Java 中保持扩展性的几种套路和实现

在日常的开发中，作者总结了平常用到的一些低成本、保持扩展性的套路，分享出来，欢迎大家讨论。

前言

SOLID(单一、开闭、里式替换、接口隔离、依赖倒置)五大原则和23种设计模式(常见的单例、构建者、装饰、适配、代理、组合、模板等等)，小伙伴们对这些肯定都很熟悉。这些原则和设计模式能够辅助我们，让我们在设计的时候有所抉择，从而达到高内聚、低耦合的目的。

那说到设计，肯定会提到架构两个字，常见的架构名词：分层架构、六边形架构、SOA架构、CQRS架构、EDA架构等等。我个人对架构的理解是边界的确认以及边界内部元素的组合，其实只要是程序员，他就一定是架构师，只不过是好的架构师还是不那么好的架构师；人人都是架构师，我认为这句话是没有问题的，区别在于他的认知决定了他所能确认的边界、如何更高效的组合内部元素；技术的架构师肯定侧重于技术，业务的架构师肯定侧重于业务，商品的架构师所能看到的边界大概率还是局限在商品域，ICBU架构组的架构师更多考虑是横向的业务支撑。以上是我个人对架构两个字的理解，今天我们不讨论具体架构，我们讨论一些套路，在日常的开发中，我总结了些我平常用到的一些低成本、保持扩展性的套路，分享出来，欢迎大家讨论。

基于管道(pipeline)的套路

关键点

• 管道(Pipeline)----用于串联阀门的管道通路
• 阀门(PipelineValue)----用于每一个节点处理实际业务诉求
• 管道上下文(PipelineContext)----用于管道上下文中数据的扭转

适用场景

• 当你的数据流需要经过很多同等逻辑处理时，可以考虑使用此套路，便于后续扩展

实现代码

• Pipeline/StandardPipeline

 package com.example.ownertest.dm.pipelline; /** * @Author: linear.zw * @Date: 2023/10/25 19:46 */ public interface Pipeline { /** * 执行 * * @return */ boolean invoke(PipelineContext pipelineContext); /** * 添加值 * * @param pipelineValue * @return */ boolean addValue(PipelineValue pipelineValue); /** * 移除值 * * @param pipelineValue * @return */ boolean removeValue(PipelineValue pipelineValue); } package com.example.ownertest.dm.pipelline; import java.util.List; import com.google.common.collect.Lists; import lombok.Data; import lombok.extern.slf4j.Slf4j; /** * @Author: linear.zw * @Date: 2023/10/25 19:46 */ @Data @Slf4j public class StandardPipeline implements Pipeline { private List<PipelineValue> pipelineValueList = Lists.newArrayList(); @Override public boolean invoke(PipelineContext pipelineContext) { boolean isResult = true; for (PipelineValue pipelineValue : pipelineValueList) { try { isResult = pipelineValue.execute(pipelineContext); if (!isResult) { log.error("{},exec is wrong", pipelineValue.getClass().getSimpleName()); } } catch (Exception e) { log.error(e.getMessage(), e); } } return isResult; } @Override public boolean addValue(PipelineValue pipelineValue) { if (pipelineValueList.contains(pipelineValue)) { return true; } return pipelineValueList.add(pipelineValue); } @Override public boolean removeValue(PipelineValue pipelineValue) { return pipelineValueList.remove(pipelineValue); } }

• PipelineContext/StandardPipelineContext

 package com.example.ownertest.dm.pipelline; /** * @Author: linear.zw * @Date: 2023/10/25 19:47 */ public interface PipelineContext { String FOR_TEST = "forTest"; /** * 设置 * * @param contextKey * @param contextValue */ void set(String contextKey, Object contextValue); /** * 获取值 * * @param contextKey * @return */ Object get(String contextKey); } package com.example.ownertest.dm.pipelline; import java.util.Map; import com.google.common.collect.Maps; /** * @Author: linear.zw * @Date: 2023/10/25 19:47 */ public class StandardPipelineContext implements PipelineContext { private Map<String, Object> contentMap = Maps.newConcurrentMap(); @Override public void set(String contextKey, Object contextValue) { contentMap.put(contextKey, contextValue); } @Override public Object get(String contextKey) { return contentMap.get(contextKey); } }

• PipelineValue/AbstractPipelineValue/GraySwitchValue/ForTestValue

 package com.example.ownertest.dm.pipelline; /** * @Author: linear.zw * @Date: 2023/10/25 19:47 */ public interface PipelineValue { /** * 节点执行 * * @param pipelineContext * @return */ boolean execute(PipelineContext pipelineContext); } package com.example.ownertest.dm.pipelline; /** * @Author: linear.zw * @Date: 2023/10/25 19:48 */ public abstract class AbstractPipelineValue implements PipelineValue { @Override public boolean execute(PipelineContext pipelineContext) { System.out.println(this.getClass().getSimpleName() + " start "); boolean result = doExec(pipelineContext); System.out.println(this.getClass().getSimpleName() + " end "); return result; } protected abstract boolean doExec(PipelineContext pipelineContext); } package com.example.ownertest.dm.pipelline; /** * @Author: linear.zw * @Date: 2023/10/25 19:48 */ public class GraySwitchValue extends AbstractPipelineValue { @Override public boolean doExec(PipelineContext pipelineContext) { pipelineContext.set(PipelineContext.FOR_TEST, true); return true; } } package com.example.ownertest.dm.pipelline; /** * @Author: linear.zw * @Date: 2023/10/25 19:48 */ public class ForTestValue extends AbstractPipelineValue { @Override public boolean doExec(PipelineContext pipelineContext) { return true; } }

• PipelineClient

 package com.example.ownertest.dm.pipelline; /** * 入口类 * * @Author: linear.zw * @Date: 2023/10/25 19:48 */ public class PipelineClient { public static void main(String[] args) { // 管道初始化 Pipeline pipeline = new StandardPipeline(); // value扩展 PipelineValue pipelineValue = new GraySwitchValue(); PipelineValue pipelineValue2 = new ForTestValue(); // 上下文 PipelineContext pipelineContext = new StandardPipelineContext(); pipeline.addValue(pipelineValue); pipeline.addValue(pipelineValue2); // 调用管道 pipeline.invoke(pipelineContext); } }

常见框架中的应用

• 网络层的扛把子netty框架中，例如ChannelPipeline、ChannelHandler、ChannelHandlerContext，分别用于处理tcp拆包、加解码等等之类。

基于责任链(filterchain)的套路

关键点

来源--https://www.oracle.com/java/technologies/intercepting-filter.html

• 过滤器(Filter)----实际处理业务的节点
• 过滤链(FilterChain)----串联过滤器的链条

适用场景

• 例如常见的web请求场景

实现代码

• Filter/ForTest1Filter/ForTest2Filter

 package com.example.ownertest.dm.filter; /** * @Author: linear.zw * @Date: 2023/10/26 19:22 */ public interface Filter { void doFilter(HttpRequest httpRequest,FilterChain filterChain); } package com.example.ownertest.dm.filter; /** * @Author: linear.zw * @Date: 2023/10/26 19:22 */ public class ForTest1Filter implements Filter { @Override public void doFilter(HttpRequest httpRequest, FilterChain filterChain) { // do System.out.println(this.getClass().getSimpleName() + " before " + System.currentTimeMillis()); filterChain.doFilter(httpRequest); // after System.out.println(this.getClass().getSimpleName() + " end " + System.currentTimeMillis()); } } package com.example.ownertest.dm.filter; /** * @Author: linear.zw * @Date: 2023/10/26 19:22 */ public class ForTest2Filter implements Filter { @Override public void doFilter(HttpRequest httpRequest, FilterChain filterChain) { // do System.out.println(this.getClass().getSimpleName() + " before " + System.currentTimeMillis()); filterChain.doFilter(httpRequest); // after System.out.println(this.getClass().getSimpleName() + " end " + System.currentTimeMillis()); } }

• FilterChain/StandardFilterChain

 package com.example.ownertest.dm.filter; /** * @Author: linear.zw * @Date: 2023/10/26 19:23 */ public interface FilterChain { void doFilter(HttpRequest httpRequest); void addFilter(Filter filter); } package com.example.ownertest.dm.filter; import java.util.List; import com.google.common.collect.Lists; /** * @Author: linear.zw * @Date: 2023/10/26 19:24 */ public class StandardFilterChain implements FilterChain { private List<Filter> filterList = Lists.newArrayList(); private int currentIndex = 0; @Override public void doFilter(HttpRequest httpRequest) { if (currentIndex == filterList.size()) { return; } Filter filter = filterList.get(currentIndex); currentIndex = currentIndex + 1; filter.doFilter(httpRequest, this); } @Override public void addFilter(Filter filter) { if (filterList.contains(filter)) { return; } filterList.add(filter); } }

• HttpRequest/StandardHttpRequest

 package com.example.ownertest.dm.filter; /** * @Author: linear.zw * @Date: 2023/10/26 19:24 */ public interface HttpRequest { } package com.example.ownertest.dm.filter; /** * @Author: linear.zw * @Date: 2023/10/26 19:24 */ public class StandardHttpRequest implements HttpRequest { }

• FilterClient----入口测试

 package com.example.ownertest.dm.filter; /** * @Author: linear.zw * @Date: 2023/10/26 19:25 */ public class FilterClient { public static void main(String[] args) { FilterChain filterChain = new StandardFilterChain(); filterChain.addFilter(new ForTest1Filter()); filterChain.addFilter(new ForTest2Filter()); filterChain.doFilter(new StandardHttpRequest()); } }

常见框架中的应用

• hsf的filter机制，服务端扩展的ServerFilter和客户端扩展的ClientFilter；

• 开发过java web的小伙伴都知道的servlet，servlet的入口即是FilterChain、Filter；

基于组合/模板的套路

关键点

• 处理器注册器----用于存储处理器的集合
• 处理器工厂----用于创建处理器
• 处理器----实际的处理器以及扩展的实现
• 处理器上下文----处理器上下文，用于参数的传递

适用场景

• 适合于有共性、后续持续扩展的场景

实现代码

• PiiHandlerRegistry----处理器注册器

 package com.example.ownertest.dm.comp; import java.lang.reflect.Field; import java.util.List; import java.util.Map; import com.google.common.collect.Maps; import lombok.extern.slf4j.Slf4j; import org.apache.commons.collections4.CollectionUtils; import org.apache.commons.lang3.StringUtils; /** * @Author: linear.zw * @Date: 2023/10/31 20:45 */ @Slf4j public class PiiHandlerRegistry { private static Map<String, PiiDomainFieldHandler> piiDomainFieldHandlerMap = Maps.newHashMap(); public static void putHandler(String piiDomainFieldName, PiiDomainFieldHandler piiDomainFieldHandler) { if (StringUtils.isEmpty(piiDomainFieldName)) { log.warn(" piiDomainFieldName is null,continue"); return; } if (piiDomainFieldHandler == null) { log.warn(piiDomainFieldName + " piiDomainFieldHandler is null,continue"); return; } if (!piiDomainFieldHandlerMap.containsKey(piiDomainFieldName)) { piiDomainFieldHandlerMap.put(piiDomainFieldName, piiDomainFieldHandler); } } public static <T extends Object> int handlerRead(T domain, Field domainField, PiiContent piiContent) { int num = 0; for (Map.Entry<String, PiiDomainFieldHandler> piiDomainFieldHandlerEntry : piiDomainFieldHandlerMap.entrySet()) { if (piiDomainFieldHandlerEntry.getValue().isSupport(domain, domainField)) { piiDomainFieldHandlerEntry.getValue().handlerRead(domain, domainField, piiContent); } } return num; } public static <T extends Object> int handlerWrite(T domain, Field domainField, PiiContent piiContent) { int num = 0; for (Map.Entry<String, PiiDomainFieldHandler> piiDomainFieldHandlerEntry : piiDomainFieldHandlerMap.entrySet()) { if (piiDomainFieldHandlerEntry.getValue().isSupport(domain, domainField)) { piiDomainFieldHandlerEntry.getValue().handlerWrite(domain, domainField, piiContent); } } return num; } public static Map<String, PiiDomainFieldHandler> getPiiDomainFieldHandlerMap() { return piiDomainFieldHandlerMap; } public static void init() { List<PiiDomainFieldHandler> piiDomainFieldHandlerList = PiiDomainFieldHandlerFactory .createPiiDomainFieldHandler(); if (CollectionUtils.isNotEmpty(piiDomainFieldHandlerList)) { for (PiiDomainFieldHandler piiDomainFieldHandler : piiDomainFieldHandlerList) { putHandler(piiDomainFieldHandler.getPiiDomainMeta(), piiDomainFieldHandler); } } } }

• PiiDomainFieldHandlerFactory----处理器工厂

 package com.example.ownertest.dm.comp; import java.util.List; import com.google.common.collect.Lists; /** * @Author: linear.zw * @Date: 2023/10/31 20:46 */ public class PiiDomainFieldHandlerFactory { /** * 创建领域处理器 * * @return */ public static List<PiiDomainFieldHandler> createPiiDomainFieldHandler() { List<PiiDomainFieldHandler> piiDomainFieldHandlerList = Lists.newArrayList(); // piiDomainFieldHandlerList.add(new ForTestSupportFieldHandler()); piiDomainFieldHandlerList.add(new ForTestNotSupportFieldHandler()); return piiDomainFieldHandlerList; } }

• PiiDomainFieldHandler/PiiDomainFieldHandlerBase/ForTestNotSupportFieldHandler/ForTestSupportFieldHandler----处理器

 package com.example.ownertest.dm.comp; import java.lang.reflect.Field; /** * @Author: linear.zw * @Date: 2023/10/31 20:46 */ public interface PiiDomainFieldHandler { /** * 处理实际操作 * 读----从PiiContent获取数据回填domain * * @param domain * @param domainField * @param piiContent * @param <T> * @return */ <T extends Object> boolean handlerRead(T domain, Field domainField, PiiContent piiContent); /** * 处理实际操作 * 写----将domain中需要写入pii的字段数据写入PiiContent * * @param domain * @param domainField * @param piiContent * @param <T> * @return */ <T extends Object> boolean handlerWrite(T domain, Field domainField, PiiContent piiContent); /** * 当前处理器是否支持该领域对象 * * @param domain * @param domainField * @param <T> * @return */ <T extends Object> boolean isSupport(T domain, Field domainField); /** * 获取处理器对应的元信息 * * @return */ String getPiiDomainMeta(); } package com.example.ownertest.dm.comp; import java.lang.reflect.Field; import lombok.extern.slf4j.Slf4j; /** * @Author: linear.zw * @Date: 2023/10/31 20:47 */ @Slf4j public abstract class PiiDomainFieldHandlerBase implements PiiDomainFieldHandler { @Override public <T extends Object> boolean handlerRead(T domain, Field domainField, PiiContent piiContent) { // to do business read return true; } @Override public <T extends Object> boolean handlerWrite(T domain, Field domainField, PiiContent piiContent) { // to do business write return true; } } package com.example.ownertest.dm.comp; import java.lang.reflect.Field; /** * @Author: linear.zw * @Date: 2023/10/31 20:47 */ public class ForTestSupportFieldHandler extends PiiDomainFieldHandlerBase { @Override public <T> boolean isSupport(T domain, Field domainField) { if (this.getClass().getSimpleName().equalsIgnoreCase(domain.getClass().getSimpleName())) { // to do business System.out.println(this.getClass().getSimpleName() + " is support, to do some business"); return true; } return false; } @Override public String getPiiDomainMeta() { return this.getClass().getSimpleName(); } } package com.example.ownertest.dm.comp; import java.lang.reflect.Field; /** * @Author: linear.zw * @Date: 2023/10/31 20:48 */ public class ForTestNotSupportFieldHandler extends PiiDomainFieldHandlerBase { @Override public <T> boolean isSupport(T domain, Field domainField) { if (this.getClass().getSimpleName().equalsIgnoreCase(domain.getClass().getSimpleName())) { // to do business System.out.println(this.getClass().getSimpleName() + " is support, to do some business"); return true; } return false; } @Override public String getPiiDomainMeta() { return this.getClass().getSimpleName(); } }

• PiiContent----上下文

 package com.example.ownertest.dm.comp; import java.util.Map; import com.google.common.collect.Maps; import lombok.Data; /** * @Author: linear.zw * @Date: 2023/10/31 20:48 */ @Data public class PiiContent { public static String FORTEST="fortest"; private Map<String, Object> piiDataMap = Maps.newHashMap(); private Map<String, Object> piiContextMap = Maps.newHashMap(); public void putPiiData(String domainFieldName, Object domainFieldValue) { piiDataMap.put(domainFieldName, domainFieldValue); } public Object getPiiData(String domainFieldName) { return piiDataMap.get(domainFieldName); } public void putPiiContext(String contextName, Object contextNameValue) { piiContextMap.put(contextName, contextNameValue); } public Object getPiiContext(String contextName) { return piiContextMap.get(contextName); } }

• PiiClient----入口的测试类

 package com.example.ownertest.dm.comp; import java.util.Map; /** * @Author: linear.zw * @Date: 2023/10/31 20:48 */ public class PiiClient { public static void main(String[] args) { PiiHandlerRegistry.init(); // 遍历处理器 for (Map.Entry<String, PiiDomainFieldHandler> entryHandler : PiiHandlerRegistry.getPiiDomainFieldHandlerMap().entrySet()) { System.out.println(entryHandler.getKey() + "\t" + entryHandler.getValue().getPiiDomainMeta()); } // PiiContent piiContent = new PiiContent(); piiContent.putPiiContext(PiiContent.FORTEST, PiiContent.FORTEST); // 请求处理 System.out.println("ForTestSupportFieldHandler start"); PiiHandlerRegistry.handlerRead(new ForTestSupportFieldHandler(), null, piiContent); System.out.println("ForTestSupportFieldHandler end"); // 请求处理 System.out.println("ForTestNotSupportFieldHandler start"); PiiHandlerRegistry.handlerRead(new ForTestNotSupportFieldHandler(), null, piiContent); System.out.println("ForTestNotSupportFieldHandler end"); } }

常见框架中的应用

• 这个就太多了，例如spring最核心的BeanPostProcessor机制，通过org.springframework.beans.factory.support.AbstractBeanFactory#beanPostProcessors管理一些列的beanPostProcessors，在spring上下文org.springframework.context.support.AbstractApplicationContext#refresh的时候，进行bean的init(InitDestroyAnnotationBeanPostProcessor)、解析注解(ScheduledAnnotationBeanPostProcessor、AutowiredAnnotationBeanPostProcessor)、解析aop（AnnotationAwareAspectJAutoProxyCreator）等等。

基于注解的套路

关键点

• 注解元定义----用来定义通用的元信息；
• 注解解析器----解析类上是否有指定的注解，进而进行对应的扩展操作；
• spring的BeanPostProcessor----这里是借用spring的BeanPostProcessor机制，在spring容器初始化的时候，进行回调，完成预期的扩展行为；

适用场景

• 简化内部使用

实现代码

• ForTestAnnotation----注解元定义

 package com.example.ownertest.dm.annotation; import java.lang.annotation.ElementType; import java.lang.annotation.Retention; import java.lang.annotation.RetentionPolicy; import java.lang.annotation.Target; import org.springframework.stereotype.Component; /** * 用于测试的标识注解 * * @Author: linear.zw * @Date: 2023/11/1 10:21 */ @Target({ElementType.TYPE, ElementType.METHOD}) @Retention(RetentionPolicy.RUNTIME) @Component public @interface ForTestAnnotation { }

• ForTestAnnotationProcessor----注解解析器

 package com.example.ownertest.dm.annotation; import org.springframework.aop.support.AopUtils; import org.springframework.beans.BeansException; import org.springframework.beans.factory.config.BeanPostProcessor; import org.springframework.core.annotation.AnnotationUtils; import org.springframework.stereotype.Component; /** * 注解解析器 * @Author: linear.zw * @Date: 2023/11/1 10:25 */ @Component public class ForTestAnnotationProcessor implements BeanPostProcessor { @Override public Object postProcessBeforeInitialization(Object bean, String beanName) throws BeansException { // 获取目标类是否有ForTestAnnotation注解 ForTestAnnotation annotation = AnnotationUtils.findAnnotation(AopUtils.getTargetClass(bean), ForTestAnnotation.class); if (annotation == null) { return bean; } // 处理想要的扩展 System.out.println(beanName + " has ForTestAnnotation"); return bean; } @Override public Object postProcessAfterInitialization(Object bean, String beanName) throws BeansException { return bean; } }

• ForTestBean----测试bean

 package com.example.ownertest.dm.annotation; /** * @Author: linear.zw * @Date: 2023/11/1 10:26 */ @ForTestAnnotation public class ForTestBean { public ForTestBean() { System.out.println(ForTestBean.class.getSimpleName() + " init"); } }

• ForTestClient---测试入口

 package com.example.ownertest.dm.annotation; import org.springframework.context.annotation.AnnotationConfigApplicationContext; /** * @Author: linear.zw * @Date: 2023/11/1 10:26 */ public class ForTestClient { public static void main(String[] args) { AnnotationConfigApplicationContext applicationContext = new AnnotationConfigApplicationContext( "com.example.ownertest.dm.annotation"); System.out.println(ForTestClient.class.getSimpleName()); } }

常见框架中的应用

• 例如集团内部的spring-boot-alibaba-diamond-autoconfigure

基于事件分发的套路

关键点

• 事件源--事件触发者
• 事件--标识产生的来源
• 事件监听器--事件的关注者，即处理者
• 事件分发器--用于将事件源的事件转发给事件监听器

实现代码

• EventSource/EventSourceForTest/EventSourceForTest2

 package com.example.ownertest.dm.event; /** * 发出事件 * @Author: linear.zw * @Date: 2023/11/1 14:12 */ public interface EventSource { /** * 发出事件 * * @return */ Event fireEvent(); } package com.example.ownertest.dm.event; /** * @Author: linear.zw * @Date: 2023/11/1 14:14 */ public class EventSourceForTest implements EventSource { @Override public Event fireEvent() { Event event = new EventForTest(); System.out.println(getClass().getSimpleName() + " \t fireEvent " + event.getName()); return event; } } package com.example.ownertest.dm.event; /** * @Author: linear.zw * @Date: 2023/11/1 14:15 */ public class EventSourceForTest2 implements EventSource { @Override public Event fireEvent() { Event event = new EventForTest2(); System.out.println(getClass().getSimpleName() + " \t fireEvent " + event.getName()); return event; } }

• Event/EventForTest/EventForTest2

 package com.example.ownertest.dm.event; /** * @Author: linear.zw * @Date: 2023/11/1 14:15 */ public interface Event { /** * 事件名称 * * @return */ String getName(); } package com.example.ownertest.dm.event; /** * @Author: linear.zw * @Date: 2023/11/1 14:17 */ public class EventForTest implements Event { @Override public String getName() { return getClass().getSimpleName(); } } package com.example.ownertest.dm.event; /** * @Author: linear.zw * @Date: 2023/11/1 14:17 */ public class EventForTest2 implements Event { @Override public String getName() { return getClass().getSimpleName(); } }

• EventListener/EventListenerForTest

 package com.example.ownertest.dm.event; /** * @Author: linear.zw * @Date: 2023/11/1 14:17 */ public interface EventListener { /** * 是否支持此事件 * * @param event * @return */ boolean supportEvent(Event event); /** * 处理事件 * * @return */ boolean handlerEvent(Event event); } package com.example.ownertest.dm.event; /** * @Author: linear.zw * @Date: 2023/11/1 14:18 */ public class EventListenerForTest implements EventListener { @Override public boolean supportEvent(Event event) { return event.getName().contains("Test"); } @Override public boolean handlerEvent(Event event) { System.out.println(this.getClass().getSimpleName() + "\t handler " + event.getName()); return true; } }

• EventDispatcher/EventListenerManager

 package com.example.ownertest.dm.event; import org.apache.commons.collections4.CollectionUtils; /** * @Author: linear.zw * @Date: 2023/11/1 14:18 */ public class EventDispatcher { /** * 单例模式 */ private static EventDispatcher eventDispatcher = new EventDispatcher(); private EventDispatcher() { } /** * 分发事件 * * @param event * @return */ public static boolean dispatchEvent(Event event) { if (CollectionUtils.isNotEmpty(EventListenerManager.getEventListenerList())) { for (EventListener eventListener : EventListenerManager.getEventListenerList()) { if (eventListener.supportEvent(event)) { eventListener.handlerEvent(event); } } } return true; } } package com.example.ownertest.dm.event; import java.util.List; import com.google.common.collect.Lists; /** * @Author: linear.zw * @Date: 2023/11/1 14:18 */ public class EventListenerManager { private static List<EventListener> eventListenerList = Lists.newArrayList(); /** * 添加事件监听器 * * @param eventListener * @return */ public static boolean addEventListener(EventListener eventListener) { if (!eventListenerList.contains(eventListener)) { return eventListenerList.add(eventListener); } return true; } /** * 移除事件监听器 * * @param eventListener * @return */ public static boolean removeEventListener(EventListener eventListener) { if (eventListenerList.contains(eventListener)) { return eventListenerList.remove(eventListener); } return true; } public static List<EventListener> getEventListenerList() { return eventListenerList; } }

• EventClient

 package com.example.ownertest.dm.event; /** * @Author: linear.zw * @Date: 2023/11/1 14:19 */ public class EventClient { public static void main(String[] args) { // 创建事件源 EventSource eventSourceForTest = new EventSourceForTest(); EventSource eventSourceForTest2 = new EventSourceForTest2(); // 创建事件监听器 EventListener eventListener = new EventListenerForTest(); EventListenerManager.addEventListener(eventListener); // 发布事件 EventDispatcher.dispatchEvent(eventSourceForTest.fireEvent()); EventDispatcher.dispatchEvent(eventSourceForTest2.fireEvent()); } }

基于SPI机制的套路

关键点

• 服务调用方
• 服务实现方----以接口名称为文件名称，放在META-INF/services，值为该接口的实现

• 标准服务接口

适用场景

实现代码

• SpiServiceLoaderHelper

 package com.example.ownertest.dm.spi; import java.util.Iterator; import java.util.Objects; import java.util.ServiceLoader; /** * @Author: linear.zw * @Date: 2023/11/1 15:32 */ public class SpiServiceLoaderHelper { public static ProductPackageRemoteServiceInterface getProductPackageRemoteServiceInterface() { // 先从缓存中加载 Object serviceCache = DependServiceRegistryHelper.getDependObject(ProductPackageRemoteServiceInterface.class); if (serviceCache != null) { return (ProductPackageRemoteServiceInterface) serviceCache; } // spi 方式加载 ProductPackageRemoteServiceInterface serviceInterface = loadSpiImpl(ProductPackageRemoteServiceInterface.class); // 防止注入的bean为空 提前进行判断 以免业务执行出现问题 boolean isExist = true; if (Objects.isNull(serviceInterface)) { isExist = false; } else if (Objects.isNull(serviceInterface.getProductPackageRemoteService())) { isExist = false; } if (!isExist) { throw new RuntimeException("getProductPackageRemoteService load impl failed,please check spi service"); } // 添加进统一的依赖管理 DependServiceRegistryHelper.registry(ProductPackageRemoteServiceInterface.class, serviceInterface); return serviceInterface; } /** * 以spi的方式加载实现类 * * @param cls * @param <P> * @return */ private static <P> P loadSpiImpl(Class<P> cls) { ServiceLoader<P> spiLoader = ServiceLoader.load(cls); Iterator<P> iaIterator = spiLoader.iterator(); if (iaIterator.hasNext()) { return iaIterator.next(); } return null; } }

• DependServiceRegistryHelper

 package com.example.ownertest.dm.spi; import java.util.Map; import com.google.common.collect.Maps; /** * @Author: linear.zw * @Date: 2023/11/1 15:35 */ public class DependServiceRegistryHelper { /** * 存储策略依赖的服务,统一管理 */ private static Map<String, Object> dependManagerMap = Maps.newHashMap(); public static boolean registryMap(Map<Class, Object> dependManagerMap) { for (Map.Entry<Class, Object> dependEntry : dependManagerMap.entrySet()) { registry(dependEntry.getKey(), dependEntry.getValue()); } return true; } public static boolean registry(Class cls, Object dependObject) { dependManagerMap.put(cls.getCanonicalName(), dependObject); return true; } public static Object getDependObject(Class cls) { return dependManagerMap.get(cls.getCanonicalName()); } }

• SpiServiceLoaderClientTest

 package com.example.ownertest.dm.spi; /** * @Author: linear.zw * @Date: 2023/11/1 15:37 */ public class SpiServiceLoaderClientTest { public static void main(String[] args) { ProductPackageRemoteServiceInterface productPackageRemoteServiceInterface = SpiServiceLoaderHelper.getProductPackageRemoteServiceInterface(); } }

常见框架中的应用

• 目前大多数中台的策略包，都是基于spi方式的，动态加载业务的实现，进而达到扩展的目的；
• 例如google开源的auto-service，通过注解的方式，自动生成spi的实现目录；

最后

程序员大多数都是实干派，所以，你的套路有哪些，评论区有你的位置，Show me the code。

作者｜高止

原文链接

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