java - 为什么在应用程序启动期间没有调用监听 DataSourceInitializedEvent 的自定义 ApplicationListener？

Question

我使用 Spring Boot 编写了一个应用程序。我添加了一个监听 DataSourceInitializedEvent 的 ApplicationListener，但在应用程序启动期间尚未调用我的监听器。以下是我的 DataSourceInitializedEvent 监听器:

package com.athena.edge;

import org.apache.commons.logging.Log;
import org.apache.commons.logging.LogFactory;
import org.springframework.boot.autoconfigure.jdbc.DataSourceInitializedEvent;
import org.springframework.context.ApplicationListener;
import org.springframework.stereotype.Component;

/**
 * Created by minggaoxi on 1/11/16.
 */
@Component
public class EdgeTestDatasourceListener implements ApplicationListener<DataSourceInitializedEvent> {
    private static Log logger = LogFactory.getLog(EdgeTestDatasourceListener.class);

    @Override
    public void onApplicationEvent(DataSourceInitializedEvent event) {
        logger.debug("EdgeTestDatasourceListener called");
    }
}

我的主要应用程序如下所示:

package com.athena.edge;

import io.undertow.servlet.api.DeploymentInfo;
import org.h2.tools.Server;
import org.springframework.boot.SpringApplication;
import org.springframework.boot.autoconfigure.SpringBootApplication;
import org.springframework.boot.context.embedded.undertow.UndertowDeploymentInfoCustomizer;
import org.springframework.boot.context.embedded.undertow.UndertowEmbeddedServletContainerFactory;
import org.springframework.cloud.netflix.zuul.EnableZuulProxy;
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Profile;
import org.springframework.session.data.redis.config.annotation.web.http.EnableRedisHttpSession;
import org.springframework.web.bind.annotation.RequestMapping;
import org.springframework.web.bind.annotation.RequestMethod;
import org.springframework.web.bind.annotation.RestController;

import java.sql.SQLException;
import java.util.Date;

@SpringBootApplication
@EnableRedisHttpSession
@EnableZuulProxy
@RestController
public class EdgeApplication {

    public static void main(String[] args) {
        SpringApplication.run(EdgeApplication.class, args);
    }

    @RequestMapping(value = "/", method = RequestMethod.GET)
    public String home() {
        return "Hello World from Edge-Server at " + new Date();
    }

    // Config H2 tcp server when we're in development stage, in order to
    // enable inspecting the in-memory database content from outside.
    @Bean(name = "org.h2.tools.Server", initMethod = "start", destroyMethod = "stop")
    @Profile("dev")
    public Server h2TcpServer() throws SQLException {
        return Server.createTcpServer("-tcp", "-tcpAllowOthers", "-tcpPort", "9980");
    }

    // Configuration related to Zuul error handling in Undertow.
    // Refer to http://blog.jmnarloch.io/2015/09/16/spring-cloud-zuul-error-handling/
    @Bean
    public UndertowEmbeddedServletContainerFactory embeddedServletContainerFactory() {
        UndertowEmbeddedServletContainerFactory factory = new UndertowEmbeddedServletContainerFactory();
        factory.addDeploymentInfoCustomizers(new UndertowDeploymentInfoCustomizer() {
            @Override
            public void customize(DeploymentInfo deploymentInfo) {
                deploymentInfo.setAllowNonStandardWrappers(true);
            }
        });
        return factory;
    }
}

我不知道为什么当“DataSourceInitializedEvent”被触发时我的监听器没有被调用，但是我注意到 Spring 内部的“DataSourceInitializer”被调用了。

Answer 1

该问题是由于在注册自定义监听器之前触发该事件而引起的。这是因为 DataSourceInitializer 肯定首先被初始化。

解决方案是实现 BeanFactoryPostProcessor 并使其依赖于 EdgeTestDatasourceListener。这将保证 BeanFactoryPostProcessor 的实例将在 EdgeTestDatasourceListener 实例之后、所有其他 bean(尤其是 DataSourceInitializer)之前创建。

否则，您不需要在BeanFactoryPostProcessor.postProcessBeanFactory中编写任何代码。当 Spring 启动时，它会检测到这个 BeanFactoryPostProcessor 并调用它的 postProcessBeanFactory，因此您不需要实例化它。

要使 BeanFactoryPostProcessor 依赖于 EdgeTestDatasourceListener，您可以在 BeanFactoryPostProcessor 的实现上使用注释 @DependsOn("classname")

 @Component
 @DependsOn("edgeTestDatasourceListener")
 public class DataSourceListenerRegistrarForcer  implements BeanFactoryPostProcessor, PriorityOrdered {  
 @Override  
 public int getOrder() {  
    return Ordered.HIGHEST_PRECEDENCE;  
 }  
 @Override  
 public void postProcessBeanFactory(  
    ConfigurableListableBeanFactory beanFactory) throws BeansException {  
 }  
}