CQRS框架:AxonFramework 之 Hello World

时间:2023-03-08 17:40:22

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:

CQRS架构简介

浅谈命令查询职责分离(CQRS)模式

DDD CQRS架构和传统架构的优缺点比较

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:

CQRS框架:AxonFramework 之 Hello World

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:

CQRS框架:AxonFramework 之 Hello World

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:

 <?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:axon="http://www.axonframework.org/schema/core"
xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.axonframework.org/schema/core http://www.axonframework.org/schema/axon-core-2.0.xsd"> <axon:command-bus id="commandBus"/>
<axon:event-bus id="eventBus"/> <axon:event-sourcing-repository id="toDoRepository"
aggregate-type="demo.axon.model.ToDoItem"/> <axon:aggregate-command-handler id="toDoItemHandler"
aggregate-type="demo.axon.model.ToDoItem"
repository="toDoRepository"
command-bus="commandBus"/> <axon:filesystem-event-store id="eventStore" base-dir="events"/> <axon:annotation-config /> <bean class="demo.axon.handler.ToDoEventHandler"/> <bean class="org.axonframework.commandhandling.gateway.CommandGatewayFactoryBean">
<property name="commandBus" ref="commandBus"/>
</bean> </beans>

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