问答平台（1），Spirng入门

Spring 全家桶

- Spring Framework(Spring的基石)
- Spring Boot(构建项目，方便开发)
- Spring Cloud(微服务，大项目拆分成若干个子项目再集成)
- Spring Cloud Data Flow

Spring Framework

- Spring Core
    - IoC、AOP
- Spring Data Access
    - Transactions、Spring MyBatis
- Web Servlet 
    - Spring MVC
- Integration
    - Email、Scheduling、AMQP、Security

Spring IoC

- Inversion of Control 
    - 控制反转，是一种面向对象编程的设计思想。
- Dependency Injection
    - 依赖注入，是IoC思想的实现方式。
- IoC Container 
    - IoC容器，是实现依赖注入的关键，本质上是一个工厂。

Ioc 注解

语义上有区别
- @Repository
- @Service
- @Controller
- @Component

示例

理解IOC的概念

// AlphaDao.java
public interface AlphaDao {

    String select();
}

// AlphaDaoHibernateImpl.java
@Repository("alphaHibernate")
public class AlphaDaoHibernateImpl implements AlphaDao {

    @Override
    public String select() {
        return "Hibernate";
    }
}

// AlphaDaoMybatisImpl.java
@Repository
@Primary
public class AlphaDaoMybatisImpl implements AlphaDao {

    @Override
    public String select() {
        return "Mybatis";
    }
}

// CommunityApplicationTests.java
@RunWith(SpringRunner.class)
@SpringBootTest
@ContextConfiguration(classes = CommunityApplication.class)
public class CommunityApplicationTests implements ApplicationContextAware {

    private ApplicationContext applicationContext;

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

    @Test
    public void testApplicationContext() {
        System.out.println(applicationContext);

        AlphaDao alphaDao = applicationContext.getBean(AlphaDao.class);
        System.out.println(alphaDao.select());

        alphaDao = applicationContext.getBean("alphaHibernate", AlphaDao.class);
        System.out.println(alphaDao.select());
    }

    @Test
    public void testBeanManagement() {
        AlphaService alphaService = applicationContext.getBean(AlphaService.class);
        System.out.println(alphaService);

        // Spring中的Bean默认单例模式
        alphaService = applicationContext.getBean(AlphaService.class);
        System.out.println(alphaService);
    }

    @Test
    public void testBeanConfig() {
        SimpleDateFormat simpleDateFormat = applicationContext.getBean(SimpleDateFormat.class);
        System.out.println(simpleDateFormat.format(new Date()));
    }

    @Autowired
    @Qualifier("alphaHibernate")
    private AlphaDao alphaDao;

    @Autowired
    private AlphaService alphaService;

    @Autowired
    private SimpleDateFormat simpleDateFormat;

    @Test
    public void testDI() {
        System.out.println(alphaDao);
        System.out.println(alphaService);
        System.out.println(simpleDateFormat);
    }
}

// AlphaService.java
@Service
//@Scope("prototype")
public class AlphaService {

    @Autowired
    private AlphaDao alphaDao;

    public AlphaService() {
        System.out.println("实例化AlphaService");
    }

    @PostConstruct
    public void init() {
        System.out.println("初始化AlphaService");
    }

    @PreDestroy
    public void destroy() {
        System.out.println("销毁AlphaService");
    }
    
    public String find() {
        return alphaDao.select();
    }
}

// AlphaConfig.java
@Configuration
public class AlphaConfig {

    @Bean
    public SimpleDateFormat simpleDateFormat() {
        return new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");
    }
}

// AlphaController.java
@Controller
@RequestMapping("/alpha")
public class AlphaController {

    @Autowired
    private AlphaService alphaService;

    @RequestMapping("/hello")
    @ResponseBody
    public String sayHello() {
        return "Hello Spring Boot.";
    }

    @RequestMapping("/data")
    @ResponseBody
    public String getData() {
        return alphaService.find();
    }
}

参考资料

• https://spring.io