使用axon-spring-boot-starter的NoHandlerForCommandException

我正在使用Axon Spring Boot创建一个简单的应用程序,只是为了确保我在实际项目中使用之前了解Axon框架中的基本组件.
在TaskAggregate类中有一个使用@CommandHandler注释的方法,当我通过CommandGateway发送命令时应该调用该方法,但是在运行应用程序后我得到了异常：

Exception in thread "main" org.axonframework.commandhandling.NoHandlerForCommandException: No handler was subscribed to command [com.xxx.axontest.task.CreateTaskCommand]

根据文档,@ CommandHandler注释应该足以将命令hander订阅到命令总线.我想我一定错过了什么.你能看看下面的代码并指出我正确的方向吗？

的pom.xml

<project xmlns="http://maven.apache.org/POM/4.0.0" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://maven.apache.org/POM/4.0.0 http://maven.apache.org/xsd/maven-4.0.0.xsd">
    <modelVersion>4.0.0</modelVersion>
    <groupId>com.xxx</groupId>
    <artifactId>axon-test</artifactId>
    <version>0.0.1-SNAPSHOT</version>

    <properties>
        <axon.version>3.0.6</axon.version>
    </properties>

    <parent>
        <groupId>org.springframework.boot</groupId>
        <artifactId>spring-boot-starter-parent</artifactId>
        <version>1.5.7.RELEASE</version>
    </parent>

    <dependencies>

        <dependency>
            <groupId>org.springframework.boot</groupId>
            <artifactId>spring-boot-starter-web</artifactId>
        </dependency>

        <dependency>
                <groupId>org.axonframework</groupId>
                <artifactId>axon-spring-boot-starter</artifactId>
                <version>${axon.version}</version>
        </dependency>

    </dependencies>

    <build>
        <plugins>
            <plugin>
                <groupId>org.springframework.boot</groupId>
                <artifactId>spring-boot-maven-plugin</artifactId>
            </plugin>
        </plugins>
    </build>

</project>

App.java

package com.xxx.axontest;

import org.axonframework.commandhandling.gateway.CommandGateway;
import org.axonframework.eventsourcing.eventstore.EventStorageEngine;
import org.axonframework.eventsourcing.eventstore.inmemory.InMemoryEventStorageEngine;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.context.ConfigurableApplicationContext;
import org.springframework.context.annotation.Bean;

import com.xxx.axontest.task.CreateTaskCommand;

@SpringBootApplication
public class App {

    public static void main(String[] args) {
        ConfigurableApplicationContext configurableApplicationContext = SpringApplication.run(App.class, args);
        CommandGateway commandGateway = configurableApplicationContext.getBean(CommandGateway.class);
        commandGateway.send(new CreateTaskCommand(123, "asd"));
    }

    @Bean
    public EventStorageEngine eventStorageEngine() {
        return new InMemoryEventStorageEngine();
    }

    @Bean
    public AnnotationCommandHandlerBeanPostProcessor 
 annotationCommandHandlerBeanPostProcessor() {
    return new AnnotationCommandHandlerBeanPostProcessor();
    }
}

CreateTaskCommand.java

package com.xxx.axontest.task;

import org.axonframework.commandhandling.TargetAggregateIdentifier;

public class CreateTaskCommand {

    @TargetAggregateIdentifier
    private int taskId;
    private String name;

    public CreateTaskCommand(int taskId, String name) {
        this.taskId = taskId;
        this.name = name;
    }

    public int getTaskId() {
        return taskId;
    }

    public String getName() {
        return name;
    }   
}

TaskCreatedEvent.java

package com.xxx.axontest.task;

import org.axonframework.commandhandling.TargetAggregateIdentifier;

public class TaskCreatedEvent {

    @TargetAggregateIdentifier
    private int taskId;
    private String name;

    public int getTaskId() {
        return taskId;
    }

    public String getName() {
        return name;
    }

}

TaskAggregate.java

package com.xxx.axontest.task;

import org.apache.log4j.LogManager;
import org.apache.log4j.Logger;
import org.axonframework.commandhandling.CommandHandler;
import org.axonframework.commandhandling.model.AggregateIdentifier;
import org.axonframework.commandhandling.model.AggregateLifecycle;
import org.axonframework.eventsourcing.EventSourcingHandler;
import org.axonframework.spring.stereotype.Aggregate;

@AggregateRoot
public class TaskAggregate {

    private Logger logger = LogManager.getLogger(TaskCreatedEvent.class);

    @AggregateIdentifier
    private int taskId;
    private String name;

    @CommandHandler
    public void handleCommand(CreateTaskCommand createTaskCommand) {
        logger.info("Command received");
        AggregateLifecycle.apply(new TaskCreatedEvent());
    }

    @EventSourcingHandler
    public void onTaskCreatedEvent(TaskCreatedEvent taskCreatedEvent) {
        logger.info("Event received");
    }

    public int getTaskId() {
        return taskId;
    }

    public void setTaskId(int taskId) {
        this.taskId = taskId;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

}

提前致谢.

解决方法:

我认为您需要使用@Aggregate而不是@AggregateRoot来注释您的聚合.
@Aggregate作为注释既是@AggregateRoot注释,也是Spring Boot Axon Starter模块使用它来表示必须为该类创建聚合工厂和存储库.
此外,这也意味着您的聚合上的@CommandHandler注释函数也将被找到并注册到CommandBus,可能解决了您捕获的异常.

否则,来自Allard的YouTube上的webinars用于在版本3中启动Axon应用程序可以为您提供一些见解.

但是,简而言之,尝试切换@Aggregate的@AggregateRoot注释:-)

另外,您应该将CreateTaskCommand的@CommandHandler注释函数调整为TaskAggregate的构造函数.
最后,Axon要求你有一个no-arg构造函数供你聚合,所以还要在那里添加一个公共TaskAggregate(){}构造函数.

标签：axon,spring,spring-boot,cqrs,spring-boot-starter
来源： https://codeday.me/bug/20190823/1698744.html