死磕源码系列【ConfigFileApplicationListener监听器源码解析】

桃扇骨 2022-12-18 00:46 174阅读 0赞

> ConfigFileApplicationListener监听器主要用来处理环境配置相关业务，其加载是在springboot启动时通过SPI方式获取（之前的文章已经将结果）；

ConfigFileApplicationListener监听器类继承SmartApplicationListener接口实现了supportsEventType方法，判定监听器实际上支持的时间类型：

@Override
    	public boolean supportsEventType(Class<? extends ApplicationEvent> eventType) { 
    		return ApplicationEnvironmentPreparedEvent.class.isAssignableFrom(eventType)
    				|| ApplicationPreparedEvent.class.isAssignableFrom(eventType);
    	}

监听器支持ApplicationEnvironmentPreparedEvent、ApplicationPreparedEvent事件，其中ApplicationEnvironmentPreparedEvent事件是在SpringApplication\#prepareEnvironment方法中通过listeners.environmentPrepared(environment)触发，ApplicationPreparedEvent事件是在SpringApplication\#prepareContext方法中通过listeners.contextLoaded(context)触发；

##### 看下事件发生时触发的方法onApplicationEvent（此方法是监听器类业务处理的入口）： #####

@Override
    	public void onApplicationEvent(ApplicationEvent event) { 
        //事件会在应用程序启动后准备Environment环境时触发
    		if (event instanceof ApplicationEnvironmentPreparedEvent) { 
    			onApplicationEnvironmentPreparedEvent((ApplicationEnvironmentPreparedEvent) event);
    		}
        //时间会在应用程序已经启动，ApplicationContext已经准备好，但是还未调用refreshed方式时触发
    		if (event instanceof ApplicationPreparedEvent) { 
    			onApplicationPreparedEvent(event);
    		}
    	}

--------------------

先看ApplicationEnvironmentPreparedEvent时间分支，这个时间主要是用来加载properties及yml配置文件的业务处理；

##### onApplicationEnvironmentPreparedEvent方法处理与环境相关的bean后置处理器： #####

private void onApplicationEnvironmentPreparedEvent(ApplicationEnvironmentPreparedEvent event) { 
        //通过SPI的方式加载环境相关EnvironmentPostProcessor后置处理器
    		List<EnvironmentPostProcessor> postProcessors = loadPostProcessors();
        //因为ConfigFileApplicationListener监听器也实现了EnvironmentPostProcessor
        //所以也将当前类加入列表中
    		postProcessors.add(this);
        //对EnvironmentPostProcessor实现类按照优先级排序
    		AnnotationAwareOrderComparator.sort(postProcessors);
        //循环调用EnvironmentPostProcessor实现类的回调方法
    		for (EnvironmentPostProcessor postProcessor : postProcessors) { 
    			postProcessor.postProcessEnvironment(event.getEnvironment(), event.getSpringApplication());
    		}
    	}

loadPostProcessors方法通过springboot SPI加载EnvironmentPostProcessor配置：

List<EnvironmentPostProcessor> loadPostProcessors() { 
    		return SpringFactoriesLoader.loadFactories(EnvironmentPostProcessor.class, getClass().getClassLoader());
    	}

spring.factories中EnvironmentPostProcessor环境相关后置处理器配置如下：

# Environment Post Processors
    org.springframework.boot.env.EnvironmentPostProcessor=\
    org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\
    org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor,\
    org.springframework.boot.env.SystemEnvironmentPropertySourceEnvironmentPostProcessor,\
    org.springframework.boot.reactor.DebugAgentEnvironmentPostProcessor

##### 现在我们只看ConfigFileApplicationListener监听器类作为EnvironmentPostProcessor实现类提供的回调方法postProcessEnvironment： #####

@Override
    	public void postProcessEnvironment(ConfigurableEnvironment environment, SpringApplication application) { 
        //添加配置文件属性源到指定的环境
    		addPropertySources(environment, application.getResourceLoader());
    	}

addPropertySources方法添加配置文件属性源到指定的环境：

protected void addPropertySources(ConfigurableEnvironment environment, ResourceLoader resourceLoader) { 
        //添加RandomValuePropertySource属性源配置到systemEnvironment环境配置之后
    		RandomValuePropertySource.addToEnvironment(environment);
        //加载候选配置源到环境属性源对象中
    		new Loader(environment, resourceLoader).load();
    	}

##### Loader类用来加载候选属性源及激活的配置文件，首先看下构造函数 #####

Loader(ConfigurableEnvironment environment, ResourceLoader resourceLoader) { 
        	//环境属性初始化
    			this.environment = environment;
    			this.placeholdersResolver = new PropertySourcesPlaceholdersResolver(this.environment);
    			//构造函数传递参数resourceLoader为null,所以三元运算符计算后的记过是DefaultResourceLoader
          //DefaultResourceLoader类实现了ResourceLoader接口
        	this.resourceLoader = (resourceLoader != null) ? resourceLoader : new DefaultResourceLoader(null);
         //通过SPI方式获取PropertySourceLoader加载接口的实现类PropertiesPropertySourceLoader、YamlPropertySourceLoader
    			this.propertySourceLoaders = SpringFactoriesLoader.loadFactories(PropertySourceLoader.class,
    					getClass().getClassLoader());
    		}

org.springframework.core.io.ResourceLoader接口加载classpath及file system下的资源配置文件，通常ApplicationContext需要这样的功能，DefaultResourceLoader是一个独立的实现在ApplicationContext之外使用的资源加载程序：

public interface ResourceLoader { 
    
    	/** 从类路径中加载的伪URL路径： "classpath:". */
    	String CLASSPATH_URL_PREFIX = ResourceUtils.CLASSPATH_URL_PREFIX;
    
    
    	/** * 返回指定资源位置的资源handle句柄 * handle句柄应该始终是可重用的在源描述符，允许多个 Resource#getInputStream（）调用。 * 必须支持完全限定的URL,例如："file:C:/test.dat" * 必须支持classpath类路径伪URL,例如："classpath:test.dat" * 应该支持相对文件路径,例如："WEB-INF/test.dat" * 这将是特定实现的，通常由ApplicationContext实现提供 * 注意：资源handle句柄并不意味着现有资源，你需要调用Resource#exists来检查是否存在 * @param 资源位置 * @return a corresponding Resource handle (never {@code null}) * @see #CLASSPATH_URL_PREFIX * @see Resource#exists() * @see Resource#getInputStream() */
    	Resource getResource(String location);
    
    	/** * 返回ResourceLoader资源加载器使用的类加载器 */
    	@Nullable
    	ClassLoader getClassLoader();
    
    }

ResourceLoader资源加载接口实现类DefaultResourceLoader，被ResourceEditor使用，通常服务于AbstractApplicationContext，也可以独立使用，在ConfigFileApplicationListener监听器中就属于独立应用（此处不再详解此类，后面会详解）。

通过SPI方式获取PropertySourceLoader加载程序的spring.factories配置是：

# PropertySource Loaders
    org.springframework.boot.env.PropertySourceLoader=\
    org.springframework.boot.env.PropertiesPropertySourceLoader,\
    org.springframework.boot.env.YamlPropertySourceLoader

##### Loader类的load方法是加载环境配置文件的核心方法 #####

void load() { 
          //PropertySource的内部实现类，被ConfigFileApplicationListener用于指定操作过滤出指定的属性配置
          //DEFAULT_PROPERTIES = "defaultProperties"
          //DEFAULT_PROPERTIES是Set集合，包含spring.profiles.active、spring.profiles.include
    			FilteredPropertySource.apply(this.environment, DEFAULT_PROPERTIES, LOAD_FILTERED_PROPERTY,
    					(defaultProperties) -> { 
                //候选配置文件后缀，如：application-test.properties指的是test
    						this.profiles = new LinkedList<>();
                //已经处理过的配置文件后缀，如：application-test.properties指的是test
    						this.processedProfiles = new LinkedList<>();
                //是否有激活的配置文件：spring.profiles.active
    						this.activatedProfiles = false;
                //存储从配置文件加载并解析后的配置文件
    						this.loaded = new LinkedHashMap<>();
                //初始化默认的profile配置
    						initializeProfiles();
    						while (!this.profiles.isEmpty()) { 
    							Profile profile = this.profiles.poll();
                  //判定是否是默认配置文件
    							if (isDefaultProfile(profile)) { 
    								addProfileToEnvironment(profile.getName());
    							}
                  //加载指定的配置文件并将加载的结果存入loaded属性中
    							load(profile, this::getPositiveProfileFilter,
    									addToLoaded(MutablePropertySources::addLast, false));
                  //添加已经处理过的配置
    							this.processedProfiles.add(profile);
    						}
    						load(null, this::getNegativeProfileFilter, addToLoaded(MutablePropertySources::addFirst, true));
                //将加载到的配置文件件属性配置添加到Environment环境
    						addLoadedPropertySources();
    						applyActiveProfiles(defaultProperties);
    					});
    		}

##### load方法加载配置文件 #####

private void load(String location, String name, Profile profile, DocumentFilterFactory filterFactory,
    				DocumentConsumer consumer) { 
      		//判定默认文件名是否为null,默认是：application
    			if (!StringUtils.hasText(name)) { 
    				for (PropertySourceLoader loader : this.propertySourceLoaders) { 
    					if (canLoadFileExtension(loader, location)) { 
    						load(loader, location, profile, filterFactory.getDocumentFilter(profile), consumer);
    						return;
    					}
    				}
    				throw new IllegalStateException("File extension of config file location '" + location
    						+ "' is not known to any PropertySourceLoader. If the location is meant to reference "
    						+ "a directory, it must end in '/'");
    			}
      		//定义Set集合
    			Set<String> processed = new HashSet<>();
    			for (PropertySourceLoader loader : this.propertySourceLoaders) { 
    				for (String fileExtension : loader.getFileExtensions()) { 
              //如果文件扩展名已经存在processed集合中就不会执行加载配置文件的方法（即不会执行对应的PropertySourceLoader加载器）
              //此处是我们自定义加载器解决中文乱码的关键
    					if (processed.add(fileExtension)) { 
    						loadForFileExtension(loader, location + name, "." + fileExtension, profile, filterFactory,
    								consumer);
    					}
    				}
    			}
    		}

##### loadForFileExtension加载配置文件 #####

//DocumentFilterFactory是使用DocumentFilter过滤器的工厂方法，包含一个getDocumentFilter方法用来创建给定的配置创建DocumentFilter过滤器
    		private void loadForFileExtension(PropertySourceLoader loader, String prefix, String fileExtension,
    				Profile profile, DocumentFilterFactory filterFactory, DocumentConsumer consumer) { 
          //DocumentFilter用于限制何时加载Document的过滤器
    			DocumentFilter defaultFilter = filterFactory.getDocumentFilter(null);
    			DocumentFilter profileFilter = filterFactory.getDocumentFilter(profile);
    			if (profile != null) { 
    				// Try profile-specific file & profile section in profile file (gh-340)
    				String profileSpecificFile = prefix + "-" + profile + fileExtension;
    				load(loader, profileSpecificFile, profile, defaultFilter, consumer);
    				load(loader, profileSpecificFile, profile, profileFilter, consumer);
    				// Try profile specific sections in files we've already processed
    				for (Profile processedProfile : this.processedProfiles) { 
    					if (processedProfile != null) { 
    						String previouslyLoaded = prefix + "-" + processedProfile + fileExtension;
    						load(loader, previouslyLoaded, profile, profileFilter, consumer);
    					}
    				}
    			}
    			// 如果存在，尝试普通文件的特定于概要文件部分
    			load(loader, prefix + fileExtension, profile, profileFilter, consumer);
    		}

##### load方法获取配置的资源对象，然后根据资源对象Resource调用加载配置方法： #####

private void load(PropertySourceLoader loader, String location, Profile profile, DocumentFilter filter,
    				DocumentConsumer consumer) { 
      		//根据参数配置文件路径获取配置文件对应的Resource资源对象
      		//classpath开头的环境变量配置返回的是ClassPathResource对象
      		//file开头的环境变量配置路径返回的是FileSystemResource对象
    			Resource[] resources = getResources(location);
    			for (Resource resource : resources) { 
    				try { 
              //如果配置文件资源不存在，则继续循环
    					if (resource == null || !resource.exists()) { 
    						if (this.logger.isTraceEnabled()) { 
    							StringBuilder description = getDescription("Skipped missing config ", location, resource,
    									profile);
    							this.logger.trace(description);
    						}
    						continue;
    					}
              //如果文件扩展名不存在，则继续循环
    					if (!StringUtils.hasText(StringUtils.getFilenameExtension(resource.getFilename()))) { 
    						if (this.logger.isTraceEnabled()) { 
    							StringBuilder description = getDescription("Skipped empty config extension ", location,
    									resource, profile);
    							this.logger.trace(description);
    						}
    						continue;
    					}
              //将资源配置文件路径拼接成为PropertySourceLoader加载程序name需要的格式
              //如：applicationConfig: [classpath:/application-test.properties]
    					String name = "applicationConfig: [" + getLocationName(location, resource) + "]";
              //核心方法，传递资源加载程序PropertySourceLoader实例、配置文件name及资源Resource对象
              //返回的是加载到的配置文件对象，包含PropertySource对象、配置profiles、激活配置activeProfiles
              //包含配置includeProfiles属性
    					List<Document> documents = loadDocuments(loader, name, resource);
              //判定返回资源配置文件是否为空
    					if (CollectionUtils.isEmpty(documents)) { 
    						if (this.logger.isTraceEnabled()) { 
    							StringBuilder description = getDescription("Skipped unloaded config ", location, resource,
    									profile);
    							this.logger.trace(description);
    						}
    						continue;
    					}
    					List<Document> loaded = new ArrayList<>();
    					for (Document document : documents) { 
    						if (filter.match(document)) { 
    							addActiveProfiles(document.getActiveProfiles());
    							addIncludedProfiles(document.getIncludeProfiles());
    							loaded.add(document);
    						}
    					}
    					Collections.reverse(loaded);
    					if (!loaded.isEmpty()) { 
                //调用消费者回调函数，将加载到的文档存放入loaded属性
    						loaded.forEach((document) -> consumer.accept(profile, document));
    						if (this.logger.isDebugEnabled()) { 
    							StringBuilder description = getDescription("Loaded config file ", location, resource,
    									profile);
    							this.logger.debug(description);
    						}
    					}
    				}
    				catch (Exception ex) { 
    					StringBuilder description = getDescription("Failed to load property source from ", location,
    							resource, profile);
    					throw new IllegalStateException(description.toString(), ex);
    				}
    			}
    		}

##### addToLoaded方法是DocumentConsumer函数式接口的回调的具体实现，将加载到的配置属性存入loaded属性值： #####

private DocumentConsumer addToLoaded(BiConsumer<MutablePropertySources, PropertySource<?>> addMethod,
    				boolean checkForExisting) { 
    			return (profile, document) -> { 
    				if (checkForExisting) { 
    					for (MutablePropertySources merged : this.loaded.values()) { 
    						if (merged.contains(document.getPropertySource().getName())) { 
    							return;
    						}
    					}
    				}
    				MutablePropertySources merged = this.loaded.computeIfAbsent(profile,
    						(k) -> new MutablePropertySources());
    				addMethod.accept(merged, document.getPropertySource());
    			};
    		}

##### loadDocument方法调用PropertySourceLoader加载程序的真实加载方法将配置加载到内存当中： #####

//loader是指属性源配置加载程序实例
    	//name指配置文件属性名，如：applicationConfig: [classpath:/application.properties]
    	//配置文件资源对象，实际是ClassPathResource实现类对象
    	private List<Document> loadDocuments(PropertySourceLoader loader, String name, Resource resource)
    				throws IOException { 
        	//创建用于保存多次加载同一文档的缓存键
    			DocumentsCacheKey cacheKey = new DocumentsCacheKey(loader, resource);
        	//获取键对应的文档信息
    			List<Document> documents = this.loadDocumentsCache.get(cacheKey);
        	//如果缓存中文档信息不存在
    			if (documents == null) { 
            //将在指定的配置文件资源
    				List<PropertySource<?>> loaded = loader.load(name, resource);
            //将资源PropertySource属性资源对象转换为Document对象
    				documents = asDocuments(loaded);
            //将加载到的资源放入缓存之中
    				this.loadDocumentsCache.put(cacheKey, documents);
    			}
    			return documents;
    		}

--------------------

#### 拓展类讲解 ####

##### Profile静态内部类，是配置可以被加载的Spring配置类（包含两个参数name和defaultProfile） #####

private static class Profile { 
    		//配置文件名
    		private final String name;
    		//配置文件是否是默认配置文件，默认：false
    		private final boolean defaultProfile;
    		//创建一个指定配置文件名，非默认配置文件的Profile配置实例
    		Profile(String name) { 
    			this(name, false);
    		}
    		//创建一个指定配置文件名，及时否是默认配置文件参数的Profile配置实例
    		Profile(String name, boolean defaultProfile) { 
    			Assert.notNull(name, "Name must not be null");
    			this.name = name;
    			this.defaultProfile = defaultProfile;
    		}
    
    		String getName() { 
    			return this.name;
    		}
    
    		boolean isDefaultProfile() { 
    			return this.defaultProfile;
    		}
    
    		@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);
    		}
    
    		@Override
    		public int hashCode() { 
    			return this.name.hashCode();
    		}
    
    		@Override
    		public String toString() { 
    			return this.name;
    		}
    
    	}

--------------------

GitHub源码：[https://github.com/mingyang66/spring-parent][https_github.com_mingyang66_spring-parent]

[https_github.com_mingyang66_spring-parent]: https://github.com/mingyang66/spring-parent