Spring - IoC(8): 基于 Annotation 的配置

除了基于 XML 的配置外，Spring 也支持基于 Annotation 的配置。Spring 提供以下介个 Annotation 来标注 Spring Bean：
　　@Component：标注一个普通的 Spring Bean
　　@Controller：标注一个控制器组件类
　　@Service：标注一个业务逻辑组件类
　　@Repository：标注一个 DAO 组件类

基于 Annotation 配置的示例

DAO 组件以 @Repository 标注：

public interface UserDao {
    public User getUserByUsername(String username);
}

@Repository("userDao")
public class UserDaoImpl implements UserDao {

    List<User> users = new ArrayList<User>();

    public UserDaoImpl() {
        users.add(new User(1001, "huey", "123"));
        users.add(new User(1002, "tmac", "abc"));
        users.add(new User(1003, "suer", "xxx"));
    }

    public User getUserByUsername(String username) {
        for (User user : users) {
            if (username.equals(user.getUsername())) {
                return user;
            }
        }
        return null;
    }

}

业务逻辑组件以 @Service 标注：

public interface UserServ {
    public User queryUserByUsername(String username);
}

@Service("userServ")
public class UserServImpl implements UserServ {

    @Resource(name="userDao")
    private UserDao userDao;

    public User queryUserByUsername(String username) {
        return userDao.getUserByUsername(username);
    }

}

Spring 配置文件，无需配置 Bean，但须配置 <context:component-scan/>：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:context="http://www.springframework.org/schema/context"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="
        http://www.springframework.org/schema/beans
        http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
        http://www.springframework.org/schema/context
        http://www.springframework.org/schema/context/spring-context-3.0.xsd">

    <!-- 自动扫描指定包及其子包下的所有 Bean 类 -->
    <context:component-scan base-package="com.huey.dream" />
</beans>

测试方法：

@Test
public void testAnnotation() throws Exception {
    ApplicationContext appCtx =
        new ClassPathXmlApplicationContext("applicationContext.xml");
    UserServ userServ = appCtx.getBean("userServ", UserServ.class);

    String username = "huey";
    User user = userServ.queryUserByUsername(username);
    System.out.println(user);
}