Question

我有以下弹簧夹豆。这个想法是它保留了一个东西的实例，并在某些东西发生变化时发出变化事件（同时提供旧值和新值）：

public class Holder<T> implements ApplicationEventPublisherAware {
    private final Class<T> payloadType; //because java generics are incomplete
    private T curr; //latest value being held
    private ApplicationEventPublisher publisher; //spring context ref

    public Holder(Class<T> payloadType) {
        this.payloadType = payloadType;
    }

    public void change() throws Exception {
        T prev = curr;
        curr = payloadType.newInstance();
        publisher.publishEvent(new ContentsChangedEvent<>(prev, curr));
    }
}

然后我有一个对这些事件做出反应的监听器类：

@Named
public class Listener {

    @EventListener
    public void onChange(ContentsChangedEvent<Cat> event) {
        //never gets called
    }

    @EventListener
    public void onErasedChange(ContentsChangedEvent<?> event) {
        //does get called
    }
}

我的问题是，通用（正确）事件侦听器方法永远不会被调用（获取Event<Cat>的方法），只有被删除的方法。

完整性＆＃39;为了这里是spring context.xml

<beans xmlns="http://www.springframework.org/schema/beans"
       xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
       xmlns:context="http://www.springframework.org/schema/context"
       xsi:schemaLocation="http://www.springframework.org/schema/beans
       http://www.springframework.org/schema/beans/spring-beans-4.2.xsd
       http://www.springframework.org/schema/context
       http://www.springframework.org/schema/context/spring-context-4.2.xsd">

    <context:annotation-config/>
    <context:component-scan base-package="net.radai"/>

    <bean id="holder" class="net.radai.Holder">
        <constructor-arg type="java.lang.Class" value="net.radai.Cat"/>
    </bean>
</beans>

我还把整件事放在github上 - https://github.com/radai-rosenblatt/spring-events。它是一个maven项目 - 你构建它并且你将得到一个失败的测试。

我做错了什么？

注意：在实际使用案例中，我希望有多个此类持有人并强制所有听众放弃与其无关的事件，这是不可接受的

Answer 1

public class ContentsChangedEvent<T> extends ApplicationEvent{

    public ContentsChangedEvent(Holder<T> source, T prev, T curr) {
        super(source);
        this.prev = prev;
        this.curr = curr;
    }                                  

}   

//Holder class
public void change() {
        T prev = curr;
        try {
        curr = payloadType.newInstance();
        } catch (Exception e) {
            int g = 8;
        }
        publisher.publishEvent(new ContentsChangedEvent<T>(this, prev, curr));
 }

将调用onChange和onErasedChange。

Answer 2

如果在通用事件类中实现org.springframework.core.ResolvableTypeProvider，则侦听器将解析它。例如：

import org.springframework.core.ResolvableType;
import org.springframework.core.ResolvableTypeProvider;

public class EventBase<T> {
    public T payload;
}

public class AppEvent<T> extends EventBase<T> implements ResolvableTypeProvider {
    @Override
    public ResolvableType getResolvableType() {
        return ResolvableType.forClassWithGenerics(
            getClass(), 
            ResolvableType.forInstance(this.payload)
        );
    }
}

@Component
public class EventHandler {
    @EventListener
    public void handleString(AppEvent<String> event) {
       System.out.println("Event[" + event.getClass().getSimpleName() + "], received:" + event);
    }
    
    @EventListener
    public void handleLong(AppEvent<Long> event) {
       System.out.println("Event[" + event.getClass().getSimpleName() + "], received:" + event);
    }

}

spring通用应用程序事件未能到达目标

2 个答案: