springcloud情操陶冶-springcloud context(二)
承接前文对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。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系统变量抑或是application.properties等文件配置
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
其余关联类
比如springcloud config-client模块下的spring.factories
# Bootstrap components
org.springframework.cloud.bootstrap.BootstrapConfiguration=\
org.springframework.cloud.config.client.ConfigServiceBootstrapConfiguration,\
org.springframework.cloud.config.client.DiscoveryClientConfigServiceBootstrapConfiguration和springcloud config-server模块下的spring.factories
# Bootstrap components
org.springframework.cloud.bootstrap.BootstrapConfiguration=\
org.springframework.cloud.config.server.bootstrap.ConfigServerBootstrapConfiguration,\
org.springframework.cloud.config.server.config.EncryptionAutoConfiguration限于本篇幅过长，就不在此讨论server和client模块对bootstrapContext的作用。后文再作详细的讨论
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，用户也可以复写PropertySourceLocator接口来获取外部源
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<>();
externalMap.put("username", "nanco");
externalMap.put("password", "nanco123");
externalMap.put("mail", "nancoasky@gmail.com");
return new MapPropertySource(EXTERNAL_KEY, externalMap);
}
}