1. BeanFactory
BeanFactory定義了 IOC 容器的最基本形式，并提供了 IOC 容器應(yīng)遵守的的最基本的接口，也就是 Spring IOC 所遵守的最底層和最基本的編程規(guī)范。在 Spring 代碼中，BeanFactory 只是個(gè)接口，并不是 IOC 容器的具體實(shí)現(xiàn)，但是 Spring 容器給出了很多種實(shí)現(xiàn)，如 DefaultListableBeanFactory 、XmlBeanFactory 、 ApplicationContext、ClassPathXmlApplicationContext 等，都是附加了某種功能的實(shí)現(xiàn)。
package org.springframework.beans.factory;
import org.springframework.beans.BeansException;
public interface BeanFactory {
String FACTORY_BEAN_PREFIX = "&";
Object getBean(String name) throws BeansException;
<T> T getBean(String name, Class<T> requiredType) throws BeansException;
<T> T getBean(Class<T> requiredType) throws BeansException;
Object getBean(String name, Object... args) throws BeansException;
boolean containsBean(String name);
boolean isSingleton(String name) throws NoSuchBeanDefinitionException;
boolean isPrototype(String name) throws NoSuchBeanDefinitionException;
boolean isTypeMatch(String name, Class<?> targetType) throws NoSuchBeanDefinitionException;
Class<?> getType(String name) throws NoSuchBeanDefinitionException;
String[] getAliases(String name);
}
2. FactoryBean
FactoryBean是一個(gè)接口，當(dāng)在IOC容器中的Bean實(shí)現(xiàn)了FactoryBean后，通過(guò)getBean(String BeanName)獲取到的Bean對(duì)象并不是FactoryBean的實(shí)現(xiàn)類對(duì)象，而是這個(gè)實(shí)現(xiàn)類中的getObject()方法返回的對(duì)象。要想獲取FactoryBean的實(shí)現(xiàn)類，就要getBean(&BeanName)，在BeanName之前加上&。
package org.springframework.beans.factory;
public interface FactoryBean<T> {
T getObject() throws Exception;
Class<?> getObjectType();
boolean isSingleton();
}
下面是一個(gè)應(yīng)用FactoryBean的例子
<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"
xmlns:aop="http://www.springframework.org/schema/aop"
xmlns:tx="http://www.springframework.org/schema/tx"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context-3.0.xsd
http://www.springframework.org/schema/aop
http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
http://www.springframework.org/schema/tx
http://www.springframework.org/schema/tx/spring-tx-3.0.xsd">
<bean id="student" class="com.spring.bean.Student">
<property name="name" value="zhangsan" />
</bean>
<bean id="school" class="com.spring.bean.School">
</bean>
<bean id="factoryBeanPojo" class="com.spring.bean.FactoryBeanPojo">
<property name="type" value="student" />
</bean>
</beans>
FactoryBean的實(shí)現(xiàn)類
import org.springframework.beans.factory.FactoryBean;
public class FactoryBeanPojo implements FactoryBean{
private String type;
@Override
public Object getObject() throws Exception {
if("student".equals(type)){
return new Student();
}else{
return new School();
}
}
@Override
public Class getObjectType() {
return School.class;
}
@Override
public boolean isSingleton() {
return true;
}
public String getType() {
return type;
}
public void setType(String type) {
this.type = type;
}
}
普通的bean
public class School {
private String schoolName;
private String address;
private int studentNumber;
public String getSchoolName() {
return schoolName;
}
public void setSchoolName(String schoolName) {
this.schoolName = schoolName;
}
public String getAddress() {
return address;
}
public void setAddress(String address) {
this.address = address;
}
public int getStudentNumber() {
return studentNumber;
}
public void setStudentNumber(int studentNumber) {
this.studentNumber = studentNumber;
}
@Override
public String toString() {
return "School [schoolName=" + schoolName + ", address=" + address
+ ", studentNumber=" + studentNumber + "]";
}
測(cè)試類
import org.springframework.context.support.ClassPathXmlApplicationContext;
import com.spring.bean.FactoryBeanPojo;
public class FactoryBeanTest {
public static void main(String[] args){
String url = "com/spring/config/BeanConfig.xml";
ClassPathXmlApplicationContext cpxa = new ClassPathXmlApplicationContext(url);
Object school= cpxa.getBean("factoryBeanPojo");
FactoryBeanPojo factoryBeanPojo= (FactoryBeanPojo) cpxa.getBean("&factoryBeanPojo");
System.out.println(school.getClass().getName());
System.out.println(factoryBeanPojo.getClass().getName());
}
}
輸出的結(jié)果：
十一月 16, 2016 10:28:24 上午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@1e8ee5c0: startup date [Wed Nov 16 10:28:24 CST 2016]; root of context hierarchy
十一月 16, 2016 10:28:24 上午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
INFO: Loading XML bean definitions from class path resource [com/spring/config/BeanConfig.xml]
十一月 16, 2016 10:28:24 上午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@35b793ee: defining beans [student,school,factoryBeanPojo]; root of factory hierarchy
com.spring.bean.Student
com.spring.bean.FactoryBeanPojo
從結(jié)果上可以看到當(dāng)從IOC容器中獲取FactoryBeanPojo對(duì)象的時(shí)候，用getBean(String BeanName)獲取的確是Student對(duì)象，可以看到在FactoryBeanPojo中的type屬性設(shè)置為student的時(shí)候，會(huì)在getObject()方法中返回Student對(duì)象。所以說(shuō)從IOC容器獲取實(shí)現(xiàn)了FactoryBean的實(shí)現(xiàn)類時(shí)，返回的卻是實(shí)現(xiàn)類中的getObject方法返回的對(duì)象，要想獲取FactoryBean的實(shí)現(xiàn)類，得在getBean(String BeanName)中的BeanName之前加上&,寫(xiě)成getBean(String &BeanName)。
3.BeanFactory和FactoryBean的區(qū)別
BeanFactory和FactoryBean其實(shí)沒(méi)有什么比較性的，只是兩者的名稱特別接近，所以有時(shí)候會(huì)拿出來(lái)比較一番，BeanFactory是提供了IOC容器最基本的形式，給具體的IOC容器的實(shí)現(xiàn)提供了規(guī)范，F(xiàn)actoryBean可以說(shuō)為IOC容器中Bean的實(shí)現(xiàn)提供了更加靈活的方式，F(xiàn)actoryBean在IOC容器的基礎(chǔ)上給Bean的實(shí)現(xiàn)加上了一個(gè)簡(jiǎn)單工廠模式和裝飾模式，我們可以在getObject()方法中靈活配置。其實(shí)在Spring源碼中有很多FactoryBean的實(shí)現(xiàn)類，要想深入準(zhǔn)確的理解FactoryBean,只有去讀讀Spring源碼了。
原文：https://blog.csdn.net/wangbiao007/article/details/53183764
