今天源码码网(www.ymama.net)给大家分享的技术是Spring IOC,IOC(Inversion of Control)控制反转,它是一种设计思想,是将我们手动创建对象及依赖代码交由IOC容器进行创建,管理。而DI即“依赖注入”和IOC其实是同一个概念的东西,只是从不同角度描述透析其本质。
下面分别做个简要阐述:
1. IOC控制反转:所谓的控制反转就是将代码里需要实现的对象的创建,管理以及对象的查找反转给IOC容器帮忙实现。从而达到对象与对象之间松耦合,可复用,可扩展;
2. DI 依赖注入:组件之间的依赖关系由动态容器主动注入,即在容器运行期间决定,将某个依赖关系注入到组件之中。依赖注入主要是为了提升组件重用的频率,提高系统的灵活性,可扩展性。
下面通过两张图对比一下,IOC到底干了那些事情,请看下图所示:
下面先看看流程图,以便更深入的理解IOC的执行原理。流程图如下:
1.首先通过BeanDefinitionReader读取配置文件生成Bean的定义信息;
2. 然后可通过BeanFactoryPostProcessor自定义修改Bean的定义信息;(注:只需要实现BeanFactoryPostProcessor接口即可)如下所示:
import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.BeanFactoryPostProcessor;import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;import org.springframework.stereotype.Component;/** * *定义BeanFactoryPostProcessor的实现类,修改Bean的定义信息 * **/@Componentpublic class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor { @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException { //DTO对BeanDefinition定义的信息进行修改 }}
3.得到修改后BeanDefinition
的定义信息后,创建对象,进入Bean的生命周期,从对象实例化开始一直到销毁的整个生命过程;
通过图3,大致描述了Bean的生命周期;其实详尽点的流程如下:
实例化前置(InstantiationAwareBeanPostProcessor.postProcessBeforeInstantiation());
对象实例化
实例化后置(InstantiationAwareBeanPostProcessor.postProcessAfterInstantiation());
属性修改(InstantiationAwareBeanPostProcessor.postProcessPropertyValues());
属性填充(即:给属性赋值);
若实现了Aware接口,执行Aware接口的方法,给容器赋值;
初始化前置(BeanPostProcessor.postProcessBeforeInitialization());
执行初始化方法;同时调用它们的afterPropertiesSet接口方法,类似的如果bean使用了init-method属性声明了初始化方法,改方法也会被调用;
初始化后置(BeanPostProcessor.postProcessAfterInitialization());
此时的Bean已经被创建好了,可以被应用程序使用了,他们将一直驻留在应用上下文中,直到该应用上下文被销毁;
销毁;
1. 首先定义一个Person实体类;
import org.springframework.beans.BeansException;import org.springframework.beans.factory.*;public class Person implements BeanFactoryAware, BeanNameAware, InitializingBean, DisposableBean { private String name; private String address; private int phone; private BeanFactory beanFactory; private String beanName; public Person() { System.out.println("执行步骤 6-->【构造器】调用Person的构造器实例化"); } public String getName() { return name; } public void setName(String name) { System.out.println("执行步骤 9-->【注入属性】注入属性name"); this.name = name; } public String getAddress() { return address; } public void setAddress(String address) { System.out.println("执行步骤 8-->【注入属性】注入属性address"); this.address = address; } public int getPhone() { return phone; } public void setPhone(int phone) { System.out.println("执行步骤 10-->【注入属性】注入属性phone"); this.phone = phone; } @Override public String toString() { return "Person [address=" + address + ", name=" + name + ", phone=" + phone + "]"; } // 这是BeanFactoryAware接口方法 @Override public void setBeanFactory(BeanFactory arg0) throws BeansException { System.out.println("执行步骤 12-->【BeanFactoryAware接口】调用BeanFactoryAware.setBeanFactory()"); this.beanFactory = arg0; } // 这是BeanNameAware接口方法 @Override public void setBeanName(String arg0) { System.out.println("执行步骤 11-->【BeanNameAware接口】调用BeanNameAware.setBeanName()"); this.beanName = arg0; } // 这是InitializingBean接口方法 @Override public void afterPropertiesSet() throws Exception { System.out .println("执行步骤 14-->【InitializingBean接口】调用InitializingBean.afterPropertiesSet()"); } // 这是DiposibleBean接口方法 @Override public void destroy() throws Exception { System.out.println("【DiposibleBean接口】调用DiposibleBean.destory()"); } // 通过<bean>的init-method属性指定的初始化方法 public void myInit() { System.out.println("执行步骤 15-->【init-method】调用<bean>的init-method属性指定的初始化方法"); } // 通过<bean>的destroy-method属性指定的初始化方法 public void myDestory() { System.out.println("执行步骤 35-->【destroy-method】调用<bean>的destroy-method属性指定的初始化方法"); }}
2. 创建需要读取bean信息的配置信息;
<?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:p="http://www.springframework.org/schema/p" xmlns:context="http://www.springframework.org/schema/context" xmlns:util="http://www.springframework.org/schema/util" xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans-4.1.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context-4.3.xsd http://www.springframework.org/schema/util http://www.springframework.org/schema/util/spring-util-4.3.xsd"> <bean id="beanPostProcessor" class="com.grq.BeanLife.MyBeanPostProcessor"> </bean> <bean id="instantiationAwareBeanPostProcessor" class="com.itcdns.MyInstantiationAwareBeanPostProcessor"> </bean> <bean id="beanFactoryPostProcessor" class="com.itcdns.MyBeanFactoryPostProcessor"> </bean> <bean id="person" class="com.itcdns.Person" init-method="myInit" destroy-method="myDestory" scope="singleton" p:name="张三" p:address="广州" p:phone="158449459481" /> </beans>
3. 实现BeanFactoryPostProcessor接口;
import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.BeanDefinition;import org.springframework.beans.factory.config.BeanFactoryPostProcessor;import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;public class MyBeanFactoryPostProcessor implements BeanFactoryPostProcessor { public MyBeanFactoryPostProcessor() { super(); System.out.println("执行步骤 1-->这是BeanFactoryPostProcessor实现类构造器!!"); } @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory arg0) throws BeansException { System.out.println("执行步骤 2-->BeanFactoryPostProcessor调用postProcessBeanFactory方法"); BeanDefinition bd = arg0.getBeanDefinition("person"); bd.getPropertyValues().addPropertyValue("phone", "110"); }}
4. 继承InstantiationAwareBeanPostProcessorAdapter ;(注:InstantiationAwareBeanPostProcessorAdapter实现SmartInstantiationAwareBeanPostProcessor接口,且SmartInstantiationAwareBeanPostProcessor继承InstantiationAwareBeanPostProcessor接口)
import org.springframework.beans.BeansException;import org.springframework.beans.PropertyValues;import org.springframework.beans.factory.config.InstantiationAwareBeanPostProcessorAdapter;import java.beans.PropertyDescriptor;public class MyInstantiationAwareBeanPostProcessor extends InstantiationAwareBeanPostProcessorAdapter { public MyInstantiationAwareBeanPostProcessor() { super(); System.out.println("执行步骤 4-->这是InstantiationAwareBeanPostProcessorAdapter实现类构造器!!"); } // 接口方法、实例化Bean之前调用 @Override public Object postProcessBeforeInstantiation(Class beanClass, String beanName) throws BeansException { System.out.println("执行步骤 5/18-->InstantiationAwareBeanPostProcessor调用postProcessBeforeInstantiation方法"); return null; } // 接口方法、实例化Bean之后调用 @Override public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { System.out.println("执行步骤 17/30-->InstantiationAwareBeanPostProcessor调用postProcessAfterInitialization方法"); return bean; } // 接口方法、设置某个属性时调用 @Override public PropertyValues postProcessPropertyValues(PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException { System.out.println("执行步骤 7/20-->InstantiationAwareBeanPostProcessor调用postProcessPropertyValues方法"); return pvs; }}
5. 实现BeanPostProcessor接口;
import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.BeanPostProcessor;public class MyBeanPostProcessor implements BeanPostProcessor { public MyBeanPostProcessor() { super(); System.out.println("执行步骤 3-->这是BeanPostProcessor实现类构造器!!"); // TODO Auto-generated constructor stub } @Override public Object postProcessAfterInitialization(Object arg0, String arg1) throws BeansException { System.out.println("执行步骤 16/29-->BeanPostProcessor接口方法postProcessAfterInitialization对属性进行更改!"); return arg0; } @Override public Object postProcessBeforeInitialization(Object arg0, String arg1) throws BeansException { System.out.println("执行步骤 13/26-->BeanPostProcessor接口方法postProcessBeforeInitialization对属性进行更改!"); return arg0; }}
6. 测试,查看执行流程;
public static void main(String[] args) { System.out.println("执行步骤 0-->现在开始初始化容器"); ApplicationContext context = new ClassPathXmlApplicationContext("bean.xml"); System.out.println("执行步骤 31-->容器初始化成功"); //得到Preson,并使用 Person person = context.getBean("person",Person.class); System.out.println(person); System.out.println("执行步骤 32-->现在开始关闭容器!"); ((ClassPathXmlApplicationContext)context).registerShutdownHook(); }
执行结果如下图所示: