实际应用-简单工厂到工厂方法到Annotation

你的名字 2022-04-16 02:47 107阅读 0赞

##### 1.刚开始的版本 #####

> 需求是监听user.queue,获取到用户的消息，消息里有用户的增删改操作

做法比较简单使用简单工厂，代码如下

@JmsListener(destination="USER.QUEUE")
    public void onMessage(Object message){
        if(message instanceof JMSObjectMessage){
    			JMSObjectMessage msgObj = (JMSObjectMessage)message;
    	    Object payload = msgObj.getObject();
            UserMessageHandlerFactory.getHandler(payload).process((PendingUserValue)payload);
        }
    }

public class UserMessageHandlerFactory{
        public static MessageHandler getHandler(PendingUserValue payload){
            ...
            if(payload.getAction()==RequestType.CREATE_USER.getStatusCode()){
                return new UserCreateHandler();
            }else if(payload.getAction()==RequestType.CREATE_USER.getStatusCode()){
                return new UserEditHandler();
            }
            ...
        }
    }

public static  enum RequestType {
    		CREATE_USER("create_user", 0),
    		EDIT_USER("edit_user", 1),
    		DELETE_USER("delete_user", 2);
    	
    		String statusName;
    		int statusCode;
    		RequestType(String statusName, int statusCode) {
    			this.statusName=statusName;
    			this.statusCode = statusCode;
    		}
    		public String getStatusName() {
    			return statusName;
    		}
    		public int getStatusCode() {
    			return statusCode;
    		}
    
    		public static RequestType valueOf(int code){
    			EnumSet<RequestType> set =EnumSet.allOf(RequestType.class);
    			return  set.stream().filter(requestType->{
    				return requestType.getStatusCode()==code;
    			}).findFirst().get();
    		}
    	}

interface MessageHandler<T>{
    	public void process(T t) throws Exception;
    }

public class UserCreateHandler implements MessageHandler<PendingUserValue>{
        	public void process(PendingUserValue p){
        	    ...
        	}
    }

public class UserEditHandler implements MessageHandler<PendingUserValue>{
        	public void process(PendingUserValue p){
        	    ...
        	}
    }

UML图如下  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2d1b194bA_size_16_color_FFFFFF_t_70]

##### 2. 二期版本 #####

> 1期开发完毕后，加入了更多的需求，例如account的增删改 ,都是走同样的模式。在1期开发完毕的基础上变成如下模式。由简单工厂变成了工厂方法

public MessageHandlerFactory{
        public static MessageHandler getHandler(Object payload){
            if(payload instanceOf PendingUserValue){
               return  UserMessageHandlerFactory.getHandler(PendingUserValue(payload));
            }else if(payload instanceOf PendingAccountValue){
                 return  AccountMessageHandlerFactory.getHandler(PendingAccountValue(payload));
            }
            ....
        }
    }

public class AccountMessageHandlerFactory{
        public static MessageHandler getHandler(PendingAccountValue payload){
            ...
            if(payload.getAction()==RequestType.CREATE_ACCOUNT.getStatusCode()){
                return new AccountCreateHandler();
            }else if(payload.getAction()==RequestType.EDIT_ACCOUNT.getStatusCode()){
                return new AccountEditHandler();
            }
            ...
        }
    }

@JmsListener(destination="USER.QUEUE")
    public void onMessage(Object message){
        if(message instanceof JMSObjectMessage){
    		JMSObjectMessage msgObj = (JMSObjectMessage)message;
    	    Object payload = msgObj.getObject();
            MessageHandlerFactory.getHandler(payload).process(payload);
        }
    }

@JmsListener(destination="ACCOUNT.QUEUE")
    public void onMessage(Object message){
        if(message instanceof JMSObjectMessage){
    		JMSObjectMessage msgObj = (JMSObjectMessage)message;
    	    Object payload = msgObj.getObject();
            MessageHandlerFactory.getHandler(payload).process(payload);
        }
    }

上面实际上演化成了工厂方法，UML图  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2d1b194bA_size_16_color_FFFFFF_t_70 1]

> 优点 ：符合开闭原则，比如后面要新加个Group的处理，只需要增加`GroupMessageHandlerFactory` 以及`GroupCreateHandler`和`GroupEditHandler`

> 缺点 `MessageHandlerFactory`这个类还是要不断的修改加入if…else。如果增加其他的action ，例如`delete`,则`GroupMessageHandlerFactory`，  
> `UserMessageHandlerFactory`，  
> `AccountMessageHandlerFactory`都需要加入判断。

由此想到了利用annotation编程

增加一个annotation

@Target({ElementType.TYPE})
    @Retention(RetentionPolicy.RUNTIME)
    @Documented
    @Component
    public @interface JMSMessageHandler {
        Class jmsPayLoad();//指定jms监听到message是哪种class,例如PendingUserValue,PendingAccoutValue
        RequestType requestType();//例如指定是CREATE_USER还是CREATE_ACCOUNT
    }

public static  enum RequestType {
    		CREATE_USER("create_user", 0),
    		EDIT_USER("edit_user", 1),
    		DELETE_USER("delete_user", 2),
    		CREATE_ACCOUNT("create_account", 4),
    		EDIT_ACCOUNT("edit_account", 5),
    		DELETE_ACCOUNT("delete_account", 6);
    		String statusName;
    		int statusCode;
    		RequestType(String statusName, int statusCode) {
    			this.statusName=statusName;
    			this.statusCode = statusCode;
    		}
    		public String getStatusName() {
    			return statusName;
    		}
    		public int getStatusCode() {
    			return statusCode;
    		}
    
    		public static RequestType valueOf(int code){
    			EnumSet<RequestType> set =EnumSet.allOf(RequestType.class);
    			return  set.stream().filter(requestType->{
    				return requestType.getStatusCode()==code;
    			}).findFirst().get();
    		}
    	}

@Service
    public class MQListenerJMSHandlerDispatcher implements ApplicationContextAware{
    
        private ApplicationContext context;
        public void process(Object payload){
        //找到所有MessageHandler的bean
            Map<String, MessageHandler> msp =BeanFactoryUtils.beansOfTypeIncludingAncestors(context,MessageHandler.class);
            try {
                msp.values().stream().filter(handler->{
                if(!handler.getClass().isAnnotationPresent(JMSMessageHandler.class))
    						return false;
                     //找到对应的annotation
                     JMSHandler[] jmsHandlers =  handler.getClass().getAnnotationsByType(JMSMessageHandler.class);
                     JMSHandler jmsHandler =jmsHandlers[0];
                     Class payloadClass = jmsHandler.jmsPayLoad();
                     RequestType choiceType = jmsHandler.requestType();
                     Base base =(Base)payload;
                     RequestType requestType = RequestType.valueOf(base.getRequestType());
                     return base.getClass().isAssignableFrom(payloadClass) &&
                             requestType==choiceType;
                 }).findFirst().get().process(payload);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    
        public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
            this.context=applicationContext;
        }
    }

@JMSMessageHandler(jmsPayLoad=PendingUserValue.class,
                requestType=RequestType.CREATE_USER)
    public class UserCreateHandler implements MessageHandler<PendingUserValue>{
        	public void process(PendingUserValue p){
        	    ...
        	}
    }

@JMSMessageHandler(jmsPayLoad=PendingUserValue.class,
                requestType=RequestType.EDIT_USER)
    public class UserEditHandler implements MessageHandler<PendingUserValue>{
        	public void process(PendingUserValue p){
        	    ...
        	}
    }

@JMSMessageHandler(jmsPayLoad=PendingAccountValue.class,
                requestType=RequestType.CREATE_ACCOUNT)
    public class UserCreateHandler implements MessageHandler<PendingAccountValue>{
        	public void process(PendingAccountValue p){
        	    ...
        	}
    }

@JMSMessageHandler(jmsPayLoad=PendingAccountValue.class,
                requestType=RequestType.EDIT_ACCOUNT)
    public class UserEditHandler implements MessageHandler<PendingAccountValue>{
        	public void process(PendingAccountValue p){
        	    ...
        	}
    }

UML图  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2d1b194bA_size_16_color_FFFFFF_t_70 2]

> 优点 : 彻底做到了开闭原则，如果要加入新的handler，只需编写后加入`@JMSMessageHandler`

参考  
[简单工厂，工厂模式，抽象工厂][Link 1]笔记

[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2d1b194bA_size_16_color_FFFFFF_t_70]: /images/20220416/9afe4c6530ad4d09b50cde07062e3c3e.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2d1b194bA_size_16_color_FFFFFF_t_70 1]: /images/20220416/647684c7b77c4f7da95cbdb6faf36724.png
[watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L2d1b194bA_size_16_color_FFFFFF_t_70 2]: /images/20220416/da460de4ae2342cb9772162f8adfe223.png
[Link 1]: http://www.runoob.com/design-pattern/abstract-factory-pattern.html