>
                <prop key="login.htm">loginAction</prop>
            </props>
        </property>
    
    </bean>
    
    <bean id="viewResolver" class="org.springframework.web.servlet.view.InternalResourceViewResolver">
        <property name="viewClass">
            <value>org.springframework.web.servlet.view.InternalResourceView</value>
        </property>
        
        <property name="prefix">
            <value>/WEB-INF/jsp/</value>
        </property>
        
        <property name="suffix">
            <value>.jsp</value>
        </property>
    </bean>

    <bean id="loginAction" class="spring.login.LoginAction">
        <property name="sessionForm">
            <value>true</value>
        </property>
        <property name="commandClass">
            <value>spring.login.LoginForm</value>        
        </property>
        <property name="successView">
            <value>success</value>
        </property>
        <property name="formView">
            <value>form</value>
        </property>
        <property name="commandName">
            <value>loginForm</value>
        </property>
    
        <property name="validator">
            <ref bean="loginValidator"/>
        </property>
    </bean>
    
    
</beans>

form.jsp

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

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

    请输入使用者
的名称与密码: <p>
    <form name="loginForm" action="login.htm" method="post">
    
        <spring:bind path="command.username"> 
        名称 <br>
        <input type="text" name="${status.expression }" value="${status.value }"/>
        </spring:bind>
        <br>
        <spring:bind path="command.password">
        密码 <br>
        <input type="password" name="${status.expression }" value="${status.value}"/><br>
        </spring:bind>
        
        <input type="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？

<property name="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。