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Spring-DI依赖注入

DI 依赖注入

`@Autowired` (spring的依赖注入注解)

1.默认优先按照类型去IOC容器中获取对应的组件

application.getBean(Apple.class);

2.如果找到多个相同类型的组件，默认再将属性名作为组件的id，去IOC容器中查找；

@Autowired
@Qualifier("apple")
Apple apple;

//首先组件上使用@Primary 在配置类中的默认首选该类型的组件
//当在其他bean中装配apple时,首选使用@Primary注解配置的bean组件
@Configuration
public class MySpringIocConfig{

    @Bean
    @Primary
    public Apple apple(){
        return new Apple();
    }

    @Bean
    public Apple apple(){
        return new Apple();
    }
}

4.@Autowired还能够在方法，构造器，参数等处使用

`@Resource @Inject` (JSRjava标准注解)

@Resource (JSR250)

功能和@Autowired相似，默认按照组件名称进行装配;

不支持@Primary的功能,不支持@Autowired(required=true)

@Inject (JSR330)

需要导入相关依赖 javax.inject；

不支持@Autowired(required=true)

装配Spring底层组件

自定义组件想要使用spring底层的组件，如ApplicationContext,BeanFactory,XXX等

自定义组件，只需要实现xxxAware接口

在创建bean的时候，会自动调用接口的相关方法，注入相关组件；类似与回调函数

@Component
public class PojoApplicationContextAwareImpl implements ApplicationContextAware,EnvironmentAware,EmbeddedValueResolverAware {
    // 获取全局信息
    private ApplicationContext applicationContext;
    // 获取运行时变量信息
    private Environment environment;
    // 获取值解析器 获取配置文件信息
    private StringValueResolver valueResolver;

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext=applicationContext;
    }

    @Override
    public void setEnvironment(Environment environment) {
        this.environment=environment;
    }

    @Override
    public void setEmbeddedValueResolver(StringValueResolver resolver) {
        this.valueResolver=resolver;
    }
}

@Profile

编写配置类and配置文件

//配置类
@Configuration
@PropertySource("classpath:/db.properties")
public class MySpringConfig {

    @Value("${db.username}")
    private String username;
    @Value("${db.password}")
    private String password;
    @Value("${db.driverClass}")
    private String driverClass;

    @Profile("dev")
    @Bean("devDataSource")
    public DataSource dataSourceDev(){
        HikariDataSource hikariDataSource = new HikariDataSource();
        hikariDataSource.setUsername(username);
        hikariDataSource.setPassword(password);
        hikariDataSource.setDriverClassName(driverClass);
        hikariDataSource.setJdbcUrl("jdbc:mysql:///devDb?useUnicode=true&characterEncoding=UTF-8");
        return hikariDataSource;
}

    @Profile("test")
    @Bean("testDatasource")
    public DataSource dataSourceTest(){
        HikariDataSource hikariDataSource = new HikariDataSource();
        hikariDataSource.setUsername(username);
        hikariDataSource.setPassword(password);
        hikariDataSource.setDriverClassName(driverClass);
        hikariDataSource.setJdbcUrl("jdbc:mysql:///testDb?useUnicode=true&characterEncoding=UTF-8");
        return hikariDataSource;
}

    @Profile("prod")
    @Bean("prodDatasource")
    public DataSource dataSourceProd(){
        HikariDataSource hikariDataSource = new HikariDataSource();
        hikariDataSource.setUsername(username);
    hikariDataSource.setPassword(password);
    hikariDataSource.setDriverClassName(driverClass);
    hikariDataSource.setJdbcUrl("jdbc:mysql:///prodDb?useUnicode=true&characterEncoding=UTF-8");
    return hikariDataSource;
    }
}

//配置文件db.properties
db.username=root
db.password=root
db.driverClass=com.mysql.cj.jdbc.Driver

编写测试类

@Test
public void test(){
    AnnotationConfigApplicationContext applicationContext=new AnnotationConfigApplicationContext();
    //添加活动的profile
    applicationContext.getEnvironment().setActiveProfiles("dev");
    applicationContext.register(MySpringConfig.class);
    applicationContext.refresh();

    String[] beanNamesForType = applicationContext.getBeanNamesForType(DataSource.class);
    for (String a:beanNamesForType) {
        System.out.println(a);
    }
}

原文 https://segmentfault.com/a/1190000020631916

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