spring 框架说明文档学习记录(3.7)

基于注解的容器配置

注解注入在XML注入之前被执行，两种方式都是后面的配置会覆盖前面的配置。

你可以注册单独的bean定义，也可以含蓄的使用如下xml配置

<?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:context="http://www.springframework.org/schema/context"
    xsi:schemaLocation="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.xsd">
  <context:annotation-config/>
</beans>

<contex：annotation-config/>仅查找当前application context下的bean上的注解，也就是说，如果我们在DispatcherServlet的WebApplication中配置<context:annotation />，它只会查找controllers中@Autowired的bean，而不会查找services。

@Required

@Required注解适用于bean的属性设置方法，如下

public class SimpleMovieLister {
  private MovieFinder movieFinder;
  @Required
  public void setMovieFinder(MovieFinder movieFinder) {
    this.movieFinder = movieFinder;
  }
  // ...
}

该注解只是简单表示，受影响的bean属性必须在配置时间内填充，通过bean的定义或自动装配。如果受影响的bean属性没有被填充，则会抛出异常。

@Autowired

JSR330的@Inject注解可以替代Spring的@Autowired注解

我们可以如下使用@Autowired注解

public class MovieRecommender {
  private final CustomerPreferenceDao customerPreferenceDao;
  @Autowired
  public MovieRecommender(CustomerPreferenceDao customerPreferenceDao) {
    this.customerPreferenceDao = customerPreferenceDao;
  }
  // ...
}

自Spring Framework4.3起，如果只定义一个构造函数，@Autowired构造函数不再必需。如果有多个构造函数，至少有一个需要被注解来让容器知道使用哪个。

@Autowired注解也可以应用于setter方法

public class SimpleMovieLister {
  private MovieFinder movieFinder;
  @Autowired
  public void setMovieFinder(MovieFinder movieFinder) {
    this.movieFinder = movieFinder;
  }
  // ...
}

也可以在多参方法上应用@Autowired注解

public class MovieRecommender {
  private MovieCatalog movieCatalog;
  private CustomerPreferenceDao customerPreferenceDao;
  @Autowired
  public void prepare(MovieCatalog movieCatalog,
        CustomerPreferenceDao customerPreferenceDao) {
    this.movieCatalog = movieCatalog;
    this.customerPreferenceDao = customerPreferenceDao;
  }
  // ...
}

也可以属性与构造函数上混合使用

public class MovieRecommender {
  private final CustomerPreferenceDao customerPreferenceDao;
  @Autowired
  private MovieCatalog movieCatalog;
  @Autowired
  public MovieRecommender(CustomerPreferenceDao customerPreferenceDao) {
    this.customerPreferenceDao = customerPreferenceDao;
  }
  // ...
}

通过在一个预期数组的属性或方法上使用@Autowired，可以从ApplicationCOntext获取该类型的所有bean

public class MovieRecommender {
  @Autowired
  private MovieCatalog[] movieCatalogs;
  // ...
}

同样可以适用于类型集合

public class MovieRecommender {
  private Set<MovieCatalog> movieCatalogs;
  @Autowired
  public void setMovieCatalogs(Set<MovieCatalog> movieCatalogs) {
    this.movieCatalogs = movieCatalogs;
  }
  // ...
}

可以适用于Map，map的values值包含所有期望的bean，keys包含bean的名称

public class MovieRecommender {
  private Map<String, MovieCatalog> movieCatalogs;
  @Autowired
  public void setMovieCatalogs(Map<String, MovieCatalog> movieCatalogs) {
    this.movieCatalogs = movieCatalogs;
  }
  // ...
}

没有候选bean时，绑定失败，默认所有的autowired是显式required的。

可以通过定义required=false来标识绑定属性为非必需的

public class SimpleMovieLister {
  private MovieFinder movieFinder;
  @Autowired(required=false)
  public void setMovieFinder(MovieFinder movieFinder) {
    this.movieFinder = movieFinder;
  }
  // ...
}

相比较@Required而言，推荐使用@Autowired的required属性，@Required强制要求属性必须被设置，否则抛出异常。

你也可以在一些公认接口上使用@Autowired，BeanFactory, ApplicationContext, Environment, ResourceLoader,
ApplicationEventPublisher, 和MessageSource

public class MovieRecommender {
  @Autowired
  private ApplicationContext context;
    public MovieRecommender() {
  }
  // ...
}

@Primary

因为通过类型绑定的@Autowired，可能会有多个候选，所有通常需要制定选择流程。如下

@Configuration
public class MovieConfiguration {
  @Bean
@Primary
  public MovieCatalog firstMovieCatalog() { ... }
  @Bean
  public MovieCatalog secondMovieCatalog() { ... }
  // ...
}

当使用该配置时，如下程序绑定到firstMovieCatalog的bean

public class MovieRecommender {
  @Autowired
  private MovieCatalog movieCatalog;
  // ...
}

同等bean定义如下

<?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:context="http://www.springframework.org/schema/context"
        xsi:schemaLocation="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.xsd">
  <context:annotation-config/>
  <bean class="example.SimpleMovieCatalog" primary="true">
    <!-- inject any dependencies required by this bean -->
  </bean>
  <bean class="example.SimpleMovieCatalog">
    <!-- inject any dependencies required by this bean -->
  </bean>
  <bean id="movieRecommender" class="example.MovieRecommender"/>
</beans>

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spring 框架说明文档学习记录(3.7)

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