springcloud情操陶冶-bootstrapContext(二)

承接前文监听器对bootstrapContext创建的引导，笔者了解到其主要入口类为BootstrapImportSelectorConfiguration。本文将基于此类进行简单的分析

BootstrapImportSelectorConfiguration

简单的配置类，看下源码

@Configuration
@Import(BootstrapImportSelector.class)
public class BootstrapImportSelectorConfiguration {
}

嗯，引入了延迟加载类BootstrapImportSelector，那笔者就继续往下看下此会延迟加载哪些类，直接去观察其主方法

	@Override
	public String[] selectImports(AnnotationMetadata annotationMetadata) {
		ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
		// Use names and ensure unique to protect against duplicates
		List<String> names = new ArrayList<>(SpringFactoriesLoader
				.loadFactoryNames(BootstrapConfiguration.class, classLoader));
		names.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(
				environment.getProperty("spring.cloud.bootstrap.sources", ""))));

		List<OrderedAnnotatedElement> elements = new ArrayList<>();
		for (String name : names) {
			try {
				elements.add(new OrderedAnnotatedElement(metadataReaderFactory, name));
			} catch (IOException e) {
				continue;
			}
		}
		AnnotationAwareOrderComparator.sort(elements);

		String[] classNames = elements.stream()
				.map(e -> e.name)
				.toArray(String[]::new);

		return classNames;
	}

上述的代码很简单，其会去加载classpath路径下所有spring.factories文件中以org.springframework.cloud.bootstrap.BootstrapConfiguration作为Key的所有类；

同时springcloud也支持通过设置spring.cloud.bootstrap.sources属性来加载指定类

笔者就先以springcloud context板块内的spring.factories作为分析的源头

# Bootstrap components
org.springframework.cloud.bootstrap.BootstrapConfiguration=\
org.springframework.cloud.bootstrap.config.PropertySourceBootstrapConfiguration,\
org.springframework.cloud.bootstrap.encrypt.EncryptionBootstrapConfiguration,\
org.springframework.cloud.autoconfigure.ConfigurationPropertiesRebinderAutoConfiguration,\
org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration

在分析上述的源码之前，笔者必须得清楚现在bootstrapContext加载的配置文件默认为bootstrap.properties抑或是bootstrap.yml，其属性已经被加入至相应的Environment对象中。基于此我们再往下走，以免犯糊涂

PropertySourceBootstrapConfiguration

配置源的加载，此Configuration主要用于确定是否外部加载的配置属性复写Spring内含的环境变量。注意其是ApplicationContextInitializer接口的实现类，前文已经提到，bootstrapContext上的此接口的bean类都会被注册至子级的SpringApplication对象上。

直接看下主要的代码片段把

	@Override
	public void initialize(ConfigurableApplicationContext applicationContext) {
		CompositePropertySource composite = new CompositePropertySource(
				BOOTSTRAP_PROPERTY_SOURCE_NAME);
		AnnotationAwareOrderComparator.sort(this.propertySourceLocators);
		boolean empty = true;
		// 此处为子级的环境变量对象
		ConfigurableEnvironment environment = applicationContext.getEnvironment();
		// 通过PropertySourceLocator接口去加载外部配置
		for (PropertySourceLocator locator : this.propertySourceLocators) {
			PropertySource<?> source = null;
			source = locator.locate(environment);
			if (source == null) {
				continue;
			}
			logger.info("Located property source: " + source);
			composite.addPropertySource(source);
			empty = false;
		}
		if (!empty) {
			MutablePropertySources propertySources = environment.getPropertySources();
			String logConfig = environment.resolvePlaceholders("${logging.config:}");
			LogFile logFile = LogFile.get(environment);
			if (propertySources.contains(BOOTSTRAP_PROPERTY_SOURCE_NAME)) {
				propertySources.remove(BOOTSTRAP_PROPERTY_SOURCE_NAME);
			}
			// 确定属性读取的先后顺序
			insertPropertySources(propertySources, composite);
			// reinitialize log
			reinitializeLoggingSystem(environment, logConfig, logFile);
			setLogLevels(applicationContext, environment);
			// active profiles process
			handleIncludedProfiles(environment);
		}
	}

上述的代码就涉及两点，一个是通过PropertySourceLocator接口加载外部配置；一个是用于解析以spring.cloud.config为开头的PropertySourceBootstrapProperties属性，默认情况下，外部配置比内部变量有更高的优先级。具体的用户可自行分析

备注：PropertiesSourceBootstrapProperties中的属性变量可通过PropertySourceLocator接口配置

PropertyPlaceholderAutoConfiguration

和spring常见的解析文件一样的操作，具体就不分析了

@Configuration
@AutoConfigureOrder(Ordered.HIGHEST_PRECEDENCE)
public class PropertyPlaceholderAutoConfiguration {

	// 配置文件属性读取常用类
	@Bean
	@ConditionalOnMissingBean(search = SearchStrategy.CURRENT)
	public static PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer() {
		return new PropertySourcesPlaceholderConfigurer();
	}

}

ConfigurationPropertiesRebinderAutoConfiguration

通过命名便会发现其跟刷新属性的功能有关，先优先看下其类结构

@Configuration
@ConditionalOnBean(ConfigurationPropertiesBindingPostProcessor.class)
public class ConfigurationPropertiesRebinderAutoConfiguration
		implements ApplicationContextAware, SmartInitializingSingleton {
}

上述代码表示其依据于当前类环境存在ConfigurationPropertiesBindingPostProcessorBean对象才会被应用，仔细查阅了下，发现只要有使用到@EnableConfigurationProperties注解即就会被注册。看来此配置跟ConfigurationProperties注解也有一定的关联性。

本文就罗列笔者比较关注的几个地方

---

1.ConfigurationPropertiesRebinder对象的创建

	@Bean
	@ConditionalOnMissingBean(search = SearchStrategy.CURRENT)
	public ConfigurationPropertiesRebinder configurationPropertiesRebinder(
			ConfigurationPropertiesBeans beans) {
		ConfigurationPropertiesRebinder rebinder = new ConfigurationPropertiesRebinder(
				beans);
		return rebinder;
	}

此类读者可以自行翻阅代码，可以发现其暴露了JMX接口以及监听了springcloud context自定义的EnvironmentChangeEvent事件。看来其主要用来刷新ApplicationContext上的beans(含@ConfigurationProperties注解)对象集合

---

2.ConfigurationPropertiesBeans对象的创建

	@Bean
	@ConditionalOnMissingBean(search = SearchStrategy.CURRENT)
	public ConfigurationPropertiesBeans configurationPropertiesBeans() {
		//
		ConfigurationBeanFactoryMetadata metaData = this.context.getBean(
				ConfigurationBeanFactoryMetadata.BEAN_NAME,
						ConfigurationBeanFactoryMetadata.class);
		ConfigurationPropertiesBeans beans = new ConfigurationPropertiesBeans();
		beans.setBeanMetaDataStore(metaData);
		return beans;
	}

配合ConfigurationProperties注解的表演，其会缓存ApplicationContext上的所有含有ConfigurationProperties注解的bean。与第一点所提的ConfigurationPropertiesRebinder对象搭配使用

---

3.实例化结束后刷新父级ApplicationContext上的属性

	@Override
	public void afterSingletonsInstantiated() {
		// refresh parent application context
		if (this.context.getParent() != null) {
			// TODO: make this optional? (E.g. when creating child contexts that prefer to
			// be isolated.)
			ConfigurationPropertiesRebinder rebinder = context
					.getBean(ConfigurationPropertiesRebinder.class);
			for (String name : context.getParent().getBeanDefinitionNames()) {
				rebinder.rebind(name);
			}
		}
	}

EncryptionBootstrapConfiguration

与属性读取的加解密有关，跟JDK的keystore也有一定的关联，具体就不去解析了。读者可自行分析

Bean加载问题

此处本文插入这个Bean的加载问题，因为笔者发现SpringApplication会被调用两次，那么ApplicationContext实例也会被创建两次。那么基于@Configuration修饰过的自定义的Bean是不是也会被加载两次呢？？

经过在cloud环境下编写了一个简单的Bean

package com.example.clouddemo;

import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.context.annotation.Configuration;

/**
 * @author nanco
 * -------------
 * -------------
 * @create 19/8/20
 */
@Configuration
public class TestApplication implements ApplicationContextAware {

    @Override
    public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
        System.out.println("application parent context id: " + applicationContext.getParent().getId());
        System.out.println("application context id: " + applicationContext.getId());
    }
}

且在application.properties文件中指定spring.application.name=springChild以及bootstrap.properties文件中也指定spring.application.name=springBootstrap

运行main方法之后打印的关键信息如下

application parent context id: bootstrap
application context id: springBootstrap-1

经过在org.springframework.boot.context.ContextIdApplicationContextInitializer类上进行断点调试发现只有用户级ApplicationContext被创建的过程中会实例化用户自定义Bean。也就是说bootstrapContext并不会去实例化用户自定义的Bean，这样就很安全。

那么为何如此呢？其实很简单，因为bootstrapContext指定的source类只有BootstrapImportSelectorConfiguration，并没有用户编写的启动类，也就无法影响用户级别Context的Bean加载实例化了~~~并且该类上无@EnableAutoConfiguration注解，表明其也不会去处理spring.factories文件中@EnableAutoConfiguration注解key对应的配置集合。

小结

1.针对springcloud context模块下的以BootstrapConfiguration作为Key的自动配置类，除了PropertySourceBootstrapConfiguration自动类的应用范围在子级ApplicationContext，其它三个均有作用于父级ApplicationContext。

2.关于外部源文件的属性，默认情况下其有更高的优先级于本地系统以及环境变量。当然用户也可以通过修改spring.cloud.config.allowOverride/spring.cloud.config.overrideSystemProperties/spring.cloud.config.overrideNone属性来进行优先级更改，通过此，用户需要复写PropertySourceLocator接口来进行配置

package com.example.cloud.external.resource;

import org.springframework.cloud.bootstrap.config.PropertySourceLocator;
import org.springframework.context.annotation.Configuration;
import org.springframework.core.env.Environment;
import org.springframework.core.env.MapPropertySource;
import org.springframework.core.env.PropertySource;

import java.util.HashMap;
import java.util.Map;

/**
 * @author nanco
 * -------------
 * cloud-demo
 * -------------
 * @create 2019/1/15 19:40
 * @descrption
 **/
@Configuration
public class ExternalPropertySourceLocator implements PropertySourceLocator {

    private static final String EXTERNAL_KEY = "external";

    @Override
    public PropertySource<?> locate(Environment environment) {
        Map<String, Object> externalMap = new HashMap<>();

        // user custom property
        externalMap.put("username", "nanco");
        externalMap.put("password", "nanco123");
        externalMap.put("mail", "nancoasky@gmail.com");

        // application property
        externalMap.put("spring.cloud.config.allowOverride", true);
        externalMap.put("spring.cloud.config.overrideSystemProperties", false); //system拥有更高的优先级
        externalMap.put("spring.cloud.config.overrideNone", false);

        return new MapPropertySource(EXTERNAL_KEY, externalMap);
    }
}

最后将上述的类放置在META-INF/spring.factories文件中便可以生效了

# Bootstrap components
org.springframework.cloud.bootstrap.BootstrapConfiguration=\
com.example.cloud.external.resource.ExternalPropertySourceLocator

3.关于针对@ConfigurationProperties注解的Beans对象的刷新操作，本文只讲解了JMX方式去调用，如果与第三方插件结合，应该会有更多的形式。

4.针对监听器环节的分析到本章暂时告一段落，下一篇便分析cloud-context板块spring.factories文件中以org.springframework.boot.autoconfigure.EnableAutoConfiguration作为Key的类集合。

熟悉的气息再次降临，迫不及待ing....