高级篇 - IOC - 《web后端》

依赖查找的例子
依赖注入的例子

IOC的两种实现方式：依赖查找（DL）和依赖注入（DI）。
DI和DL的区别在于依赖的对象是否为主动获取，是的话，就是依赖查找，否则就是依赖注入，由框架绑定完成。如下面例子中的UserRepository，两者在main函数中没有区别，都是通过Context上下文API实现的；

依赖查找的例子

dependency-lookup-context.xml

<?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
        https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/context
        https://www.springframework.org/schema/context/spring-context.xsd">
<!--    <context:annotation-config/>-->
<!--    <context:component-scan base-package="org.acme" />-->
    <!-- Root BeanDefinition 不需要合并，不存在 parent -->
    <!-- 普通 beanDefinition GenericBeanDefinition -->
    <!-- 经过合并后 GenericBeanDefinition 变成 RootBeanDefinition -->
    <bean id="user" class="org.geekbang.thinking.in.spring.ioc.overview.domain.User">
        <property name="id" value="1"/>
        <property name="name" value="小马哥"/>
        <property name="city" value="HANGZHOU"/>
        <property name="workCities" value="BEIJING,HANGZHOU"/>
        <property name="lifeCities">
            <list>
                <value>BEIJING</value>
                <value>SHANGHAI</value>
            </list>
        </property>
        <property name="configFileLocation" value="classpath:/META-INF/user-config.properties"/>
    </bean>
    <!-- 普通 beanDefinition GenericBeanDefinition -->
    <!-- 合并后 GenericBeanDefinition 变成 RootBeanDefinition，并且覆盖 parent 相关配置-->
    <!-- primary = true , 增加了一个 address 属性 -->
    <bean id="superUser" class="org.geekbang.thinking.in.spring.ioc.overview.domain.SuperUser" parent="user"
          primary="true">
        <property name="address" value="杭州"/>
    </bean>
    <bean id="objectFactory" class="org.springframework.beans.factory.config.ObjectFactoryCreatingFactoryBean">
        <property name="targetBeanName" value="user"/>
    </bean>
</beans>

User

public class User implements BeanNameAware {
    private Long id;
    private String name;
    private City city;
    private City[] workCities;
    private List<City> lifeCities;
    private Resource configFileLocation;
    private Company company;
    private Properties context;
    private String contextAsText;
    /**
     * 当前 Bean 的名称
     */
    private transient String beanName;
    public Long getId() {
        return id;
    }
    public void setId(Long id) {
        this.id = id;
    }
    public String getName() {
        return name;
    }
    public void setName(String name) {
        this.name = name;
    }
    public City getCity() {
        return city;
    }
    public void setCity(City city) {
        this.city = city;
    }
    public Resource getConfigFileLocation() {
        return configFileLocation;
    }
    public void setConfigFileLocation(Resource configFileLocation) {
        this.configFileLocation = configFileLocation;
    }
    public City[] getWorkCities() {
        return workCities;
    }
    public void setWorkCities(City[] workCities) {
        this.workCities = workCities;
    }
    public List<City> getLifeCities() {
        return lifeCities;
    }
    public void setLifeCities(List<City> lifeCities) {
        this.lifeCities = lifeCities;
    }
    public Company getCompany() {
        return company;
    }
    public void setCompany(Company company) {
        this.company = company;
    }
    public static User createUser() {
        User user = new User();
        user.setId(1L);
        user.setName("小马哥");
        return user;
    }
    @PostConstruct
    public void init() {
        System.out.println("User Bean [" + beanName + "] 初始化...");
    }
    @PreDestroy
    public void destroy() {
        System.out.println("User Bean [" + beanName + "] 销毁中...");
    }
    @Override
    public void setBeanName(String name) {
        this.beanName = name;
    }
    public Properties getContext() {
        return context;
    }
    public void setContext(Properties context) {
        this.context = context;
    }
    public String getContextAsText() {
        return contextAsText;
    }
    public void setContextAsText(String contextAsText) {
        this.contextAsText = contextAsText;
    }
    @Override
    public String toString() {
        return "User{" +
                "id=" + id +
                ", name='" + name + '\'' +
                ", city=" + city +
                ", workCities=" + Arrays.toString(workCities) +
                ", lifeCities=" + lifeCities +
                ", configFileLocation=" + configFileLocation +
                ", company=" + company +
                ", context=" + context +
                ", contextAsText='" + contextAsText + '\'' +
                ", beanName='" + beanName + '\'' +
                '}';
    }

SuperUser

@Super
public class SuperUser extends User {
    private String address;
    public String getAddress() {
        return address;
    }
    public void setAddress(String address) {
        this.address = address;
    }
    @Override
    public String toString() {
        return "SuperUser{" +
                "address='" + address + '\'' +
                "} " + super.toString();
    }
}

 public static void main(String[] args) {
        // 配置 XML 配置文件
        // 启动 Spring 应用上下文
        BeanFactory beanFactory = new ClassPathXmlApplicationContext("classpath:/META-INF/dependency-lookup-context.xml");
        // 按照类型查找
        lookupByType(beanFactory);
        // 按照类型查找结合对象
        lookupCollectionByType(beanFactory);
        // 通过注解查找对象
        lookupByAnnotationType(beanFactory);
//        lookupInRealTime(beanFactory);
//        lookupInLazy(beanFactory);
    }
    private static void lookupByAnnotationType(BeanFactory beanFactory) {
        if (beanFactory instanceof ListableBeanFactory) {
            ListableBeanFactory listableBeanFactory = (ListableBeanFactory) beanFactory;
            Map<String, User> users = (Map) listableBeanFactory.getBeansWithAnnotation(Super.class);
            System.out.println("查找标注 @Super 所有的 User 集合对象：" + users);
        }
    }
    private static void lookupCollectionByType(BeanFactory beanFactory) {
        if (beanFactory instanceof ListableBeanFactory) {
            ListableBeanFactory listableBeanFactory = (ListableBeanFactory) beanFactory;
            Map<String, User> users = listableBeanFactory.getBeansOfType(User.class);
            System.out.println("查找到的所有的 User 集合对象：" + users);
        }
    }
    private static void lookupByType(BeanFactory beanFactory) {
        User user = beanFactory.getBean(User.class);
        System.out.println("实时查找：" + user);
    }
    private static void lookupInLazy(BeanFactory beanFactory) {
        ObjectFactory<User> objectFactory = (ObjectFactory<User>) beanFactory.getBean("objectFactory");
        User user = objectFactory.getObject();
        System.out.println("延迟查找：" + user);
    }
    private static void lookupInRealTime(BeanFactory beanFactory) {
        User user = (User) beanFactory.getBean("user");
        System.out.println("实时查找：" + user);
    }

依赖注入的例子

dependency-injection-context.xml

<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:util="http://www.springframework.org/schema/util"
       xsi:schemaLocation="
        http://www.springframework.org/schema/beans https://www.springframework.org/schema/beans/spring-beans.xsd
        http://www.springframework.org/schema/util https://www.springframework.org/schema/util/spring-util.xsd">
    <!-- 通过导入复用 dependency-lookup-context.xml -->
    <import resource="dependency-lookup-context.xml"/>
    <bean id="userRepository" class="org.geekbang.thinking.in.spring.ioc.overview.repository.UserRepository"
          autowire="byType"> <!-- Auto-Wiring -->
        <!-- 手动配置 -->
        <!--        <property name="users">-->
        <!--            <util:list>-->
        <!--                <ref bean="superUser" />-->
        <!--                <ref bean="user" />-->
        <!--            </util:list>-->
        <!--        </property>-->
    </bean>
</beans>

UserRepository

public class UserRepository {
    private Collection<User> users; // 自定义 Bean
    private BeanFactory beanFactory; // 內建非 Bean 对象（依赖）
    private ObjectFactory<ApplicationContext> objectFactory;
    public Collection<User> getUsers() {
        return users;
    }
    public void setUsers(Collection<User> users) {
        this.users = users;
    }
    public void setBeanFactory(BeanFactory beanFactory) {
        this.beanFactory = beanFactory;
    }
    public BeanFactory getBeanFactory() {
        return beanFactory;
    }
    public ObjectFactory<ApplicationContext> getObjectFactory() {
        return objectFactory;
    }
    public void setObjectFactory(ObjectFactory<ApplicationContext> objectFactory) {
        this.objectFactory = objectFactory;
    }
}

public static void main(String[] args) {
        // 配置 XML 配置文件
        // 启动 Spring 应用上下文
//        BeanFactory beanFactory = new ClassPathXmlApplicationContext("classpath:/META-INF/dependency-injection-context.xml");
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("classpath:/META-INF/dependency-injection-context.xml");
        // 依赖来源一：自定义 Bean
        UserRepository userRepository = applicationContext.getBean("userRepository", UserRepository.class);
//        System.out.println(userRepository.getUsers());
        // 依赖来源二：依赖注入（內建依赖）
        System.out.println(userRepository.getBeanFactory());
        ObjectFactory userFactory = userRepository.getObjectFactory();
        System.out.println(userFactory.getObject() == applicationContext);
        // 依赖查找（错误）
//        System.out.println(beanFactory.getBean(BeanFactory.class));
        // 依赖来源三：容器內建 Bean
        Environment environment = applicationContext.getBean(Environment.class);
        System.out.println("获取 Environment 类型的 Bean：" + environment);
    }
    private static void whoIsIoCContainer(UserRepository userRepository, ApplicationContext applicationContext) {
        // ConfigurableApplicationContext <- ApplicationContext <- BeanFactory
        // ConfigurableApplicationContext#getBeanFactory()
        // 这个表达式为什么不会成立
        System.out.println(userRepository.getBeanFactory() == applicationContext);
        // ApplicationContext is BeanFactory
    }