Using JSR 330 Standard Annotations

1.11. Using JSR 330 Standard Annotations

Starting with Spring 3.0, Spring offers support for JSR-330 standard annotations (Dependency Injection). Those annotations are scanned in the same way as the Spring annotations. To use them, you need to have the relevant jars in your classpath.

从Spring 3.0开始，Spring提供了对JSR-330标准注释(依赖注入)的支持。这些注释以与Spring注释相同的方式扫描。要使用它们，您需要在类路径中有相关的jar。

If you use Maven, the javax.inject artifact is available in the standard Maven repository ( https://repo1.maven.org/maven2/javax/inject/javax.inject/1/). You can add the following dependency to your file pom.xml:

<dependency>
    <groupId>javax.inject</groupId>
    <artifactId>javax.inject</artifactId>
    <version>1</version>
</dependency>

1.11.1. Dependency Injection with `@Inject` and `@Named`

Instead of @Autowired, you can use @javax.inject.Inject as follows:

您可以使用@javax.inject.Inject而不是@Autowired。注入如下:

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(...);
        // ...
    }
}

As with @Autowired, you can use @Inject at the field level, method level and constructor-argument level. Furthermore, you may declare your injection point as a Provider, allowing for on-demand access to beans of shorter scopes or lazy access to other beans through a Provider.get() call. The following example offers a variant of the preceding example:

和@Autowired一样，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，允许按需访问范围较短的bean或通过Provider.get()调用延迟访问其他bean。下面的例子是上一个例子的变体:

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(...);
        // ...
    }
}

If you would like to use a qualified name for the dependency that should be injected, you should use the @Named annotation, as the following example shows:

如果你想为要注入的依赖项使用限定名，你应该使用@Named注释，如下面的例子所示:

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;
    }

    // ...
}

As with @Autowired, @Inject can also be used with java.util.Optional or @Nullable. This is even more applicable here, since @Inject does not have a required attribute. The following pair of examples show how to use @Inject and @Nullable:

和@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没有必需的属性。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) {
        // ...
    }
}

public class SimpleMovieLister {

    @Inject
    public void setMovieFinder(@Nullable MovieFinder movieFinder) {
        // ...
    }
}

1.11.2. `@Named` and `@ManagedBean`: Standard Equivalents to the `@Component` Annotation

Instead of @Component, you can use @javax.inject.Named or javax.annotation.ManagedBean, as the following example shows:

您可以使用@javax.inject.Named或javax.annotation.ManagedBean而不是@Component命名，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;
    }

    // ...
}

It is very common to use @Component without specifying a name for the component. @Named can be used in a similar fashion, as the following example shows:

使用@Component而不为组件指定名称是很常见的。@Named也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;
    }

    // ...
}

When you use @Named or @ManagedBean, you can use component scanning in the exact same way as when you use Spring annotations, as the following example shows:

当您使用@Named或@ManagedBean时，您可以使用与使用Spring注释完全相同的方式使用组件扫描，如下面的示例所示:

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

In contrast to @Component, the JSR-330 @Named and the JSR-250 @ManagedBean annotations are not composable. You should use Spring’s stereotype model for building custom component annotations.

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。

1.11.3. Limitations of JSR-330 Standard Annotations

When you work with standard annotations, you should know that some significant features are not available, as the following table shows:

在使用标准注释时，您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	javax.inject限制/说明
@Autowired	@Inject	@Inject has no 'required' attribute. Can be used with Java 8’s Optional instead.	@Inject没有'required'属性。可以与Java 8的可选选项一起使用。
@Component	@Named / @ManagedBean	JSR-330 does not provide a composable model, only a way to identify named components.	JSR-330不提供可组合模型，只提供一种识别命名组件的方法。
@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.	JSR-330的默认作用域类似于Spring的原型。然而，为了使它与Spring的一般默认值保持一致，在Spring容器中声明的JSR-330 bean在默认情况下是单例的。为了使用作用域而不是单例，你应该使用Spring的@Scope注释。javax。inject还提供了@Scope注释。然而，这个选项仅用于创建您自己的注释。
@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.	qualifier只是一个用于构建自定义限定符的元注释。具体的字符串限定符(像Spring的带有值的@Qualifier)可以通过javax.inject.Named进行关联。
@Value	-	no equivalent	无
@Required	-	no equivalent	无
@Lazy	-	no equivalent	无
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.	provider是Spring的ObjectFactory的直接替代品，只是有一个更短的get()方法名。它还可以与Spring的@Autowired或与无注释的构造函数和setter方法结合使用。