Spring @Autowired注解使用

@Autowired 自动装载

@Autowired注解可以使用的地方很多，比如常见的setter方法，constructors方法，普通方法等，一下逐一罗列并举例说明

1. Constructors 中使用

@Service
public class MovieService {
    
    private static final Logger logger = LoggerFactory.getLogger(MovieService.class);
    
    private final MovieRepository movieRepository;
    
    // 构造方法注入
    @Autowired public MovieService(MovieRepository movieRepository) {
        this.movieRepository = movieRepository;
    }
    
    public void printName() {
        String name = this.movieRepository.getMovieName();
        logger.info("Movie Name: {}",name);
    }
}

从Spring4.3开始如果类仅有一个构造函数，可以不使用@Autowired来标记构造函数，但是如果类中有几个构造函数，则至少需要有一个构造函数被@Autowired标记，来告诉IoC容器使用那个构造函数进行初始化。

2. 传统的setter方法中使用

@Service
public class MovieService {
    
    private static final Logger logger = LoggerFactory.getLogger(MovieService.class);
    private MovieRepository movieRepository;
    
    public void printName() {
        String name = this.movieRepository.getMovieName();
        logger.info("Movie Name: {}",name);
    }
    
    // setter 方法注入
    @Autowired public void setMovieRepository(MovieRepository movieRepository) {
        this.movieRepository = movieRepository;
    }
}

3. 任意方法上使用

@Service
public class MovieService {

    private static final Logger logger = LoggerFactory.getLogger(MovieService.class);
    private MovieRepository movieRepository;
    private MovieCatalogRepository movieCatalog;

    public void printName() {
        String name = this.movieRepository.getMovieName();
        String catalog = this.movieCatalog.getCatalog();
        logger.info("Movie Name: {},Catalog: {}", new Object[] { name, catalog });
    }

    // 任意方法名称，和多个参数的注入
    @Autowired public void prepare(MovieRepository movieRepository, MovieCatalogRepository movieCatalog) {
        this.movieCatalog = movieCatalog;
        this.movieRepository = movieRepository;
    }
}

@Autowired除了在setter和constructors上之外还可以在任意方法名称中使用，将依据传入参数进行注入

4. 注入一组特定类型的bean

public interface BasicRepository {
}
@Repository
public class MovieCatalogRepository implements BasicRepository{
    public String getCatalog() {
        return "Catalog..";
    }
}
@Repository
public class MovieRepository implements BasicRepository{
    public String getMovieName() {
        return "King..";
    }
}

@Service
public class MovieService {

    private static final Logger logger = LoggerFactory.getLogger(MovieService.class);

    // 以Set形式注入所有实现BasicRepository接口的bean
    @Autowired private Set<BasicRepository> repositorySet;

    // 以数组形式注入所有实现了BasicRepository接口的bean
    @Autowired private BasicRepository[] repositoryArray;

    // 以Map形式注入所有实现了BasicRepository接口的bean
    @Autowired private Map<String, BasicRepository> repositoryMap;

    // 注入spring上下文
    @Autowired private ApplicationContext applicationContext;

    public void printName() {
        logger.info("打印Set中注入的bean...");
        // 打印set中注入的bean
        this.repositorySet.forEach(System.out::println);

        logger.info("打印数组中注入的bean...");
        // 打印数组中注入的bean
        Arrays.stream(this.repositoryArray).forEach(System.out::println);

        logger.info("打印Map中注入的bean...");
        // 打印Map中注入的bean
        this.repositoryMap.forEach((key, value) -> {
            System.out.println(String.format("Key:%s,Value:%s", key, value));
        });

        logger.info("打印ApplicationContext中所有BasicRepository类型的bean");
        this.applicationContext.getBeansOfType(BasicRepository.class).forEach((key, value) -> {
            System.out.println(String.format("Key:%s,Value:%s", key, value));
        });
    }
}

2018-12-06 10:09:53.800  INFO 15940 --- [           main] o.s.a.MovieService                       : 打印Set中注入的bean...
org.samples.annotations.MovieCatalogRepository@2d83c5a5
org.samples.annotations.MovieRepository@48d7ad8b
2018-12-06 10:09:53.801  INFO 15940 --- [           main] o.s.a.MovieService                       : 打印数组中注入的bean...
org.samples.annotations.MovieCatalogRepository@2d83c5a5
org.samples.annotations.MovieRepository@48d7ad8b
2018-12-06 10:09:53.801  INFO 15940 --- [           main] o.s.a.MovieService                       : 打印Map中注入的bean...
Key:movieCatalogRepository,Value:org.samples.annotations.MovieCatalogRepository@2d83c5a5
Key:movieRepository,Value:org.samples.annotations.MovieRepository@48d7ad8b
2018-12-06 10:09:53.802  INFO 15940 --- [           main] o.s.a.MovieService                       : 打印ApplicationContext中所有BasicRepository类型的bean
Key:movieCatalogRepository,Value:org.samples.annotations.MovieCatalogRepository@2d83c5a5
Key:movieRepository,Value:org.samples.annotations.MovieRepository@48d7ad8b

当以Key-Value形式注入一组特定类型的bean时，key为bean的名称，value为bean的引用。

5. 结合@Primary、@Qualifier注入特定类型的bean

如上例中所示，实现同一个接口的一组bean可以同时被注入，也可以被单个注入，在单个注入时可以结合@Primary或者@Qualifer注解使用。

• 使用@Primary注解默认注入beanPrimary用于指定多个相同类型bean中，在没有指定候选bean的情况下默认注入的bean

public interface BasicRepository {
}
@Repository
@Primary
public class MovieCatalogRepository implements BasicRepository{
    public String getCatalog() {
        return "Catalog..";
    }
}
@Repository
public class MovieRepository implements BasicRepository{
    public String getMovieName() {
        return "King..";
    }
}
@Service
public class MovieService {

    private static final Logger logger = LoggerFactory.getLogger(MovieService.class);

    /* 
     *  此处只指定了接口类型，设置@Primary以后，将默认注入@Primary标记的bean
     *  若多个实现类中都没有标记@Primary则会抛出运行时异常[UnsatisfiedDependencyException]
     */ 
    @Autowired private BasicRepository repository;

    public void printName() {
        logger.info("打印默认注入的bean");
        logger.info("Bean Name:{},Bean HashCode:{}", this.repository.getClass().getName(),
                this.repository.getClass().hashCode());
    }
}

2018-12-06 11:14:09,960 INFO :-- [main .. ] o.s.a.MovieService 打印默认注入的bean 
2018-12-06 11:14:09,961 INFO :-- [main .. ] o.s.a.MovieService Bean Name:org.samples.annotations.MovieCatalogRepository,Bean HashCode:1852661033 

上面MovieCatalogRepository、MovieRepository都是实现了BasicRepository，在注入时如果采用接口注入的方式，我们可以使用@Primary注解标明在默认情况下注入的bean，此例中为MovieCatalogRepository。

• 使用@Qualifier来指出候选bean在接口注入中，若要注入指定的实现类，可以使用@Qualifier来指出候选bean的名称

public interface BasicRepository {
}
@Repository
@Primary
public class MovieCatalogRepository implements BasicRepository{
    public String getCatalog() {
        return "Catalog..";
    }
}
@Repository
public class MovieRepository implements BasicRepository{
    public String getMovieName() {
        return "King..";
    }
}
@Service
public class MovieService {

    private static final Logger logger = LoggerFactory.getLogger(MovieService.class);

    /* 
     * 此处使用@Qualifier注解来标记了默认候选bean为movieRepository,则在Ioc容器注入时将
     * 注入名称为movieRepository的bean
     * 虽然MovieCatalogRepository类标记了@Primary，但是这只是在没有指定候选bean时默认的选择
     * 当指定了候选Bean时，会注入候选的Bean
     * 
     */ 
    @Autowired @Qualifier("movieRepository") private BasicRepository repository;

    public void printName() {
        logger.info("打印默认注入的bean");
        logger.info("Bean Name:{},Bean HashCode:{}", this.repository.getClass().getName(),
                this.repository.getClass().hashCode());
    }
}

2018-12-06 11:25:21,385 INFO :-- [main .. ] o.s.a.MovieService 打印默认注入的bean 
2018-12-06 11:25:21,387 INFO :-- [main .. ] o.s.a.MovieService Bean Name:org.samples.annotations.MovieRepository,Bean HashCode:1027319653 

6. 泛型注入

public interface Store<T> {
    T get();
}
@Component
public class StringStore implements Store<String>{
    @Override
    public String get() {
        return "String..";
    }
}
@Component
public class IntegerStore implements Store<Integer>{
    @Override
    public Integer get() {
        return 1;
    }
}
@Component
public class StoreHandler {
    private static final Logger logger= LoggerFactory.getLogger(StoreHandler.class);
    
    @Autowired private Store<Integer> integerStore;
    @Autowired private Store<String> stringStore;
    
    public void test() {
        logger.info("test bean type");
        logger.info("IntegerStore get():{},StringStore get():{}",integerStore.get(),stringStore.get());
    }
}

2018-12-06 13:29:05,424 INFO :-- [main .. ] o.s.a.StoreHandler test bean type 
2018-12-06 13:29:05,424 INFO :-- [main .. ] o.s.a.StoreHandler IntegerStore get():1,StringStore get():String..