从 Spring 3.0 开始,Spring 提供对 JSR-330 标准注解(依赖注入)的支持。这些注释的扫描方式与 Spring 注释相同。要使用它们,您需要在类路径中包含相关的 jar。
注意:
如果您使用 Maven,则该javax.inject
工件在标准 Maven 存储库 ( https://repo1.maven.org/maven2/javax/inject/javax.inject/1/ ) 中可用 。您可以将以下依赖项添加到文件 pom.xml 中:
<dependency>
<groupId>javax.inject</groupId>
<artifactId>javax.inject</artifactId>
<version>1</version>
</dependency>
2.11.1. 依赖注入@Inject
和@Named
代替@Autowired
,您可以使用@javax.inject.Inject
如下:
import javax.inject.Inject;
public class SimpleMovieLister {
private MovieFinder movieFinder;
@Inject
public void setMovieFinder(MovieFinder movieFinder) {
this.movieFinder = movieFinder;
}
public void listMovies() {
this.movieFinder.findMovies(...);
// ...
}
}
与@Autowired一样,您可以在字段级、方法级和构造函数参数级使用@Inject。
此外,您可以将注入点声明为提供者,从而允许按需访问作用域更短的bean,或通过Provider.get()调用延迟访问其他bean。
下面的例子提供了上一个例子的变体:
import javax.inject.Inject;
import javax.inject.Provider;
public class SimpleMovieLister {
private Provider<MovieFinder> movieFinder;
@Inject
public void setMovieFinder(Provider<MovieFinder> movieFinder) {
this.movieFinder = movieFinder;
}
public void listMovies() {
this.movieFinder.get().findMovies(...);
// ...
}
}
如果你想为应该注入的依赖项使用限定名,你应该使用@Named注释,如下例所示:
import javax.inject.Inject;
import javax.inject.Named;
public class SimpleMovieLister {
private MovieFinder movieFinder;
@Inject
public void setMovieFinder(@Named("main") MovieFinder movieFinder) {
this.movieFinder = movieFinder;
}
// ...
}
与@Autowired一样,@Inject也可以与java.util.Optional或@Nullable一起使用。这在这里更适用,因为@Inject没有required属性。下面的两个例子展示了如何使用@Inject和@Nullable:
public class SimpleMovieLister {
@Inject
public void setMovieFinder(Optional<MovieFinder> movieFinder) {
// ...
}
}
publInstead of @Component, you can use @javax.inject.Named or javax.annotation.ManagedBean, as the following example shows:
@Inject
public void setMovieFinder(@Nullable MovieFinder movieFinder) {
// ...
}
}
2.11.2. @Named和@ManagedBean:与@Component注释的标准等价物
代替 @Component
, 你可以使用 @javax.inject.Named
或 javax.annotation.ManagedBean
, 如下例所示:
import javax.inject.Inject;
import javax.inject.Named;
@Named("movieListener") // @ManagedBean("movieListener") could be used as well
public class SimpleMovieLister {
private MovieFinder movieFinder;
@Inject
public void setMovieFinder(MovieFinder movieFinder) {
this.movieFinder = movieFinder;
}
// ...
}
在不指定组件名称的情况下使用@Component是很常见的。@Named可以以类似的方式使用,如下例所示:
import javax.inject.Inject;
import javax.inject.Named;
@Named
public class SimpleMovieLister {
private MovieFinder movieFinder;
@Inject
public void setMovieFinder(MovieFinder movieFinder) {
this.movieFinder = movieFinder;
}
// ...
}
当你使用' @Named '或' @ManagedBean '时,你可以像使用Spring注释一样使用组件扫描,如下面的例子所示:
@Configuration
@ComponentScan(basePackages = "org.example")
public class AppConfig {
// ...
}
注意:
与@Component相比,JSR-330 @Named和JSR-250 ManagedBean注释是不可组合的。
您应该使用Spring的原型模型来构建自定义组件注释。
2.11.3. JSR-330 标准注解的限制
当你使用标准注释时,你应该知道一些重要的特性是不可用的,如下表所示:
Spring | javax.inject.* | javax.inject restrictions / comments |
---|---|---|
@Autowired | @Inject |
@Inject has no 'required' attribute. Can be used with Java 8’s Optional instead. |
@Component | @Named / @ManagedBean | JSR-330 does not provide a composable model, only a way to identify named components. |
@Scope("singleton") | @Singleton | The JSR-330 default scope is like Spring’s prototype . However, in order to keep it consistent with Spring’s general defaults, a JSR-330 bean declared in the Spring container is a singleton by default. In order to use a scope other than singleton , you should use Spring’s @Scope annotation. javax.inject also provides a@Scope annotation. Nevertheless, this one is only intended to be used for creating your own annotations. |
@Qualifier | @Qualifier / @Named |
javax.inject.Qualifier is just a meta-annotation for building custom qualifiers. Concrete String qualifiers (like Spring’s @Qualifier with a value) can be associated through javax.inject.Named . |
@Value | - | no equivalent |
@Required | - | no equivalent |
@Lazy | - | no equivalent |
ObjectFactory | Provider |
javax.inject.Provider is a direct alternative to Spring’s ObjectFactory , only with a shorter get() method name. It can also be used in combination with Spring’s @Autowired or with non-annotated constructors and setter methods. |