Java 自动连线在控制器的窗体处理方法中不起作用

我正在开发我的第一个SpringMVC应用程序，但我遇到了一个特殊的情况

应用程序有一个Offer类，它有一个User类型的私有成员，显然是另一个类

我正在使用注释配置。我在两个类构造函数中都有一个sys out。我可以看到，在所有情况下，都会创建一个offer对象，同时也会创建一个user对象，这样自动连接就可以工作了

但是，控制器的doCreate方法并非如此。一个offer对象被传递到其中以验证并绑定到一个HTML表单，但是Spring不创建它的用户对象

因此，我在这一行得到一个NullPointerException：

offer.getUser().setUsername(username);

那么，既然Spring在使用Offer对象的所有其他情况下都能正常工作，为什么它不在这种情况下创建Offer对象的从属用户对象呢。是什么影响了这种行为

控制器类。有问题的方法在末尾

package com.offers.controllers;

import java.security.Principal;
import java.util.List;
import java.util.Map;

import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpSession;
import javax.validation.Valid;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.validation.BindingResult;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.servlet.ModelAndView;

import com.offers.dao.Offer;
import com.offers.service.OffersService;

@Controller
public class OffersController {

    private OffersService offersService;

    @Autowired
    public void setOffersService(OffersService offersService) {
        this.offersService = offersService;
    }


    @RequestMapping("/offers")
    public String showOffers(Model model){

        //offersService.throwTestException();

        List<Offer> offers = offersService.getCurrent();

        model.addAttribute("offers", offers);

        return "offers";

    }

    @RequestMapping("/createoffer")
    public String createOffer(Model model){

        model.addAttribute("offer", new Offer());
        return "createoffer";

    }

    @RequestMapping(value = "/docreate", method = RequestMethod.POST)
    public String doCreate(Model model, @Valid Offer offer, BindingResult result, Principal principal) {


        if (result.hasErrors()) {

            return "createoffer";

        } 

        String username = principal.getName();

        offer.getUser().setUsername(username);
        offersService.create(offer);

        return "offercreated";

    }


}

用户类

package com.offers.dao;

import javax.annotation.Resource;
import javax.validation.constraints.Pattern;
import javax.validation.constraints.Size;

import org.hibernate.validator.constraints.NotBlank;
import org.springframework.context.annotation.Scope;
import org.springframework.stereotype.Component;

import com.offers.validation.ValidEmail;

@Component
@Scope("prototype")
public class User {

    // MEMBERS

    @NotBlank(message="Username cannot be blank")
    @Size(min=8, max=15)
    @Pattern(regexp="^\\w{8,}$", message="Username can only consists of numbers, letters and underscore")
    private String username;

    @NotBlank(message="Password cannot be blank")
    @Pattern(regexp="^\\S+$", message="Password must not contain spaces")
    @Size(min=8, max=15, message="Password must be between 8 and 15 characters long")
    private String password;

    @ValidEmail
    private String email;

    @NotBlank
    @Size(min=2, max=60)
    private String name;

    private boolean enabled = false;
    private String authority;

    // CONSTRUCTORS
    public User() {
        System.out.println("************* user created");
    }

    public User(String username, String password, boolean enabled, String authority, String email, String name) {

        this.username = username;
        this.password = password;
        this.enabled = enabled;
        this.authority = authority;
        this.email = email;
        this.name = name;

    }

    // GETTERS AND SETTERS
    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;
    }

    public boolean isEnabled() {
        return enabled;
    }

    public void setEnabled(boolean enabled) {
        this.enabled = enabled;
    }

    public String getAuthority() {
        return authority;
    }

    public void setAuthority(String authority) {
        this.authority = authority;
    }

    public String getEmail() {
        return email;
    }

    public void setEmail(String email) {
        this.email = email;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    @Override
    public int hashCode() {
        final int prime = 31;
        int result = 1;
        result = prime * result + ((authority == null) ? 0 : authority.hashCode());
        result = prime * result + ((email == null) ? 0 : email.hashCode());
        result = prime * result + (enabled ? 1231 : 1237);
        result = prime * result + ((name == null) ? 0 : name.hashCode());
        result = prime * result + ((username == null) ? 0 : username.hashCode());
        return result;
    }

    @Override
    public boolean equals(Object obj) {
        if (this == obj)
            return true;
        if (obj == null)
            return false;
        if (getClass() != obj.getClass())
            return false;
        User other = (User) obj;
        if (authority == null) {
            if (other.authority != null)
                return false;
        } else if (!authority.equals(other.authority))
            return false;
        if (email == null) {
            if (other.email != null)
                return false;
        } else if (!email.equals(other.email))
            return false;
        if (enabled != other.enabled)
            return false;
        if (name == null) {
            if (other.name != null)
                return false;
        } else if (!name.equals(other.name))
            return false;
        if (username == null) {
            if (other.username != null)
                return false;
        } else if (!username.equals(other.username))
            return false;
        return true;
    }

    @Override
    public String toString() {
        return "User [username=" + username + ", email=" + email + ", name=" + name + ", enabled=" + enabled + ", authority=" + authority + "]";
    }


}

Servlet XML配置文件

<?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:mvc="http://www.springframework.org/schema/mvc" xmlns:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="http://www.springframework.org/schema/mvc http://www.springframework.org/schema/mvc/spring-mvc-4.0.xsd
        http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.0.xsd">



    <context:component-scan base-package="com.offers"></context:component-scan>

    <context:annotation-config></context:annotation-config>
    <mvc:annotation-driven></mvc:annotation-driven>

    <mvc:resources location="/resources/" mapping="/static/**" />


    <bean id="messageSource" class="org.springframework.context.support.ResourceBundleMessageSource">
        <property name="basename" value="com.offers.messages.messages"></property>
    </bean>

    <bean id="tilesViewResolver" class="org.springframework.web.servlet.view.tiles2.TilesViewResolver">
    </bean>

    <bean id="TilesConfigurer" class="org.springframework.web.servlet.view.tiles2.TilesConfigurer">
        <property name="definitions">
            <list>
                <value>/WEB-INF/layouts/default.xml</value>
            </list>
        </property>
    </bean>



</beans>  

报价服务类

package com.offers.service;

import java.util.List;

import org.springframework.beans.factory.annotation.Autowired;
import org.springframework.stereotype.Service;

import com.offers.dao.Offer;
import com.offers.dao.OfferDao;

@Service("offersService")
public class OffersService {

    private OfferDao offerDao;

    @Autowired
    public void setOffersDao(OfferDao offersDao) {
        this.offerDao = offersDao;
    }


    public List<Offer> getCurrent(){

        return offerDao.getOffers();

    }


    public boolean create(Offer offer){

        return offerDao.create(offer);

    }


}

---

谢谢

您将获得NPE，因为您的对象在默认情况下标记为空

您是否正在调用带有@Autowired注释的setter

您可以只自动关联字段

 @Autowired
 private OffersService offersService;

 @Autowired
 private OfferDao offerDao;

---

谢谢你的反馈。我从setter中删除了Autowired注释，并对字段进行了注释，即@Autowired private User；但是用户对象仍然没有与Offer对象一起生成，NPE仍然被抛出。

 @Autowired
 private OffersService offersService;

 @Autowired
 private OfferDao offerDao;