Spring framework learning - JSR 330 standard annotation for the use of spring IOC

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12、 Use JSR 330 Standard notes

from Spring 3.0 Start ,Spring Provide right JSR-330 Standard notes （ Dependency injection ） Support for . These annotations are scanned in the same way as Spring Annotations are scanned in the same way . Use them , You need to include the relevant... In the classpath jar.

If you use Maven, Criterion Maven The repository (https://repo1.maven.org/maven2/javax/inject/javax.inject/1/) Provided in javax.inject workpiece . You can add the following dependencies to the file pom.xml in ：

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

12.1 Use @Inject and @Named Do dependency injection

You can use @javax.inject.Inject Instead of @Autowired, As shown below ：

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

And @Autowired equally , You can at the field level 、 Method level and constructor parameter level use @Inject. Besides , You can declare the injection point as Provider, This allows on-demand access to a shorter range of bean Or through Provider.get() Call deferred access to other bean. The following example provides a variation of the above example ：

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 want to use qualified names for dependencies that should be injected , You should use @Named annotation , This is shown in the following example ：

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;
}
// ...
}

And @Autowired equally ,@Inject with java.util.Optional or @Nullable Use it together . This is more applicable here , because @Inject No required attributes . The following two examples show how to use @Inject and @Nullable：

public class SimpleMovieLister {

@Inject
public void setMovieFinder(Optional<MovieFinder> movieFinder) {

// ...
}
}

public class SimpleMovieLister {

@Inject
public void setMovieFinder(@Nullable MovieFinder movieFinder) {

// ...
}
}

12.2 @Named and @ManagedBean：@Component The standard equivalent of annotation

You can use @javax.inject.Named or javax.annotation.ManagedBean Instead of @Component, As shown in the following example ：

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;
}
// ...
}

Use... Without specifying a component name @Component It's very common . @Named Can be used in a similar way , This is shown in the following example ：

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 when , You can use with Spring Use component scanning in exactly the same way as annotation , This is shown in the following example ：

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

// ...
}

And @Component comparison ,JSR-330 @Named and JSR-250 ManagedBean Annotations are not composable . You should use Spring Construct a custom component annotation based on a stereotyped model .

12.3 JSR-330 Limitations of standard annotations

When you use standard annotations , You should know that some important features are not available , As shown in the following table ：

Spring	javax.inject.*	javax.inject Limit / notes
@Autowired	@Inject	@Inject No, “ It's necessary ” attribute . It can be done with Java 8 Use it together Optional.
@Component	@Named / @ManagedBean	JSR-330 Composable models are not provided , There is only one way to identify named components .
@Scope(“singleton”)	@Singleton	JSR-330 The default range is similar to Spring Of prototype. however , In order to Spring The general default values of are consistent ,Spring Declared in the container JSR-330 bean yes singleton default . In order to use division Beyond the scope of singleton, You should use Spring Of @Scope annotation .javax.inject One is also provided @Scope annotation . However , This is only for creating your own annotations .
@Qualifier	@Qualifier / @Named	javax.inject.Qualifier Just meta annotations for building custom qualifiers . Concrete String qualifiers （ Such as @Qualifier With value Spring ） Can pass javax.inject.Named.
@Value	——	There is no equivalent
@Required	——	There is no equivalent
@Lazy	——	There is no equivalent
ObjectFactory	Provider	javax.inject.Provider yes Spring A direct alternative to ObjectFactory, It's just get() The method name is shorter . It can also be associated with Spring Of @Autowired Or uncommented constructors and setter Methods used in combination .

Article reference ：https://docs.spring.io/spring-framework/docs/current/reference/html/core.html#beans-standard-annotations