spring---FactoryBean与BeanFactory的区别
1.BeanFactory
BeanFactory是IOC最基本的容器，负责生产和管理bean，它为其他具体的IOC容器提供了最基本的规范，例如DefaultListableBeanFactory,
XmlBeanFactory,ApplicationContext 等具体的容器都是实现了BeanFactory，再在其基础之上附加了其他的功能。
BeanFactory源码
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package org.springframework.beans.factory;
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import org.springframework.beans.BeansException;
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public interface BeanFactory {
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String FACTORY_BEAN_PREFIX = "&";
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Object getBean(String name) throws BeansException;
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<T> T getBean(String name, Class<T> requiredType) throws BeansException;
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<T> T getBean(Class<T> requiredType) throws BeansException;
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Object getBean(String name, Object... args) throws BeansException;
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boolean containsBean(String name);
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boolean isSingleton(String name) throws NoSuchBeanDefinitionException;
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boolean isPrototype(String name) throws NoSuchBeanDefinitionException;
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boolean isTypeMatch(String name, Class<?> targetType) throws NoSuchBeanDefinitionException;
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Class<?> getType(String name) throws NoSuchBeanDefinitionException;
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String[] getAliases(String name);
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}
2.FactoryBean
FactoryBean是一个接口，当在IOC容器中的Bean实现了FactoryBean后，通过getBean(String BeanName)获取到的Bean对象并不是FactoryBean的实现类对象，而是这个实现类中的getObject()方法返回的对象。要想获取FactoryBean的实现类，就要getBean(&BeanName)，在BeanName之前加上&。
FactoryBean源码
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package org.springframework.beans.factory;
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public interface FactoryBean<T> {
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T getObject() throws Exception;
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Class<?> getObjectType();
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boolean isSingleton();
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}
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<beans xmlns="http://www.springframework.org/schema/beans"
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xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
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xmlns:context="http://www.springframework.org/schema/context"
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xmlns:aop="http://www.springframework.org/schema/aop"
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xmlns:tx="http://www.springframework.org/schema/tx"
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xsi:schemaLocation="http://www.springframework.org/schema/beans
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http://www.springframework.org/schema/beans/spring-beans-3.0.xsd
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http://www.springframework.org/schema/context
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http://www.springframework.org/schema/context/spring-context-3.0.xsd
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http://www.springframework.org/schema/aop
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http://www.springframework.org/schema/aop/spring-aop-3.0.xsd
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http://www.springframework.org/schema/tx
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http://www.springframework.org/schema/tx/spring-tx-3.0.xsd">
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<bean id="student" class="com.spring.bean.Student">
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<property name="name" value="zhangsan" />
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</bean>
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<bean id="school" class="com.spring.bean.School">
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</bean>
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<bean id="factoryBeanPojo" class="com.spring.bean.FactoryBeanPojo">
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<property name="type" value="student" />
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</bean>
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</beans>
FactoryBean的实现类
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import org.springframework.beans.factory.FactoryBean;
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/**
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* @author 作者 wangbiao
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* @date 创建时间：2016年11月14日 上午11:19:31
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* @parameter
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* @return
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*/
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public class FactoryBeanPojo implements FactoryBean{
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private String type;
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public Object getObject() throws Exception {
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if("student".equals(type)){
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return new Student();
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}else{
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return new School();
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}
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}
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public Class getObjectType() {
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return School.class;
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}
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public boolean isSingleton() {
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return true;
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}
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public String getType() {
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return type;
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}
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public void setType(String type) {
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this.type = type;
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}
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}
普通的bean
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/**
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* @author 作者 wangbiao
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* @date 创建时间：2016年11月14日 上午11:13:18
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* @parameter
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* @return
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*/
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public class School {
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private String schoolName;
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private String address;
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private int studentNumber;
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public String getSchoolName() {
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return schoolName;
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}
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public void setSchoolName(String schoolName) {
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this.schoolName = schoolName;
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}
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public String getAddress() {
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return address;
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}
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public void setAddress(String address) {
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this.address = address;
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}
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public int getStudentNumber() {
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return studentNumber;
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}
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public void setStudentNumber(int studentNumber) {
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this.studentNumber = studentNumber;
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}
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public String toString() {
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return "School [schoolName=" + schoolName + ", address=" + address
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+ ", studentNumber=" + studentNumber + "]";
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}
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}
测试类
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import org.springframework.context.support.ClassPathXmlApplicationContext;
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import com.spring.bean.FactoryBeanPojo;
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/**
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* @author 作者 wangbiao
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* @date 创建时间：2016年11月14日 上午11:11:35
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* @parameter
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* @return
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*/
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public class FactoryBeanTest {
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public static void main(String[] args){
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String url = "com/spring/config/BeanConfig.xml";
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ClassPathXmlApplicationContext cpxa = new ClassPathXmlApplicationContext(url);
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Object school= cpxa.getBean("factoryBeanPojo");
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FactoryBeanPojo factoryBeanPojo= (FactoryBeanPojo) cpxa.getBean("&factoryBeanPojo");
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System.out.println(school.getClass().getName());
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System.out.println(factoryBeanPojo.getClass().getName());
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}
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}
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十一月 16, 2016 10:28:24 上午 org.springframework.context.support.AbstractApplicationContext prepareRefresh
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INFO: Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@1e8ee5c0: startup date [Wed Nov 16 10:28:24 CST 2016]; root of context hierarchy
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十一月 16, 2016 10:28:24 上午 org.springframework.beans.factory.xml.XmlBeanDefinitionReader loadBeanDefinitions
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INFO: Loading XML bean definitions from class path resource [com/spring/config/BeanConfig.xml]
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十一月 16, 2016 10:28:24 上午 org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
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INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@35b793ee: defining beans [student,school,factoryBeanPojo]; root of factory hierarchy
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com.spring.bean.Student
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com.spring.bean.FactoryBeanPojo
从结果上可以看到当从IOC容器中获取FactoryBeanPojo对象的时候，用getBean(String BeanName)获取的确是Student对象，可以看到在FactoryBeanPojo中的type属性设置为student的时候，会在getObject()方法中返回Student对象。所以说从IOC容器获取实现了FactoryBean的实现类时，返回的却是实现类中的getObject方法返回的对象，要想获取FactoryBean的实现类，得在getBean(String BeanName)中的BeanName之前加上&,写成getBean(String &BeanName)。
3.BeanFactory和FactoryBean的区别
BeanFactory和FactoryBean其实没有什么比较性的，只是两者的名称特别接近，所以有时候会拿出来比较一番，BeanFactory是提供了OC容器最基本的形式，给具体的IOC容器的实现提供了规范，FactoryBean可以说为IOC容器中Bean的实现提供了更加灵活的方式，FactoryBean在IOC容器的基础上给Bean的实现加上了一个简单工厂模式和装饰模式，我们可以在getObject()方法中灵活配置。其实在Spring源码中有很多FactoryBean的实现类，要想深入准确的理解FactoryBean,只有去读读Spring源码了。
