spring的@Bean注解

@Bean可以用于方法，注解上面

@Target({ElementType.METHOD, ElementType.ANNOTATION_TYPE})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface Bean {
    @AliasFor("name")
    String[] value() default {};

    @AliasFor("value")
    String[] name() default {};

    /** @deprecated */
    @Deprecated
    Autowire autowire() default Autowire.NO;

    boolean autowireCandidate() default true;

    String initMethod() default "";

    String destroyMethod() default "(inferred)";
}

@Configuration
public class SpringConfiguration {

    //创建数据源对象
    @Bean(value = "dataSource")
    public DataSource createDataSource() {
        return new DriverManagerDataSource();
    }

    @Bean(value = "jdbcTemplate")
    public JdbcTemplate JDBCTemplate(@Autowired DataSource dataSource) {
        return new JdbcTemplate(dataSource);
    }
}

public class BeanTest {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext("config");
        DataSource dataSource = context.getBean("dataSource", DataSource.class);
        System.out.println(dataSource);
    }
}

 

当有指定的属性值value=dataSource，在ioc容器中就可以根据id=dataSource来注入对应的对象

如果没有，默认使用的时方法名作为注入的id

@Configuration
public class SpringConfiguration {

    //创建数据源对象
    @Bean
    public DataSource createDataSource() {
        return new DriverManagerDataSource();
    }

    @Bean
    public JdbcTemplate JDBCTemplate(@Autowired DataSource dataSource) {
        return new JdbcTemplate(dataSource);
    }
}

public class BeanTest {
    public static void main(String[] args) {
        AnnotationConfigApplicationContext context = new AnnotationConfigApplicationContext("config");
        DataSource dataSource = context.getBean("createDataSource", DataSource.class);
        System.out.println(dataSource);
    }
}