Spring事件监听器之@EventListener原理分析-Java开发

Spring事件监听器之@EventListener原理分析目录 Spring事件监听器之@EventListener原理一.解析@EventListener前的准备工作二.开始解析@EventListener EventListener.Factory EventListener.Factory监听网络请求全过程问题是如何将这些数据回传回来呢 Spring事件监听器之@Ev

Spring事件监听器之@EventListener原理

Spring为我们提供的一个事件监听、订阅的实现，内部实现原理是观察者设计模式；为的就是业务系统逻辑的解耦,提高可扩展性以及可维护性。事件发布者并不需要考虑谁去监听，监听具体的实现内容是什么，发布者的工作只是为了发布事件而已。

在spring中我们可以通过实现ApplicationListener接口或者@EventListener接口来实现事件驱动编程

比如我们做一个电商系统,用户下单支付成功后，我们一般要发短信或者邮箱给用户提示什么的,这时候就可以把这个通知业务做成一个单独事件监听,等待通知就可以了；把它解耦处理。


public class OrderEvent extends ApplicationEvent {
    public OrderEvent(Object source) {
        super(source);
    }
}
@Component
public class OrderEventListener  {
    @EventListener
    public void listener(OrderEvent event) {
        System.out.println("i do OrderEventListener" );
    }
}
@Controller
@RequestMapping("person")
public class PersonController implements ApplicationContextAware {
    private ApplicationContext applicationContext;
    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        this.applicationContext = applicationContext;
    }
    @ResponseBody
    @GetMapping("publishOrderEvent")
    public String publishOrderEvent() {
        applicationContext.publishEvent(new OrderEvent("我发布了事件！！！"));
        System.out.println(" publishOrderEvent ");
        return "发送事件了！";
    }
}

EventListenerMethodProcessor是@EventListener的解析类，他是一个SmartInitializingSingleton和BeanFactoryPostProcessor

一、解析@EventListener前的准备工作

1.1 EventListenerFactory和EventListenerMethodProcessor的注入

EventListenerFactory是把@EventListener标注的方法变成ApplicationListener的关键，其是在容器最初期(refresh方法发生前)就放到容器中去


public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors( BeanDefinitionRegistry registry, Object source) {
        //获取对象
		DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);

        //org.springframework.context.event.internalEventListenerProcessor
        //@EventListener注解处理器
		if (!registry.containsBeanDefinition(EVENT_LISTENER_PROCESSOR_BEAN_NAME)) {
			RootBeanDefinition def = new RootBeanDefinition(EventListenerMethodProcessor.class);
			def.setSource(source);
			beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_PROCESSOR_BEAN_NAME));
		}
        //org.springframework.context.event.internalEventListenerProcessor
        //内部管理的EventListenerFactory的bean名称
		if (!registry.containsBeanDefinition(EVENT_LISTENER_FACTORY_BEAN_NAME)) {
			RootBeanDefinition def = new RootBeanDefinition(DefaultEventListenerFactory.class);
			def.setSource(source);
			beanDefs.add(registerPostProcessor(registry, def, EVENT_LISTENER_FACTORY_BEAN_NAME));
		}
		return beanDefs;
	}

如果容器中没有名字是org.springframework.context.event.internalEventListenerProcessor的bean，那么就注入一个EventListenerMethodProcessor到容器中
如果容器中没有名字是org.springframework.context.event.internalEventListenerProcessor的bean，那么就注入一个DefaultEventListenerFactory到容器中

1.2 EventListenerMethodProcessor和EventListenerFactory关系的建立

EventListenerMethodProcessor会在容器启动时被注入到容器中，他是一个BeanFactoryPostProcessor，EventListenerMethodProcessor和EventListenerFactory关系的建立就发生在其方法postProcessBeanFactory中


public class EventListenerMethodProcessor implements SmartInitializingSingleton, ApplicationContextAware, BeanFactoryPostProcessor {
	@Nullable
	private List<EventListenerFactory> eventListenerFactories;
    //初始化eventListenerFactories
	@Override
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) {
		this.beanFactory = beanFactory;
		//获取容器中所有的EventListenerFactory，并把他们实例化
		Map<String, EventListenerFactory> beans = beanFactory.getBeansOfType(EventListenerFactory.class, false, false);

		List<EventListenerFactory> factories = new ArrayList<>(beans.values());
		AnnotationAwareOrderComparator.sort(factories);
		//将EventListenerFactory储存到缓存eventListenerFactories中，便于后来使用
		this.eventListenerFactories = factories;
	}
}

EventListenerFactory的实例化时机只比BeanFactoryPostProcessor完点，他比BeanPostProcessor实例化时机早

二、开始解析@EventListener

EventListenerMethodProcessor是一个SmartInitializingSingleton，所以他会在所以bean实例化后，执行其afterSingletonsInstantiated方法

注意：只有单例的SmartInitializingSingleton，才会执行其afterSingletonsInstantiated方法

2.1 基本流程


public class EventListenerMethodProcessor implements SmartInitializingSingleton, ApplicationContextAware, BeanFactoryPostProcessor {
    @Override
	public void afterSingletonsInstantiated() {
		ConfigurableListableBeanFactory beanFactory = this.beanFactory;
		Assert.state(this.beanFactory != null, "No ConfigurableListableBeanFactory set");
		// 这里厉害了，用Object.class 是拿出容器里面所有的Bean定义~~~  一个一个的检查
		String[] beanNames = beanFactory.getBeanNamesForType(Object.class);
		for (String beanName : beanNames) {
		     //
			if (!ScopedProxyUtils.isScopedTarget(beanName)) {
				Class<?> type = null;
				try {
				     // 防止是代理，吧真实的类型拿出来
					type = AutoProxyUtils.determineTargetClass(beanFactory, beanName);
				}
				catch (Throwable ex) {
					if (logger.isDebugEnabled()) {
						logger.debug("", ex);
					}
				}
				if (type != null) {
				    // 对专门的作用域对象进行兼容~~~~（绝大部分都用不着）
					if (ScopedObject.class.isAssignableFrom(type)) {
						try {
							Class<?> targetClass = AutoProxyUtils.determineTargetClass(
									beanFactory, ScopedProxyUtils.getTargetBeanName(beanName));
							if (targetClass != null) {
								type = targetClass;
							}
						}
						catch (Throwable ex) {
							// An invalid scoped proxy arrangement - let's ignore it.
							if (logger.isDebugEnabled()) {
								logger.debug("Could not resolve target bean for scoped proxy '" + beanName + "'", ex);
							}
						}
					}
					try {
					    // 真正处理这个Bean里面的方法们。。。
						processBean(beanName, type);
					}
					catch (Throwable ex) {
						throw new BeanInitializationException("", ex);
					}
				}
			}
		}
	}
	private void processBean(final String beanName, final Class<?> targetType) {
	         //类上有@Component注解
			if (!this.nonAnnotatedClasses.contains(targetType) &&!targetType.getName().startsWith("java") &&!isSpringContainerClass(targetType)) {
	 			Map<Method, EventListener> annotatedMethods = null;
				try {
				    //获取类中用@EventListener标注方法的信息
					annotatedMethods = MethodIntrospector.selectMethods(targetType,
							(MethodIntrospector.MetadataLookup<EventListener>) method ->
									AnnotatedElementUtils.findMergedAnnotation(method, EventListener.class));
				}
				catch (Throwable ex) {
					// An unresolvable type in a method signature, probably from a lazy bean - let's ignore it.
					if (logger.isDebugEnabled()) {
						logger.debug("Could not resolve methods for bean with name '" + beanName + "'", ex);
					}
				}
	            //如果annotatedMethods为空，那代表类中没有用@EventListener标注的方法
				if (CollectionUtils.isEmpty(annotatedMethods)) {
					this.nonAnnotatedClasses.add(targetType);
					if (logger.isTraceEnabled()) {
						logger.trace("" + targetType.getName());
					}
				}
				else {
					// 类中存在用@EventListener标注的方法
					ConfigurableApplicationContext context = this.applicationContext;
					Assert.state(context != null, "No ApplicationContext set");
					//获取容器中所有EventListenerFactory
					List<EventListenerFactory> factories = this.eventListenerFactories;
					Assert.state(factories != null, "EventListenerFactory List not initialized");
					for (Method method : annotatedMethods.keySet()) {
						for (EventListenerFactory factory : factories) {
							if (factory.supportsMethod(method)) {
								// 简单的说，就是把这个方法弄成一个可以执行的方法（主要和访问权限有关）
							  // 这里注意：若你是JDK的代理类，请不要在实现类里书写@EventListener注解的监听器，否则会报错的。（CGLIB代理的木关系）
								Method methodToUse = AopUtils.selectInvocableMethod(method, context.getType(beanName));
                                //利用EventListenerFactory创建ApplicationListener，详情后面说
								ApplicationListener<?> applicationListener =
										factory.createApplicationListener(beanName, targetType, methodToUse);
								//如果ApplicationListener是ApplicationListenerMethodAdapter类，那么执行其init方法
								if (applicationListener instanceof ApplicationListenerMethodAdapter) {
									((ApplicationListenerMethodAdapter) applicationListener).init(context, this.evaluator);
								}
								//放到容器中
								context.addApplicationListener(applicationListener);
								//@EventListener方法只能解析一次
								break;
							}
						}
					}
					if (logger.isDebugEnabled()) {
						logger.debug();
					}
				}
			}
		}
}

获取容器中所有的类，把用@Component标注的类上所有的@EventListener方法用EventListenerFactory解析成一个ApplicationListener

@EventListener方法只要有到一个可以解析他的EventListenerFactory，就不会让其他EventListenerFactory解析他了所以如果容器中存在多个EventListenerFactory，我要注意他的顺序

2.2 EventListenerFactory解析@EventListener


public interface EventListenerFactory {
    //是否支持当前方法
	boolean supportsMethod(Method method);

	//生成一个ApplicationListener
	ApplicationListener<?> createApplicationListener(String beanName, Class<?> type, Method method);
}

EventListenerFactory有2个字类DefaultEventListenerFactory和TransactionalEventListenerFactory，DefaultEventListenerFactory是处理@EventListener，而TransactionalEventListenerFactory是处理@TransactionalEventListener的，Spring默认就有DefaultEventListenerFactory，而TransactionalEventListenerFactory是没有的，所以我们想要支持@TransactionalEventListener，就要注册一个TransactionalEventListenerFactory,也就是要说要使用@EnableTransactionManagement注解


public class DefaultEventListenerFactory implements EventListenerFactory, Ordered {
	private int order = LOWEST_PRECEDENCE;
	@Override
	public boolean supportsMethod(Method method) {
		return true;
	}
	@Override
	public ApplicationListener<?> createApplicationListener(String beanName, Class<?> type, Method method) {
		return new ApplicationListenerMethodAdapter(beanName, type, method);
	}
}

ApplicationListenerMethodAdapter一个ApplicationListener，他是用来包装@EventListener标注的方法


public class ApplicationListenerMethodAdapter implements GenericApplicationListener {
	private final String beanName; //@EventListener方法所属bean的名字
	private final Method method;//@EventListener标注的方法
	private final Method targetMethod;//@EventListener标注的真实方法对象，防止其是代理方法
    //方法申明，如public void demo.Ball.applicationContextEvent(demo.OrderEvent)
	private final AnnotatedElementKey methodKey;
	private final List<ResolvableType> declaredEventTypes;//存储方法的参数
	private final String condition;//@EventListener的condition
	private final int order;
	private ApplicationContext applicationContext;
	private EventExpressionEvaluator evaluator;//@EventListener的EventExpressionEvaluator
	public ApplicationListenerMethodAdapter(String beanName, Class<?> targetClass, Method method) {
		this.beanName = beanName;
		this.method = BridgeMethodResolver.findBridgedMethod(method);
		this.targetMethod = (!Proxy.isProxyClass(targetClass) ?AopUtils.getMostSpecificMethod(method, targetClass) : this.method);
		this.methodKey = new AnnotatedElementKey(this.targetMethod, targetClass);
		//获取方法上的@EventListener注解对象
		EventListener ann = AnnotatedElementUtils.findMergedAnnotation(this.targetMethod, EventListener.class);
		this.declaredEventTypes = resolveDeclaredEventTypes(method, ann);
		this.condition = (ann != null ? ann.condition() : null);
		this.order = resolveOrder(this.targetMethod);
	}
    public void onApplicationEvent(ApplicationEvent event) {
		processEvent(event);
	}

    public void processEvent(ApplicationEvent event) {
		Object[] args = resolveArguments(event);
		//根据@EventListener的condition，判断是否要处理
		if (shouldHandle(event, args)) {
		    //调用方法
			Object result = doInvoke(args);
			if (result != null) {
			    //如果有监听器可以监听这个结果，那么可以触发那个监听器
				handleResult(result);
			}
			else {
				logger.trace("No result object given - no result to handle");
			}
		}
	}
}

EventListener.Factory

EventListener.Factory监听网络请求全过程

网上介绍的并不多，关于它的使用方式，可能会存在很多坑。

主要是为了监听网络请求过程。

首先OkHttpClient.Builder.eventListenerFactory需要的是一个实现了EventListener接口的工厂类。

简单的实现方式。


public class HttpEventListener extends EventListener {
      private final long callId;
  	  final AtomicLong nextCallId = new AtomicLong(1L);
        @Override
        public EventListener create(Call call) {
            long callId = nextCallId.getAndIncrement();
            return new HttpEventListener(callId, System.nanoTime());
        }
    public HttpEventListener(long callId, long callStartNanos) {
        this.callId = callId;
        this.callStartNanos = callStartNanos;
    }
    private long dnsStartTime;
    private long dnsParseTime;
    @Override
    public void dnsStart(Call call, String domainName) {
        super.dnsStart(call, domainName);
        dnsStartTime = System.nanoTime();
    }
    @Override
    public void dnsEnd(Call call, String domainName, List<InetAddress> inetAddressList) {
        super.dnsEnd(call, domainName, inetAddressList);
        dnsParseTime = System.nanoTime() - dnsStartTime;//dns解析耗时
    }
//自动补全剩余实现方法
}

EventListener.create方法在okHttpClient.newCall后执行

dnsParseTime可以算出dns解析耗时，还可以监听每次dns解析的domain，解析的结果inetAddressList。

这个是比较好用的。

问题是如何将这些数据回传回来呢

在OkHttpClient构造时传入自定义参数


OkHttpClient.Builder builder = new OkHttpClient.Builder();
final ResponseTag tag = new ResponseTag();
        tag.logHandler = logHandler;
        httpClient.newCall(requestBuilder.tag(tag).build()).enqueue(new Callback() {
            @Override
            public void onFailure(Call call, IOException e) {

            }
            @Override
            public void onResponse(Call call, Response response) throws IOException {

            }
        });
    //自动补全剩余实现方法
public class HttpEventListener extends EventListener {
    /**
     * 每次请求的标识
     */
    private long callId = 1L;
    /**
     * 每次请求的开始时间，单位纳秒
     */
    private final long callStartNanos;
    private long total_elapsed_time;
    private long dns_elapsed_time;
    private long connect_elapsed_time;
    private long tls_connect_elapsed_time;
    private long request_elapsed_time;
    private long wait_elapsed_time;
    private long response_elapsed_time;
    private Client.ResponseTag responseTag;
    private LogHandler logHandler;
    private long start_dns_elapsed_time;
    private long start_total_elapsed_time;
    private long start_connect_elapsed_time;
    private long start_tls_connect_elapsed_time;
    private long start_request_elapsed_time;
    private long start_response_elapsed_time;
    public HttpEventListener(long callId, Client.ResponseTag responseTag, long callStartNanos) {
        this.callId = callId;
        this.callStartNanos = callStartNanos;
        this.responseTag = responseTag;
        this.logHandler = responseTag.logHandler;
    }
    public static final Factory FACTORY = new Factory() {
        final AtomicLong nextCallId = new AtomicLong(1L);
        @Override
        public EventListener create(@NotNull Call call) {
            long callId = nextCallId.getAndIncrement();
            return new HttpEventListener(callId, (Client.ResponseTag) call.request().tag(), System.nanoTime());
        }
    };
    @Override
    public void callStart(Call call) {
        super.callStart(call);
        start_total_elapsed_time = System.currentTimeMillis();
    }
    @Override
    public void dnsStart(Call call, String domainName) {
        super.dnsStart(call, domainName);
        start_dns_elapsed_time = System.currentTimeMillis();
    }
    @Override
    public void dnsEnd(Call call, String domainName, List<InetAddress> inetAddressList) {
        super.dnsEnd(call, domainName, inetAddressList);
        dns_elapsed_time = System.currentTimeMillis() - start_dns_elapsed_time;//dns解析耗时
        logHandler.send("dns_elapsed_time", dns_elapsed_time);
    }
    @Override
    public void connectStart(Call call, InetSocketAddress inetSocketAddress, Proxy proxy) {
        super.connectStart(call, inetSocketAddress, proxy);
        start_connect_elapsed_time = System.currentTimeMillis();
    }
    @Override
    public void secureConnectStart(Call call) {
        super.secureConnectStart(call);
        start_tls_connect_elapsed_time = System.currentTimeMillis();
    }
    @Override
    public void secureConnectEnd(Call call, Handshake handshake) {
        super.secureConnectEnd(call, handshake);
        tls_connect_elapsed_time = System.currentTimeMillis() - start_tls_connect_elapsed_time;
        logHandler.send("tls_connect_elapsed_time", tls_connect_elapsed_time);
    }
    @Override
    public void connectEnd(Call call, InetSocketAddress inetSocketAddress, Proxy proxy, Protocol protocol) {
        super.connectEnd(call, inetSocketAddress, proxy, protocol);
        connect_elapsed_time = System.currentTimeMillis() - start_connect_elapsed_time;
        logHandler.send("connect_elapsed_time", connect_elapsed_time);
    }
    @Override
    public void connectFailed(Call call, InetSocketAddress inetSocketAddress, Proxy proxy, Protocol protocol, IOException ioe) {
        super.connectFailed(call, inetSocketAddress, proxy, protocol, ioe);
    }
    @Override
    public void connectionAcquired(Call call, Connection connection) {
        super.connectionAcquired(call, connection);
    }
    @Override
    public void connectionReleased(Call call, Connection connection) {
        super.connectionReleased(call, connection);
    }
    @Override
    public void requestHeadersStart(Call call) {
        super.requestHeadersStart(call);
        start_request_elapsed_time = System.currentTimeMillis();
    }
    @Override
    public void requestHeadersEnd(Call call, Request request) {
        super.requestHeadersEnd(call, request);
    }
    @Override
    public void requestBodyStart(Call call) {
        super.requestBodyStart(call);
    }
    @Override
    public void requestBodyEnd(Call call, long byteCount) {
        super.requestBodyEnd(call, byteCount);
        request_elapsed_time = System.currentTimeMillis() - start_request_elapsed_time;
        logHandler.send("request_elapsed_time", request_elapsed_time);
    }
    @Override
    public void responseHeadersStart(Call call) {
        super.responseHeadersStart(call);
        start_response_elapsed_time = System.currentTimeMillis();
    }
    @Override
    public void responseHeadersEnd(Call call, Response response) {
        super.responseHeadersEnd(call, response);
    }
    @Override
    public void responseBodyStart(Call call) {
        super.responseBodyStart(call);
    }
    @Override
    public void responseBodyEnd(Call call, long byteCount) {
        super.responseBodyEnd(call, byteCount);
        response_elapsed_time = System.currentTimeMillis() - start_response_elapsed_time;
        wait_elapsed_time = System.currentTimeMillis() - start_request_elapsed_time;
        logHandler.send("response_elapsed_time", response_elapsed_time);
        logHandler.send("wait_elapsed_time", wait_elapsed_time);
    }
    @Override
    public void callEnd(Call call) {
        super.callEnd(call);
        total_elapsed_time = System.currentTimeMillis() - start_total_elapsed_time;
        logHandler.send("total_elapsed_time", total_elapsed_time);
    }
    @Override
    public void callFailed(Call call, IOException ioe) {
        super.callFailed(call, ioe);
    }
}
//利用反射将logHandler打回来的数据存到对象
public static LogHandler getUplogHandler(final Object obj) {
        final String setMethod = "set";
        LogHandler logHandler = new LogHandler() {
            @Override
            public void send(String key, Object value) {
                try {
                    if (value instanceof String) {
                        Method setByKey = obj.getClass().getMethod(setMethod + StringUtils.upperCase(key), Class.forName("java.lang.String"));
                        setByKey.invoke(obj, value);
                    } else if (value instanceof Integer) {
                        Method setByKey = obj.getClass().getMethod(setMethod + StringUtils.upperCase(key), int.class);
                        setByKey.invoke(obj, value);
                    } else if (value instanceof Long) {
                        Method setByKey = obj.getClass().getMethod(setMethod + StringUtils.upperCase(key), long.class);
                        setByKey.invoke(obj, value);
                    }
                } catch (NoSuchMethodException e) {
                    e.printStackTrace();
                } catch (IllegalAccessException e) {
                    e.printStackTrace();
                } catch (InvocationTargetException e) {
                    e.printStackTrace();
                } catch (ClassNotFoundException e) {
                    e.printStackTrace();
                }
            }
            @Override
            public Object getUploadInfo() {
                return obj;
            }
        };
        return logHandler;
    }

以上为个人经验，希望能给大家一个参考，也希望大家多多支持我们。