Java中保持扩展性的几种套路和实现

原创高止阿里云开发者

阿里妹导读

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@Slf4jpublic 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 */@Slf4jpublic 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 */@Slf4jpublic 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 */@Datapublic 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)@Componentpublic @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 */@Componentpublic 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 */@ForTestAnnotationpublic 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。

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