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8 Nacos配置中心之环境准备
Nacos配置中心的工作流程是怎么样的呢？ 首先启动SpringBoot项目，在启动项目之后，需要把远程服务器的配置文件加载到Spring容器中
@SpringBootApplication
public class SpringCloudNacosConfigApplication {
public static void main(String[] args) {
ConfigurableApplicationContext context=
SpringApplication.run(SpringCloudNacosConfigApplication.class, args);
String info=context.getEnvironment().getProperty("info");
System.out.println(info);
}
}
复制代码如何从远处服务器上的配置加载到Environment？
SpringBoot启动时，SpringApplication.run()方法进行环境准备
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
//环境准备
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
configureIgnoreBeanInfo(environment);
Banner printedBanner = printBanner(environment);
context = createApplicationContext();
exceptionReporters = getSpringFactoriesInstances(
SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
refreshContext(context);
afterRefresh(context, applicationArguments);
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
}
listeners.started(context);
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, listeners);
throw new IllegalStateException(ex);
}
try {
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, null);
throw new IllegalStateException(ex);
}
return context;
}
复制代码调用prepareEnvironment方法：
private ConfigurableEnvironment prepareEnvironment(
SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments) {
// Create and configure the environment
ConfigurableEnvironment environment = getOrCreateEnvironment();
configureEnvironment(environment, applicationArguments.getSourceArgs());
listeners.environmentPrepared(environment);
bindToSpringApplication(environment);
if (!this.isCustomEnvironment) {
environment = new EnvironmentConverter(getClassLoader())
.convertEnvironmentIfNecessary(environment, deduceEnvironmentClass());
}
ConfigurationPropertySources.attach(environment);
return environment;
}
复制代码listeners.environmentPrepared(environment);中发布一个ApplicationEnvironmentPreparedEvent事件，所有感兴趣的Listener都会监听到这个事件。
BootstrapApplicationListener就会收到该事件并进行处理
@Override
public void onApplicationEvent(ApplicationEnvironmentPreparedEvent event) {
ConfigurableEnvironment environment = event.getEnvironment();
if (!environment.getProperty("spring.cloud.bootstrap.enabled", Boolean.class,
true)) {
return;
}
// don't listen to events in a bootstrap context
if (environment.getPropertySources().contains(BOOTSTRAP_PROPERTY_SOURCE_NAME)) {
return;
}
ConfigurableApplicationContext context = null;
String configName = environment
.resolvePlaceholders("${spring.cloud.bootstrap.name:bootstrap}");
for (ApplicationContextInitializer<?> initializer : event.getSpringApplication()
.getInitializers()) {
if (initializer instanceof ParentContextApplicationContextInitializer) {
context = findBootstrapContext(
(ParentContextApplicationContextInitializer) initializer,
configName);
}
}
if (context == null) {
context = bootstrapServiceContext(environment, event.getSpringApplication(),
configName);
event.getSpringApplication()
.addListeners(new CloseContextOnFailureApplicationListener(context));
}
apply(context, event.getSpringApplication(), environment);
}
复制代码bootstrapServiceContext方法中调用builder.sources(BootstrapImportSelectorConfiguration.class)，进行自动装配
BootstrapImportSelectorConfiguration是配置类
@Configuration
@Import(BootstrapImportSelector.class)
public class BootstrapImportSelectorConfiguration {
}
复制代码用@Import导入BootstrapImportSelector实现自动装配
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BootstrapImportSelector的selectImports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(
this.environment.getProperty("spring.cloud.bootstrap.sources", ""))));
List<OrderedAnnotatedElement> elements = new ArrayList<>();
for (String name : names) {
try {
elements.add(
new OrderedAnnotatedElement(this.metadataReaderFactory, name));
}
catch (IOException e) {
continue;
}
}
AnnotationAwareOrderComparator.sort(elements);
String[] classNames = elements.stream().map(e -> e.name).toArray(String[]::new);
return classNames;
}
复制代码利用Spring的SPI机制查找META-INF/spring.factories扩展点
key是BootstrapConfiguration
在spring-cloud-context.jar中的spring.factories：PropertySourceBootstrapConfiguration
# 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
复制代码在spring-cloud-context.jar中的spring.factories：
NacosConfigBootstrapConfiguration
org.springframework.cloud.bootstrap.BootstrapConfiguration=\
com.alibaba.cloud.nacos.NacosConfigBootstrapConfiguration
org.springframework.boot.autoconfigure.EnableAutoConfiguration=\
com.alibaba.cloud.nacos.NacosConfigAutoConfiguration,\
com.alibaba.cloud.nacos.endpoint.NacosConfigEndpointAutoConfiguration
org.springframework.boot.diagnostics.FailureAnalyzer=\
com.alibaba.cloud.nacos.diagnostics.analyzer.NacosConnectionFailureAnalyzer
复制代码这就是Nacos配置中心的环境准备方面，其实nacos最重要的功能就是注册中心和配置中心，作为nacos的使用者，我们要掌握好nacos的流程和工作原理，才能定位到问题，并在合适的业务场景中进行对nacos服务的功能优化和利用好nacos，这篇文章仅仅是对nacos作为配置中心功能的环境准备方面的结束，后续还会进一步分析nacos配置文件的流程和工作原理。如果你觉得这篇文章对你有帮助的话，欢迎给我留言点赞评论转发