Command Query Responsibility Segregation,CQRS 這個架構好象最近博客園裡討論得比較多，有幾篇園友的文章很有深度，推薦閱讀：
CQRS架構簡介
淺談命令查詢職責分離(CQRS)模式
DDD CQRS架構和傳統架構的優缺點比較
比較有趣的是，以往一斷談及架構思路、OO這些，往往都是java大佬們的專長，而CQRS這個話題，好象.NET占了上風。園友湯雪華的ENODE開源大作，在github上人氣也很旺。
於是，我逆向思路搜索了下java的類似項目，果然有一個AxonFramework，甚至還有一個專門的網站。按文檔上的介紹，弄了一個hello world，記錄一下：
CRQS是基於事件驅動的，其主要架構並不復雜，見下圖：
項目結構：
gradle依賴項：
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：
這裡我們假設了二個命令：創建命令、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事件處理
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());
}
}
上面的代碼只是演示，將事件信息輸出而已，真實應用中，這裡可以完成對db的更新操作。
領域模型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));
}
}
然後讓Spring將這些東西串在一起，配置文件如下：
最後，提供一個舞台，讓整個應用run起來：
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));
}
}
輸出結果：
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框架測試也很容易：
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，給(given)一個事件，然後當(when)某個命令被調用時，期待(expectEvents)某個事件被觸發。
最後 github上還有一個比較復雜的示例項目：https://github.com/AxonFramework/Axon-trader，想深入了解的可以研究下
