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尝试使用Spring Data JPA使用<repositories />自动生成 DAO 对象，其中 base-package 链接包含 DAO 接口的包，例如：

public interface UserDAO extends JpaRepository<User, String> {
}

但它无法在服务 bean 中连接 DAO 对象，确切的错误是：

org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'ACLService': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private pkg.service.UserServ pkg.service.ACLServ.userServ; nested exception is org.springframework.beans.factory.BeanCreationException: Error creating bean with name 'userServ': Injection of autowired dependencies failed; nested exception is org.springframework.beans.factory.BeanCreationException: Could not autowire field: private pkg.repositories.UserDAO pkg.service.UserServ.userDAO; nested exception is org.springframework.beans.factory.NoSuchBeanDefinitionException: No matching bean of type [pkg.repositories.UserDAO] found for dependency: expected at least 1 bean which qualifies as autowire candidate for this dependency. Dependency annotations: {@org.springframework.beans.factory.annotation.Autowired(required=true)}
at org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor.postProcessPropertyValues(AutowiredAnnotationBeanPostProcessor.java:287)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.populateBean(AbstractAutowireCapableBeanFactory.java:1106)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.doCreateBean(AbstractAutowireCapableBeanFactory.java:517)
at org.springframework.beans.factory.support.AbstractAutowireCapableBeanFactory.createBean(AbstractAutowireCapableBeanFactory.java:456)
at org.springframework.beans.factory.support.AbstractBeanFactory$1.getObject(AbstractBeanFactory.java:294)
at org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(DefaultSingletonBeanRegistry.java:225)
at org.springframework.beans.factory.support.AbstractBeanFactory.doGetBean(AbstractBeanFactory.java:291)
at org.springframework.beans.factory.support.AbstractBeanFactory.getBean(AbstractBeanFactory.java:193)
at org.springframework.beans.factory.support.DefaultListableBeanFactory.preInstantiateSingletons(DefaultListableBeanFactory.java:585)
at org.springframework.context.support.AbstractApplicationContext.finishBeanFactoryInitialization(AbstractApplicationContext.java:913)
at org.springframework.context.support.AbstractApplicationContext.refresh(AbstractApplicationContext.java:464)
at pkg.config.WebAppInit.onStartup(WebAppInit.java:35)

应用程序引导从WebAppInit.Java开始，因为它实现了 WebApplicationInitializer 接口，web.xml 代码为：

<web-app xmlns="http://java.sun.com/xml/ns/javaee" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://java.sun.com/xml/ns/javaee http://java.sun.com/xml/ns/javaee/web-app_3_0.xsd" version="3.0"></web-app>

WebAppInit.Java将onStartup 方法编码为：

public class WebAppInit implements WebApplicationInitializer {
public void onStartup(ServletContext container) throws ServletException {
    AnnotationConfigWebApplicationContext context  = 
        new AnnotationConfigWebApplicationContext();
    context.register(ApplicationContextConfig.class);
    context.refresh();
    ...

然后ApplicationContextConfig类用@Configuration注解，代码为：

@Configuration
@PropertySource("classpath:application.properties")
@ImportResource("classpath:*springDataConfig.xml")
@Import({BasicDataSourceConfig.class,PersistenceSpringDataJpaConfig.class})
@ComponentScan(basePackages={"pkg.service","pkg.utils"})
public class ApplicationContextConfig {
}

所以这只是Java配置的主要/入口点，然后它遵循application.properties（不包括但只是要求它），然后是带有代码的springDataConfig.xml ：

<?xml version="1.0" encoding="UTF-8"?>
<beans:beans xmlns:beans="http://www.springframework.org/schema/beans"
  xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
  xmlns="http://www.springframework.org/schema/data/jpa"
  xsi:schemaLocation="http://www.springframework.org/schema/beans
    http://www.springframework.org/schema/beans/spring-beans.xsd
    http://www.springframework.org/schema/data/jpa
    http://www.springframework.org/schema/data/jpa/spring-jpa.xsd">

  <repositories base-package="pkg.repositories" />

</beans:beans>

BasicDataSourceConfig.Java将DataSource @Bean配置为：

@Bean
public DataSource dataSource() {
    BasicDataSource dataSource = new BasicDataSource();
    ...

PersistenceSpringDataJpaConfig.Java将LocalContainerEntityManagerFactoryBean配置为：

@Configuration
public class PersistenceSpringDataJpaConfig {
    ...

    @Autowired
    DataSource dataSource;

    @Bean
    public LocalContainerEntityManagerFactoryBean entityManagerFactoryBean(){
        LocalContainerEntityManagerFactoryBean entityManagerFactoryBean = new LocalContainerEntityManagerFactoryBean();
    ...

如果我切断了删除/注释代码的依赖项，则其他文件没有直接关系：

@Autorire 
private UserDAO userDAO

在 UserService 类中；应用程序运行没有错误，我的意思是在访问服务 bean 中的 dao 对象时出现空指针异常。

所以问题是：为什么 Spring Data JPA 不创建 userDAO bean？

PS：我确实故意摆脱了所有@Transactions 管理以简化它，除了它应该在没有事务的情况下工作，不是吗？

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