整体项目结构

image.png

MyService 为服务接口
CallbackListener 为回调接口
MyServiceImpl 为服务实现
CallbackListenerImpl 为回调实现
CallbackProvider 为Provider启动类
CallbackConsumer 为Consumer启动类
callback-provider.xml 为Provider配置
callback-consumer.xml 为Consumer配置

代码参考

参数回调example

具体实现

MyService

package org.apache.dubbo.samples.callback.api;

public interface CallbackListener {

    void changed(String msg);

}

CallbackListener

package org.apache.dubbo.samples.callback.api;

public interface CallbackListener {

    void changed(String msg);

}

MyServiceImpl

public class CallbackListenerImpl implements CallbackListener {
    @Override
    public void changed(String msg) {
        System.out.println("callback: " + msg);
    }
}

CallbackListenerImpl

package org.apache.dubbo.samples.callback.impl;

import org.apache.dubbo.samples.callback.api.CallbackListener;
import org.apache.dubbo.samples.callback.api.MyService;

import java.text.SimpleDateFormat;
import java.util.Date;

public class MyServiceImpl implements MyService {

    @Override
    public void gogogo(String key, CallbackListener listener) {
        listener.changed(getChanged(1));
        listener.changed(getChanged(2));
        listener.changed(getChanged(3));
    }

    private String getChanged(int batchId) {
        return String.format("返回批次【%s】: ", batchId)
                + new SimpleDateFormat("yyyy-MM-dd HH:mm:ss").format(new Date());
    }

}

CallbackProvider

package org.apache.dubbo.samples.callback;

import org.springframework.context.support.ClassPathXmlApplicationContext;

import java.util.concurrent.CountDownLatch;

public class CallbackProvider {

    public static void main(String[] args) throws Exception {
        new EmbeddedZooKeeper(2181, false).start();

        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("spring/callback-provider.xml");
        context.start();

        System.out.println("dubbo service started");
        new CountDownLatch(1).await();
    }
}

CallbackConsumer

public class CallbackConsumer {

    public static void main(String[] args) throws Exception {
        ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext("spring/callback-consumer.xml");
        context.start();
        MyService callbackService = context.getBean("myService", MyService.class);
        CallbackListener callbackListener = context.getBean("callback", CallbackListener.class);

        callbackService.gogogo("foo.bar", callbackListener);
    }

}

callback-provider.xml

<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:dubbo="http://dubbo.apache.org/schema/dubbo"
       xmlns="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
       http://dubbo.apache.org/schema/dubbo http://dubbo.apache.org/schema/dubbo/dubbo.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
    <context:property-placeholder/>

    <dubbo:application name="callback-provider"/>

    <dubbo:registry address="zookeeper://${zookeeper.address:127.0.0.1}:2181"/>

    <dubbo:protocol name="dubbo" port="20880"/>

    <bean id="myService" class="org.apache.dubbo.samples.callback.impl.MyServiceImpl"/>

    <dubbo:service
            interface="org.apache.dubbo.samples.callback.api.MyService"
            ref="myService"
            connections="1"
            callbacks="1000">

        <dubbo:method name="gogogo">
            <dubbo:argument index="1" callback="true"/>
        </dubbo:method>

    </dubbo:service>

</beans>

callback-consumer.xml

<beans xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:dubbo="http://dubbo.apache.org/schema/dubbo"
       xmlns="http://www.springframework.org/schema/beans" xmlns:context="http://www.springframework.org/schema/context"
       xmlns:spring="http://www.springframework.org/schema/c"
       xsi:schemaLocation="http://www.springframework.org/schema/beans http://www.springframework.org/schema/beans/spring-beans.xsd
       http://dubbo.apache.org/schema/dubbo http://dubbo.apache.org/schema/dubbo/dubbo.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd">
    <context:property-placeholder/>

    <dubbo:application name="callback-consumer"/>

    <dubbo:registry address="zookeeper://${zookeeper.address:127.0.0.1}:2181"/>

    <dubbo:reference id="myService" interface="org.apache.dubbo.samples.callback.api.MyService"/>

    <bean id="callback" class="org.apache.dubbo.samples.callback.impl.CallbackListenerImpl"/>

</beans>

最终输出

image.png

说明

服务（MyService）配置为Callback后，允许Provider在处理业务时，通过回调接口（CallbackListener）去回调Consumer。