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