FactoryBean與BeanFactory：
這倆貨在拼寫上很是相似，很多同學在看IOC源碼或者其他地方並不能分清有啥區別，前面的IOC源碼中我簡單說過，現在統一簡單來講一下：
- FactoryBean：是一個Java Bean，但是它是一個能生產對象的工廠Bean，它的實現和工廠模式及修飾器模式很像。比如下：我們把bean比作是人，那麼FactoryBean可以算是一個女人，首先它本身也是一個人，但它能夠生產人。【挺尷尬的比喻】。
- BeanFactory：這就是一個Factory，是一個IOC容器或者叫對象工廠，它裏面存着很多的bean。還用上面那個比如：如果bean是人，那麼它可以理解成學校，學校裏面很多人，學校管理這麼多的人。
FactoryBean在IOC的應用：
前面我們在看IOC源碼的時候，發現即使我們已經創建出來了對象的實例，還是要走一個方法再去處理下，這裏就是對FactoryBean的處理，因爲它可以產生對象，所以你getBean的時候取到的不是它本身，而是通過它生成的產品。【如果要取它本身，getBean(&+beanName)】 我們先來回憶下IOC源碼中那個處理FactoryBean的簡略代碼：
代碼1.1：AbstractBeanFactory類的dogetBean方法
protected <T> T doGetBean(
final String name, final Class<T> requiredType, final Object[] args, boolean typeCheckOnly)
throws BeansException {
<span style="white-space:pre"> </span>...
if (sharedInstance != null && args == null) {
...
bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
}
else {
<span style="white-space:pre"> </span> // Create bean instance.
if (mbd.isSingleton()) {
sharedInstance = getSingleton(beanName, new ObjectFactory() {
public Object getObject() throws BeansException {
try {
return createBean(beanName, mbd, args);
}
catch (BeansException ex) {
destroySingleton(beanName);
throw ex;
}
}
});
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
}
else if (mbd.isPrototype()) {
Object prototypeInstance = null;
try {
beforePrototypeCreation(beanName);
prototypeInstance = createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
}
else {
String scopeName = mbd.getScope();
final Scope scope = this.scopes.get(scopeName);
try {
Object scopedInstance = scope.get(beanName, new ObjectFactory() {
public Object getObject() throws BeansException {
beforePrototypeCreation(beanName);
try {
return createBean(beanName, mbd, args);
}
finally {
afterPrototypeCreation(beanName);
}
}
});
bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
}
}
}
<span style="white-space:pre"> </span>...
return (T) bean;
}代碼1.2：AbstractBeanFactory類的getObjectForBeanInstance方法
protected Object getObjectForBeanInstance(
Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {
//如果是對FactoryBean的解引用，但bean對象不是FactoryBean，拋出異常
if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
}
//如果Bean實例不是FactoryBean，或者指定名稱是FactoryBean的解引用，也就是普通的bean調用，則直接返回當前的Bean實例
if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
return beanInstance;
}
//處理對FactoryBean的調用
Object object = null;
if (mbd == null) {
//從Bean工廠緩存中獲取給定名稱的實例對象
object = getCachedObjectForFactoryBean(beanName);
}
if (object == null) {
// Return bean instance from factory.
FactoryBean factory = (FactoryBean) beanInstance;
//如果從Bean工廠生產的Bean是單態模式的，則緩存
if (mbd == null && containsBeanDefinition(beanName)) {
mbd = getMergedLocalBeanDefinition(beanName);
}
boolean synthetic = (mbd != null && mbd.isSynthetic());
//調用FactoryBeanRegistrySupport類的getObjectFromFactoryBean方法，實現FactoryBean生產Bean對象實例的過程
object = getObjectFromFactoryBean(factory, beanName, !synthetic);
}
return object;
}Dereference(解引用)：一個在C/C++中應用的比較多術語，在C++中，“*”是解引用符號，“&”是引用符號。
解引用：變量所指向的是所引用對象的本身數據，而不是對象的內存地址。
上面的代碼可以看到，對於大多數bean的getBean，一般走到第二步就返回了，也就是說我們創建的Bean對象就是想要的bean，但對於FactoryBean的創建，如果是對內存地址的引用，那麼取到的是它生產的bean，而不是它本身。所以我們繼續看怎麼取到生產的對象的：
代碼1.3：FactoryBeanRegistrySupport類的getObjectFromFactoryBean方法
// Bean工廠生產Bean實例對象
protected Object getObjectFromFactoryBean(FactoryBean factory,
String beanName, boolean shouldPostProcess) {
// Bean工廠是單態模式，並且Bean工廠緩存中存在指定名稱的Bean實例對象
if (factory.isSingleton() && containsSingleton(beanName)) {
synchronized (getSingletonMutex()) {
// 直接從Bean工廠緩存中獲取指定名稱的Bean實例對象
Object object = this.factoryBeanObjectCache.get(beanName);
// Bean工廠緩存中沒有指定名稱的實例對象，則生產該實例對象
if (object == null) {
// 調用Bean工廠的getObject方法生產指定Bean的實例對象
object = doGetObjectFromFactoryBean(factory, beanName,
shouldPostProcess);
// 將生產的實例對象添加到Bean工廠緩存中
this.factoryBeanObjectCache.put(beanName,
(object != null ? object : NULL_OBJECT));
}
return (object != NULL_OBJECT ? object : null);
}
}
// 調用Bean工廠的getObject方法生產指定Bean的實例對象
else {
return doGetObjectFromFactoryBean(factory, beanName,
shouldPostProcess);
}
}
//調用Bean工廠的getObject方法生產指定Bean的實例對象
private Object doGetObjectFromFactoryBean(
final FactoryBean factory, final String beanName, final boolean shouldPostProcess)
throws BeanCreationException {
Object object;
try {
if (System.getSecurityManager() != null) {
AccessControlContext acc = getAccessControlContext();
try {
//實現PrivilegedExceptionAction接口的匿名內置類
//根據JVM檢查權限，然後決定BeanFactory創建實例對象
object = AccessController.doPrivileged(new PrivilegedExceptionAction<Object>() {
public Object run() throws Exception {
//調用BeanFactory接口實現類的創建對象方法
return factory.getObject();
}
}, acc);
}
catch (PrivilegedActionException pae) {
throw pae.getException();
}
}
else {
//調用BeanFactory接口實現類的創建對象方法
object = factory.getObject();
}
}
catch (FactoryBeanNotInitializedException ex) {
throw new BeanCurrentlyInCreationException(beanName, ex.toString());
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "FactoryBean threw exception on object creation", ex);
}
//創建出來的實例對象爲null，或者因爲單態對象正在創建而返回null
if (object == null && isSingletonCurrentlyInCreation(beanName)) {
throw new BeanCurrentlyInCreationException(
beanName, "FactoryBean which is currently in creation returned null from getObject");
}
//爲創建出來的Bean實例對象添加BeanPostProcessor後置處理器
if (object != null && shouldPostProcess) {
try {
object = postProcessObjectFromFactoryBean(object, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Post-processing of the FactoryBean's object failed", ex);
}
}
return object;
} 
FactoryBean的舉例理解
我們先來看下FactoryBean的接口定義：
<span style="white-space:pre"> </span>public interface FactoryBean<T> {
//返回由FactoryBean創建的bean實例，如果isSingleton()返回true，則該實例會放到Spring容器中單實例緩存池中。
T getObject() throws Exception;
//返回FactoryBean創建的bean類型。
Class<?> getObjectType();
//返回由FactoryBean創建的bean實例的作用域是singleton還是prototype。
boolean isSingleton();
}我們下面就通過一個簡單的例子來體驗下getObject方法【講道理，這裏實際意義不多，重在理解方法含義】
假如：我們有個Person對象，裏面包含 name，address，age。set、get方法不寫了
public class Person {
private String name;
private String address;
private int age;
}<bean id="personBean" class="com.gh.MavenTest.Person">
<property name="name" value="gh1" />
<property name="address" value="address1" />
<property name="age" value="28" />
</bean>public class PersonFactoryBean implements FactoryBean<Person>{
private String personInfo;
public Person getObject() throws Exception {
Person person = new Person () ;
String [] infos = personInfo.split ( "," ) ;
person.setName(infos[0]);
person.setAddress(infos[1]);
person.setAge(Integer.parseInt(infos[2]));
return person;
}
public Class<Person> getObjectType() {
return Person.class;
}
public boolean isSingleton() {
return true;
}
}<bean id="personFactory" class="com.hik.MavenTest.PersonFactory">
<property name="personInfo" value="gh2,address2,22"></property>
</bean> 通過上面的小案例的代碼，我們可以看到如果一個類實現了FactoryBean接口，那麼getBean得到的不是他本身了，而是它所產生的對象，如果我們希望得到它本身，只需要加上&符號即可。至於FactoryBean的實際應用，需要大家去發現理解，後面如果有機會會繼續聊聊這個東西。