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@ -7,7 +7,7 @@
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确保某个类只有一个实例，并提供该实例的获取方法。
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#### 实现方式
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使用一个私有构造函数、一个私有静态变量，以及一个公共静态方法来实现。懒汉式、饿汉式等简单实现就不多BB咯，这里强调一下双检锁懒汉式实现的坑，以及枚举方式的实现吧，最后再结合spring源码 扩展一下单例bean的实现原理。
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最简单的就是 使用一个私有构造函数、一个私有静态变量，以及一个公共静态方法的方式来实现。懒汉式、饿汉式等简单实现就不多BB咯，这里强调一下双检锁懒汉式实现的坑，以及枚举方式的实现吧，最后再结合spring源码 扩展一下单例bean的实现原理。
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**1. 双检锁实现的坑**
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```java
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@ -26,8 +26,8 @@ public class Singleton3 {
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* 3、将instance指向分配的内存地址。
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* 但JVM具有指令重排的特性，实际的执行顺序可能会是1、3、2，导致多线程情况下出问题，
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* 使用volatile修饰instance变量 可以 避免上述的指令重排
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* tips：不太理解的是 第一个线程在执行第2步之前就已经释放了锁？导致其它线程进入synchronized代码块
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* 执行 instance == null 的判断？
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* tips：不太理解的是 第一个线程在执行第2步之前就已经释放了锁吗？导致其它线程进入synchronized代码块
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* 执行 instance == null 的判断？
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*/
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private volatile static Singleton3 instance;
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@ -124,46 +124,46 @@ Spring实现单例bean是使用map注册表和synchronized同步机制实现的
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```java
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public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {
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......
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......
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/**
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* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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* 真正实现向IOC容器获取Bean的功能，也是触发依赖注入(DI)功能的地方
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* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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*/
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@SuppressWarnings("unchecked")
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protected <T> T doGetBean(final String name, final Class<T> requiredType, final Object[] args,
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boolean typeCheckOnly) throws BeansException {
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......
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//创建单例模式bean的实例对象
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if (mbd.isSingleton()) {
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//这里使用了一个匿名内部类，创建Bean实例对象，并且注册给所依赖的对象
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sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
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public Object getObject() throws BeansException {
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try {
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/**
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* ！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！
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* 创建一个指定的Bean实例对象，如果有父级继承，则合并子类和父类的定义
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* 走子类中的实现
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* ！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！
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*/
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return createBean(beanName, mbd, args);
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}
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catch (BeansException ex) {
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destroySingleton(beanName);
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throw ex;
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}
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}
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});
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//获取给定Bean的实例对象
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bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
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}
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......
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}
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/**
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* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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* 真正实现向IOC容器获取Bean的功能，也是触发依赖注入(DI)功能的地方
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* !!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!
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*/
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@SuppressWarnings("unchecked")
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protected <T> T doGetBean(final String name, final Class<T> requiredType, final Object[] args,
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boolean typeCheckOnly) throws BeansException {
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......
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//创建单例模式bean的实例对象
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if (mbd.isSingleton()) {
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//这里使用了一个匿名内部类，创建Bean实例对象，并且注册给所依赖的对象
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sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
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public Object getObject() throws BeansException {
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try {
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/**
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* ！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！
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* 创建一个指定的Bean实例对象，如果有父级继承，则合并子类和父类的定义
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* 走子类中的实现
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* ！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！！
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*/
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return createBean(beanName, mbd, args);
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}
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catch (BeansException ex) {
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destroySingleton(beanName);
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throw ex;
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}
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}
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});
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//获取给定Bean的实例对象
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bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
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}
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......
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}
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}
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@ -172,56 +172,56 @@ public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport imp
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*/
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public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements SingletonBeanRegistry {
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/** 单例的bean实例的缓存 */
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private final Map<String, Object> singletonObjects = new ConcurrentHashMap<String, Object>(64);
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/** 单例的bean实例的缓存 */
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private final Map<String, Object> singletonObjects = new ConcurrentHashMap<String, Object>(64);
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/**
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* 返回给定beanName的 已经注册的 单例bean，如果没有注册，则注册并返回
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*/
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public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
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Assert.notNull(beanName, "'beanName' must not be null");
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// 加锁，保证单例bean在多线程环境下不会创建多个
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synchronized (this.singletonObjects) {
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// 先从缓存中取，有就直接返回，没有就创建、注册到singletonObjects、返回
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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 the 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 recordSuppressedExceptions = (this.suppressedExceptions == null);
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if (recordSuppressedExceptions) {
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this.suppressedExceptions = new LinkedHashSet<Exception>();
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}
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try {
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singletonObject = singletonFactory.getObject();
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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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// 注册到单例bean的缓存
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addSingleton(beanName, singletonObject);
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}
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return (singletonObject != NULL_OBJECT ? singletonObject : null);
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}
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}
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/**
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* 返回给定beanName的 已经注册的 单例bean，如果没有注册，则注册并返回
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*/
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public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
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Assert.notNull(beanName, "'beanName' must not be null");
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// 加锁，保证单例bean在多线程环境下不会创建多个
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synchronized (this.singletonObjects) {
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// 先从缓存中取，有就直接返回，没有就创建、注册到singletonObjects、返回
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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 the 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 recordSuppressedExceptions = (this.suppressedExceptions == null);
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if (recordSuppressedExceptions) {
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this.suppressedExceptions = new LinkedHashSet<Exception>();
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}
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try {
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singletonObject = singletonFactory.getObject();
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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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// 注册到单例bean的缓存
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addSingleton(beanName, singletonObject);
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}
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return (singletonObject != NULL_OBJECT ? singletonObject : null);
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}
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}
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}
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```
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@ -231,33 +231,33 @@ public class DefaultSingletonBeanRegistry extends SimpleAliasRegistry implements
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#### 简单实现
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```java
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public interface Hero {
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void speak();
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void speak();
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}
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public class DaJi implements Hero {
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@Override
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public void speak() {
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System.out.println("妲己，陪你玩 ~");
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}
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@Override
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public void speak() {
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System.out.println("妲己，陪你玩 ~");
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}
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}
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public class LiBai implements Hero{
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@Override
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public void speak() {
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System.out.println("今朝有酒 今朝醉 ~");
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}
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@Override
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public void speak() {
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System.out.println("今朝有酒 今朝醉 ~");
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}
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}
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/** 对各种英雄进行集中管理 */
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public class HeroFactory {
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public static Hero getShibing(String name){
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if("LiBai".equals(name))
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return new LiBai();
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else if("DaJi".equals(name))
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return new DaJi();
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else
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return null;
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}
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public static Hero getShibing(String name){
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if("LiBai".equals(name))
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return new LiBai();
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else if("DaJi".equals(name))
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return new DaJi();
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else
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return null;
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}
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}
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```
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|
这种设计方式只在我们产品的“FBM资金管理”模块有看到过，其中对100+个按钮类进行了集中管控，不过其设计结构比上面这种要复杂的多。
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|
@ -361,51 +361,51 @@ https://github.com/doocs/source-code-hunter
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```java
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public abstract class AbstractFactory {
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abstract protected AbstractProductA createProductA();
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abstract protected AbstractProductA createProductA();
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abstract protected AbstractProductB createProductB();
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abstract protected AbstractProductB createProductB();
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}
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public class ConcreteFactory1 extends AbstractFactory {
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@Override
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protected AbstractProductA createProductA() {
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return new ProductA1();
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}
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@Override
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protected AbstractProductA createProductA() {
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return new ProductA1();
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}
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@Override
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protected AbstractProductB createProductB() {
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return new ProductB1();
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}
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@Override
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|
protected AbstractProductB createProductB() {
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return new ProductB1();
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}
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}
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public class ConcreteFactory2 extends AbstractFactory {
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@Override
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protected AbstractProductA createProductA() {
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|
|
return new ProductA2();
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}
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|
@Override
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|
|
protected AbstractProductA createProductA() {
|
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|
|
return new ProductA2();
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}
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@Override
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protected AbstractProductB createProductB() {
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return new ProductB2();
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}
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@Override
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protected AbstractProductB createProductB() {
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return new ProductB2();
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}
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}
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public class Client {
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public static void main(String[] args) {
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AbstractFactory factory = new ConcreteFactory1();
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AbstractProductA productA = factory.createProductA();
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AbstractProductB productB = factory.createProductB();
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public static void main(String[] args) {
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AbstractFactory factory = new ConcreteFactory1();
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AbstractProductA productA = factory.createProductA();
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AbstractProductB productB = factory.createProductB();
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...
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// 结合使用productA和productB进行后续操作
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...
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}
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...
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// 结合使用productA和productB进行后续操作
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...
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}
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}
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```
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AmyliaY
5 years ago