02.011 Spring文档之使用 JSR 330 标准注解

Z时代
2024-01-10
分类：综合

本文内容纲要：02.011 Spring文档之使用 JSR 330 标准注解

2.11.1. 依赖注入@Inject和@Named

2.11.2. @Named和@ManagedBean:与@Component注释的标准等价物

2.11.3. JSR-330 标准注解的限制

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.