huifer
5 years ago
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# DefaultSingletonBeanRegistry
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- Author: [HuiFer](https://github.com/huifer)
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- 源码阅读仓库: [huifer-spring](https://github.com/huifer/spring-framework-read)
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- 源码路径: `org.springframework.beans.factory.support.DefaultSingletonBeanRegistry`
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- 官方提供的测试类: `org.springframework.beans.factory.support.DefaultSingletonBeanRegistryTests`
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类图
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## 注册方法解析
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- 从名字可以看出这是一个单例对象的注册类
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- `org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.registerSingleton`
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- 测试用例出发
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```java
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@Test
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public void testSingletons() {
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DefaultSingletonBeanRegistry beanRegistry = new DefaultSingletonBeanRegistry();
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TestBean tb = new TestBean();
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beanRegistry.registerSingleton("tb", tb);
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assertSame(tb, beanRegistry.getSingleton("tb"));
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TestBean tb2 = (TestBean) beanRegistry.getSingleton("tb2", new ObjectFactory<Object>() {
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@Override
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public Object getObject() throws BeansException {
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return new TestBean();
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}
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});
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assertSame(tb2, beanRegistry.getSingleton("tb2"));
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assertSame(tb, beanRegistry.getSingleton("tb"));
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assertSame(tb2, beanRegistry.getSingleton("tb2"));
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assertEquals(2, beanRegistry.getSingletonCount());
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String[] names = beanRegistry.getSingletonNames();
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assertEquals(2, names.length);
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assertEquals("tb", names[0]);
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assertEquals("tb2", names[1]);
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beanRegistry.destroySingletons();
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assertEquals(0, beanRegistry.getSingletonCount());
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assertEquals(0, beanRegistry.getSingletonNames().length);
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}
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```
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- 第一个关注的方法`org.springframework.beans.factory.support.DefaultSingletonBeanRegistry#registerSingleton` 注册单例对象
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```java
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/**
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* 注册一个单例对象
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*
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* @param beanName the name of the bean
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* @param singletonObject the existing singleton object
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* @throws IllegalStateException
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*/
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@Override
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public void registerSingleton(String beanName, Object singletonObject) throws IllegalStateException {
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Assert.notNull(beanName, "Bean name must not be null");
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Assert.notNull(singletonObject, "Singleton object must not be null");
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synchronized (this.singletonObjects) {
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// 通过beanName获取单例对象
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Object oldObject = this.singletonObjects.get(beanName);
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// 不为空异常
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if (oldObject != null) {
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throw new IllegalStateException("Could not register object [" + singletonObject +
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"] under bean name '" + beanName + "': there is already object [" + oldObject + "] bound");
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}
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// 添加方法
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addSingleton(beanName, singletonObject);
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}
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}
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```
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```java
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/**
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* Add the given singleton object to the singleton cache of this factory.
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* <p>To be called for eager registration of singletons.
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* <p>
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* 添加单例对象的操作方法
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*
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* @param beanName the name of the bean
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* @param singletonObject the singleton object
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*/
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protected void addSingleton(String beanName, Object singletonObject) {
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synchronized (this.singletonObjects) {
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this.singletonObjects.put(beanName, singletonObject);
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this.singletonFactories.remove(beanName);
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this.earlySingletonObjects.remove(beanName);
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this.registeredSingletons.add(beanName);
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}
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}
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```
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- 这些变量是什么
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```java
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/**
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* 单例对象的缓存: beanName -> Object
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*/
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private final Map<String, Object> singletonObjects = new ConcurrentHashMap<>(256);
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/**
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* 单例工厂的缓存: beanName -> ObjectFactory。
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*/
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private final Map<String, ObjectFactory<?>> singletonFactories = new HashMap<>(16);
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/**
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* 延迟加载的单例对象缓存: beanName -> Object
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*/
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private final Map<String, Object> earlySingletonObjects = new HashMap<>(16);
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/**
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* 已经注册过的单例对象名称(beanName)
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*/
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private final Set<String> registeredSingletons = new LinkedHashSet<>(256);
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/**
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* 当前正在创建的单例对象名称(beanName)
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*/
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private final Set<String> singletonsCurrentlyInCreation =
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Collections.newSetFromMap(new ConcurrentHashMap<>(16));
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private final Set<String> inCreationCheckExclusions =
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Collections.newSetFromMap(new ConcurrentHashMap<>(16));
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/**
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* 摧毁单例对象
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*/
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private final Map<String, Object> disposableBeans = new LinkedHashMap<>();
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private final Map<String, Set<String>> containedBeanMap = new ConcurrentHashMap<>(16);
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/**
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* bean 和beanName的关系
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*/
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private final Map<String, Set<String>> dependentBeanMap = new ConcurrentHashMap<>(64);
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/**
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* bean 依赖关系 beanName -> 依赖关系
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*/
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private final Map<String, Set<String>> dependenciesForBeanMap = new ConcurrentHashMap<>(64);
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/**
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* 异常列表
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*/
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@Nullable
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private Set<Exception> suppressedExceptions;
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/**
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* 标记是否在 destroySingletons 上
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*/
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private boolean singletonsCurrentlyInDestruction = false;
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```
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- 注册方法至此结束
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## 获取方法解析
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- `org.springframework.beans.factory.support.DefaultSingletonBeanRegistry.getSingleton(java.lang.String)`
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```java
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@Override
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@Nullable
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public Object getSingleton(String beanName) {
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return getSingleton(beanName, true);
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}
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```
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```java
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@Nullable
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protected Object getSingleton(String beanName, boolean allowEarlyReference) {
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// 从列表中获取单例对象
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Object singletonObject = this.singletonObjects.get(beanName);
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// 判断当前beanName是否存在
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if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) {
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synchronized (this.singletonObjects) {
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// 从延迟加载中获取
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singletonObject = this.earlySingletonObjects.get(beanName);
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if (singletonObject == null && allowEarlyReference) {
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// 从singletonFactories获取ObjectFactory
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ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);
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if (singletonFactory != null) {
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// 获取对象
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singletonObject = singletonFactory.getObject();
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// 加入缓存
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this.earlySingletonObjects.put(beanName, singletonObject);
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this.singletonFactories.remove(beanName);
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}
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}
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}
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}
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return singletonObject;
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}
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```
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- 获取单例对象的本质就是从map中获取 ObjectFactory 进而执行 getObject()
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`ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName);`
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- 测试方法
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```java
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TestBean tb2 = (TestBean) beanRegistry.getSingleton("tb2", new ObjectFactory<Object>() {
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@Override
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public Object getObject() throws BeansException {
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return new TestBean();
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}
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});
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```
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- 获取单例对象的方式
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```java
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public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
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Assert.notNull(beanName, "Bean name must not be null");
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synchronized (this.singletonObjects) {
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// 从单例对象中获取一个对象
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Object singletonObject = this.singletonObjects.get(beanName);
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if (singletonObject == null) {
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if (this.singletonsCurrentlyInDestruction) {
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throw new BeanCreationNotAllowedException(beanName,
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"Singleton bean creation not allowed while singletons of this factory are in destruction " +
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"(Do not request a bean from a BeanFactory in a destroy method implementation!)");
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}
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if (logger.isDebugEnabled()) {
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logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
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}
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beforeSingletonCreation(beanName);
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boolean newSingleton = false;
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boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
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if (recordSuppressedExceptions) {
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this.suppressedExceptions = new LinkedHashSet<>();
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}
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try {
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// 调用自定义实现,或者接口实现
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singletonObject = singletonFactory.getObject();
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newSingleton = true;
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}
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catch (IllegalStateException ex) {
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// Has the singleton object implicitly appeared in the meantime ->
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// if yes, proceed with it since the exception indicates that state.
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singletonObject = this.singletonObjects.get(beanName);
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if (singletonObject == null) {
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throw ex;
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}
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}
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catch (BeanCreationException ex) {
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if (recordSuppressedExceptions) {
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for (Exception suppressedException : this.suppressedExceptions) {
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ex.addRelatedCause(suppressedException);
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}
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}
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throw ex;
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}
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finally {
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if (recordSuppressedExceptions) {
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this.suppressedExceptions = null;
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}
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afterSingletonCreation(beanName);
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}
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if (newSingleton) {
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addSingleton(beanName, singletonObject);
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}
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}
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return singletonObject;
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}
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}
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```
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不难发现最后都是通过`singletonObject = singletonFactory.getObject();`进行获取
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这个地方的方法实际上就是测试类中的
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```java
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new ObjectFactory<Object>() {
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@Override
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public Object getObject() throws BeansException {
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return new TestBean();
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}
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}
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```
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通过`getObject`就可以获取当前对象
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