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

2022-01-27 02:58:26 TyuIn

Follow up with a blog :https://blog.csdn.net/qq_43605444/article/details/121979781?spm=1001.2014.3001.5502

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

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