SpringApplication是SpringBoot的启动程序,我们通过它的run方法可以快速启动一个SpringBoot应用。可是这里面到底发生了什么?它是处于什么样的机制简化我们程序启动的?接下来我们就带着这两个问题来揭开SpringBoot启动过程的神秘面纱。
一、基于Springframework的事件机制
事件是SpringBoot的启动核心之一。对于事件我想大家都不陌生,在javaAWT中事件是在常见不过的了。
1.1、JDK中的事件接口与类
首先我们看一下EventObject,这个类定义了一个事件,该类中的source属性可以用来表示事件源(哪个对象触发的事件)
/* * Copyright (c) 1996, 2003, Oracle and/or its affiliates. All rights reserved. * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. * * * * * * * * * * * * * * * * * * * * */ package java.util; /** * <p> * The root class from which all event state objects shall be derived. * <p> * All Events are constructed with a reference to the object, the "source", * that is logically deemed to be the object upon which the Event in question * initially occurred upon. * * @since JDK1.1 */ public class EventObject implements java.io.Serializable { private static final long serialVersionUID = 5516075349620653480L; /** * The object on which the Event initially occurred. */ protected transient Object source; /** * Constructs a prototypical Event. * * @param source The object on which the Event initially occurred. * @exception IllegalArgumentException if source is null. */ public EventObject(Object source) { if (source == null) throw new IllegalArgumentException("null source"); this.source = source; } /** * The object on which the Event initially occurred. * * @return The object on which the Event initially occurred. */ public Object getSource() { return source; } /** * Returns a String representation of this EventObject. * * @return A a String representation of this EventObject. */ public String toString() { return getClass().getName() + "[source=" + source + "]"; } }
我们看一下在AWT中很经典的MouseEvent的类关系图:
其次我们需要了解一下关于事件监听的接口EventListener:
package java.util; /** * A tagging interface that all event listener interfaces must extend. * @since JDK1.1 */ public interface EventListener { }
这个接口很简单,没有任何方法,但是JDK文档已经明确告诉我们:所有事件的监听必须继承此接口,那么我在贴出来一个MouseListener接口示例:
/* * Copyright (c) 1996, 2013, Oracle and/or its affiliates. All rights reserved. * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. * * * * * * * * * * * * * * * * * * * * */ package java.awt.event; import java.util.EventListener; /** * The listener interface for receiving "interesting" mouse events * (press, release, click, enter, and exit) on a component. * (To track mouse moves and mouse drags, use the * <code>MouseMotionListener</code>.) * <P> * The class that is interested in processing a mouse event * either implements this interface (and all the methods it * contains) or extends the abstract <code>MouseAdapter</code> class * (overriding only the methods of interest). * <P> * The listener object created from that class is then registered with a * component using the component's <code>addMouseListener</code> * method. A mouse event is generated when the mouse is pressed, released * clicked (pressed and released). A mouse event is also generated when * the mouse cursor enters or leaves a component. When a mouse event * occurs, the relevant method in the listener object is invoked, and * the <code>MouseEvent</code> is passed to it. * * @author Carl Quinn * * @see MouseAdapter * @see MouseEvent * @see <a href="https://docs.oracle.com/javase/tutorial/uiswing/events/mouselistener.html">Tutorial: Writing a Mouse Listener</a> * * @since 1.1 */ public interface MouseListener extends EventListener { /** * Invoked when the mouse button has been clicked (pressed * and released) on a component. */ public void mouseClicked(MouseEvent e); /** * Invoked when a mouse button has been pressed on a component. */ public void mousePressed(MouseEvent e); /** * Invoked when a mouse button has been released on a component. */ public void mouseReleased(MouseEvent e); /** * Invoked when the mouse enters a component. */ public void mouseEntered(MouseEvent e); /** * Invoked when the mouse exits a component. */ public void mouseExited(MouseEvent e); }
我们可以看到MouseListener继承了EventListener接口,接口中的方法参数都为MouseEvent。
1.2、spring中的事件类
Spring中也给我们提供了一套事件处理机制,其中几个较为关键的接口和类分别是:
ApplicationEvent
ApplicationListener
ApplicationEventPublisher
ApplicationEventMulticaster
下面我们来依次看一下这几个类与接口:
ApplicationEvent:
/* * Copyright 2002-2015 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.context; import java.util.EventObject; /** * Class to be extended by all application events. Abstract as it * doesn't make sense for generic events to be published directly. * * @author Rod Johnson * @author Juergen Hoeller */ public abstract class ApplicationEvent extends EventObject { /** use serialVersionUID from Spring 1.2 for interoperability */ private static final long serialVersionUID = 7099057708183571937L; /** System time when the event happened */ private final long timestamp; /** * Create a new ApplicationEvent. * @param source the object on which the event initially occurred (never {@code null}) */ public ApplicationEvent(Object source) { super(source); this.timestamp = System.currentTimeMillis(); } /** * Return the system time in milliseconds when the event happened. */ public final long getTimestamp() { return this.timestamp; } }
在这里我们可以明确看到该类直接继承EventObject
ApplicationListener:
/* * Copyright 2002-2015 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.context; import java.util.EventListener; /** * Interface to be implemented by application event listeners. * Based on the standard {@code java.util.EventListener} interface * for the Observer design pattern. * * <p>As of Spring 3.0, an ApplicationListener can generically declare the event type * that it is interested in. When registered with a Spring ApplicationContext, events * will be filtered accordingly, with the listener getting invoked for matching event * objects only. * * @author Rod Johnson * @author Juergen Hoeller * @param <E> the specific ApplicationEvent subclass to listen to * @see org.springframework.context.event.ApplicationEventMulticaster */ public interface ApplicationListener<E extends ApplicationEvent> extends EventListener { /** * Handle an application event. * @param event the event to respond to */ void onApplicationEvent(E event); }
我们可以看到该接口继承EventListener
ApplicationEventPublisher:
/* * Copyright 2002-2015 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.context; /** * Interface that encapsulates event publication functionality. * Serves as super-interface for {@link ApplicationContext}. * * @author Juergen Hoeller * @author Stephane Nicoll * @since 1.1.1 * @see ApplicationContext * @see ApplicationEventPublisherAware * @see org.springframework.context.ApplicationEvent * @see org.springframework.context.event.EventPublicationInterceptor */ public interface ApplicationEventPublisher { /** * Notify all <strong>matching</strong> listeners registered with this * application of an application event. Events may be framework events * (such as RequestHandledEvent) or application-specific events. * @param event the event to publish * @see org.springframework.web.context.support.RequestHandledEvent */ void publishEvent(ApplicationEvent event); /** * Notify all <strong>matching</strong> listeners registered with this * application of an event. * <p>If the specified {@code event} is not an {@link ApplicationEvent}, * it is wrapped in a {@link PayloadApplicationEvent}. * @param event the event to publish * @since 4.2 * @see PayloadApplicationEvent */ void publishEvent(Object event); }
这个接口比较重要,它使用来触发一个事件的(虽然方法的名称为发布事件),调用方法publishEvent过后,事件对应的listener将会执行相应的内容
ApplicationEventMulticaster
该接口管理ApplicationListener的同时可以执行listener监听事件的方法:
/* * Copyright 2002-2017 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.context.event; import org.springframework.context.ApplicationEvent; import org.springframework.context.ApplicationListener; import org.springframework.core.ResolvableType; /** * Interface to be implemented by objects that can manage a number of * {@link ApplicationListener} objects, and publish events to them. * * <p>An {@link org.springframework.context.ApplicationEventPublisher}, typically * a Spring {@link org.springframework.context.ApplicationContext}, can use an * ApplicationEventMulticaster as a delegate for actually publishing events. * * @author Rod Johnson * @author Juergen Hoeller * @author Stephane Nicoll */ public interface ApplicationEventMulticaster { /** * Add a listener to be notified of all events. * @param listener the listener to add */ void addApplicationListener(ApplicationListener<?> listener); /** * Add a listener bean to be notified of all events. * @param listenerBeanName the name of the listener bean to add */ void addApplicationListenerBean(String listenerBeanName); /** * Remove a listener from the notification list. * @param listener the listener to remove */ void removeApplicationListener(ApplicationListener<?> listener); /** * Remove a listener bean from the notification list. * @param listenerBeanName the name of the listener bean to add */ void removeApplicationListenerBean(String listenerBeanName); /** * Remove all listeners registered with this multicaster. * <p>After a remove call, the multicaster will perform no action * on event notification until new listeners are being registered. */ void removeAllListeners(); /** * Multicast the given application event to appropriate listeners. * <p>Consider using {@link #multicastEvent(ApplicationEvent, ResolvableType)} * if possible as it provides a better support for generics-based events. * @param event the event to multicast */ void multicastEvent(ApplicationEvent event); /** * Multicast the given application event to appropriate listeners. * <p>If the {@code eventType} is {@code null}, a default type is built * based on the {@code event} instance. * @param event the event to multicast * @param eventType the type of event (can be null) * @since 4.2 */ void multicastEvent(ApplicationEvent event, ResolvableType eventType); }
我们可以看一下其子类SimpleApplicationEventMulticaster 的源码:
/* * Copyright 2002-2017 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.context.event; import java.util.concurrent.Executor; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.beans.factory.BeanFactory; import org.springframework.context.ApplicationEvent; import org.springframework.context.ApplicationListener; import org.springframework.core.ResolvableType; import org.springframework.util.ErrorHandler; /** * Simple implementation of the {@link ApplicationEventMulticaster} interface. * * <p>Multicasts all events to all registered listeners, leaving it up to * the listeners to ignore events that they are not interested in. * Listeners will usually perform corresponding {@code instanceof} * checks on the passed-in event object. * * <p>By default, all listeners are invoked in the calling thread. * This allows the danger of a rogue listener blocking the entire application, * but adds minimal overhead. Specify an alternative task executor to have * listeners executed in different threads, for example from a thread pool. * * @author Rod Johnson * @author Juergen Hoeller * @author Stephane Nicoll * @see #setTaskExecutor */ public class SimpleApplicationEventMulticaster extends AbstractApplicationEventMulticaster { private Executor taskExecutor; private ErrorHandler errorHandler; /** * Create a new SimpleApplicationEventMulticaster. */ public SimpleApplicationEventMulticaster() { } /** * Create a new SimpleApplicationEventMulticaster for the given BeanFactory. */ public SimpleApplicationEventMulticaster(BeanFactory beanFactory) { setBeanFactory(beanFactory); } /** * Set a custom executor (typically a {@link org.springframework.core.task.TaskExecutor}) * to invoke each listener with. * <p>Default is equivalent to {@link org.springframework.core.task.SyncTaskExecutor}, * executing all listeners synchronously in the calling thread. * <p>Consider specifying an asynchronous task executor here to not block the * caller until all listeners have been executed. However, note that asynchronous * execution will not participate in the caller's thread context (class loader, * transaction association) unless the TaskExecutor explicitly supports this. * @see org.springframework.core.task.SyncTaskExecutor * @see org.springframework.core.task.SimpleAsyncTaskExecutor */ public void setTaskExecutor(Executor taskExecutor) { this.taskExecutor = taskExecutor; } /** * Return the current task executor for this multicaster. */ protected Executor getTaskExecutor() { return this.taskExecutor; } /** * Set the {@link ErrorHandler} to invoke in case an exception is thrown * from a listener. * <p>Default is none, with a listener exception stopping the current * multicast and getting propagated to the publisher of the current event. * If a {@linkplain #setTaskExecutor task executor} is specified, each * individual listener exception will get propagated to the executor but * won't necessarily stop execution of other listeners. * <p>Consider setting an {@link ErrorHandler} implementation that catches * and logs exceptions (a la * {@link org.springframework.scheduling.support.TaskUtils#LOG_AND_SUPPRESS_ERROR_HANDLER}) * or an implementation that logs exceptions while nevertheless propagating them * (e.g. {@link org.springframework.scheduling.support.TaskUtils#LOG_AND_PROPAGATE_ERROR_HANDLER}). * @since 4.1 */ public void setErrorHandler(ErrorHandler errorHandler) { this.errorHandler = errorHandler; } /** * Return the current error handler for this multicaster. * @since 4.1 */ protected ErrorHandler getErrorHandler() { return this.errorHandler; } @Override public void multicastEvent(ApplicationEvent event) { multicastEvent(event, resolveDefaultEventType(event)); } @Override public void multicastEvent(final ApplicationEvent event, ResolvableType eventType) { ResolvableType type = (eventType != null ? eventType : resolveDefaultEventType(event)); for (final ApplicationListener<?> listener : getApplicationListeners(event, type)) { Executor executor = getTaskExecutor(); if (executor != null) { executor.execute(new Runnable() { @Override public void run() { invokeListener(listener, event); } }); } else { invokeListener(listener, event); } } } private ResolvableType resolveDefaultEventType(ApplicationEvent event) { return ResolvableType.forInstance(event); } /** * Invoke the given listener with the given event. * @param listener the ApplicationListener to invoke * @param event the current event to propagate * @since 4.1 */ protected void invokeListener(ApplicationListener<?> listener, ApplicationEvent event) { ErrorHandler errorHandler = getErrorHandler(); if (errorHandler != null) { try { doInvokeListener(listener, event); } catch (Throwable err) { errorHandler.handleError(err); } } else { doInvokeListener(listener, event); } } @SuppressWarnings({"unchecked", "rawtypes"}) private void doInvokeListener(ApplicationListener listener, ApplicationEvent event) { try { listener.onApplicationEvent(event); } catch (ClassCastException ex) { String msg = ex.getMessage(); if (msg == null || msg.startsWith(event.getClass().getName())) { // Possibly a lambda-defined listener which we could not resolve the generic event type for Log logger = LogFactory.getLog(getClass()); if (logger.isDebugEnabled()) { logger.debug("Non-matching event type for listener: " + listener, ex); } } else { throw ex; } } } }
请大家看一下 doInvokeListener方法,该方法用于执行事件的监听方法
1.3、基于Spring的自定义事件
在这里我们模拟一个场景,当感到饥饿时,通知厨师做饭
定义事件:
package org.hzgj.spring.study.event; import org.springframework.context.ApplicationEvent; /** * 定义一个描饥饿状态的事件 * * @author chen.nie * @date 2018/4/26 **/ public class HungryEvent extends ApplicationEvent { /** * Create a new ApplicationEvent. * * @param source the object on which the event initially occurred (never {@code null}) */ public HungryEvent(Object source) { super(source); } }
定义Person:
package org.hzgj.spring.study.event; import org.springframework.context.ApplicationEventPublisher; import org.springframework.context.ApplicationEventPublisherAware; import org.springframework.stereotype.Component; /** * Person类,如果属性hungry的值为0,则通知厨师做饭吃。 */ @Component public class Person implements ApplicationEventPublisherAware { private int hungry; private String name; public int getHungry() { return hungry; } public void setHungry(int hungry) { this.hungry = hungry; } public String getName() { return name; } public void setName(String name) { this.name = name; } private ApplicationEventPublisher applicationEventPublisher; @Override public void setApplicationEventPublisher(ApplicationEventPublisher applicationEventPublisher) { this.applicationEventPublisher = applicationEventPublisher; } public void isNeedEat() { if (this.hungry == 0) { System.out.println("太饿了,需要吃东西"); new Thread(() -> this.applicationEventPublisher.publishEvent(new HungryEvent(this))).start(); System.out.println("通知完毕"); } } }
注意这里面利用spring的aware模式拿到ApplicationEventPublisher对象,在Spring里有若干个Aware,比如说ApplicationContextAware BeanFactoryAware等。
定义厨师类:
package org.hzgj.spring.study.event; import org.springframework.context.ApplicationListener; import org.springframework.stereotype.Component; /** * 厨师类用于对饥饿事件的监听... * * @author chen.nie * @date 2018/4/26 **/ @Component public class Chef implements ApplicationListener<HungryEvent> { @Override public void onApplicationEvent(HungryEvent event) { if (event.getSource() instanceof Person) { Person person = (Person) event.getSource(); System.out.println(person.getName() + "饿了,开始做饭"); try { Thread.sleep(2000); } catch (InterruptedException e) { e.printStackTrace(); } System.out.println("做饭完毕....开始吃吧"); } } }
spring-config.xml:
<?xml version="1.0" encoding="UTF-8"?> <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.xsd http://www.springframework.org/schema/context http://www.springframework.org/schema/context/spring-context.xsd"> <context:component-scan base-package="org.hzgj"/> </beans>
Main方法:
package org.hzgj.spring.study; import org.hzgj.spring.study.event.Person; import org.springframework.context.support.ClassPathXmlApplicationContext; import javax.naming.NamingException; import java.io.IOException; public class Main { public static void main(String[] args) throws IOException, NamingException { ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring-config.xml"); Person person = applicationContext.getBean(Person.class); person.setHungry(0); person.setName("admin"); person.isNeedEat(); } }
执行Main方法后,我们可以看到如下结果:
二、SpringApplication启动分析
2.1、SpringApplication初始化分析
在这里我们先追踪一下SpringApplication.run的方法:
/** * Static helper that can be used to run a {@link SpringApplication} from the * specified sources using default settings and user supplied arguments. * @param sources the sources to load * @param args the application arguments (usually passed from a Java main method) * @return the running {@link ApplicationContext} */ public static ConfigurableApplicationContext run(Object[] sources, String[] args) { return new SpringApplication(sources).run(args); }
该方法会创建SpringApplication对象,我们继续看一下关键代码:
//...... /** * Create a new {@link SpringApplication} instance. The application context will load * beans from the specified sources (see {@link SpringApplication class-level} * documentation for details. The instance can be customized before calling * {@link #run(String...)}. * @param sources the bean sources * @see #run(Object, String[]) * @see #SpringApplication(ResourceLoader, Object...) */ public SpringApplication(Object... sources) { initialize(sources); } //...... @SuppressWarnings({ "unchecked", "rawtypes" }) private void initialize(Object[] sources) { if (sources != null && sources.length > 0) { this.sources.addAll(Arrays.asList(sources)); } this.webEnvironment = deduceWebEnvironment(); setInitializers((Collection) getSpringFactoriesInstances( ApplicationContextInitializer.class)); setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); this.mainApplicationClass = deduceMainApplicationClass(); }
这里大家重点关注一下源代码中getSpringFacoriesInstances方法, ApplicationListener接口,ApplicationContextInitializer接口,这些接口都是通过SpringFactoriesLoader从META-INF/spring.factories文件里加载的
其中getSpringFactoriesInstances的关键代码:
private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) { ClassLoader classLoader = Thread.currentThread().getContextClassLoader(); // Use names and ensure unique to protect against duplicates Set<String> names = new LinkedHashSet<String>( SpringFactoriesLoader.loadFactoryNames(type, classLoader)); List<T> instances = createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names); AnnotationAwareOrderComparator.sort(instances); return instances; }
这里面有一个关键类叫做SpringFactoriesLoader 该类的主要作用是读取META-INF/spring.factories配置文件里配置的引导对象,我们来看一下代码:
/* * Copyright 2002-2016 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.core.io.support; import java.io.IOException; import java.lang.reflect.Constructor; import java.net.URL; import java.util.ArrayList; import java.util.Arrays; import java.util.Enumeration; import java.util.List; import java.util.Properties; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.core.annotation.AnnotationAwareOrderComparator; import org.springframework.core.io.UrlResource; import org.springframework.util.Assert; import org.springframework.util.ClassUtils; import org.springframework.util.ReflectionUtils; import org.springframework.util.StringUtils; /** * General purpose factory loading mechanism for internal use within the framework. * * <p>{@code SpringFactoriesLoader} {@linkplain #loadFactories loads} and instantiates * factories of a given type from {@value #FACTORIES_RESOURCE_LOCATION} files which * may be present in multiple JAR files in the classpath. The {@code spring.factories} * file must be in {@link Properties} format, where the key is the fully qualified * name of the interface or abstract class, and the value is a comma-separated list of * implementation class names. For example: * * <pre class="code">example.MyService=example.MyServiceImpl1,example.MyServiceImpl2</pre> * * where {@code example.MyService} is the name of the interface, and {@code MyServiceImpl1} * and {@code MyServiceImpl2} are two implementations. * * @author Arjen Poutsma * @author Juergen Hoeller * @author Sam Brannen * @since 3.2 */ public abstract class SpringFactoriesLoader { private static final Log logger = LogFactory.getLog(SpringFactoriesLoader.class); /** * The location to look for factories. * <p>Can be present in multiple JAR files. */ public static final String FACTORIES_RESOURCE_LOCATION = "META-INF/spring.factories"; /** * Load and instantiate the factory implementations of the given type from * {@value #FACTORIES_RESOURCE_LOCATION}, using the given class loader. * <p>The returned factories are sorted in accordance with the {@link AnnotationAwareOrderComparator}. * <p>If a custom instantiation strategy is required, use {@link #loadFactoryNames} * to obtain all registered factory names. * @param factoryClass the interface or abstract class representing the factory * @param classLoader the ClassLoader to use for loading (can be {@code null} to use the default) * @see #loadFactoryNames * @throws IllegalArgumentException if any factory implementation class cannot * be loaded or if an error occurs while instantiating any factory */ public static <T> List<T> loadFactories(Class<T> factoryClass, ClassLoader classLoader) { Assert.notNull(factoryClass, "'factoryClass' must not be null"); ClassLoader classLoaderToUse = classLoader; if (classLoaderToUse == null) { classLoaderToUse = SpringFactoriesLoader.class.getClassLoader(); } List<String> factoryNames = loadFactoryNames(factoryClass, classLoaderToUse); if (logger.isTraceEnabled()) { logger.trace("Loaded [" + factoryClass.getName() + "] names: " + factoryNames); } List<T> result = new ArrayList<T>(factoryNames.size()); for (String factoryName : factoryNames) { result.add(instantiateFactory(factoryName, factoryClass, classLoaderToUse)); } AnnotationAwareOrderComparator.sort(result); return result; } /** * Load the fully qualified class names of factory implementations of the * given type from {@value #FACTORIES_RESOURCE_LOCATION}, using the given * class loader. * @param factoryClass the interface or abstract class representing the factory * @param classLoader the ClassLoader to use for loading resources; can be * {@code null} to use the default * @see #loadFactories * @throws IllegalArgumentException if an error occurs while loading factory names */ public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) { String factoryClassName = factoryClass.getName(); try { Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) : ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION)); List<String> result = new ArrayList<String>(); while (urls.hasMoreElements()) { URL url = urls.nextElement(); Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url)); String factoryClassNames = properties.getProperty(factoryClassName); result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames))); } return result; } catch (IOException ex) { throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() + "] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex); } } @SuppressWarnings("unchecked") private static <T> T instantiateFactory(String instanceClassName, Class<T> factoryClass, ClassLoader classLoader) { try { Class<?> instanceClass = ClassUtils.forName(instanceClassName, classLoader); if (!factoryClass.isAssignableFrom(instanceClass)) { throw new IllegalArgumentException( "Class [" + instanceClassName + "] is not assignable to [" + factoryClass.getName() + "]"); } Constructor<?> constructor = instanceClass.getDeclaredConstructor(); ReflectionUtils.makeAccessible(constructor); return (T) constructor.newInstance(); } catch (Throwable ex) { throw new IllegalArgumentException("Unable to instantiate factory class: " + factoryClass.getName(), ex); } } }
这里面的ApplicationListener略微特殊,它被定义到META-INF/spring.factories里,该监听器主要监听SpringApplicationEvent事件,SpringApplicationEvent有如下子类:
1. ApplicationStartingEvent
2. ApplicationEnvironmentPreparedEvent
3. ApplicationPreparedEvent
4. ApplicationFailedEvent
5. ApplicationReadyEvent
ApplicationContextInitializer该接口
/* * Copyright 2002-2011 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.context; /** * Callback interface for initializing a Spring {@link ConfigurableApplicationContext} * prior to being {@linkplain ConfigurableApplicationContext#refresh() refreshed}. * * <p>Typically used within web applications that require some programmatic initialization * of the application context. For example, registering property sources or activating * profiles against the {@linkplain ConfigurableApplicationContext#getEnvironment() * context's environment}. See {@code ContextLoader} and {@code FrameworkServlet} support * for declaring a "contextInitializerClasses" context-param and init-param, respectively. * * <p>{@code ApplicationContextInitializer} processors are encouraged to detect * whether Spring's {@link org.springframework.core.Ordered Ordered} interface has been * implemented or if the @{@link org.springframework.core.annotation.Order Order} * annotation is present and to sort instances accordingly if so prior to invocation. * * @author Chris Beams * @since 3.1 * @see org.springframework.web.context.ContextLoader#customizeContext * @see org.springframework.web.context.ContextLoader#CONTEXT_INITIALIZER_CLASSES_PARAM * @see org.springframework.web.servlet.FrameworkServlet#setContextInitializerClasses * @see org.springframework.web.servlet.FrameworkServlet#applyInitializers */ public interface ApplicationContextInitializer<C extends ConfigurableApplicationContext> { /** * Initialize the given application context. * @param applicationContext the application to configure */ void initialize(C applicationContext); }
该接口doc文档上描述很清楚了,在调用ConfigurableApplicationContext的refresh()之前进行的初始化操作,比如说:激活profile , 注册PropertySource , FrameworkServlet(DispacherServlet的父类)设置 contextConfigLocation等。
2.2、SpringApplication的run方法分析
这里我贴一下关键代码:
/** * Run the Spring application, creating and refreshing a new * {@link ApplicationContext}. * @param args the application arguments (usually passed from a Java main method) * @return a running {@link ApplicationContext} */ public ConfigurableApplicationContext run(String... args) { StopWatch stopWatch = new StopWatch(); stopWatch.start(); ConfigurableApplicationContext context = null; FailureAnalyzers analyzers = null; configureHeadlessProperty(); SpringApplicationRunListeners listeners = getRunListeners(args); listeners.starting(); try { ApplicationArguments applicationArguments = new DefaultApplicationArguments( args); ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments); Banner printedBanner = printBanner(environment); context = createApplicationContext(); analyzers = new FailureAnalyzers(context); prepareContext(context, environment, listeners, applicationArguments, printedBanner); refreshContext(context); afterRefresh(context, applicationArguments); listeners.finished(context, null); stopWatch.stop(); if (this.logStartupInfo) { new StartupInfoLogger(this.mainApplicationClass) .logStarted(getApplicationLog(), stopWatch); } return context; } catch (Throwable ex) { handleRunFailure(context, listeners, analyzers, ex); throw new IllegalStateException(ex); } }
1. 获取SpringApplicationRunListener
private SpringApplicationRunListeners getRunListeners(String[] args) { Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class }; return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances( SpringApplicationRunListener.class, types, this, args)); }
该接口首先从META-INF/spring.factories文件里获取所有配置的SpringApplicationRunner ,那么这个接口时干啥的呢?我们来看一下源代码:
/* * Copyright 2012-2016 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.boot; import org.springframework.context.ApplicationContext; import org.springframework.context.ConfigurableApplicationContext; import org.springframework.core.env.ConfigurableEnvironment; import org.springframework.core.io.support.SpringFactoriesLoader; /** * Listener for the {@link SpringApplication} {@code run} method. * {@link SpringApplicationRunListener}s are loaded via the {@link SpringFactoriesLoader} * and should declare a public constructor that accepts a {@link SpringApplication} * instance and a {@code String[]} of arguments. A new * {@link SpringApplicationRunListener} instance will be created for each run. * * @author Phillip Webb * @author Dave Syer */ public interface SpringApplicationRunListener { /** * Called immediately when the run method has first started. Can be used for very * early initialization. */ void starting(); /** * Called once the environment has been prepared, but before the * {@link ApplicationContext} has been created. * @param environment the environment */ void environmentPrepared(ConfigurableEnvironment environment); /** * Called once the {@link ApplicationContext} has been created and prepared, but * before sources have been loaded. * @param context the application context */ void contextPrepared(ConfigurableApplicationContext context); /** * Called once the application context has been loaded but before it has been * refreshed. * @param context the application context */ void contextLoaded(ConfigurableApplicationContext context); /** * Called immediately before the run method finishes. * @param context the application context or null if a failure occurred before the * context was created * @param exception any run exception or null if run completed successfully. */ void finished(ConfigurableApplicationContext context, Throwable exception); }
其实简单点来说就是在SpringBoot启动过程中各个阶段需要做的事情,阶段包括:程序准备启动,准备环境,ApplicationContext准备加载,程序启动完成等等。
其中该接口默认有一个实现类EventPublishingRunListener至关重要大家需要了解一下:
/* * Copyright 2012-2017 the original author or authors. * * Licensed under the Apache License, Version 2.0 (the "License"); * you may not use this file except in compliance with the License. * You may obtain a copy of the License at * * http://www.apache.org/licenses/LICENSE-2.0 * * Unless required by applicable law or agreed to in writing, software * distributed under the License is distributed on an "AS IS" BASIS, * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. * See the License for the specific language governing permissions and * limitations under the License. */ package org.springframework.boot.context.event; import org.apache.commons.logging.Log; import org.apache.commons.logging.LogFactory; import org.springframework.boot.SpringApplication; import org.springframework.boot.SpringApplicationRunListener; import org.springframework.context.ApplicationContextAware; import org.springframework.context.ApplicationListener; import org.springframework.context.ConfigurableApplicationContext; import org.springframework.context.event.ApplicationEventMulticaster; import org.springframework.context.event.SimpleApplicationEventMulticaster; import org.springframework.context.support.AbstractApplicationContext; import org.springframework.core.Ordered; import org.springframework.core.env.ConfigurableEnvironment; import org.springframework.util.ErrorHandler; /** * {@link SpringApplicationRunListener} to publish {@link SpringApplicationEvent}s. * <p> * Uses an internal {@link ApplicationEventMulticaster} for the events that are fired * before the context is actually refreshed. * * @author Phillip Webb * @author Stephane Nicoll */ public class EventPublishingRunListener implements SpringApplicationRunListener, Ordered { private final SpringApplication application; private final String[] args; private final SimpleApplicationEventMulticaster initialMulticaster; public EventPublishingRunListener(SpringApplication application, String[] args) { this.application = application; this.args = args; this.initialMulticaster = new SimpleApplicationEventMulticaster(); for (ApplicationListener<?> listener : application.getListeners()) { this.initialMulticaster.addApplicationListener(listener); } } @Override public int getOrder() { return 0; } @Override @SuppressWarnings("deprecation") public void starting() { this.initialMulticaster .multicastEvent(new ApplicationStartedEvent(this.application, this.args)); } @Override public void environmentPrepared(ConfigurableEnvironment environment) { this.initialMulticaster.multicastEvent(new ApplicationEnvironmentPreparedEvent( this.application, this.args, environment)); } @Override public void contextPrepared(ConfigurableApplicationContext context) { } @Override public void contextLoaded(ConfigurableApplicationContext context) { for (ApplicationListener<?> listener : this.application.getListeners()) { if (listener instanceof ApplicationContextAware) { ((ApplicationContextAware) listener).setApplicationContext(context); } context.addApplicationListener(listener); } this.initialMulticaster.multicastEvent( new ApplicationPreparedEvent(this.application, this.args, context)); } @Override public void finished(ConfigurableApplicationContext context, Throwable exception) { SpringApplicationEvent event = getFinishedEvent(context, exception); if (context != null && context.isActive()) { // Listeners have been registered to the application context so we should // use it at this point if we can context.publishEvent(event); } else { // An inactive context may not have a multicaster so we use our multicaster to // call all of the context's listeners instead if (context instanceof AbstractApplicationContext) { for (ApplicationListener<?> listener : ((AbstractApplicationContext) context) .getApplicationListeners()) { this.initialMulticaster.addApplicationListener(listener); } } if (event instanceof ApplicationFailedEvent) { this.initialMulticaster.setErrorHandler(new LoggingErrorHandler()); } this.initialMulticaster.multicastEvent(event); } } private SpringApplicationEvent getFinishedEvent( ConfigurableApplicationContext context, Throwable exception) { if (exception != null) { return new ApplicationFailedEvent(this.application, this.args, context, exception); } return new ApplicationReadyEvent(this.application, this.args, context); } private static class LoggingErrorHandler implements ErrorHandler { private static Log logger = LogFactory.getLog(EventPublishingRunListener.class); @Override public void handleError(Throwable throwable) { logger.warn("Error calling ApplicationEventListener", throwable); } } }
这个类里面有一个SimpleApplicationEventMulticaster的属性,根据前面分析,该属性就是执行关于SpringApplicationEvent的事件监听方法的。该类最主要作用就是通知各个阶段的listener处理对应阶段的事件
2、调用所有的SpringApplicationRunListenner的start方法
我们可以看一下SpringApplicationRunListeners类里的方法:
public void starting() { for (SpringApplicationRunListener listener : this.listeners) { listener.starting(); } }
3、执行prepareEnvironment方法
public void environmentPrepared(ConfigurableEnvironment environment) { for (SpringApplicationRunListener listener : this.listeners) { listener.environmentPrepared(environment); } }
4、根据当前的Environment打印Banner
5、创建ConfigurableApplicationContext对象与FailureAnalyzers
在这里会根据this.webEnvironment的属性值来确定创建的ApplicationContext对象:
/** * Strategy method used to create the {@link ApplicationContext}. By default this * method will respect any explicitly set application context or application context * class before falling back to a suitable default. * @return the application context (not yet refreshed) * @see #setApplicationContextClass(Class) */ protected ConfigurableApplicationContext createApplicationContext() { Class<?> contextClass = this.applicationContextClass; if (contextClass == null) { try { contextClass = Class.forName(this.webEnvironment ? DEFAULT_WEB_CONTEXT_CLASS : DEFAULT_CONTEXT_CLASS); } catch (ClassNotFoundException ex) { throw new IllegalStateException( "Unable create a default ApplicationContext, " + "please specify an ApplicationContextClass", ex); } } return (ConfigurableApplicationContext) BeanUtils.instantiate(contextClass); }
如果是web环境那就创建org.springframework.boot.context.embedded.AnnotationConfigEmbeddedWebApplicationContext ,否则就创建org.springframework.context.annotation.AnnotationConfigApplicationContext
6、调用prepareContext方法
public void contextPrepared(ConfigurableApplicationContext context) { for (SpringApplicationRunListener listener : this.listeners) { listener.contextPrepared(context); } }
7、调用 refreshContext方法
该方法最终会执行AbstractApplicationContext的refresh()方法,我在这里贴一下源代码
@Override public void refresh() throws BeansException, IllegalStateException { synchronized (this.startupShutdownMonitor) { // Prepare this context for refreshing. prepareRefresh(); // Tell the subclass to refresh the internal bean factory. ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory(); // Prepare the bean factory for use in this context. prepareBeanFactory(beanFactory); try { // Allows post-processing of the bean factory in context subclasses. postProcessBeanFactory(beanFactory); // Invoke factory processors registered as beans in the context. invokeBeanFactoryPostProcessors(beanFactory); // Register bean processors that intercept bean creation. registerBeanPostProcessors(beanFactory); // Initialize message source for this context. initMessageSource(); // Initialize event multicaster for this context. initApplicationEventMulticaster(); // Initialize other special beans in specific context subclasses. onRefresh(); // Check for listener beans and register them. registerListeners(); // Instantiate all remaining (non-lazy-init) singletons. finishBeanFactoryInitialization(beanFactory); // Last step: publish corresponding event. finishRefresh(); } catch (BeansException ex) { if (logger.isWarnEnabled()) { logger.warn("Exception encountered during context initialization - " + "cancelling refresh attempt: " + ex); } // Destroy already created singletons to avoid dangling resources. destroyBeans(); // Reset 'active' flag. cancelRefresh(ex); // Propagate exception to caller. throw ex; } finally { // Reset common introspection caches in Spring's core, since we // might not ever need metadata for singleton beans anymore... resetCommonCaches(); } } }
在这个方法里会初始化BeanFactory 初始化BeanFactoryPostProcessor 注册BeanPostProcessor 初始化MessageSource 注册事件监听器等操作。建议大家深入了解Spring的IOC加载原理
8、执行afterRefresh()
/** * Called after the context has been refreshed. * @param context the application context * @param args the application arguments */ protected void afterRefresh(ConfigurableApplicationContext context, ApplicationArguments args) { callRunners(context, args); } private void callRunners(ApplicationContext context, ApplicationArguments args) { List<Object> runners = new ArrayList<Object>(); runners.addAll(context.getBeansOfType(ApplicationRunner.class).values()); runners.addAll(context.getBeansOfType(CommandLineRunner.class).values()); AnnotationAwareOrderComparator.sort(runners); for (Object runner : new LinkedHashSet<Object>(runners)) { if (runner instanceof ApplicationRunner) { callRunner((ApplicationRunner) runner, args); } if (runner instanceof CommandLineRunner) { callRunner((CommandLineRunner) runner, args); } } }
private void callRunner(ApplicationRunner runner, ApplicationArguments args) {
try {
(runner).run(args);
}
catch (Exception ex) {
throw new IllegalStateException("Failed to execute ApplicationRunner", ex);
}
}
该方法会从IOC容器里找到ApplicationRunner或者CommandLineRunner并执行其run方法,当我们需要在SpringBoot程序启动时处理我们自己的逻辑,那么就可以实现上述接口
9、调用 listeners.finished方法
public void finished(ConfigurableApplicationContext context, Throwable exception) { for (SpringApplicationRunListener listener : this.listeners) { callFinishedListener(listener, context, exception); } }
private void callFinishedListener(SpringApplicationRunListener listener, ConfigurableApplicationContext context, Throwable exception) { try { listener.finished(context, exception); } catch (Throwable ex) { if (exception == null) { ReflectionUtils.rethrowRuntimeException(ex); } if (this.log.isDebugEnabled()) { this.log.error("Error handling failed", ex); } else { String message = ex.getMessage(); message = (message == null ? "no error message" : message); this.log.warn("Error handling failed (" + message + ")"); } } }
10、启动时的异常处理
private void handleRunFailure(ConfigurableApplicationContext context, SpringApplicationRunListeners listeners, FailureAnalyzers analyzers, Throwable exception) { try { try { handleExitCode(context, exception); listeners.finished(context, exception); } finally { reportFailure(analyzers, exception); if (context != null) { context.close(); } } } catch (Exception ex) { logger.warn("Unable to close ApplicationContext", ex); } ReflectionUtils.rethrowRuntimeException(exception); }
我们可以看到在SpringApplicationRunnerListener的作用至关重要,几乎每做一件事情都涉及到此接口的方法 ,另外 EventPublishingRunListener会在各个阶段通知各个listener处理启动周期内各个阶段性事件
三、测试示例
通过在META-INF/spring.factories里配置引导类,来验证一下我们上述分析的启动过程
1、创建MyBootStrapApplicationListener示例:
package com.hzgj.lyrk.member.applicationlistener; import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent; import org.springframework.context.ApplicationListener; /** * META-INF/spring.factories 配置的listener测试 * @author chen.nie * @date 2018/4/26 **/ public class MyBootStrapApplicationListener implements ApplicationListener<ApplicationEnvironmentPreparedEvent> { @Override public void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) { System.out.println("BootStrapApplicationListener"); } }
2、创建MyCommandRunner
package com.hzgj.lyrk.member.commandlinerunner; import org.springframework.boot.CommandLineRunner; import org.springframework.stereotype.Component; /** * commandLineRunner测试 * * @author chen.nie * @date 2018/4/26 **/ @Component public class MyCommandRunner implements CommandLineRunner { @Override public void run(String... args) throws Exception { System.out.println("MyCommandRunner execute ....."); } }
3、在spring.factories配置ApplicationListener
org.springframework.context.ApplicationListener=\
com.hzgj.lyrk.member.applicationlistener.MyBootStrapApplicationListener
当我们启动SpringBoot项目时,可以发现如下结果:
我们可以发现我们配置的ApplicationListener在最开始就会执行,而CommandLineRunner在最后才执行
四、SpringBoot启动总结
1. SpringBoot启动时SpringApplicationRunListener接口的相关方法至关重要,它定义了启动时的各个“时间点”。
2. SpringBoot可以从spring.factoies文件里读取配置的ApplicationListener
3. META-INF文件夹下的spring.factoies文件是SpringBoot启动的核心文件,SpringFatoriesLoader会读取该文件夹下的相关配置作为引导
4. SpringBoot启动时利用了事件机制,来发送启动时各个周期阶段的事件