我们知道在SpringCloud中，当配置变更时，我们通过访问http://xxxx/refresh，可以在不启动服务的情况下获取最新的配置，那么它是如何做到的呢，当我们更改数据库配置并刷新后，如何能获取最新的数据源对象呢？下面我们看SpringCloud如何做到的。
一、环境变化
1.1、关于ContextRefresher
当我们访问/refresh时，会被RefreshEndpoint类所处理。我们来看源代码：
/* * Copyright 2013-2014 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.cloud.endpoint;import java.util.Arrays;import java.util.Collection;import java.util.Set;import org.springframework.boot.actuate.endpoint.AbstractEndpoint;import org.springframework.boot.context.properties.ConfigurationProperties;import org.springframework.cloud.context.refresh.ContextRefresher;import org.springframework.jmx.export.annotation.ManagedOperation;import org.springframework.jmx.export.annotation.ManagedResource;/** * @author Dave Syer * @author Venil Noronha */@ConfigurationProperties(prefix = "endpoints.refresh", ignoreUnknownFields = false)@ManagedResourcepublic class RefreshEndpoint extends AbstractEndpoint<Collection<String>> { private ContextRefresher contextRefresher; public RefreshEndpoint(ContextRefresher contextRefresher) { super("refresh"); this.contextRefresher = contextRefresher; } @ManagedOperation public String[] refresh() { Set<String> keys = contextRefresher.refresh(); return keys.toArray(new String[keys.size()]); } @Override public Collection<String> invoke() { return Arrays.asList(refresh()); }}通过源代码我们了解到：当访问refresh端点时，实际上执行的是ContextRefresher的refresh方法，那么我们继续追踪源代码，找到其refresh方法：
public synchronized Set<String> refresh() { Map<String, Object> before = extract( this.context.getEnvironment().getPropertySources()); addConfigFilesToEnvironment(); Set<String> keys = changes(before, extract(this.context.getEnvironment().getPropertySources())).keySet(); this.context.publishEvent(new EnvironmentChangeEvent(context, keys)); this.scope.refreshAll(); return keys; }我们可以看到refresh方法做了如下几件事情：
1）获取刷新之前的所有PropertySource
2) 调用addConfigFilesToEnvironment方法获取最新的配置
3) 调用changes方法更新配置信息
4) 发布EnvironmentChangeEnvent事件
5）调用refreshScope的refreshAll方法刷新范围
我们重点关注一下2，3，4步骤
1.2、addConfigFilesToEnvironment方法
我们先来看看这个方法是怎么实现的：
/* for testing */ ConfigurableApplicationContext addConfigFilesToEnvironment() { ConfigurableApplicationContext capture = null; try { StandardEnvironment environment = copyEnvironment( this.context.getEnvironment()); SpringApplicationBuilder builder = new SpringApplicationBuilder(Empty.class) .bannerMode(Mode.OFF).web(false).environment(environment); // Just the listeners that affect the environment (e.g. excluding logging // listener because it has side effects) builder.application() .setListeners(Arrays.asList(new BootstrapApplicationListener(), new ConfigFileApplicationListener())); capture = builder.run(); if (environment.getPropertySources().contains(REFRESH_ARGS_PROPERTY_SOURCE)) { environment.getPropertySources().remove(REFRESH_ARGS_PROPERTY_SOURCE); } MutablePropertySources target = this.context.getEnvironment() .getPropertySources(); String targetName = null; for (PropertySource<?> source : environment.getPropertySources()) { String name = source.getName(); if (target.contains(name)) { targetName = name; } if (!this.standardSources.contains(name)) { if (target.contains(name)) { target.replace(name, source); } else { if (targetName != null) { target.addAfter(targetName, source); } else { // targetName was null so we are at the start of the list target.addFirst(source); targetName = name; } } } } } finally { ConfigurableApplicationContext closeable = capture; while (closeable != null) { try { closeable.close(); } catch (Exception e) { // Ignore; } if (closeable.getParent() instanceof ConfigurableApplicationContext) { closeable = (ConfigurableApplicationContext) closeable.getParent(); } else { break; } } } return capture; }1) 该方法首先拷贝当前的Environment
2) 通过SpringApplicationBuilder构建了一个简单的SpringBoot启动程序并启动
builder.application().setListeners(Arrays.asList(new BootstrapApplicationListener(), new ConfigFileApplicationListener()));
这里面会添加两个监听器分别为：BootstrapApplicationListener与ConfigFileApplicationListener，通过先前的学习，我们知道BootstrapApplicationListener是引导程序的核心监听器，而ConfigFileApplicationListener也是非常重要的类：
/* * 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.config;import java.io.IOException;import java.util.ArrayList;import java.util.Arrays;import java.util.Collection;import java.util.Collections;import java.util.Iterator;import java.util.LinkedHashSet;import java.util.LinkedList;import java.util.List;import java.util.Queue;import java.util.Set;import org.apache.commons.logging.Log;import org.springframework.beans.BeansException;import org.springframework.beans.CachedIntrospectionResults;import org.springframework.beans.factory.config.BeanFactoryPostProcessor;import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;import org.springframework.boot.SpringApplication;import org.springframework.boot.bind.PropertiesConfigurationFactory;import org.springframework.boot.bind.PropertySourcesPropertyValues;import org.springframework.boot.bind.RelaxedDataBinder;import org.springframework.boot.bind.RelaxedPropertyResolver;import org.springframework.boot.context.event.ApplicationEnvironmentPreparedEvent;import org.springframework.boot.context.event.ApplicationPreparedEvent;import org.springframework.boot.env.EnumerableCompositePropertySource;import org.springframework.boot.env.EnvironmentPostProcessor;import org.springframework.boot.env.PropertySourcesLoader;import org.springframework.boot.logging.DeferredLog;import org.springframework.context.ApplicationEvent;import org.springframework.context.ConfigurableApplicationContext;import org.springframework.context.annotation.ConfigurationClassPostProcessor;import org.springframework.context.event.SmartApplicationListener;import org.springframework.core.Ordered;import org.springframework.core.annotation.AnnotationAwareOrderComparator;import org.springframework.core.convert.ConversionService;import org.springframework.core.convert.support.DefaultConversionService;import org.springframework.core.env.ConfigurableEnvironment;import org.springframework.core.env.EnumerablePropertySource;import org.springframework.core.env.MutablePropertySources;import org.springframework.core.env.PropertySource;import org.springframework.core.env.PropertySources;import org.springframework.core.io.DefaultResourceLoader;import org.springframework.core.io.Resource;import org.springframework.core.io.ResourceLoader;import org.springframework.core.io.support.SpringFactoriesLoader;import org.springframework.util.Assert;import org.springframework.util.ResourceUtils;import org.springframework.util.StringUtils;import org.springframework.validation.BindException;/** * {@link EnvironmentPostProcessor} that configures the context environment by loading * properties from well known file locations. By default properties will be loaded from * 'application.properties' and/or 'application.yml' files in the following locations: * <ul> * <li>classpath:</li> * <li>file:./</li> * <li>classpath:config/</li> * <li>file:./config/:</li> * </ul> * <p> * Alternative search locations and names can be specified using * {@link #setSearchLocations(String)} and {@link #setSearchNames(String)}. * <p> * Additional files will also be loaded based on active profiles. For example if a 'web' * profile is active 'application-web.properties' and 'application-web.yml' will be * considered. * <p> * The 'spring.config.name' property can be used to specify an alternative name to load * and the 'spring.config.location' property can be used to specify alternative search * locations or specific files. * <p> * Configuration properties are also bound to the {@link SpringApplication}. This makes it * possible to set {@link SpringApplication} properties dynamically, like the sources * ("spring.main.sources" - a CSV list) the flag to indicate a web environment * ("spring.main.web_environment=true") or the flag to switch off the banner * ("spring.main.show_banner=false"). * * @author Dave Syer * @author Phillip Webb * @author Stephane Nicoll * @author Andy Wilkinson * @author Eddú Meléndez */public class ConfigFileApplicationListener implements EnvironmentPostProcessor, SmartApplicationListener, Ordered { private static final String DEFAULT_PROPERTIES = "defaultProperties"; // Note the order is from least to most specific (last one wins) private static final String DEFAULT_SEARCH_LOCATIONS = "classpath:/,classpath:/config/,file:./,file:./config/"; private static final String DEFAULT_NAMES = "application"; /** * The "active profiles" property name. */ public static final String ACTIVE_PROFILES_PROPERTY = "spring.profiles.active"; /** * The "includes profiles" property name. */ public static final String INCLUDE_PROFILES_PROPERTY = "spring.profiles.include"; /** * The "config name" property name. */ public static final String CONFIG_NAME_PROPERTY = "spring.config.name"; /** * The "config location" property name. */ public static final String CONFIG_LOCATION_PROPERTY = "spring.config.location"; /** * The default order for the processor. */ public static final int DEFAULT_ORDER = Ordered.HIGHEST_PRECEDENCE + 10; /** * Name of the application configuration {@link PropertySource}. */ public static final String APPLICATION_CONFIGURATION_PROPERTY_SOURCE_NAME = "applicationConfigurationProperties"; private final DeferredLog logger = new DeferredLog(); private String searchLocations; private String names; private int order = DEFAULT_ORDER; private final ConversionService conversionService = new DefaultConversionService(); @Override public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) { return ApplicationEnvironmentPreparedEvent.class.isAssignableFrom(eventType) || ApplicationPreparedEvent.class.isAssignableFrom(eventType); } @Override public boolean supportsSourceType(Class<?> aClass) { return true; } @Override public void onApplicationEvent(ApplicationEvent event) { if (event instanceof ApplicationEnvironmentPreparedEvent) { onApplicationEnvironmentPreparedEvent( (ApplicationEnvironmentPreparedEvent) event); } if (event instanceof ApplicationPreparedEvent) { onApplicationPreparedEvent(event); } } private void onApplicationEnvironmentPreparedEvent( ApplicationEnvironmentPreparedEvent event) { List<EnvironmentPostProcessor> postProcessors = loadPostProcessors(); postProcessors.add(this); AnnotationAwareOrderComparator.sort(postProcessors); for (EnvironmentPostProcessor postProcessor : postProcessors) { postProcessor.postProcessEnvironment(event.getEnvironment(), event.getSpringApplication()); } } List<EnvironmentPostProcessor> loadPostProcessors() { return SpringFactoriesLoader.loadFactories(EnvironmentPostProcessor.class, getClass().getClassLoader()); } @Override public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) { addPropertySources(environment, application.getResourceLoader()); configureIgnoreBeanInfo(environment); bindToSpringApplication(environment, application); } private void configureIgnoreBeanInfo(ConfigurableEnvironment environment) { if (System.getProperty( CachedIntrospectionResults.IGNORE_BEANINFO_PROPERTY_NAME) == null) { RelaxedPropertyResolver resolver = new RelaxedPropertyResolver(environment, "spring.beaninfo."); Boolean ignore = resolver.getProperty("ignore", Boolean.class, Boolean.TRUE); System.setProperty(CachedIntrospectionResults.IGNORE_BEANINFO_PROPERTY_NAME, ignore.toString()); } } private void onApplicationPreparedEvent(ApplicationEvent event) { this.logger.replayTo(ConfigFileApplicationListener.class); addPostProcessors(((ApplicationPreparedEvent) event).getApplicationContext()); } /** * Add config file property sources to the specified environment. * @param environment the environment to add source to * @param resourceLoader the resource loader * @see #addPostProcessors(ConfigurableApplicationContext) */ protected void addPropertySources(ConfigurableEnvironment environment, ResourceLoader resourceLoader) { RandomValuePropertySource.addToEnvironment(environment); new Loader(environment, resourceLoader).load(); } /** * Bind the environment to the {@link SpringApplication}. * @param environment the environment to bind * @param application the application to bind to */ protected void bindToSpringApplication(ConfigurableEnvironment environment, SpringApplication application) { PropertiesConfigurationFactory<SpringApplication> binder = new PropertiesConfigurationFactory<SpringApplication>( application); binder.setTargetName("spring.main"); binder.setConversionService(this.conversionService); binder.setPropertySources(environment.getPropertySources()); try { binder.bindPropertiesToTarget(); } catch (BindException ex) { throw new IllegalStateException("Cannot bind to SpringApplication", ex); } } /** * Add appropriate post-processors to post-configure the property-sources. * @param context the context to configure */ protected void addPostProcessors(ConfigurableApplicationContext context) { context.addBeanFactoryPostProcessor( new PropertySourceOrderingPostProcessor(context)); } public void setOrder(int order) { this.order = order; } @Override public int getOrder() { return this.order; } /** * Set the search locations that will be considered as a comma-separated list. Each * search location should be a directory path (ending in "/") and it will be prefixed * by the file names constructed from {@link #setSearchNames(String) search names} and * profiles (if any) plus file extensions supported by the properties loaders. * Locations are considered in the order specified, with later items taking precedence * (like a map merge). * @param locations the search locations */ public void setSearchLocations(String locations) { Assert.hasLength(locations, "Locations must not be empty"); this.searchLocations = locations; } /** * Sets the names of the files that should be loaded (excluding file extension) as a * comma-separated list. * @param names the names to load */ public void setSearchNames(String names) { Assert.hasLength(names, "Names must not be empty"); this.names = names; } /** * {@link BeanFactoryPostProcessor} to re-order our property sources below any * {@code @PropertySource} items added by the {@link ConfigurationClassPostProcessor}. */ private class PropertySourceOrderingPostProcessor implements BeanFactoryPostProcessor, Ordered { private ConfigurableApplicationContext context; PropertySourceOrderingPostProcessor(ConfigurableApplicationContext context) { this.context = context; } @Override public int getOrder() { return Ordered.HIGHEST_PRECEDENCE; } @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException { reorderSources(this.context.getEnvironment()); } private void reorderSources(ConfigurableEnvironment environment) { ConfigurationPropertySources .finishAndRelocate(environment.getPropertySources()); PropertySource<?> defaultProperties = environment.getPropertySources() .remove(DEFAULT_PROPERTIES); if (defaultProperties != null) { environment.getPropertySources().addLast(defaultProperties); } } } /** * Loads candidate property sources and configures the active profiles. */ private class Loader { private final Log logger = ConfigFileApplicationListener.this.logger; private final ConfigurableEnvironment environment; private final ResourceLoader resourceLoader; private PropertySourcesLoader propertiesLoader; private Queue<Profile> profiles; private List<Profile> processedProfiles; private boolean activatedProfiles; Loader(ConfigurableEnvironment environment, ResourceLoader resourceLoader) { this.environment = environment; this.resourceLoader = resourceLoader == null ? new DefaultResourceLoader() : resourceLoader; } public void load() { this.propertiesLoader = new PropertySourcesLoader(); this.activatedProfiles = false; this.profiles = Collections.asLifoQueue(new LinkedList<Profile>()); this.processedProfiles = new LinkedList<Profile>(); // Pre-existing active profiles set via Environment.setActiveProfiles() // are additional profiles and config files are allowed to add more if // they want to, so don't call addActiveProfiles() here. Set<Profile> initialActiveProfiles = initializeActiveProfiles(); this.profiles.addAll(getUnprocessedActiveProfiles(initialActiveProfiles)); if (this.profiles.isEmpty()) { for (String defaultProfileName : this.environment.getDefaultProfiles()) { Profile defaultProfile = new Profile(defaultProfileName, true); if (!this.profiles.contains(defaultProfile)) { this.profiles.add(defaultProfile); } } } // The default profile for these purposes is represented as null. We add it // last so that it is first out of the queue (active profiles will then // override any settings in the defaults when the list is reversed later). this.profiles.add(null); while (!this.profiles.isEmpty()) { Profile profile = this.profiles.poll(); for (String location : getSearchLocations()) { if (!location.endsWith("/")) { // location is a filename already, so don't search for more // filenames load(location, null, profile); } else { for (String name : getSearchNames()) { load(location, name, profile); } } } this.processedProfiles.add(profile); } addConfigurationProperties(this.propertiesLoader.getPropertySources()); } private Set<Profile> initializeActiveProfiles() { if (!this.environment.containsProperty(ACTIVE_PROFILES_PROPERTY) && !this.environment.containsProperty(INCLUDE_PROFILES_PROPERTY)) { return Collections.emptySet(); } // Any pre-existing active profiles set via property sources (e.g. System // properties) take precedence over those added in config files. SpringProfiles springProfiles = bindSpringProfiles( this.environment.getPropertySources()); Set<Profile> activeProfiles = new LinkedHashSet<Profile>( springProfiles.getActiveProfiles()); activeProfiles.addAll(springProfiles.getIncludeProfiles()); maybeActivateProfiles(activeProfiles); return activeProfiles; } /** * Return the active profiles that have not been processed yet. If a profile is * enabled via both {@link #ACTIVE_PROFILES_PROPERTY} and * {@link ConfigurableEnvironment#addActiveProfile(String)} it needs to be * filtered so that the {@link #ACTIVE_PROFILES_PROPERTY} value takes precedence. * <p> * Concretely, if the "cloud" profile is enabled via the environment, it will take * less precedence that any profile set via the {@link #ACTIVE_PROFILES_PROPERTY}. * @param initialActiveProfiles the profiles that have been enabled via * {@link #ACTIVE_PROFILES_PROPERTY} * @return the unprocessed active profiles from the environment to enable */ private List<Profile> getUnprocessedActiveProfiles( Set<Profile> initialActiveProfiles) { List<Profile> unprocessedActiveProfiles = new ArrayList<Profile>(); for (String profileName : this.environment.getActiveProfiles()) { Profile profile = new Profile(profileName); if (!initialActiveProfiles.contains(profile)) { unprocessedActiveProfiles.add(profile); } } // Reverse them so the order is the same as from getProfilesForValue() // (last one wins when properties are eventually resolved) Collections.reverse(unprocessedActiveProfiles); return unprocessedActiveProfiles; } private void load(String location, String name, Profile profile) { String group = "profile=" + (profile == null ? "" : profile); if (!StringUtils.hasText(name)) { // Try to load directly from the location loadIntoGroup(group, location, profile); } else { // Search for a file with the given name for (String ext : this.propertiesLoader.getAllFileExtensions()) { if (profile != null) { // Try the profile-specific file loadIntoGroup(group, location + name + "-" + profile + "." + ext, null); for (Profile processedProfile : this.processedProfiles) { if (processedProfile != null) { loadIntoGroup(group, location + name + "-" + processedProfile + "." + ext, profile); } } // Sometimes people put "spring.profiles: dev" in // application-dev.yml (gh-340). Arguably we should try and error // out on that, but we can be kind and load it anyway. loadIntoGroup(group, location + name + "-" + profile + "." + ext, profile); } // Also try the profile-specific section (if any) of the normal file loadIntoGroup(group, location + name + "." + ext, profile); } } } private PropertySource<?> loadIntoGroup(String identifier, String location, Profile profile) { try { return doLoadIntoGroup(identifier, location, profile); } catch (Exception ex) { throw new IllegalStateException( "Failed to load property source from location '" + location + "'", ex); } } private PropertySource<?> doLoadIntoGroup(String identifier, String location, Profile profile) throws IOException { Resource resource = this.resourceLoader.getResource(location); PropertySource<?> propertySource = null; StringBuilder msg = new StringBuilder(); if (resource != null && resource.exists()) { String name = "applicationConfig: [" + location + "]"; String group = "applicationConfig: [" + identifier + "]"; propertySource = this.propertiesLoader.load(resource, group, name, (profile == null ? null : profile.getName())); if (propertySource != null) { msg.append("Loaded "); handleProfileProperties(propertySource); } else { msg.append("Skipped (empty) "); } } else { msg.append("Skipped "); } msg.append("config file "); msg.append(getResourceDescription(location, resource)); if (profile != null) { msg.append(" for profile ").append(profile); } if (resource == null || !resource.exists()) { msg.append(" resource not found"); this.logger.trace(msg); } else { this.logger.debug(msg); } return propertySource; } private String getResourceDescription(String location, Resource resource) { String resourceDescription = "'" + location + "'"; if (resource != null) { try { resourceDescription = String.format("'%s' (%s)", resource.getURI().toASCIIString(), location); } catch (IOException ex) { // Use the location as the description } } return resourceDescription; } private void handleProfileProperties(PropertySource<?> propertySource) { SpringProfiles springProfiles = bindSpringProfiles(propertySource); maybeActivateProfiles(springProfiles.getActiveProfiles()); addProfiles(springProfiles.getIncludeProfiles()); } private SpringProfiles bindSpringProfiles(PropertySource<?> propertySource) { MutablePropertySources propertySources = new MutablePropertySources(); propertySources.addFirst(propertySource); return bindSpringProfiles(propertySources); } private SpringProfiles bindSpringProfiles(PropertySources propertySources) { SpringProfiles springProfiles = new SpringProfiles(); RelaxedDataBinder dataBinder = new RelaxedDataBinder(springProfiles, "spring.profiles"); dataBinder.bind(new PropertySourcesPropertyValues(propertySources, false)); springProfiles.setActive(resolvePlaceholders(springProfiles.getActive())); springProfiles.setInclude(resolvePlaceholders(springProfiles.getInclude())); return springProfiles; } private List<String> resolvePlaceholders(List<String> values) { List<String> resolved = new ArrayList<String>(); for (String value : values) { resolved.add(this.environment.resolvePlaceholders(value)); } return resolved; } private void maybeActivateProfiles(Set<Profile> profiles) { if (this.activatedProfiles) { if (!profiles.isEmpty()) { this.logger.debug("Profiles already activated, '" + profiles + "' will not be applied"); } return; } if (!profiles.isEmpty()) { addProfiles(profiles); this.logger.debug("Activated profiles " + StringUtils.collectionToCommaDelimitedString(profiles)); this.activatedProfiles = true; removeUnprocessedDefaultProfiles(); } } private void removeUnprocessedDefaultProfiles() { for (Iterator<Profile> iterator = this.profiles.iterator(); iterator .hasNext();) { if (iterator.next().isDefaultProfile()) { iterator.remove(); } } } private void addProfiles(Set<Profile> profiles) { for (Profile profile : profiles) { this.profiles.add(profile); if (!environmentHasActiveProfile(profile.getName())) { // If it's already accepted we assume the order was set // intentionally prependProfile(this.environment, profile); } } } private boolean environmentHasActiveProfile(String profile) { for (String activeProfile : this.environment.getActiveProfiles()) { if (activeProfile.equals(profile)) { return true; } } return false; } private void prependProfile(ConfigurableEnvironment environment, Profile profile) { Set<String> profiles = new LinkedHashSet<String>(); environment.getActiveProfiles(); // ensure they are initialized // But this one should go first (last wins in a property key clash) profiles.add(profile.getName()); profiles.addAll(Arrays.asList(environment.getActiveProfiles())); environment.setActiveProfiles(profiles.toArray(new String[profiles.size()])); } private Set<String> getSearchLocations() { Set<String> locations = new LinkedHashSet<String>(); // User-configured settings take precedence, so we do them first if (this.environment.containsProperty(CONFIG_LOCATION_PROPERTY)) { for (String path : asResolvedSet( this.environment.getProperty(CONFIG_LOCATION_PROPERTY), null)) { if (!path.contains("$")) { path = StringUtils.cleanPath(path); if (!ResourceUtils.isUrl(path)) { path = ResourceUtils.FILE_URL_PREFIX + path; } } locations.add(path); } } locations.addAll( asResolvedSet(ConfigFileApplicationListener.this.searchLocations, DEFAULT_SEARCH_LOCATIONS)); return locations; } private Set<String> getSearchNames() { if (this.environment.containsProperty(CONFIG_NAME_PROPERTY)) { return asResolvedSet(this.environment.getProperty(CONFIG_NAME_PROPERTY), null); } return asResolvedSet(ConfigFileApplicationListener.this.names, DEFAULT_NAMES); } private Set<String> asResolvedSet(String value, String fallback) { List<String> list = Arrays.asList(StringUtils.trimArrayElements( StringUtils.commaDelimitedListToStringArray(value != null ? this.environment.resolvePlaceholders(value) : fallback))); Collections.reverse(list); return new LinkedHashSet<String>(list); } private void addConfigurationProperties(MutablePropertySources sources) { List<PropertySource<?>> reorderedSources = new ArrayList<PropertySource<?>>(); for (PropertySource<?> item : sources) { reorderedSources.add(item); } addConfigurationProperties( new ConfigurationPropertySources(reorderedSources)); } private void addConfigurationProperties( ConfigurationPropertySources configurationSources) { MutablePropertySources existingSources = this.environment .getPropertySources(); if (existingSources.contains(DEFAULT_PROPERTIES)) { existingSources.addBefore(DEFAULT_PROPERTIES, configurationSources); } else { existingSources.addLast(configurationSources); } } } private static class Profile { private final String name; private final boolean defaultProfile; Profile(String name) { this(name, false); } Profile(String name, boolean defaultProfile) { Assert.notNull(name, "Name must not be null"); this.name = name; this.defaultProfile = defaultProfile; } public String getName() { return this.name; } public boolean isDefaultProfile() { return this.defaultProfile; } @Override public String toString() { return this.name; } @Override public int hashCode() { return this.name.hashCode(); } @Override public boolean equals(Object obj) { if (obj == this) { return true; } if (obj == null || obj.getClass() != getClass()) { return false; } return ((Profile) obj).name.equals(this.name); } } /** * Holds the configuration {@link PropertySource}s as they are loaded can relocate * them once configuration classes have been processed. */ static class ConfigurationPropertySources extends EnumerablePropertySource<Collection<PropertySource<?>>> { private final Collection<PropertySource<?>> sources; private final String[] names; ConfigurationPropertySources(Collection<PropertySource<?>> sources) { super(APPLICATION_CONFIGURATION_PROPERTY_SOURCE_NAME, sources); this.sources = sources; List<String> names = new ArrayList<String>(); for (PropertySource<?> source : sources) { if (source instanceof EnumerablePropertySource) { names.addAll(Arrays.asList( ((EnumerablePropertySource<?>) source).getPropertyNames())); } } this.names = names.toArray(new String[names.size()]); } @Override public Object getProperty(String name) { for (PropertySource<?> propertySource : this.sources) { Object value = propertySource.getProperty(name); if (value != null) { return value; } } return null; } public static void finishAndRelocate(MutablePropertySources propertySources) { String name = APPLICATION_CONFIGURATION_PROPERTY_SOURCE_NAME; ConfigurationPropertySources removed = (ConfigurationPropertySources) propertySources .get(name); if (removed != null) { for (PropertySource<?> propertySource : removed.sources) { if (propertySource instanceof EnumerableCompositePropertySource) { EnumerableCompositePropertySource composite = (EnumerableCompositePropertySource) propertySource; for (PropertySource<?> nested : composite.getSource()) { propertySources.addAfter(name, nested); name = nested.getName(); } } else { propertySources.addAfter(name, propertySource); } } propertySources.remove(APPLICATION_CONFIGURATION_PROPERTY_SOURCE_NAME); } } @Override public String[] getPropertyNames() { return this.names; } } /** * Holder for {@code spring.profiles} properties. */ static final class SpringProfiles { private List<String> active = new ArrayList<String>(); private List<String> include = new ArrayList<String>(); public List<String> getActive() { return this.active; } public void setActive(List<String> active) { this.active = active; } public List<String> getInclude() { return this.include; } public void setInclude(List<String> include) { this.include = include; } Set<Profile> getActiveProfiles() { return asProfileSet(this.active); } Set<Profile> getIncludeProfiles() { return asProfileSet(this.include); } private Set<Profile> asProfileSet(List<String> profileNames) { List<Profile> profiles = new ArrayList<Profile>(); for (String profileName : profileNames) { profiles.add(new Profile(profileName)); } Collections.reverse(profiles); return new LinkedHashSet<Profile>(profiles); } }}根据javadoc注释的说明，这个类会从指定的位置加载application.properties或者application.yml并将它们的属性读到Envrionment当中，其中这几个方法大家关注下：
@Override public void onApplicationEvent(ApplicationEvent event) { if (event instanceof ApplicationEnvironmentPreparedEvent) { onApplicationEnvironmentPreparedEvent( (ApplicationEnvironmentPreparedEvent) event); } if (event instanceof ApplicationPreparedEvent) { onApplicationPreparedEvent(event); } } 当springboot程序启动时一定会触发该事件监听，如果当前是 ApplicationEnvironmentPreparedEvent事件就会调用 onApplicationEnvironmentPreparedEvent方法，最终该方法会执行：
@Override public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) { addPropertySources(environment, application.getResourceLoader()); configureIgnoreBeanInfo(environment); bindToSpringApplication(environment, application); }其中 bindToSpringApplication方法为：
/** * Bind the environment to the {@link SpringApplication}. * @param environment the environment to bind * @param application the application to bind to */ protected void bindToSpringApplication(ConfigurableEnvironment environment, SpringApplication application) { PropertiesConfigurationFactory<SpringApplication> binder = new PropertiesConfigurationFactory<SpringApplication>( application); binder.setTargetName("spring.main"); binder.setConversionService(this.conversionService); binder.setPropertySources(environment.getPropertySources()); try { binder.bindPropertiesToTarget(); } catch (BindException ex) { throw new IllegalStateException("Cannot bind to SpringApplication", ex); } }很明显该方法是将Environment绑定到对应SpringApplication上，通过这个类就可以获取到我们更改过后的配置了
1.3、changes方法
private Map<String, Object> changes(Map<String, Object> before, Map<String, Object> after) { Map<String, Object> result = new HashMap<String, Object>(); for (String key : before.keySet()) { if (!after.containsKey(key)) { result.put(key, null); } else if (!equal(before.get(key), after.get(key))) { result.put(key, after.get(key)); } } for (String key : after.keySet()) { if (!before.containsKey(key)) { result.put(key, after.get(key)); } } return result; }changes方法其实就是处理配置变更信息的，分以下几种情况：
1）如果刷新过后配置文件新增配置就添加到Map里
2) 如果有配置变更就添加变更后的配置
3) 如果删除了原先的配置，就把原先的key对应的值设置为null
至此经过changes方法后，上下文环境已经拥有最新的配置了。
1.4、发布事件
当上述步骤都执行完毕后，紧接着会发布EnvrionmentChangeEvent事件，可是这个事件谁来监听呢？在这里我贴出官网的一段描述：
应用程序将收听EnvironmentChangeEvent，并以几种标准方式进行更改（用户可以以常规方式添加ApplicationListeners附加ApplicationListeners）。当观察到EnvironmentChangeEvent时，它将有一个已更改的键值列表，应用程序将使用以下内容：
1.重新绑定上下文中的任何@ConfigurationProperties bean
2.为logging.level.*中的任何属性设置记录器级别
根据官网描述我们知道将变更一下操作行为@ConfigurationProperties的bean与更改日志level，那么如何做到的呢？结合官网文档我们来关注以下两个类：
ConfigurationPropertiesRebinder:
/* * Copyright 2013-2014 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.cloud.context.properties;import java.util.HashSet;import java.util.Map;import java.util.Set;import java.util.concurrent.ConcurrentHashMap;import org.springframework.aop.framework.Advised;import org.springframework.aop.support.AopUtils;import org.springframework.beans.BeansException;import org.springframework.boot.context.properties.ConfigurationProperties;import org.springframework.cloud.context.config.annotation.RefreshScope;import org.springframework.cloud.context.environment.EnvironmentChangeEvent;import org.springframework.context.ApplicationContext;import org.springframework.context.ApplicationContextAware;import org.springframework.context.ApplicationListener;import org.springframework.core.env.Environment;import org.springframework.jmx.export.annotation.ManagedAttribute;import org.springframework.jmx.export.annotation.ManagedOperation;import org.springframework.jmx.export.annotation.ManagedResource;import org.springframework.stereotype.Component;/** * Listens for {@link EnvironmentChangeEvent} and rebinds beans that were bound to the * {@link Environment} using {@link ConfigurationProperties * <code>@ConfigurationProperties</code>}. When these beans are re-bound and * re-initialized the changes are available immediately to any component that is using the * <code>@ConfigurationProperties</code> bean. * * @see RefreshScope for a deeper and optionally more focused refresh of bean components * * @author Dave Syer * */@Component@ManagedResourcepublic class ConfigurationPropertiesRebinder implements ApplicationContextAware, ApplicationListener<EnvironmentChangeEvent> { private ConfigurationPropertiesBeans beans; private ApplicationContext applicationContext; private Map<String, Exception> errors = new ConcurrentHashMap<>(); public ConfigurationPropertiesRebinder(ConfigurationPropertiesBeans beans) { this.beans = beans; } @Override public void setApplicationContext(ApplicationContext applicationContext) throws BeansException { this.applicationContext = applicationContext; } /** * A map of bean name to errors when instantiating the bean. * * @return the errors accumulated since the latest destroy */ public Map<String, Exception> getErrors() { return this.errors; } @ManagedOperation public void rebind() { this.errors.clear(); for (String name : this.beans.getBeanNames()) { rebind(name); } } @ManagedOperation public boolean rebind(String name) { if (!this.beans.getBeanNames().contains(name)) { return false; } if (this.applicationContext != null) { try { Object bean = this.applicationContext.getBean(name); if (AopUtils.isAopProxy(bean)) { bean = getTargetObject(bean); } this.applicationContext.getAutowireCapableBeanFactory().destroyBean(bean); this.applicationContext.getAutowireCapableBeanFactory() .initializeBean(bean, name); return true; } catch (RuntimeException e) { this.errors.put(name, e); throw e; } } return false; } @SuppressWarnings("unchecked") private static <T> T getTargetObject(Object candidate) { try { if (AopUtils.isAopProxy(candidate) && (candidate instanceof Advised)) { return (T) ((Advised) candidate).getTargetSource().getTarget(); } } catch (Exception ex) { throw new IllegalStateException("Failed to unwrap proxied object", ex); } return (T) candidate; } @ManagedAttribute public Set<String> getBeanNames() { return new HashSet<String>(this.beans.getBeanNames()); } @Override public void onApplicationEvent(EnvironmentChangeEvent event) { if (this.applicationContext.equals(event.getSource()) // Backwards compatible || event.getKeys().equals(event.getSource())) { rebind(); } }}我们可以看到该类监听了ChangeEnvrionmentEvent事件，它最主要作用是拿到更新的配置以后，重新绑定@ConfigurationProperties标记的类使之能够读取最新的属性
LoggingRebinder:
/* * Copyright 2013-2014 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.cloud.logging;import java.util.Map;import java.util.Map.Entry;import org.apache.commons.logging.Log;import org.apache.commons.logging.LogFactory;import org.springframework.boot.bind.RelaxedPropertyResolver;import org.springframework.boot.logging.LogLevel;import org.springframework.boot.logging.LoggingSystem;import org.springframework.cloud.context.environment.EnvironmentChangeEvent;import org.springframework.context.ApplicationListener;import org.springframework.context.EnvironmentAware;import org.springframework.core.env.Environment;/** * Listener that looks for {@link EnvironmentChangeEvent} and rebinds logger levels if any * changed. * * @author Dave Syer * */public class LoggingRebinder implements ApplicationListener<EnvironmentChangeEvent>, EnvironmentAware { private final Log logger = LogFactory.getLog(getClass()); private Environment environment; @Override public void setEnvironment(Environment environment) { this.environment = environment; } @Override public void onApplicationEvent(EnvironmentChangeEvent event) { if (this.environment == null) { return; } LoggingSystem system = LoggingSystem.get(LoggingSystem.class.getClassLoader()); setLogLevels(system, this.environment); } protected void setLogLevels(LoggingSystem system, Environment environment) { Map<String, Object> levels = new RelaxedPropertyResolver(environment) .getSubProperties("logging.level."); for (Entry<String, Object> entry : levels.entrySet()) { setLogLevel(system, environment, entry.getKey(), entry.getValue().toString()); } } private void setLogLevel(LoggingSystem system, Environment environment, String name, String level) { try { if (name.equalsIgnoreCase("root")) { name = null; } level = environment.resolvePlaceholders(level); system.setLogLevel(name, LogLevel.valueOf(level.toUpperCase())); } catch (RuntimeException ex) { this.logger.error("Cannot set level: " + level + " for '" + name + "'"); } }}该类也是监听了ChangeEnvrionmentEvent事件，用于重新绑定日志级别
二、刷新范围
我们考虑如下场景，当我们变更数据库配置后，通过refresh刷新，虽然能获取到最新的配置，可是我们的DataSource对象早就被初始化好了，换句话说即便配置刷新了我们拿到的依然是配置刷新前的对象。怎么解决这个问题呢？
我们继续看ContextRefresher的refresh方法，最后有一处代码值得我们关注一下this.scope.refreshAll()，此处scope对象是RefreshScope类型，那么这个类有什么作用呢？那么我们先要关注一下@RefreshScope注解。在这里我在贴出官网一段解释：
当配置更改时，标有@RefreshScope的Spring @Bean将得到特殊处理。这解决了状态bean在初始化时只注入配置的问题。例如，如果通过Environment更改数据库URL时DataSource有开放连接，那么我们可能希望这些连接的持有人能够完成他们正在做的工作。然后下一次有人从游泳池借用一个连接，他得到一个新的URL
刷新范围bean是在使用时初始化的懒惰代理（即当调用一个方法时），并且作用域作为初始值的缓存。要强制bean重新初始化下一个方法调用，您只需要使其缓存条目无效。RefreshScope是上下文中的一个bean，它有一个公共方法refreshAll()来清除目标缓存中的范围内的所有bean。还有一个refresh(String)方法可以按名称刷新单个bean。此功能在/refresh端点（通过HTTP或JMX）中公开。
这里我贴出@RefreshScope源码：
/* * Copyright 2013-2014 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.cloud.context.config.annotation;import java.lang.annotation.Documented;import java.lang.annotation.ElementType;import java.lang.annotation.Retention;import java.lang.annotation.RetentionPolicy;import java.lang.annotation.Target;import org.springframework.context.annotation.Scope;import org.springframework.context.annotation.ScopedProxyMode;/** * Convenience annotation to put a <code>@Bean</code> definition in * {@link org.springframework.cloud.context.scope.refresh.RefreshScope refresh scope}. * Beans annotated this way can be refreshed at runtime and any components that are using * them will get a new instance on the next method call, fully initialized and injected * with all dependencies. * * @author Dave Syer * */@Target({ ElementType.TYPE, ElementType.METHOD })@Retention(RetentionPolicy.RUNTIME)@Scope("refresh")@Documentedpublic @interface RefreshScope { /** * @see Scope#proxyMode() */ ScopedProxyMode proxyMode() default ScopedProxyMode.TARGET_CLASS;}在这个注解上我们关注一下此处标记了@Scope("refresh")，我们知道Spring的Bean属性有个叫scope的，它定义了bean的作用范围，常见的有singleon,prototype,session等。此处新定义了一个范围叫做refresh，在此我贴出RefreshScope的源代码来分析一下：
/* * Copyright 2002-2009 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.cloud.context.scope.refresh;import java.io.Serializable;import org.springframework.beans.BeansException;import org.springframework.beans.factory.config.BeanDefinition;import org.springframework.beans.factory.support.BeanDefinitionRegistry;import org.springframework.cloud.context.scope.GenericScope;import org.springframework.context.ApplicationContext;import org.springframework.context.ApplicationContextAware;import org.springframework.context.event.ContextRefreshedEvent;import org.springframework.context.event.EventListener;import org.springframework.core.Ordered;import org.springframework.jmx.export.annotation.ManagedOperation;import org.springframework.jmx.export.annotation.ManagedResource;/** * <p> * A Scope implementation that allows for beans to be refreshed dynamically at runtime * (see {@link #refresh(String)} and {@link #refreshAll()}). If a bean is refreshed then * the next time the bean is accessed (i.e. a method is executed) a new instance is * created. All lifecycle methods are applied to the bean instances, so any destruction * callbacks that were registered in the bean factory are called when it is refreshed, and * then the initialization callbacks are invoked as normal when the new instance is * created. A new bean instance is created from the original bean definition, so any * externalized content (property placeholders or expressions in string literals) is * re-evaluated when it is created. * </p> * * <p> * Note that all beans in this scope are <em>only</em> initialized when first accessed, so * the scope forces lazy initialization semantics. The implementation involves creating a * proxy for every bean in the scope, so there is a flag * {@link #setProxyTargetClass(boolean) proxyTargetClass} which controls the proxy * creation, defaulting to JDK dynamic proxies and therefore only exposing the interfaces * implemented by a bean. If callers need access to other methods then the flag needs to * be set (and CGLib present on the classpath). Because this scope automatically proxies * all its beans, there is no need to add <code><aop:auto-proxy/></code> to any bean * definitions. * </p> * * <p> * The scoped proxy approach adopted here has a side benefit that bean instances are * automatically {@link Serializable}, and can be sent across the wire as long as the * receiver has an identical application context on the other side. To ensure that the two * contexts agree that they are identical they have to have the same serialization id. One * will be generated automatically by default from the bean names, so two contexts with * the same bean names are by default able to exchange beans by name. If you need to * override the default id then provide an explicit {@link #setId(String) id} when the * Scope is declared. * </p> * * @author Dave Syer * * @since 3.1 * */@ManagedResourcepublic class RefreshScope extends GenericScope implements ApplicationContextAware, Ordered { private ApplicationContext context; private BeanDefinitionRegistry registry; private boolean eager = true; private int order = Ordered.LOWEST_PRECEDENCE - 100; /** * Create a scope instance and give it the default name: "refresh". */ public RefreshScope() { super.setName("refresh"); } @Override public int getOrder() { return this.order; } public void setOrder(int order) { this.order = order; } /** * Flag to determine whether all beans in refresh scope should be instantiated eagerly * on startup. Default true. * * @param eager the flag to set */ public void setEager(boolean eager) { this.eager = eager; } @Override public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException { this.registry = registry; super.postProcessBeanDefinitionRegistry(registry); } @EventListener public void start(ContextRefreshedEvent event) { if (event.getApplicationContext() == this.context && this.eager && this.registry != null) { eagerlyInitialize(); } } private void eagerlyInitialize() { for (String name : this.context.getBeanDefinitionNames()) { BeanDefinition definition = this.registry.getBeanDefinition(name); if (this.getName().equals(definition.getScope()) && !definition.isLazyInit()) { Object bean = this.context.getBean(name); if (bean != null) { bean.getClass(); } } } } @ManagedOperation(description = "Dispose of the current instance of bean name provided and force a refresh on next method execution.") public boolean refresh(String name) { if (!name.startsWith(SCOPED_TARGET_PREFIX)) { // User wants to refresh the bean with this name but that isn't the one in the // cache... name = SCOPED_TARGET_PREFIX + name; } // Ensure lifecycle is finished if bean was disposable if (super.destroy(name)) { this.context.publishEvent(new RefreshScopeRefreshedEvent(name)); return true; } return false; } @ManagedOperation(description = "Dispose of the current instance of all beans in this scope and force a refresh on next method execution.") public void refreshAll() { super.destroy(); this.context.publishEvent(new RefreshScopeRefreshedEvent()); } @Override public void setApplicationContext(ApplicationContext context) throws BeansException { this.context = context; }}该类继承了GenericScope：
/* * Copyright 2002-2009 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.cloud.context.scope;import java.lang.reflect.Method;import java.util.ArrayList;import java.util.Arrays;import java.util.Collection;import java.util.Collections;import java.util.LinkedHashSet;import java.util.List;import java.util.Map;import java.util.UUID;import java.util.concurrent.ConcurrentHashMap;import java.util.concurrent.ConcurrentMap;import java.util.concurrent.locks.Lock;import java.util.concurrent.locks.ReadWriteLock;import java.util.concurrent.locks.ReentrantReadWriteLock;import org.aopalliance.intercept.MethodInterceptor;import org.aopalliance.intercept.MethodInvocation;import org.apache.commons.logging.Log;import org.apache.commons.logging.LogFactory;import org.springframework.aop.framework.Advised;import org.springframework.aop.scope.ScopedObject;import org.springframework.aop.scope.ScopedProxyFactoryBean;import org.springframework.aop.support.AopUtils;import org.springframework.beans.BeansException;import org.springframework.beans.factory.BeanFactory;import org.springframework.beans.factory.DisposableBean;import org.springframework.beans.factory.ObjectFactory;import org.springframework.beans.factory.config.BeanDefinition;import org.springframework.beans.factory.config.BeanFactoryPostProcessor;import org.springframework.beans.factory.config.ConfigurableListableBeanFactory;import org.springframework.beans.factory.config.Scope;import org.springframework.beans.factory.support.BeanDefinitionRegistry;import org.springframework.beans.factory.support.BeanDefinitionRegistryPostProcessor;import org.springframework.beans.factory.support.DefaultListableBeanFactory;import org.springframework.beans.factory.support.RootBeanDefinition;import org.springframework.expression.Expression;import org.springframework.expression.ExpressionParser;import org.springframework.expression.ParseException;import org.springframework.expression.spel.standard.SpelExpressionParser;import org.springframework.expression.spel.support.StandardEvaluationContext;import org.springframework.util.ReflectionUtils;import org.springframework.util.StringUtils;/** * <p> * A generic Scope implementation. * </p> * * @author Dave Syer * * @since 3.1 * */public class GenericScope implements Scope, BeanFactoryPostProcessor, BeanDefinitionRegistryPostProcessor, DisposableBean { private static final Log logger = LogFactory.getLog(GenericScope.class); public static final String SCOPED_TARGET_PREFIX = "scopedTarget."; private BeanLifecycleWrapperCache cache = new BeanLifecycleWrapperCache( new StandardScopeCache()); private String name = "generic"; private ConfigurableListableBeanFactory beanFactory; private StandardEvaluationContext evaluationContext; private String id; private Map<String, Exception> errors = new ConcurrentHashMap<>(); private ConcurrentMap<String, ReadWriteLock> locks = new ConcurrentHashMap<>(); /** * Manual override for the serialization id that will be used to identify the bean * factory. The default is a unique key based on the bean names in the bean factory. * * @param id the id to set */ public void setId(String id) { this.id = id; } /** * The name of this scope. Default "generic". * * @param name the name value to set */ public void setName(String name) { this.name = name; } /** * The cache implementation to use for bean instances in this scope. * * @param cache the cache to use */ public void setScopeCache(ScopeCache cache) { this.cache = new BeanLifecycleWrapperCache(cache); } /** * A map of bean name to errors when instantiating the bean. * * @return the errors accumulated since the latest destroy */ public Map<String, Exception> getErrors() { return this.errors; } @Override public void destroy() { List<Throwable> errors = new ArrayList<Throwable>(); Collection<BeanLifecycleWrapper> wrappers = this.cache.clear(); for (BeanLifecycleWrapper wrapper : wrappers) { try { Lock lock = locks.get(wrapper.getName()).writeLock(); lock.lock(); try { wrapper.destroy(); } finally { lock.unlock(); } } catch (RuntimeException e) { errors.add(e); } } if (!errors.isEmpty()) { throw wrapIfNecessary(errors.get(0)); } this.errors.clear(); } /** * Destroy the named bean (i.e. flush it from the cache by default). * * @param name the bean name to flush * @return true if the bean was already cached, false otherwise */ protected boolean destroy(String name) { BeanLifecycleWrapper wrapper = this.cache.remove(name); if (wrapper != null) { Lock lock = locks.get(wrapper.getName()).writeLock(); lock.lock(); try { wrapper.destroy(); } finally { lock.unlock(); } this.errors.remove(name); return true; } return false; } @Override public Object get(String name, ObjectFactory<?> objectFactory) { BeanLifecycleWrapper value = this.cache.put(name, new BeanLifecycleWrapper(name, objectFactory)); locks.putIfAbsent(name, new ReentrantReadWriteLock()); try { return value.getBean(); } catch (RuntimeException e) { this.errors.put(name, e); throw e; } } @Override public String getConversationId() { return this.name; } @Override public void registerDestructionCallback(String name, Runnable callback) { BeanLifecycleWrapper value = this.cache.get(name); if (value == null) { return; } value.setDestroyCallback(callback); } @Override public Object remove(String name) { BeanLifecycleWrapper value = this.cache.remove(name); if (value == null) { return null; } // Someone might have added another object with the same key, but we // keep the method contract by removing the // value we found anyway return value.getBean(); } @Override public Object resolveContextualObject(String key) { Expression expression = parseExpression(key); return expression.getValue(this.evaluationContext, this.beanFactory); } private Expression parseExpression(String input) { if (StringUtils.hasText(input)) { ExpressionParser parser = new SpelExpressionParser(); try { return parser.parseExpression(input); } catch (ParseException e) { throw new IllegalArgumentException("Cannot parse expression: " + input, e); } } else { return null; } } @Override public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException { this.beanFactory = beanFactory; beanFactory.registerScope(this.name, this); setSerializationId(beanFactory); } @Override public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException { for (String name : registry.getBeanDefinitionNames()) { BeanDefinition definition = registry.getBeanDefinition(name); if (definition instanceof RootBeanDefinition) { RootBeanDefinition root = (RootBeanDefinition) definition; if (root.getDecoratedDefinition() != null && root.hasBeanClass() && root.getBeanClass() == ScopedProxyFactoryBean.class) { if (getName().equals(root.getDecoratedDefinition().getBeanDefinition() .getScope())) { root.setBeanClass(LockedScopedProxyFactoryBean.class); } } } } } /** * If the bean factory is a DefaultListableBeanFactory then it can serialize scoped * beans and deserialize them in another context (even in another JVM), as long as the * ids of the bean factories match. This method sets up the serialization id to be * either the id provided to the scope instance, or if that is null, a hash of all the * bean names. * * @param beanFactory the bean factory to configure */ private void setSerializationId(ConfigurableListableBeanFactory beanFactory) { if (beanFactory instanceof DefaultListableBeanFactory) { String id = this.id; if (id == null) { List<String> list = new ArrayList<>( Arrays.asList(beanFactory.getBeanDefinitionNames())); Collections.sort(list); String names = list.toString(); logger.debug("Generating bean factory id from names: " + names); id = UUID.nameUUIDFromBytes(names.getBytes()).toString(); } logger.info("BeanFactory id=" + id); ((DefaultListableBeanFactory) beanFactory).setSerializationId(id); } else { logger.warn( "BeanFactory was not a DefaultListableBeanFactory, scoped proxy beans " + "cannot be serialized."); } } static RuntimeException wrapIfNecessary(Throwable throwable) { if (throwable instanceof RuntimeException) { return (RuntimeException) throwable; } if (throwable instanceof Error) { throw (Error) throwable; } return new IllegalStateException(throwable); } protected String getName() { return this.name; } private static class BeanLifecycleWrapperCache { private final ScopeCache cache; public BeanLifecycleWrapperCache(ScopeCache cache) { this.cache = cache; } public BeanLifecycleWrapper remove(String name) { return (BeanLifecycleWrapper) this.cache.remove(name); } public Collection<BeanLifecycleWrapper> clear() { Collection<Object> values = this.cache.clear(); Collection<BeanLifecycleWrapper> wrappers = new LinkedHashSet<BeanLifecycleWrapper>(); for (Object object : values) { wrappers.add((BeanLifecycleWrapper) object); } return wrappers; } public BeanLifecycleWrapper get(String name) { return (BeanLifecycleWrapper) this.cache.get(name); } public BeanLifecycleWrapper put(String name, BeanLifecycleWrapper value) { return (BeanLifecycleWrapper) this.cache.put(name, value); } } /** * Wrapper for a bean instance and any destruction callback (DisposableBean etc.) that * is registered for it. Also decorates the bean to optionally guard it from * concurrent access (for instance). * * @author Dave Syer * */ private static class BeanLifecycleWrapper { private Object bean; private Runnable callback; private final String name; private final ObjectFactory<?> objectFactory; public BeanLifecycleWrapper(String name, ObjectFactory<?> objectFactory) { this.name = name; this.objectFactory = objectFactory; } public String getName() { return this.name; } public void setDestroyCallback(Runnable callback) { this.callback = callback; } public Object getBean() { if (this.bean == null) { synchronized (this.name) { if (this.bean == null) { this.bean = this.objectFactory.getObject(); } } } return this.bean; } public void destroy() { if (this.callback == null) { return; } synchronized (this.name) { Runnable callback = this.callback; if (callback != null) { callback.run(); } this.callback = null; this.bean = null; } } @Override public int hashCode() { final int prime = 31; int result = 1; result = prime * result + ((this.name == null) ? 0 : this.name.hashCode()); return result; } @Override public boolean equals(Object obj) { if (this == obj) { return true; } if (obj == null) { return false; } if (getClass() != obj.getClass()) { return false; } BeanLifecycleWrapper other = (BeanLifecycleWrapper) obj; if (this.name == null) { if (other.name != null) { return false; } } else if (!this.name.equals(other.name)) { return false; } return true; } } @SuppressWarnings("serial") public class LockedScopedProxyFactoryBean extends ScopedProxyFactoryBean implements MethodInterceptor { private String targetBeanName; @Override public void setBeanFactory(BeanFactory beanFactory) { super.setBeanFactory(beanFactory); Object proxy = getObject(); if (proxy instanceof Advised) { Advised advised = (Advised) proxy; advised.addAdvice(0, this); } } @Override public void setTargetBeanName(String targetBeanName) { super.setTargetBeanName(targetBeanName); this.targetBeanName = targetBeanName; } @Override public Object invoke(MethodInvocation invocation) throws Throwable { Method method = invocation.getMethod(); if (AopUtils.isEqualsMethod(method) || AopUtils.isToStringMethod(method) || AopUtils.isHashCodeMethod(method) || isScopedObjectGetTargetObject(method)) { return invocation.proceed(); } Object proxy = getObject(); Lock lock = locks.get(this.targetBeanName).readLock(); lock.lock(); try { if (proxy instanceof Advised) { Advised advised = (Advised) proxy; ReflectionUtils.makeAccessible(method); return ReflectionUtils.invokeMethod(method, advised.getTargetSource().getTarget(), invocation.getArguments()); } return invocation.proceed(); } finally { lock.unlock(); } } private boolean isScopedObjectGetTargetObject(Method method) { return method.getDeclaringClass().equals(ScopedObject.class) && method.getName().equals("getTargetObject") && method.getParameterTypes().length == 0; } }}这里面我们先看一下RefreshScope的构造函数：
/** * Create a scope instance and give it the default name: "refresh". */ public RefreshScope() { super.setName("refresh"); }这里面创建了一个名字为refresh的scope。
紧接着在它的父类里我们可以看一下这个方法：
@Override public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException { this.beanFactory = beanFactory; beanFactory.registerScope(this.name, this); setSerializationId(beanFactory); }此方法中使用BeanFactory注册了一个refresh的范围，使得scope为refresh的bean生效。@RefreshScope标注的类还有一个特点：会使用代理对象并进行延迟加载。我们来看一下postProcessBeanDefinitionRegistry方法
@Override public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException { for (String name : registry.getBeanDefinitionNames()) { BeanDefinition definition = registry.getBeanDefinition(name); if (definition instanceof RootBeanDefinition) { RootBeanDefinition root = (RootBeanDefinition) definition; if (root.getDecoratedDefinition() != null && root.hasBeanClass() && root.getBeanClass() == ScopedProxyFactoryBean.class) { if (getName().equals(root.getDecoratedDefinition().getBeanDefinition() .getScope())) { root.setBeanClass(LockedScopedProxyFactoryBean.class); } } } } }该方法遍历所有的bean定义 如果当前的bean的scope为refresh,那么就把当前的bean设置为 LockedScopedProxyFactoryBean的代理对象。
RefreshScope还会监听一个ContextRefreshedEvent，该事件会在ApplicationContext初始化或者refreshed时触发，我们来看一下代码：
@EventListener public void start(ContextRefreshedEvent event) { if (event.getApplicationContext() == this.context && this.eager && this.registry != null) { eagerlyInitialize(); } } private void eagerlyInitialize() { for (String name : this.context.getBeanDefinitionNames()) { BeanDefinition definition = this.registry.getBeanDefinition(name); if (this.getName().equals(definition.getScope()) && !definition.isLazyInit()) { Object bean = this.context.getBean(name); if (bean != null) { bean.getClass(); } } } }注意此处获取refreshscope的bean，其中getBean是一个复杂而又繁琐的过程，此处我们先不在这里讨论，只不过经过这个方法以后，其通过代理机制会在GernericScope的BeanLifecycleWrapperCache缓存里把这个@RefreshScope标记的bean添加进去。
最后我们回过头来看一看RefreshScope的refreshAll方法：
@ManagedOperation(description = "Dispose of the current instance of all beans in this scope and force a refresh on next method execution.") public void refreshAll() { super.destroy(); this.context.publishEvent(new RefreshScopeRefreshedEvent()); }//.......GernericScope的destroy方法 @Override public void destroy() { List<Throwable> errors = new ArrayList<Throwable>(); Collection<BeanLifecycleWrapper> wrappers = this.cache.clear(); for (BeanLifecycleWrapper wrapper : wrappers) { try { Lock lock = locks.get(wrapper.getName()).writeLock(); lock.lock(); try { wrapper.destroy(); } finally { lock.unlock(); } } catch (RuntimeException e) { errors.add(e); } } if (!errors.isEmpty()) { throw wrapIfNecessary(errors.get(0)); } this.errors.clear(); }这里的代码逻辑很简单清除与释放缓存里被@RefreshScope标记的bean 。
当我们要获取对象时，我们可以关注如下方法：
@Override public Object get(String name, ObjectFactory<?> objectFactory) { BeanLifecycleWrapper value = this.cache.put(name, new BeanLifecycleWrapper(name, objectFactory)); locks.putIfAbsent(name, new ReentrantReadWriteLock()); try { return value.getBean(); } catch (RuntimeException e) { this.errors.put(name, e); throw e; } } //..... BeanLifecycleWrapper的方法 public Object getBean() { if (this.bean == null) { synchronized (this.name) { if (this.bean == null) { this.bean = this.objectFactory.getObject(); } } } return this.bean; } BeanLifecycleWrapper这个是@RefreshScope标记bean的一个包装类，会被存储到缓存里，在这里取不到值的话就会从objectFactory里去拿
三、示例与总结
3.1、示例
创建AppConfig类代码如下：
package com.bdqn.lyrk.refresh.scope.server;import org.springframework.boot.context.properties.EnableConfigurationProperties;import org.springframework.cloud.context.config.annotation.RefreshScope;import org.springframework.context.annotation.Bean;import org.springframework.context.annotation.Configuration;@Configuration@EnableConfigurationProperties(StudentConfig.class)public class AppConfig { @RefreshScope @Bean public Student student(StudentConfig config) { Student student = new Student(); student.setName(config.getName()); return student; }}在这里，将Student设置为@RefreshScope 那么刷新以后会获取最新的Bean
启动类：
package com.bdqn.lyrk.refresh.scope.server;import org.springframework.beans.factory.annotation.Autowired;import org.springframework.boot.SpringApplication;import org.springframework.boot.autoconfigure.SpringBootApplication;import org.springframework.web.bind.annotation.GetMapping;import org.springframework.web.bind.annotation.RestController;@SpringBootApplication@RestControllerpublic class RefreshScopeApplication { @Autowired private Student student; @GetMapping public String student() { return student.getName(); } public static void main(String[] args) throws InterruptedException { SpringApplication.run(RefreshScopeApplication.class, args); }}application.yml文件：
spring: application: name: refresh-scope-serverendpoints: refresh: sensitive: falseserver: port: 8089student: name: admin
这里把refresh端点开放出来，然后变更配置后就可以获取最新的对象了
3.2、总结
1) 当配置更新并通过refresh端点刷新后，会执行ContextRefresher的refresh方法，该方法会记录当前的Environment，而后构建一个简易的SpringApplicationBuilder并执行其run方法，此时ConfigFileApplicationListener会读取我们修改过后的配置并绑定到SpringApplication对象上，最后进行changes操作来变更已有的PropertySource
2) @RefreshScope最好配合@Bean使用，当且仅当变更配置后，需要重新获取最新的bean时使用。加上该注解的Bean会被代理并且延迟加载，所有的scope属性为Refresh的bean会被包装成BeanLifecycleWrapper存入缓存(ConcurrentHashMap)中,所有的读取，修改，删除都是基于该缓存的。
总结
以上所述是小编给大家介绍的SpringCloud配置刷新原理解析，希望对大家有所帮助，如果大家有任何疑问欢迎给我留言，小编会及时回复大家的！