Command Query Responsibility Segregation,CQRS 这个架构好象最近博客园里讨论得比较多，有几篇园友的文章很有深度，推荐阅读：
比较有趣的是，以往一断谈及架构思路、OO这些，往往都是java大佬们的专长，而CQRS这个话题，好象.NET占了上风。园友汤雪华的ENODE开源大作，在github上人气也很旺。
于是，我逆向思路搜索了下java的类似项目，果然有一个AxonFramework，甚至还有一个专门的网站。按文档上的介绍，弄了一个hello world，记录一下：
CRQS是基于事件驱动的，其主要架构并不复杂，见下图：
简单来讲，对数据库的修改操作，UI层只管发送各种命令(Command)，触发事件(Event)，然后由EventHandler去异步处理，最终写入master DB，对于数据库的查询，则查询slave DB（注：这里的master db, slave db只是一个逻辑上的区分，可以是真正的主-从库，也可以都是一个库）。 这样的架构，很容易实现读写分离，也易于大型项目的扩展。
项目结构：
package的名称上大概就能看出用途：
command包定义各种命令，
event包定义各种事件，
handler包定义事件处理逻辑，
model包相当于领域模型
最外层的ToDOItemRunner相当于应用程序入口。
gradle依赖项：
group 'yjmyzz'
version '1.0'
apply plugin: 'java'
apply plugin: 'application'
sourceCompatibility = 1.8
repositories {
mavenLocal()
maven {
url 'http://maven.oschina.net/content/groups/public/'
}
mavenCentral()
}
dependencies {
testCompile group: 'junit', name: 'junit', version: '4.12'
compile "org.axonframework:axon:2.4.3"
compile "org.axonframework:axon-core:2.4.3"
compile "org.axonframework:axon-test:2.4.3"
compile 'org.springframework:spring-core:4.2.3.RELEASE'
compile 'org.springframework:spring-beans:4.2.3.RELEASE'
compile 'org.springframework:spring-context:4.2.3.RELEASE'
compile 'org.springframework:spring-context-support:4.2.3.RELEASE'
compile 'org.springframework:spring-aop:4.2.3.RELEASE'
compile 'org.springframework:spring-test:4.2.3.RELEASE'
compile 'org.apache.logging.log4j:log4j-slf4j-impl:2.5'
compile 'org.apache.logging.log4j:log4j-core:2.5'
compile 'javax.persistence:persistence-api:2.1'
}
mainClassName='demo.axon.ToDoItemRunner'
command命令：
这里我们假设了二个命令：创建命令、完成命令
CreateToDoItemCommand
package demo.axon.command;
import org.axonframework.commandhandling.annotation.TargetAggregateIdentifier;
public class CreateToDoItemCommand {
@TargetAggregateIdentifier
private final String todoId;
private final String description;
public CreateToDoItemCommand(String todoId, String description) {
this.todoId = todoId;
this.description = description;
}
public String getTodoId() {
return todoId;
}
public String getDescription() {
return description;
}
}
MarkCompletedCommand
package demo.axon.command;
import org.axonframework.commandhandling.annotation.TargetAggregateIdentifier;
public class MarkCompletedCommand {
@TargetAggregateIdentifier
private final String todoId;
public MarkCompletedCommand(String todoId) {
this.todoId = todoId;
}
public String getTodoId() {
return todoId;
}
}
Event事件：
ToDoItemCreatedEvent
package demo.axon.event;
public class ToDoItemCreatedEvent {
private final String todoId;
private final String description;
public ToDoItemCreatedEvent(String todoId, String description) {
this.todoId = todoId;
this.description = description;
}
public String getTodoId() {
return todoId;
}
public String getDescription() {
return description;
}
}
ToDoItemCompletedEvent
package demo.axon.event;
public class ToDoItemCompletedEvent {
private final String todoId;
public ToDoItemCompletedEvent(String todoId) {
this.todoId = todoId;
}
public String getTodoId() {
return todoId;
}
}
EventHandler事件处理
package demo.axon.handler;
import demo.axon.event.ToDoItemCompletedEvent;
import demo.axon.event.ToDoItemCreatedEvent;
import org.axonframework.eventhandling.annotation.EventHandler;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;
public class ToDoEventHandler {
Logger logger = LoggerFactory.getLogger(ToDoEventHandler.class);
@EventHandler
public void handle(ToDoItemCreatedEvent event) {
logger.info("We've got something to do: " + event.getDescription() + " (" + event.getTodoId() + ")");
}
@EventHandler
public void handle(ToDoItemCompletedEvent event) {
logger.info("We've completed a task: " + event.getTodoId());
}
}
上面的代码只是演示，将事件信息输出而已，真实应用中，这里可以完成对db的更新操作。
领域模型model
package demo.axon.model;
import demo.axon.command.CreateToDoItemCommand;
import demo.axon.command.MarkCompletedCommand;
import demo.axon.event.ToDoItemCompletedEvent;
import demo.axon.event.ToDoItemCreatedEvent;
import org.axonframework.commandhandling.annotation.CommandHandler;
import org.axonframework.eventhandling.annotation.EventHandler;
import org.axonframework.eventsourcing.annotation.AbstractAnnotatedAggregateRoot;
import org.axonframework.eventsourcing.annotation.AggregateIdentifier;
public class ToDoItem extends AbstractAnnotatedAggregateRoot {
@AggregateIdentifier
private String id;
public ToDoItem() {
}
@CommandHandler
public ToDoItem(CreateToDoItemCommand command) {
apply(new ToDoItemCreatedEvent(command.getTodoId(), command.getDescription()));
}
@EventHandler
public void on(ToDoItemCreatedEvent event) {
this.id = event.getTodoId();
}
@CommandHandler
public void markCompleted(MarkCompletedCommand command) {
apply(new ToDoItemCompletedEvent(id));
}
}
然后让Spring将这些东西串在一起，配置文件如下：
1 <?xml version="1.0" encoding="UTF-8"?> 2 <beans xmlns="http://www.springframework.org/schema/beans" 3 xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" 4 xmlns:axon="http://www.axonframework.org/schema/core" 5 xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd 6 http://www.axonframework.org/schema/core http://www.axonframework.org/schema/axon-core-2.0.xsd"> 7 8 <axon:command-bus id="commandBus"/> 9 <axon:event-bus id="eventBus"/> 10 11 <axon:event-sourcing-repository id="toDoRepository" 12 aggregate-type="demo.axon.model.ToDoItem"/> 13 14 <axon:aggregate-command-handler id="toDoItemHandler" 15 aggregate-type="demo.axon.model.ToDoItem" 16 repository="toDoRepository" 17 command-bus="commandBus"/> 18 19 <axon:filesystem-event-store id="eventStore" base-dir="events"/> 20 21 <axon:annotation-config /> 22 23 <bean class="demo.axon.handler.ToDoEventHandler"/> 24 25 <bean class="org.axonframework.commandhandling.gateway.CommandGatewayFactoryBean"> 26 <property name="commandBus" ref="commandBus"/> 27 </bean> 28 29 </beans>
View Code
最后，提供一个舞台，让整个应用run起来：
package demo.axon;
import demo.axon.command.CreateToDoItemCommand;
import demo.axon.command.MarkCompletedCommand;
import org.axonframework.commandhandling.gateway.CommandGateway;
import org.springframework.context.ApplicationContext;
import org.springframework.context.support.ClassPathXmlApplicationContext;
import java.util.UUID;
public class ToDoItemRunner {
private CommandGateway commandGateway;
public ToDoItemRunner(CommandGateway commandGateway) {
this.commandGateway = commandGateway;
}
public static void main(String[] args) {
ApplicationContext applicationContext = new ClassPathXmlApplicationContext("sampleContext.xml");
ToDoItemRunner runner = new ToDoItemRunner(applicationContext.getBean(CommandGateway.class));
runner.run();
}
private void run() {
final String itemId = UUID.randomUUID().toString();
commandGateway.send(new CreateToDoItemCommand(itemId, "Need to do this"));
commandGateway.send(new MarkCompletedCommand(itemId));
}
}
输出结果：
12:01:36,113 <demo.axon.handler.ToDoEventHandler> INFO [main]: We've got something to do: Need to do this (3126f293-67fd-4bb7-b152-069acba775b6) 12:01:36,114 <org.axonframework.commandhandling.callbacks.LoggingCallback> INFO [main]: Command executed successfully: demo.axon.command.CreateToDoItemCommand 12:01:36,205 <demo.axon.handler.ToDoEventHandler> INFO [main]: We've completed a task: 3126f293-67fd-4bb7-b152-069acba775b6 12:01:36,206 <org.axonframework.commandhandling.callbacks.LoggingCallback> INFO [main]: Command executed successfully: demo.axon.command.MarkCompletedCommand
axon框架测试也很容易：
package test.demo.axon;
import demo.axon.command.CreateToDoItemCommand;
import demo.axon.command.MarkCompletedCommand;
import demo.axon.event.ToDoItemCompletedEvent;
import demo.axon.event.ToDoItemCreatedEvent;
import demo.axon.model.ToDoItem;
import org.axonframework.test.FixtureConfiguration;
import org.axonframework.test.Fixtures;
import org.junit.Before;
import org.junit.Test;
public class ToDoItemTest {
private FixtureConfiguration fixture;
@Before
public void setUp() throws Exception {
fixture = Fixtures.newGivenWhenThenFixture(ToDoItem.class);
}
@Test
public void testCreateToDoItem() throws Exception {
fixture.given()
.when(new CreateToDoItemCommand("todo1", "need to implement the aggregate"))
.expectEvents(new ToDoItemCreatedEvent("todo1", "need to implement the aggregate"));
}
@Test
public void testMarkToDoItemAsCompleted() throws Exception {
fixture.given(new ToDoItemCreatedEvent("todo1", "need to implement the aggregate"))
.when(new MarkCompletedCommand("todo1"))
.expectEvents(new ToDoItemCompletedEvent("todo1"));
}
}
given/when/expectEvents的意思是，给(given)一个事件，然后当(when)某个命令被调用时，期待(expectEvents)某个事件被触发。
最后 github上还有一个比较复杂的示例项目：https://github.com/AxonFramework/Axon-trader，想深入了解的可以研究下
时间： 2024-09-11 11:35:12