spring3 mvc引文校验@NotNull不起作用

package com.zed.model;import javax.validation.constraints.NotNull;import javax.validation.constraints.Size;public class User {        @NotNull(message="用户名不能为空")    private String uname;        @Size(min=4,max=8, message="密码长度应为{min}-{max}位")    private String password;    public String getUname() {        return uname;    }    public void setUname(String uname) {        this.uname = uname;    }    public String getPassword() {        return password;    }    public void setPassword(String password) {        this.password = password;    }        }

package com.zed.web;import javax.validation.Valid;import org.springframework.stereotype.Controller;import org.springframework.validation.BindingResult;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RequestMethod;import com.zed.model.User;@Controllerpublic class UserController {    @RequestMapping(value="/userLogin", method=RequestMethod.POST)    public String userLogin(@Valid User user, BindingResult result) {                if(result.hasErrors()) {            return "home";        } else {                        return "success";        }    }}

<context:component-scan base-package="com.zed" /><mvc:annotation-driven /><bean class="org.springframework.web.servlet.view.InternalResourceViewResolver">    <property name="prefix" value="/WEB-INF/views/" />    <property name="suffix" value=".jsp" /></bean>

    <form action="userLogin" method="post">        <label>user name</label>        <input name="uname" type="text">        <label>password</label>        <input name="password" type="text">        <input type="submit" value="submit">    </form>