装配Bean

一、XML

1.1 application.xml配置文件

其中写了依赖关系。如：

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="http://www.springframework.org/schema/beans
        https://www.springframework.org/schema/beans/spring-beans.xsd">
    <bean id="userService" class="com.itranswarp.learnjava.service.UserService">
        <property name="mailService" ref="mailService" />
    </bean>
    <bean id="mailService" class="com.itranswarp.learnjava.service.MailService" />
</beans>

以下代码表明userService依赖mailService

<bean id="userService" class="com.itranswarp.learnjava.service.UserService">
    <property name="mailService" ref="mailService" />
</bean>

1.2 例子

public class Main {
    public static void main(String[] args) {
        ApplicationContext context = new ClassPathXmlApplicationContext("application.xml");
        UserService userService = context.getBean(UserService.class);
        User user = userService.login("bob@example.com", "password");
        System.out.println(user.getName());
    }
}

Spring容器就是ApplicationContext

- ApplicationContext context = new ClassPathXmlApplicationContext("application.xml");读取application.xml文件。
- UserService userService = context.getBean(UserService.class);根据Bean的类型获取Bean。

二、Annotation

2.1 类

@Component
public class UserService {
    @Autowired
    MailService mailService;
    ...
}

@Component表示此类是个Bean。
@Autowired将把指定类型的Bean注入到指定的字段中。

2.2 main

@Configuration
@ComponentScan
public class AppConfig {
    public static void main(String[] args) {
        ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);
        UserService userService = context.getBean(UserService.class);
        User user = userService.login("bob@example.com", "password");
        System.out.println(user.getName());
    }
}

• @Configuration表明AppConfig是一个配置类。作为ApplicationContext context = new AnnotationConfigApplicationContext(AppConfig.class);的参数。
• @ComponentScan告诉容器，自动搜索当前类所在的包以及子包，把所有标注为@Component的Bean自动创建出来，并根据@Autowired进行装配。

  参考

1. 装配Bean - 廖雪峰的官方网站