Spring IOC 是 Spring 最重要也是最基礎(chǔ)的兩個(gè)特性之一(另外一個(gè)是 AOP 僻造，現(xiàn)不在討論)。Spring 框架的實(shí)現(xiàn)控制反轉(zhuǎn)(IoC)的原則邻遏，也被稱為依賴注入(DI)滴须。過(guò)程對(duì)象定義它們的依賴關(guān)系,也就是說(shuō),他們使用的其它對(duì)象,只能通過(guò)構(gòu)造函數(shù)參數(shù),參數(shù)工廠方法或?qū)ο髮?shí)例上設(shè)置的屬性構(gòu)造或從工廠回來(lái)后的方法。然后容器注入這些依賴項(xiàng)時(shí)創(chuàng)建bean朽合。這個(gè)過(guò)程從根本上是反,因此得名“控制反轉(zhuǎn)(IoC),控制實(shí)例化 bean 本身或者它的位置依賴關(guān)系通過(guò)使用直接建設(shè)類,或者一個(gè)Service Locator模式等機(jī)制俱两。

而創(chuàng)建 Spring 可以通過(guò)以下幾種方式：

• xml,這是Spring創(chuàng)建Bean最早的一種方式
• annotation,因?yàn)閤ml創(chuàng)建 bean 需要配置很多配置文件,Spring 為了簡(jiǎn)化操作，所以在2.5 以后支持以注解的形式來(lái)創(chuàng)建 bean.
• class,后面提倡元數(shù)據(jù)編程,因?yàn)樵赼nnotation中不可避免的還是需要使用xml曹步，所以在spring3.0以后宪彩，可以使用@Configration,@Bean的類注解的形式來(lái)創(chuàng)建Spring bean.
• properties,``yml ,在最新的 Spring boot 項(xiàng)目當(dāng)中可以使用properties以及yml文件來(lái)創(chuàng)建bean.

1、xml bean

這是從Spring最開(kāi)始就支持的一種bean的配置方式讲婚。
定義實(shí)體類：

User.java尿孔，用戶類,擁有簡(jiǎn)單屬性int,String類型以及復(fù)雜的對(duì)象引用Car.

public class User implements Serializable {

    private int id;
    private String name;
    private Car car;

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public Car getCar() {
        return car;
    }

    public void setCar(Car car) {
        this.car = car;
    }
}

Car.java

public class Car {

    private String color;
    private double price;

    public String getColor() {
        return color;
    }

    public void setColor(String color) {
        this.color = color;
    }

    public double getPrice() {
        return price;
    }

    public void setPrice(double price) {
        this.price = price;
    }
}

配置文件:

<?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
       http://www.springframework.org/schema/beans/spring-beans.xsd">

    <bean id="user" class="com.segmentfault.spring.ioc.pogo.User">
        <property name="id" value="1" />
        <property name="name" value="carl" />
        <property name="car" ref="car" />
    </bean>

    <bean id="car" class="com.segmentfault.spring.ioc.pogo.Car">
        <property name="color" value="red" />
        <property name="price" value="20000" />
    </bean>

</beans>

測(cè)試類：

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = {"classpath:xml-bean.xml"})
public class XmlBeanTest implements ApplicationContextAware {

    private ApplicationContext context;

    @Test
    public void testXmlBean() {
        User user = context.getBean(User.class);
        Assert.assertEquals("Spring xml依賴注入失敗:" + user.getName(),"carl", user.getName());
        Assert.assertEquals("Spring xml依賴注入失敗:" + user.getCar().getPrice(), "red", user.getCar().getColor());
    }

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

2、注解類Bean

定義注解Bean.

@Component
public class Computer {

    @Autowired
    private User owner;

    public User getOwner() {
        return owner;
    }

    public void setOwner(User owner) {
        this.owner = owner;
    }
}

配置文件：

<?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:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">

    <context:component-scan base-package="com.segmentfault.spring.ioc.beans.annotation" />

    <bean class="com.segmentfault.spring.ioc.pogo.User" >
        <property name="name" value="xiaomage" />
        <property name="id" value="1" />
    </bean>

</beans>

測(cè)試類：

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(locations = {"classpath:annotation-bean.xml"})
public class AnnotationBeanTest implements ApplicationContextAware {

    private ApplicationContext context;

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

    @Test
    public void testAnnotationBean() {
        Computer computer = context.getBean(Computer.class);
        Assert.assertEquals("Spring 注解注入失敗" + computer.getOwner().getName(),"xiaomage", computer.getOwner().getName());
    }

}

3筹麸、Class類型的Bean

通過(guò)Class來(lái)定義Bean對(duì)象活合。

@Configuration
public class ClazzBeanConfig {

    @Bean
    public Computer computer(User user) {
        Computer computer = new Computer();
        computer.setOwner(user);
        return computer;
    }

    @Bean
    public User  user(){
        User user = new User();
        user.setId(1);
        user.setName("carl");
        return user;
    }

    @Bean
    public CustomBeanPostProcessor customBeanPostProcessor(){
        return new CustomBeanPostProcessor();
    }

}

測(cè)試類：

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration(classes = {ClazzBeanConfig.class})
public class ClazzBeanTest implements ApplicationContextAware {

    private ApplicationContext context;

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

    @Test
    public void testClazzBean(){
        Computer computer = context.getBean(Computer.class);
        Assert.assertEquals("Spring class注入失敗","carl", computer.getOwner().getName());
    }

}

4、properties bean

properties配置文件

spring.properties.bean.age=20
spring.properties.bean.name=美女

定義實(shí)體類竹捉，并通過(guò)@ConfigurationProperties注解指定在配置文件中的前綴芜辕。

@ConfigurationProperties(prefix = "spring.properties.bean")
public class Woman {

    private int age;
    private String name;

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}

工具類：

@Component
public class ApplicationContextUtils implements ApplicationContextAware {

    private static ApplicationContext context;

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

    public static Object getBean(String name) throws BeansException {
        if(context == null) {
            throw new RuntimeException("context is null");
        }
        return context.getBean(name);
    }

    public static <T> T getBean(Class<T> requiredType) throws BeansException{
        if(context == null) {
            throw new RuntimeException("context is null");
        }
        return context.getBean(requiredType);
    }

}

Spring boot啟動(dòng)類：并通過(guò)@EnableConfigurationProperties指定可以使用properites來(lái)實(shí)例化bean的對(duì)象類型。

@SpringBootApplication
@EnableConfigurationProperties(Woman.class)
public class SpringBootRunner {

    public static void main(String[] args) {
        SpringApplication.run(SpringBootRunner.class, args);
    }

}

測(cè)試類：

@RunWith(SpringJUnit4ClassRunner.class)
@SpringBootTest(classes = {SpringBootRunner.class})
public class PropertiesBeanTest {

    @Test
    public void testPropertiesBean(){
        Woman woman = ApplicationContextUtils.getBean(Woman.class);
        Assert.assertEquals("Spring properties注入失敗" , 20, woman.getAge());
    }

}