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Inject Bean By Annotation

Spring IoC容器允許BeanFactoryPostProcessor在容器實際實例化任何其它的bean之前讀取配置元數(shù)據(jù)，并有可能修改它。本文就是以annotation的方式對bean進行依賴注入。

代碼如下：
Annotation

import java.lang.annotation.Inherited;

import java.lang.annotation.Retention;

import java.lang.annotation.RetentionPolicy;

import java.lang.annotation.Target;

import static java.lang.annotation.ElementType.METHOD;

import static java.lang.annotation.ElementType.FIELD;

@Target({METHOD, FIELD})

@Retention(RetentionPolicy.RUNTIME)

@Inherited

public @interface Inject {

// 默認(rèn)注入方式是byName

String value() default "";

}

BeanFactoryPostProcessor

import java.beans.PropertyDescriptor;

import java.lang.reflect.Method;

import org.springframework.beans.BeanUtils;

import org.springframework.beans.BeansException;

import org.springframework.beans.MutablePropertyValues;

import org.springframework.beans.PropertyValue;

import org.springframework.beans.factory.CannotLoadBeanClassException;

import org.springframework.beans.factory.config.BeanDefinition;

import org.springframework.beans.factory.config.BeanFactoryPostProcessor;

import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;

import org.springframework.beans.factory.config.RuntimeBeanReference;

import org.springframework.core.annotation.AnnotationUtils;

import org.springframework.util.StringUtils;

public class InjectProcessor implements BeanFactoryPostProcessor {

public void postProcessBeanFactory(

ConfigurableListableBeanFactory configurablelistablebeanfactory)

throws BeansException {

String[] beanDefinitionNames = configurablelistablebeanfactory.getBeanDefinitionNames();

BeanDefinition beanDefinition = null;

MutablePropertyValues propertyValues = null;

Method method = null;

Inject inject = null;

String propertyName = null;

for (String beanDefinitionName : beanDefinitionNames) {

beanDefinition = configurablelistablebeanfactory.getBeanDefinition(beanDefinitionName);

if (beanDefinition.isAbstract())

continue;

// 返回指定Bean定義信息的屬性集合，此集合在bean factory post-processing期間可以被修改?

propertyValues = beanDefinition.getPropertyValues();

/*

* 找回指定類的屬?性?描述(PropertyDescriptor)列表

* PropertyDescriptor主要描述?一個屬性和此屬性的?一對訪問方?法(getter and setter)

*/

for (PropertyDescriptor descriptor : BeanUtils.getPropertyDescriptors(

getBeanClassByName(beanDefinitionName, beanDefinition))) {

// 屬?性?集合中已經(jīng)存在此屬性則返回

if (propertyValues.getPropertyValue(propertyName = descriptor.getName()) != null)

continue;

// 屬性?描述類中有寫方法(setter)并且指定方法上有注解標(biāo)記

if ((method = descriptor.getWriteMethod()) != null

&& (inject = AnnotationUtils.getAnnotation(method, Inject.class)) != null) {

// 關(guān)聯(lián)Bean的名?稱

String targetBeanName = StringUtils.hasText(inject

.value()) ? inject.value() : propertyName;

// 建立關(guān)聯(lián)Bean的屬性類

propertyValues.addPropertyValue(new PropertyValue(propertyName,

new RuntimeBeanReference(targetBeanName)));

}

/**

* 根據(jù)Bean定義信息名得到Bean Class

*

* @param name Bean定義信息名稱

* @param definition Bean定義信息

* @return Bean Class

* @throws BeansException

*/

@SuppressWarnings("unchecked")

private Class getBeanClassByName(String name, BeanDefinition definition)

throws BeansException {

try {

return Class.forName(definition.getBeanClassName());

} catch (ClassNotFoundException e) {

throw new CannotLoadBeanClassException("No class found", name,

definition.getBeanClassName(), e);

}

public class DaoA implements IDaoA {

private String param;

public void operationA() {

System.out.println("DaoA.operationA(" + param + ")");

}

public String getParam() {

return param;

}

public void setParam(String param) {

this.param = param;

}

public class DaoB implements IDaoB {

public void operationB() {

System.out.println("DaoB.operationB()");

}

public class Service implements IService {

private IDaoA daoA = null;

private IDaoB daoB = null;

public void service() {

System.out.println("********service begin ***********");

daoA.operationA();

daoB.operationB();

System.out.println("********service end *************");

}

public IDaoA getDaoA() {

return daoA;

}

@Inject

public void setDaoA(IDaoA daoA) {

this.daoA = daoA;

}

public IDaoB getDaoB() {

return daoB;

}

@Inject

public void setDaoB(IDaoB daoB) {

this.daoB = daoB;

}

(注意set方法)

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-2.0.xsd">

</property>

</bean>

</beans>

ApplicationContext會檢測部署在它之上實現(xiàn)了BeanFactoryPostProcessor接口的bean，并在適當(dāng)?shù)臅r候會自動調(diào)用bean工廠后配置處理器。部署一個后配置處理器同部署其它bean沒什么區(qū)別。

測試類

import org.springframework.context.ApplicationContext;

import org.springframework.context.support.ClassPathXmlApplicationContext;

public class AnnotationInjectTest {

public static void main(String[] args) {

ApplicationContext ac = new ClassPathXmlApplicationContext("injection/applicationContext.xml");

IService service = (IService) ac.getBean("service");

service.service();

}

測試結(jié)果如下：
********service begin ***********
DaoA.operationA(lg)
DaoB.operationB()
********service end *************

posted on 2008-12-17 01:17 永遠(yuǎn)的火焰舞者閱讀(567) 評論(0) 編輯收藏所屬分類: spring

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