![[spring源码学习]六 IOC源码-BeanFactory和factory-bean](https://200zi.50zi.cn/uploadfile/img/15/269/4108b07c9bfb9b3c8ff098ced421ff60.jpg)
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一、代码实例
在我们分析spring的IOC源码的时候，发现除了配置标准的bean，并且通过getBean(beanName)的方法获取到一个bean的实例外，似乎还有这不少其他获取的方法，例如在第四节，我们发现得到bean实例后，在第26节，会判断是否继承了FactoryBean，然后调用它的方法获取真实的bean，在配置文件中我们发现一个factory-bean方法，这些都说明，我们应该可以使用一个beanFactory获取一个bean，此节重点讨论这部分的实现。
代码如下：
1、car类
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package com.zjl.factorybean;
public class Car {
public Car(String name) {
this.name=name;
}
String name;
public void run(){
System.out.println(this.name+" is running");
}
}
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2、person类
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package com.zjl.factorybean;
public class Person {
public Person(String name) {
this.name=name;
}
public String name;
public int age;
public Car car;
public void sayHello(){
System.out.println(this.name+" say hello");
}
public Car createCar(){
return new Car("奥迪");
}
}
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3、用来获取person的FactoryBean，必须继承FactoryBean接口
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package com.zjl.factorybean;
import org.springframework.beans.factory.FactoryBean;
public class PersonFactory implements FactoryBean<Person> {
String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
@Override
public Person getObject() throws Exception {
return new Person(name);
}
@Override
public Class<Person> getObjectType() {
return Person.class;
}
@Override
public boolean isSingleton() {
return true;
}
}
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4、配置文件
<bean id="personFactory" class="com.zjl.factorybean.PersonFactory">
<property name="name" value="zhangsan"></property>
</bean>
<bean id="car" factory-method="createCar" factory-bean="personFactory"></bean>
5、测试类
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package com.zjl.factorybean;
import org.springframework.beans.factory.support.DefaultListableBeanFactory;
import org.springframework.beans.factory.xml.XmlBeanDefinitionReader;
import org.springframework.core.io.ClassPathResource;
public class Test {
public static void main(String[] args) throws Exception {
DefaultListableBeanFactory beanFacory=new DefaultListableBeanFactory();
XmlBeanDefinitionReader reader=new XmlBeanDefinitionReader(beanFacory);
reader.loadBeanDefinitions(new ClassPathResource("factorybean.xml"));
Person person=(Person)beanFacory.getBean("personFactory");
person.sayHello();
Person person2=(Person)beanFacory.getBean("personFactory");
System.out.println("person==person2 is "+(person==person2));
Car car=(Car)beanFacory.getBean("car");
car.run();
Car car2=(Car)beanFacory.getBean("car");
System.out.println("car==car2 is "+(car==car2));
}
}
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6、测试结果
zhangsan say hello
person==person2 is true
奥迪 is running
car==car2 is true
7、结论
我们可以看到：
a)通过getBean(beanName)方法获取到的直接就是Person的实例，而不是BeanFactory或者PersonFactory的实例。
b)每次获取到的Person实例都是同一个，根据接口中的方法isSingleton方法，猜测于此有关
c)bean的id为car，并没有配置我们常见的class配置，他应该是执行了Person的createCar方法
d)car也遵循单例模式
二、FactoryBean代码解析
1、通过我们对bean的加载过程，发现所有的配置无论是spring默认bean的 配置，还是客户自定义的配置均无差别的被解析后存放在beanDefinitionMap中，所以解析配置文件过程不再重复。
2、Person person=(Person)beanFacory.getBean("personFactory");生成bean过程与第四部分重复的跳过
3、来到bean生成实例后的地方
bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd)
4、进入方法，判断如果是bean不是FactoryBean的实例且beanName是&开头，抛出错误。是FactoryBean的实例，且以&开头，则直接返回实例。
将实例转化为FactoryBean的实例，并且调用getObjectFromFactoryBean(factory, beanName, !synthetic)方法
注：也就是我们要获得定义的通过personFactory返回PersonFactory的实例，可以使用beanFacory.getBean("&personFactory")进行获取，然后调用getObject也可以返回Person的实例，不过这个需要自己控制单例模式
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protected Object getObjectForBeanInstance(
Object beanInstance, String name, String beanName, RootBeanDefinition mbd) {
// Don't let calling code try to dereference the factory if the bean isn't a factory.
if (BeanFactoryUtils.isFactoryDereference(name) && !(beanInstance instanceof FactoryBean)) {
throw new BeanIsNotAFactoryException(transformedBeanName(name), beanInstance.getClass());
}//bean不是FactoryBean的实例且beanName是&开头,报错
// Now we have the bean instance, which may be a normal bean or a FactoryBean.
// If it's a FactoryBean, we use it to create a bean instance, unless the
// caller actually wants a reference to the factory.
//bean是FactoryBean的实例，且beanName以&开头，返回实例
if (!(beanInstance instanceof FactoryBean) || BeanFactoryUtils.isFactoryDereference(name)) {
return beanInstance;
}
Object object = null;
if (mbd == null) {
object = getCachedObjectForFactoryBean(beanName);
}
if (object == null) {
// Return bean instance from factory.
FactoryBean<?> factory = (FactoryBean<?>) beanInstance;
// Caches object obtained from FactoryBean if it is a singleton.
if (mbd == null && containsBeanDefinition(beanName)) {
mbd = getMergedLocalBeanDefinition(beanName);
}
boolean synthetic = (mbd != null && mbd.isSynthetic());
object = getObjectFromFactoryBean(factory, beanName, !synthetic);
}
return object;
}
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5、调用factory实例的isSingleton方法和containsSingleton(beanName)，判断是否是单例模式，单例模式的话，从factoryBeanObjectCache中尝试读取，否则直接生成。
注：我们可以看到，通过FactoryBean的对象是否是单例模式取决于bean定义的范围和方法isSingleton同时为单例才可以
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protected Object getObjectFromFactoryBean(FactoryBean<?> factory, String beanName, boolean shouldPostProcess) {
if (factory.isSingleton() && containsSingleton(beanName)) {
synchronized (getSingletonMutex()) {
Object object = this.factoryBeanObjectCache.get(beanName);
if (object == null) {
//入口，调用getObject方法
object = doGetObjectFromFactoryBean(factory, beanName);
// Only post-process and store if not put there already during getObject() call above
// (e.g. because of circular reference processing triggered by custom getBean calls)
Object alreadyThere = this.factoryBeanObjectCache.get(beanName);
if (alreadyThere != null) {
object = alreadyThere;
}
else {
if (object != null && shouldPostProcess) {
try {
object = postProcessObjectFromFactoryBean(object, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName,
"Post-processing of FactoryBean's singleton object failed", ex);
}
}
this.factoryBeanObjectCache.put(beanName, (object != null ? object : NULL_OBJECT));
}
}
return (object != NULL_OBJECT ? object : null);
}
}
else {
Object object = doGetObjectFromFactoryBean(factory, beanName);
if (object != null && shouldPostProcess) {
try {
object = postProcessObjectFromFactoryBean(object, beanName);
}
catch (Throwable ex) {
throw new BeanCreationException(beanName, "Post-processing of FactoryBean's object failed", ex);
}
}
return object;
}
}
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6、doGetObjectFromFactoryBean中调用getObject方法，返回实例
7、调用bean后处理postProcessObjectFromFactoryBean并放入缓存factoryBeanObjectCache
到此，我们已经获取到了真正的bean，并且也知道了怎么获取原来定义的FactoryBean的实例，但是，似乎少了一个方法，那就说FactoryBean中的getObjectType，我们需要回头去找哪里漏掉了
我翻遍了源代码，并没有找到此方法调用的地方，事实上通过改动
@Override
public Class<Car> getObjectType() {
return Car.class;
}
或者
@Override
public Class<Person> getObjectType() {
return null;
}
都不会影响代码执行结果的正确性，那么我们猜想，是否仅仅是一个预留，并无实际用处，或者客户自定义使用方法。
三、FactoryBean实例
在上一步查找源代码过程中，我们有了新的发现，spring自定义了抽象类AbstractFactoryBean和大量他的子类，包括我们常见的list，map，set，object等，我们也来研究下
1、首先是他的继承关系
public abstract class AbstractFactoryBean<T>
implements FactoryBean<T>, BeanClassLoaderAware, BeanFactoryAware, InitializingBean, DisposableBean {
我们看到继承了几个熟悉的接口，包括FactoryBean和InitializingBean，还有几个BeanClassLoaderAware, BeanFactoryAware, DisposableBean，这些接口分别是：
FactoryBean：通过getObjectBean生成bean实例
InitializingBean：在实例化后执行afterPropertiesSet方法
以上我们比较熟悉，其余三个接口简单了解下
BeanClassLoaderAware：注入classLoad
BeanFactoryAware:注入一个BeanFactory
DisposableBean：销毁bean默认调用destroy方法
我们这里重点关注FactoryBean的三个接口实现：
2、是否单例，通过外部注入
public boolean isSingleton() {
return this.singleton;
}
3、getObject方法，如果是单例且已经创建，返回单例模式，未创建调用getEarlySingletonInstance方法，不是单例模式，调用createInstance方法
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@Override
public final T getObject() throws Exception {
if (isSingleton()) {
return (this.initialized ? this.singletonInstance : getEarlySingletonInstance());
}
else {
return createInstance();
}
}
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4、getEarlySingletonInstance方法，通过第5步判断，是否为接口，如果是通过动态代理，创建对象
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private T getEarlySingletonInstance() throws Exception {
Class<?>[] ifcs = getEarlySingletonInterfaces();
if (ifcs == null) {
throw new FactoryBeanNotInitializedException(
getClass().getName() + " does not support circular references");
}
if (this.earlySingletonInstance == null) {
this.earlySingletonInstance = (T) Proxy.newProxyInstance(
this.beanClassLoader, ifcs, new EarlySingletonInvocationHandler());
}
return this.earlySingletonInstance;
}
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5、此处调用getObjectType，判断是否为空或者是否为接口，如果是，返回，否则为空
protected Class<?>[] getEarlySingletonInterfaces() {
Class<?> type = getObjectType();
return (type != null && type.isInterface() ? new Class<?>[] {type} : null);
}
6、动态代理的InvocationHandler 类，似乎什么都没干，存疑
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private class EarlySingletonInvocationHandler implements InvocationHandler {
@Override
public Object invoke(Object proxy, Method method, Object[] args) throws Throwable {
if (ReflectionUtils.isEqualsMethod(method)) {
// Only consider equal when proxies are identical.
return (proxy == args[0]);
}
else if (ReflectionUtils.isHashCodeMethod(method)) {
// Use hashCode of reference proxy.
return System.identityHashCode(proxy);
}
else if (!initialized && ReflectionUtils.isToStringMethod(method)) {
return "Early singleton proxy for interfaces " +
ObjectUtils.nullSafeToString(getEarlySingletonInterfaces());
}
try {
return method.invoke(getSingletonInstance(), args);
}
catch (InvocationTargetException ex) {
throw ex.getTargetException();
}
}
}
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分析到这里，似乎这个类什么都没做，我们具体看个实例类ListFactoryBean，此类注入了以下参数：
a、sourceList是一个list
b、targetListClass是一个Class
c、重写了createInstance()，将sourceList修改后注入
ListFactoryBean
7、配置文件
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<bean id="list" class="org.springframework.beans.factory.config.ListFactoryBean">
<property name="targetListClass">
<value>java.util.ArrayList</value>
</property>
<property name="sourceList">
<list>
<value>zhangsan</value>
<value>lisi</value>
<value>wangwu</value>
</list>
</property>
</bean>
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8、测试代码
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public static void main(String[] args) throws Exception {
DefaultListableBeanFactory beanFacory=new DefaultListableBeanFactory();
XmlBeanDefinitionReader reader=new XmlBeanDefinitionReader(beanFacory);
reader.loadBeanDefinitions(new ClassPathResource("factorybean.xml"));
@SuppressWarnings("unchecked")
List<String> list=(List<String>)beanFacory.getBean("list");
System.out.println(list.toString());
}
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四、factory-bean的源码解析
1、与之前解析类似，直到进入，如果有beancalss，直接返回beanClass，此处返回值为null
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protected Class<?> resolveBeanClass(final RootBeanDefinition mbd, String beanName, final Class<?>... typesToMatch)
throws CannotLoadBeanClassException {
try {
if (mbd.hasBeanClass()) {
return mbd.getBeanClass();
}
if (System.getSecurityManager() != null) {
return AccessController.doPrivileged(new PrivilegedExceptionAction<Class<?>>() {
@Override
public Class<?> run() throws Exception {
return doResolveBeanClass(mbd, typesToMatch);
}
}, getAccessControlContext());
}
else {
return doResolveBeanClass(mbd, typesToMatch);
}
}
catch (PrivilegedActionException pae) {
ClassNotFoundException ex = (ClassNotFoundException) pae.getException();
throw new CannotLoadBeanClassException(mbd.getResourceDescription(), beanName, mbd.getBeanClassName(), ex);
}
catch (ClassNotFoundException ex) {
throw new CannotLoadBeanClassException(mbd.getResourceDescription(), beanName, mbd.getBeanClassName(), ex);
}
catch (LinkageError err) {
throw new CannotLoadBeanClassException(mbd.getResourceDescription(), beanName, mbd.getBeanClassName(), err);
}
}
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2、开始创建bean实例，判断是否有beanClass，如果有FactoryMethodname，调用instantiateUsingFactoryMethod(beanName, mbd, args)
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protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, Object[] args) {
// Make sure bean class is actually resolved at this point.
Class<?> beanClass = resolveBeanClass(mbd, beanName);
if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
}
if (mbd.getFactoryMethodName() != null) {
return instantiateUsingFactoryMethod(beanName, mbd, args);
}
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3、进入instantiateUsingFactoryMethod方法，判断factoryBeanName是否为空，如果不为空，判断是否为自身，自身则报错。不是自身，获取factoryBean和factoryClass，设定为非静态；如果factoryBeanName为空，且没有classname则报错，有的话，获得factoryClass，设定为静态
注：此处应该是由两种方式，一种通过其他bean来生成，一种是通过class的静态方法生成
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String factoryBeanName = mbd.getFactoryBeanName();
if (factoryBeanName != null) {
if (factoryBeanName.equals(beanName)) {
throw new BeanDefinitionStoreException(mbd.getResourceDescription(), beanName,
"factory-bean reference points back to the same bean definition");
}
factoryBean = this.beanFactory.getBean(factoryBeanName);
if (factoryBean == null) {
throw new BeanCreationException(mbd.getResourceDescription(), beanName,
"factory-bean '" + factoryBeanName + "' (or a BeanPostProcessor involved) returned null");
}
if (mbd.isSingleton() && this.beanFactory.containsSingleton(beanName)) {
throw new IllegalStateException("About-to-be-created singleton instance implicitly appeared " +
"through the creation of the factory bean that its bean definition points to");
}
factoryClass = factoryBean.getClass();
isStatic = false;
}
else {
// It's a static factory method on the bean class.
if (!mbd.hasBeanClass()) {
throw new BeanDefinitionStoreException(mbd.getResourceDescription(), beanName,
"bean definition declares neither a bean class nor a factory-bean reference");
}
factoryBean = null;
factoryClass = mbd.getBeanClass();
isStatic = true;
}
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4、从factoryClass中检查是否有FactoryBeanMethod,此处获得的是数组，说明可能可以根据重写的方法和参数生成不同的bean
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factoryClass = ClassUtils.getUserClass(factoryClass);
Method[] rawCandidates = getCandidateMethods(factoryClass, mbd);
List<Method> candidateSet = new ArrayList<Method>();
for (Method candidate : rawCandidates) {
if (Modifier.isStatic(candidate.getModifiers()) == isStatic && mbd.isFactoryMethod(candidate)) {
candidateSet.add(candidate);
}
}
Method[] candidates = candidateSet.toArray(new Method[candidateSet.size()]);
AutowireUtils.sortFactoryMethods(candidates);
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5、进入instantiate，反射生成真正的bean
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public Object instantiate(RootBeanDefinition bd, String beanName, BeanFactory owner,
Object factoryBean, final Method factoryMethod, Object... args) {
try {
if (System.getSecurityManager() != null) {
AccessController.doPrivileged(new PrivilegedAction<Object>() {
@Override
public Object run() {
ReflectionUtils.makeAccessible(factoryMethod);
return null;
}
});
}
else {
ReflectionUtils.makeAccessible(factoryMethod);
}
Method priorInvokedFactoryMethod = currentlyInvokedFactoryMethod.get();
try {
currentlyInvokedFactoryMethod.set(factoryMethod);
return factoryMethod.invoke(factoryBean, args);
}
finally {
if (priorInvokedFactoryMethod != null) {
currentlyInvokedFactoryMethod.set(priorInvokedFactoryMethod);
}
else {
currentlyInvokedFactoryMethod.remove();
}
}
}
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到这里bean就真正的生成了
五、bean-factory验证
主要需要验证的有两点：
1、如过没有factory-bean，我们可以使用一个class的静态方法进行生成bean
2、可以使用多个重写的方法选择进行生成bean，参数可以从外部传递
我们增加一个CarFactory类，其中有一个静态方法createCar()
public class CarFactory {
public static Car createCar(){
return new Car();
}
}
修改Car类,与一般的bean相同
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package com.zjl.factorybean;
public class Car {
public Car() {
}
String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public void run(){
System.out.println(this.name+" is running");
}
}
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编写配置文件
<bean id="car" factory-method="createCar" class="com.zjl.factorybean.CarFactory"><!-- 使用class的静态方法 -->
<property name="name" value="奔驰"></property><!-- 属性注入 -->
</bean>
测试类：
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public class Test {
public static void main(String[] args) throws Exception {
DefaultListableBeanFactory beanFacory=new DefaultListableBeanFactory();
XmlBeanDefinitionReader reader=new XmlBeanDefinitionReader(beanFacory);
reader.loadBeanDefinitions(new ClassPathResource("factorybean.xml"));
Car car=(Car)beanFacory.getBean("car");
car.run();
Car car2=(Car)beanFacory.getBean("car");
System.out.println("car==car2 is "+(car==car2));
}
}
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结果：
奔驰 is running
car==car2 is true
可以看到，结果跟我们在阅读源码时候的猜想完全一致
六、总结
1、FactoryBean与factory-bean的作用都是通过其他的一个bean工厂产生一个真实的bean，不同的是，FactoryBean是使用了spring默认的接口，具有一定侵入性，对框架造成依赖，factory-bean不会改变代码接口，属于注入方式。spring中很多类似的组队，比如init-method和InitializingBean。
2、从原则上，我们使用spring，很大的优点在于它没有侵略性。那么为什么会提供接口形式呢。接口形式更倾向于框架的使用，比如spirng的另一个重要的特性AOP，框架编写了AOPFactoryBean，我们不需要知道他内部实现，也不会获取他的实力，只需要配置它需要代理的类和接口，便可以成功返回一个真实的bean，也就是目标类的代理类，从而完成各种工作。
3、可以说spirng的很多扩展工作都是基于预留接口提供，同时新扩展的功能也会提供新的预留接口，比如aop的切面等。
