IoC = DI（Dependency Injection ） + 生命周期钩子事件 + 外部配置 ...

IoC核心设计模式

Factory 模式和 Observer 模式，强制使用依赖注入模式。

DI原则

1/2 高层模块不应该依赖低层模块，而是依赖抽象，低层模块也应该依赖抽象。比如 controller 依赖 IXXXService ，而不是依赖 XXXServiceImpl。

DI注入方式

1 Setter注入
2 构造注入
3 接口注入 spring没有实现 avalon有实现
go cloud —— wired 可能是第4种

POJO 注册成 Bean

public class DefaultMessage {

    private String message = "Spring is fun.";

    /**
     * Gets message.
     */
    public String getMessage() {
        return message;
    }

    /**
     * Sets message.
     */
    public void setMessage(String message) {
        this.message = message;
    }

}
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<?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="message"
          class="org.springbyexample.di.xml.DefaultMessage" />

</beans>
             
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构造注入

public class ConstructorMessage {

    private String message = null;

    /**
     * Constructor
     */
    public ConstructorMessage(String message) {
        this.message = message;
    }

    /**
     * Gets message.
     */
    public String getMessage() {
        return message;
    }

    /**
     * Sets message.
     */
    public void setMessage(String message) {
        this.message = message;
    }

}
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<?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="message"
          class="org.springbyexample.di.xml.ConstructorMessage">
        <constructor-arg value="Spring is fun." />
    </bean>

</beans>
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Setter注入

public class SetterMessage {

    private String message = null;

    /**
     * Gets message.
     */
    public String getMessage() {
        return message;
    }

    /**
     * Sets message.
     */
    public void setMessage(String message) {
        this.message = message;
    }

}

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<?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="message"
          class="org.springbyexample.di.xml.SetterMessage">
        <property name="message" value="Spring is fun." />
    </bean>

</beans>
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Bean跟Bean之间依赖

                
<?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="springMessage" 
          class="java.lang.String">
        <constructor-arg value="Spring is fun." />
    </bean>

    <bean id="message"
          class="org.springbyexample.di.xml.SetterMessage">
        <property name="message" ref="springMessage" />
    </bean>

</beans>
             
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从外部配置启动应用程序

Spring可以加载来自

classpath
file sys
ftp
http
...任何外部的配置文件

ApplicationContext是应用程序级别，BeanFactory是系统级别。使用 AppCtx 不同实现，比如 ClassPathXmlApplicationContext

public class MessageRunner {

    final static Logger logger = LoggerFactory.getLogger(MessageRunner.class);
    
    /**
     * Main method.
     */
    public static void main(String[] args) {
        logger.info("Initializing Spring context.");
        
        ApplicationContext applicationContext = new ClassPathXmlApplicationContext("/application-context.xml");
        
        logger.info("Spring context initialized.");

        Message message = (Message) applicationContext.getBean("message");

        logger.debug("message='" + message.getMessage() + "'");
    }

}
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<?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="message"
          class="org.springbyexample.di.app.Message">
        <property name="message" value="Spring is fun." />
    </bean>

</beans>
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单元测试

@RunWith(SpringJUnit4ClassRunner.class)
@ContextConfiguration
public class SetterMessageTest {

    final Logger logger = LoggerFactory.getLogger(SetterMessageTest.class);

    @Autowired
    private SetterMessage message = null;

    /**
     * Tests message.
     */
    @Test
    public void testMessage() {   
        assertNotNull("Constructor message instance is null.", message);
        
        String msg = message.getMessage();
        
        assertNotNull("Message is null.", msg);
        
        String expectedMessage = "Spring is fun.";
        
        assertEquals("Message should be '" + expectedMessage + "'.", expectedMessage, msg);

        logger.info("message='{}'", msg);
    }
    
}
                
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<?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="message"
          class="org.springbyexample.di.xml.SetterMessage">
        <property name="message" value="Spring is fun." />
    </bean>

</beans>
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获取源代码文件

github.com/spring-by-e…

1/ 注意如果使用IDEA , 使用改命令转换

mvn idea:idea
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Spring 框架核心概念IoC 随笔