设计模式—— 工厂方法模式（Factory Pattern）+ Spring相关源码

一、工厂模式 / 工厂方法模式

类型： 创建型模式
目的： 可以将对象的创建与使用代码分离，提供统一的接口来创建不同类型的对象。

二、例子

2.1 菜鸟例子

2.1.1 定义要被创建对象

public interface Shape {
   void draw();
}
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public class Rectangle implements Shape {
 
   @Override
   public void draw() {
      System.out.println("Inside Rectangle::draw() method.");
   }
}
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public class Circle implements Shape {
 
   @Override
   public void draw() {
      System.out.println("Inside Circle::draw() method.");
   }
}
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2.1.2 工厂类

public class ShapeFactory {
 
   //使用 getShape 方法获取形状类型的对象
   public Shape getShape(String shapeType){
      if(shapeType == null){
         return null;
      }        
      if(shapeType.equalsIgnoreCase("CIRCLE")){
         return new Circle();
      } else if(shapeType.equalsIgnoreCase("RECTANGLE")){
         return new Rectangle();
      }
      return null;
   }
}
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2.1.3 使用

public class FactoryPatternDemo {
 
   public static void main(String[] args) {
      ShapeFactory shapeFactory = new ShapeFactory();
 
      //获取 Circle 的对象，并调用它的 draw 方法
      Shape shape1 = shapeFactory.getShape("CIRCLE");
      shape1.draw();
 
      //获取 Rectangle 的对象，并调用它的 draw 方法
      Shape shape2 = shapeFactory.getShape("RECTANGLE");
      shape2.draw();
   }
}
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2.2 Spring源码——AbstractBeanFactory

public abstract class AbstractBeanFactory extends FactoryBeanRegistrySupport implements ConfigurableBeanFactory {

	public Object getBean(String name) throws BeansException {
        return this.doGetBean(name, (Class)null, (Object[])null, false);
    }

    protected <T> T doGetBean(String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly) throws BeansException {
        String beanName = this.transformedBeanName(name);
        Object sharedInstance = this.getSingleton(beanName);
        Object beanInstance;
        if (sharedInstance != null && args == null) {
            if (this.logger.isTraceEnabled()) {
                if (this.isSingletonCurrentlyInCreation(beanName)) {
                    this.logger.trace("Returning eagerly cached instance of singleton bean '" + beanName + "' that is not fully initialized yet - a consequence of a circular reference");
                } else {
                    this.logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
                }
            }

            beanInstance = this.getObjectForBeanInstance(sharedInstance, name, beanName, (RootBeanDefinition)null);
        } else {
            if (this.isPrototypeCurrentlyInCreation(beanName)) {
                throw new BeanCurrentlyInCreationException(beanName);
            }

            BeanFactory parentBeanFactory = this.getParentBeanFactory();
            if (parentBeanFactory != null && !this.containsBeanDefinition(beanName)) {
                String nameToLookup = this.originalBeanName(name);
                if (parentBeanFactory instanceof AbstractBeanFactory) {
                    return ((AbstractBeanFactory)parentBeanFactory).doGetBean(nameToLookup, requiredType, args, typeCheckOnly);
                }

                if (args != null) {
                    return parentBeanFactory.getBean(nameToLookup, args);
                }

                if (requiredType != null) {
                    return parentBeanFactory.getBean(nameToLookup, requiredType);
                }

                return parentBeanFactory.getBean(nameToLookup);
            }

            if (!typeCheckOnly) {
                this.markBeanAsCreated(beanName);
            }

            StartupStep beanCreation = this.applicationStartup.start("spring.beans.instantiate").tag("beanName", name);

            try {
                if (requiredType != null) {
                    beanCreation.tag("beanType", requiredType::toString);
                }

                RootBeanDefinition mbd = this.getMergedLocalBeanDefinition(beanName);
                this.checkMergedBeanDefinition(mbd, beanName, args);
                String[] dependsOn = mbd.getDependsOn();
                String[] prototypeInstance;
                if (dependsOn != null) {
                    prototypeInstance = dependsOn;
                    int var13 = dependsOn.length;

                    for(int var14 = 0; var14 < var13; ++var14) {
                        String dep = prototypeInstance[var14];
                        if (this.isDependent(beanName, dep)) {
                            throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
                        }

                        this.registerDependentBean(dep, beanName);

                        try {
                            this.getBean(dep);
                        } catch (NoSuchBeanDefinitionException var31) {
                            throw new BeanCreationException(mbd.getResourceDescription(), beanName, "'" + beanName + "' depends on missing bean '" + dep + "'", var31);
                        }
                    }
                }

                if (mbd.isSingleton()) {
                    sharedInstance = this.getSingleton(beanName, () -> {
                        try {
                            return this.createBean(beanName, mbd, args);
                        } catch (BeansException var5) {
                            this.destroySingleton(beanName);
                            throw var5;
                        }
                    });
                    beanInstance = this.getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
                } else if (mbd.isPrototype()) {
                    prototypeInstance = null;

                    Object prototypeInstance;
                    try {
                        this.beforePrototypeCreation(beanName);
                        prototypeInstance = this.createBean(beanName, mbd, args);
                    } finally {
                        this.afterPrototypeCreation(beanName);
                    }

                    beanInstance = this.getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
                } else {
                    String scopeName = mbd.getScope();
                    if (!StringUtils.hasLength(scopeName)) {
                        throw new IllegalStateException("No scope name defined for bean '" + beanName + "'");
                    }

                    Scope scope = (Scope)this.scopes.get(scopeName);
                    if (scope == null) {
                        throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
                    }

                    try {
                        Object scopedInstance = scope.get(beanName, () -> {
                            this.beforePrototypeCreation(beanName);

                            Object var4;
                            try {
                                var4 = this.createBean(beanName, mbd, args);
                            } finally {
                                this.afterPrototypeCreation(beanName);
                            }

                            return var4;
                        });
                        beanInstance = this.getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
                    } catch (IllegalStateException var30) {
                        throw new ScopeNotActiveException(beanName, scopeName, var30);
                    }
                }
            } catch (BeansException var32) {
                beanCreation.tag("exception", var32.getClass().toString());
                beanCreation.tag("message", String.valueOf(var32.getMessage()));
                this.cleanupAfterBeanCreationFailure(beanName);
                throw var32;
            } finally {
                beanCreation.end();
            }
        }

        return this.adaptBeanInstance(name, beanInstance, requiredType);
    }
}

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2.3 slf4j源码——SubstituteLoggerFactory

public class SubstituteLoggerFactory implements ILoggerFactory {

	 public synchronized Logger getLogger(String name) {
        SubstituteLogger logger = (SubstituteLogger)this.loggers.get(name);
        if (logger == null) {
            logger = new SubstituteLogger(name, this.eventQueue, this.postInitialization);
            this.loggers.put(name, logger);
        }

        return logger;
    }

}
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---

三、其他设计模式

创建型模式
结构型模式

• 1、设计模式——装饰器模式（Decorator Pattern）+ Spring相关源码

行为型模式

• 1、设计模式——访问者模式（Visitor Pattern）+ Spring相关源码
• 2、设计模式——中介者模式（Mediator Pattern）+ JDK相关源码
• 3、设计模式——策略模式（Strategy Pattern）+ Spring相关源码
• 4、设计模式——状态模式（State Pattern）
• 5、设计模式——命令模式（Command Pattern）+ Spring相关源码
• 6、设计模式——观察者模式（Observer Pattern）+ Spring相关源码
• 7、设计模式——备忘录模式（Memento Pattern）
• 8、设计模式——模板方法模式（Template Pattern）+ Spring相关源码
• 9、设计模式——迭代器模式（Iterator Pattern）+ Spring相关源码
• 10、设计模式——责任链模式（Chain of Responsibility Pattern）+ Spring相关源码
• 11、设计模式——解释器模式（Interpreter Pattern）+ Spring相关源码