Spring依赖注入不起作用 [英] Spring dependency injection not working

问题描述

我的独立Java应用程序出现问题.事实是，我试图自动连接服务和DAO，但是当我从UI调用服务方法时会收到 NullPointerException ，因为依赖项注入无法正常工作.我已经尝试了很多方法，其中许多是基于类似的问题，但问题仍然存在.我正在使用Spring 4.0.6.RELEASE和Hibernate 4.3.11.Final.这是我的代码:

I've got a problem in my standalone Java application. The thing is that I'm trying to Autowire both my Services and my DAOs, but I get a NullPointerException when I invoke service methods from the UI since dependency injection is not working properly. I've tried a lot of things, many of them from similar questions, but the problem is still there. I'm using Spring 4.0.6.RELEASE and Hibernate 4.3.11.Final. Here is my code:

1-服务调用:

public class LoginView {

    @Autowired
    private UsuarioService usuarioService;
    ...
    ...
    JButton btnAutenticarse = new JButton("Autenticar");
    btnAutenticarse.addActionListener(new ActionListener() {
        public void actionPerformed(ActionEvent e) {
            try {
                Usuario usuario = usuarioService.login(textField.getText(),
                        String.valueOf(passwordField.getPassword()), false); // NullPointerException

            } catch (InstanceNotFoundException e1) {
     ...

2-服务定义:

@Service("usuarioService")
public class UsuarioServiceImpl implements UsuarioService {

    @Autowired
    private UsuarioDao usuarioDao;
    ...

3-DAO的定义:

@Repository("usuarioDao")
public class UsuarioDaoHibernate extends GenericDaoHibernate <Usuario, Long>
    implements UsuarioDao {
    ...

4-GenericDAO的定义:

4 - Definition of GenericDAO:

public class GenericDaoHibernate<E, PK extends Serializable> implements
    GenericDao<E, PK> {

@Autowired
private SessionFactory sessionFactory;
....

5- AppConfig.java :

@Configuration
@ComponentScan(basePackages = "org.example.model")
public class AppConfig {

@Bean(name = "usuarioService")
public UsuarioService usuarioService() {
    return new UsuarioServiceImpl();
}

@Bean(name = "usuarioDao")
public UsuarioDao usuarioDao() {
    return new UsuarioDaoHibernate();
}

6- spring-config.xml :

<!-- Enable usage of @Autowired. -->
<context:annotation-config/>

<!-- Enable component scanning for defining beans with annotations. -->
<context:component-scan base-package="org.example.model"/>

<!--  For translating native persistence exceptions to Spring's 
      DataAccessException hierarchy. -->
<bean class="org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor"/>

<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
    <property name="driverClassName" value="com.mysql.jdbc.Driver" />
    <property name="url" value="jdbc:mysql://localhost:3306/appdb" />
    <property name="username" value="username" />
    <property name="password" value="password"/>
</bean>

<bean id="dataSourceProxy" class="org.springframework.jdbc.datasource.LazyConnectionDataSourceProxy"
    p:targetDataSource-ref="dataSource"/>

<bean id="sessionFactory" class="org.springframework.orm.hibernate4.LocalSessionFactoryBean" >
    <property name="dataSource" ref="dataSource"/>
    <property name="packagesToScan">
        <list>
            <value>org.example.model</value>
        </list>
    </property>
    <property name="hibernateProperties">
        <props>
            <prop key="hibernate.dialect">org.hibernate.dialect.MySQLDialect</prop>
            <prop key="hibernate.show_sql">false</prop>
            <prop key="hibernate.format_sql">false</prop>
        </props>
    </property>       
</bean>

<bean id="transactionManager"  class="org.springframework.orm.hibernate4.HibernateTransactionManager">
    <property name="sessionFactory" ref="sessionFactory" />
</bean>

<bean id="persistenceExceptionTranslationPostProcessor"
    class="org.springframework.dao.annotation.PersistenceExceptionTranslationPostProcessor"/>

<!-- Enable the configuration of transactional behavior based on
     annotations. -->
<tx:annotation-driven transaction-manager="transactionManager" />

推荐答案

Spring只会在Spring托管的bean中注入自动装配字段.如果您使用的是 new LoginView() Spring，则无法注入依赖项.

Spring will only inject Autowired fields in Spring managed beans. AKA if you are using new LoginView() Spring cannot inject dependencies.

public class LoginView {

  @Autowired
  private UsuarioService usuarioService;
}

应该是

@Component
public class LoginView {

  @Autowired
  private UsuarioService usuarioService;
}

如果您不能让Spring管理该类，则需要以其他方式设计它.

If you can't let Spring manage that class, you'll need to design it a different way.

顺便说一句，我建议您使用构造函数注入而不是字段注入.

I'd recommend you use constructor injection instead of field injection, by the way.

我可能要做的是使另一个类成为Spring托管的bean，并执行以下操作:

What I might do is make another class to be a Spring managed bean and do something like this:

@Component
public class InitClass{

  private UsarioService usarioService;

  @Autowired
  public InitClass(UsarioService usarioService){
    this.usarioService = usarioService;
  }         

  @PostConstruct
  public void init(){
    new LoginView(usarioService);
  }         
}

然后，此类将处理您现在在 @PostConstruct 中进行的所有初始化.可能需要在 @PostConstruct 中执行此操作，因为直到那时Spring Bean才可能尚未完全初始化.

Then this class will handle all the initialization you're doing now in @PostConstruct. It may be required to do this in @PostConstruct as Spring beans may not be fully initialized until then.

但是，在不了解如何初始化所有内容的情况下，很难说出最佳策略是什么.

However, without seeing how everything is initialized, it's hard to tell what the best strategy would be.

这篇关于Spring依赖注入不起作用的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！