SpringCloud配置刷新原理解析

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)
@ManagedResource
public 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 *)
   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
@ManagedResource
public 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")
@Documented
public @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>&lt;aop:auto-proxy/&gt;</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
 *
 */
@ManagedResource
public 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
@RestController
public 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-server
endpoints:
 refresh:
 sensitive: false
server:
 port: 8089
student:
 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！

原文链接：http://www.cnblogs.com/niechen/p/8979578.html