spring boot容器啟動流程
更新時間：2018年01月25日 09:30:13 作者：只會一點java
spring cloud是基于spring boot快速搭建的，今天咱們就看看spring boot容器啟動流程，需要的朋友跟隨腳本之家小編一起學習吧
一、前言
spring cloud大行其道的當下，如果不了解基本原理那么是很糾結(jié)的(看見的都是 約定大于配置 ，但是原理呢？為什么要這么做？)。spring cloud是基于spring boot快速搭建的，今天咱們就看看spring boot容器啟動流程。(本文不講解如何快速啟動spring boot，那些直接官方看即可， 官網(wǎng)文檔飛機票 )
二、容器啟動
spring boot一般是 指定容器啟動main方法，然后以命令行方式啟動Jar包 ，如下圖：
@SpringBootApplication
public class Application {
public static void main(String[] args) {
SpringApplication.run(Application.class, args);
}
}
這里核心關(guān)注2個東西：
2. SpringApplication.run()靜態(tài)方法
下面我們就分別探究這兩塊內(nèi)容。
2.1 @SpringBootApplication注解
源碼如下：
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@SpringBootConfiguration
@EnableAutoConfiguration
@ComponentScan(excludeFilters = {
@Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),
@Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })
public @interface SpringBootApplication {
核心注解：
@SpringBootConfiguration（實際就是個@Configuration）：表示這是一個JavaConfig配置類，可以在這個類中自定義bean,依賴關(guān)系等。-》這個是spring-boot特有的注解，常用到。
@EnableAutoConfiguration：借助@Import的幫助，將所有符合自動配置條件的bean定義加載到IoC容器（建議放在根包路徑下，這樣可以掃描子包和類）。-》這個需要詳細深挖！
@ComponentScan：spring的自動掃描注解，可定義掃描范圍，加載到IOC容器。-》這個不多說，spring的注解大家肯定眼熟
其中@EnableAutoConfiguration這個注解的源碼：
@SuppressWarnings("deprecation")
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@AutoConfigurationPackage
@Import(EnableAutoConfigurationImportSelector.class)
public @interface EnableAutoConfiguration {
核心是一個EnableAutoConfigurationImportSelector類圖如下：
核心方法在頂級接口 ImportSelector 的 selectImports（） ，源碼如下：
@Override
public String[] selectImports(AnnotationMetadata annotationMetadata) {
if (!isEnabled(annotationMetadata)) {
return NO_IMPORTS;
}
try { //1.從META-INF/spring-autoconfigure-metadata.properties文件中載入483條配置屬性（有一些有默認值），
AutoConfigurationMetadata autoConfigurationMetadata = AutoConfigurationMetadataLoader
.loadMetadata(this.beanClassLoader);
AnnotationAttributes attributes = getAttributes(annotationMetadata);//2.獲取注解屬性
List<String> configurations = getCandidateConfigurations(annotationMetadata,//3.獲取97個自動配置類
attributes);
configurations = removeDuplicates(configurations);//4.移除重復的
configurations = sort(configurations, autoConfigurationMetadata);//5.排序
Set<String> exclusions = getExclusions(annotationMetadata, attributes);//6.獲取需要排除的
checkExcludedClasses(configurations, exclusions);//7.校驗排除類
configurations.removeAll(exclusions);//8.刪除所有需要排除的
configurations = filter(configurations, autoConfigurationMetadata);//9.過濾器OnClassCondition（注解中配置的當存在某類才生效）
fireAutoConfigurationImportEvents(configurations, exclusions);//10.觸發(fā)自動配置導入監(jiān)聽事件
return configurations.toArray(new String[configurations.size()]);
}
catch (IOException ex) {
throw new IllegalStateException(ex);
}
}
這里注意3個核心方法：
1） loadMetadata 加載配置
其實就是用類加載器去加載： META-INF/spring-autoconfigure-metadata.properties （spring-boot-autoconfigure-1.5.9.RELEASE-sources.jar） 文件中定義的配置，返回PropertiesAutoConfigurationMetadata（實現(xiàn)了AutoConfigurationMetadata接口，封裝了屬性的get set方法）
2） getCandidateConfigurations 獲取默認支持的自動配置類名列表
自動配置靈魂方法， SpringFactoriesLoader.loadFactoryNames 從 META-INF/spring.factories （spring-boot-autoconfigure-1.5.9.RELEASE-sources.jar）文件中獲取自動配置類key=EnableAutoConfiguration.class的配置。
protected List<String> getCandidateConfigurations(AnnotationMetadata metadata,
AnnotationAttributes attributes) {//話說這里2個入?yún)]啥用啊...誰來給我解釋一下...
List<String> configurations = SpringFactoriesLoader.loadFactoryNames(
getSpringFactoriesLoaderFactoryClass(), getBeanClassLoader());
Assert.notEmpty(configurations,
"No auto configuration classes found in META-INF/spring.factories. If you "
+ "are using a custom packaging, make sure that file is correct.");
return configurations;
}
//返回的是EnableAutoConfiguration類
protected Class<?> getSpringFactoriesLoaderFactoryClass() {
return EnableAutoConfiguration.class;
}
實際獲取了什么？ spring.factories 文件如下，實際獲取了 # Auto Configure 自動配置模塊的所有類。
# Initializers org.springframework.context.ApplicationContextInitializer=\ org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\ org.springframework.boot.autoconfigure.logging.AutoConfigurationReportLoggingInitializer # Application Listeners org.springframework.context.ApplicationListener=\ org.springframework.boot.autoconfigure.BackgroundPreinitializer # Auto Configuration Import Listeners org.springframework.boot.autoconfigure.AutoConfigurationImportListener=\ org.springframework.boot.autoconfigure.condition.ConditionEvaluationReportAutoConfigurationImportListener # Auto Configuration Import Filters org.springframework.boot.autoconfigure.AutoConfigurationImportFilter=\ org.springframework.boot.autoconfigure.condition.OnClassCondition # Auto Configure 這里就是全部的自動配置類 org.springframework.boot.autoconfigure.EnableAutoConfiguration=\ org.springframework.boot.autoconfigure.admin.SpringApplicationAdminJmxAutoConfiguration,\ org.springframework.boot.autoconfigure.aop.AopAutoConfiguration,\ org.springframework.boot.autoconfigure.amqp.RabbitAutoConfiguration,\ org.springframework.boot.autoconfigure.batch.BatchAutoConfiguration,\ org.springframework.boot.autoconfigure.cache.CacheAutoConfiguration,\ org.springframework.boot.autoconfigure.cassandra.CassandraAutoConfiguration,\ org.springframework.boot.autoconfigure.cloud.CloudAutoConfiguration,\ org.springframework.boot.autoconfigure.context.ConfigurationPropertiesAutoConfiguration,\ org.springframework.boot.autoconfigure.context.MessageSourceAutoConfiguration,\ org.springframework.boot.autoconfigure.context.PropertyPlaceholderAutoConfiguration,\ org.springframework.boot.autoconfigure.couchbase.CouchbaseAutoConfiguration,\ org.springframework.boot.autoconfigure.dao.PersistenceExceptionTranslationAutoConfiguration,\ org.springframework.boot.autoconfigure.data.cassandra.CassandraDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.cassandra.CassandraRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.couchbase.CouchbaseDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.couchbase.CouchbaseRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchAutoConfiguration,\ org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.elasticsearch.ElasticsearchRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.jpa.JpaRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.ldap.LdapDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.ldap.LdapRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.mongo.MongoDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.mongo.MongoRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.neo4j.Neo4jDataAutoConfiguration,\ org.springframework.boot.autoconfigure.data.neo4j.Neo4jRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.solr.SolrRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.redis.RedisAutoConfiguration,\ org.springframework.boot.autoconfigure.data.redis.RedisRepositoriesAutoConfiguration,\ org.springframework.boot.autoconfigure.data.rest.RepositoryRestMvcAutoConfiguration,\ org.springframework.boot.autoconfigure.data.web.SpringDataWebAutoConfiguration,\ org.springframework.boot.autoconfigure.elasticsearch.jest.JestAutoConfiguration,\ org.springframework.boot.autoconfigure.freemarker.FreeMarkerAutoConfiguration,\ org.springframework.boot.autoconfigure.gson.GsonAutoConfiguration,\ org.springframework.boot.autoconfigure.h2.H2ConsoleAutoConfiguration,\ org.springframework.boot.autoconfigure.hateoas.HypermediaAutoConfiguration,\ org.springframework.boot.autoconfigure.hazelcast.HazelcastAutoConfiguration,\ org.springframework.boot.autoconfigure.hazelcast.HazelcastJpaDependencyAutoConfiguration,\ org.springframework.boot.autoconfigure.info.ProjectInfoAutoConfiguration,\ org.springframework.boot.autoconfigure.integration.IntegrationAutoConfiguration,\ org.springframework.boot.autoconfigure.jackson.JacksonAutoConfiguration,\ org.springframework.boot.autoconfigure.jdbc.DataSourceAutoConfiguration,\ org.springframework.boot.autoconfigure.jdbc.JdbcTemplateAutoConfiguration,\ org.springframework.boot.autoconfigure.jdbc.JndiDataSourceAutoConfiguration,\ org.springframework.boot.autoconfigure.jdbc.XADataSourceAutoConfiguration,\ org.springframework.boot.autoconfigure.jdbc.DataSourceTransactionManagerAutoConfiguration,\ org.springframework.boot.autoconfigure.jms.JmsAutoConfiguration,\ org.springframework.boot.autoconfigure.jmx.JmxAutoConfiguration,\ org.springframework.boot.autoconfigure.jms.JndiConnectionFactoryAutoConfiguration,\ org.springframework.boot.autoconfigure.jms.activemq.ActiveMQAutoConfiguration,\ org.springframework.boot.autoconfigure.jms.artemis.ArtemisAutoConfiguration,\ org.springframework.boot.autoconfigure.flyway.FlywayAutoConfiguration,\ org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAutoConfiguration,\ org.springframework.boot.autoconfigure.jersey.JerseyAutoConfiguration,\ org.springframework.boot.autoconfigure.jooq.JooqAutoConfiguration,\ org.springframework.boot.autoconfigure.kafka.KafkaAutoConfiguration,\ org.springframework.boot.autoconfigure.ldap.embedded.EmbeddedLdapAutoConfiguration,\ org.springframework.boot.autoconfigure.ldap.LdapAutoConfiguration,\ org.springframework.boot.autoconfigure.liquibase.LiquibaseAutoConfiguration,\ org.springframework.boot.autoconfigure.mail.MailSenderAutoConfiguration,\ org.springframework.boot.autoconfigure.mail.MailSenderValidatorAutoConfiguration,\ org.springframework.boot.autoconfigure.mobile.DeviceResolverAutoConfiguration,\ org.springframework.boot.autoconfigure.mobile.DeviceDelegatingViewResolverAutoConfiguration,\ org.springframework.boot.autoconfigure.mobile.SitePreferenceAutoConfiguration,\ org.springframework.boot.autoconfigure.mongo.embedded.EmbeddedMongoAutoConfiguration,\ org.springframework.boot.autoconfigure.mongo.MongoAutoConfiguration,\ org.springframework.boot.autoconfigure.mustache.MustacheAutoConfiguration,\ org.springframework.boot.autoconfigure.orm.jpa.HibernateJpaAutoConfiguration,\ org.springframework.boot.autoconfigure.reactor.ReactorAutoConfiguration,\ org.springframework.boot.autoconfigure.security.SecurityAutoConfiguration,\ org.springframework.boot.autoconfigure.security.SecurityFilterAutoConfiguration,\ org.springframework.boot.autoconfigure.security.FallbackWebSecurityAutoConfiguration,\ org.springframework.boot.autoconfigure.security.oauth2.OAuth2AutoConfiguration,\ org.springframework.boot.autoconfigure.sendgrid.SendGridAutoConfiguration,\ org.springframework.boot.autoconfigure.session.SessionAutoConfiguration,\ org.springframework.boot.autoconfigure.social.SocialWebAutoConfiguration,\ org.springframework.boot.autoconfigure.social.FacebookAutoConfiguration,\ org.springframework.boot.autoconfigure.social.LinkedInAutoConfiguration,\ org.springframework.boot.autoconfigure.social.TwitterAutoConfiguration,\ org.springframework.boot.autoconfigure.solr.SolrAutoConfiguration,\ org.springframework.boot.autoconfigure.thymeleaf.ThymeleafAutoConfiguration,\ org.springframework.boot.autoconfigure.transaction.TransactionAutoConfiguration,\ org.springframework.boot.autoconfigure.transaction.jta.JtaAutoConfiguration,\ org.springframework.boot.autoconfigure.validation.ValidationAutoConfiguration,\ org.springframework.boot.autoconfigure.web.DispatcherServletAutoConfiguration,\ org.springframework.boot.autoconfigure.web.EmbeddedServletContainerAutoConfiguration,\ org.springframework.boot.autoconfigure.web.ErrorMvcAutoConfiguration,\ org.springframework.boot.autoconfigure.web.HttpEncodingAutoConfiguration,\ org.springframework.boot.autoconfigure.web.HttpMessageConvertersAutoConfiguration,\ org.springframework.boot.autoconfigure.web.MultipartAutoConfiguration,\ org.springframework.boot.autoconfigure.web.ServerPropertiesAutoConfiguration,\ org.springframework.boot.autoconfigure.web.WebClientAutoConfiguration,\ org.springframework.boot.autoconfigure.web.WebMvcAutoConfiguration,\ org.springframework.boot.autoconfigure.websocket.WebSocketAutoConfiguration,\ org.springframework.boot.autoconfigure.websocket.WebSocketMessagingAutoConfiguration,\ org.springframework.boot.autoconfigure.webservices.WebServicesAutoConfiguration # Failure analyzers org.springframework.boot.diagnostics.FailureAnalyzer=\ org.springframework.boot.autoconfigure.diagnostics.analyzer.NoSuchBeanDefinitionFailureAnalyzer,\ org.springframework.boot.autoconfigure.jdbc.DataSourceBeanCreationFailureAnalyzer,\ org.springframework.boot.autoconfigure.jdbc.HikariDriverConfigurationFailureAnalyzer # Template availability providers org.springframework.boot.autoconfigure.template.TemplateAvailabilityProvider=\ org.springframework.boot.autoconfigure.freemarker.FreeMarkerTemplateAvailabilityProvider,\ org.springframework.boot.autoconfigure.mustache.MustacheTemplateAvailabilityProvider,\ org.springframework.boot.autoconfigure.groovy.template.GroovyTemplateAvailabilityProvider,\ org.springframework.boot.autoconfigure.thymeleaf.ThymeleafTemplateAvailabilityProvider,\ org.springframework.boot.autoconfigure.web.JspTemplateAvailabilityProvider
3）filter過濾器 根據(jù) OnClassCondition 注解把不滿足條件的過濾掉
private List<String> filter(List<String> configurations,
AutoConfigurationMetadata autoConfigurationMetadata) {
long startTime = System.nanoTime();
String[] candidates = configurations.toArray(new String[configurations.size()]);
boolean[] skip = new boolean[candidates.length];
boolean skipped = false;
//獲取需要過濾的自動配置導入攔截器，spring.factories配置中就一個：org.springframework.boot.autoconfigure.condition.OnClassCondition
for (AutoConfigurationImportFilter filter : getAutoConfigurationImportFilters()) {
invokeAwareMethods(filter);
boolean[] match = filter.match(candidates, autoConfigurationMetadata);
for (int i = 0; i < match.length; i++) {
if (!match[i]) {
skip[i] = true;
skipped = true;
}
}
}
if (!skipped) {//多條件只要有一個不匹配->skipped = true，全部匹配-》skipped = false->直接返回
return configurations;
}
List<String> result = new ArrayList<String>(candidates.length);
for (int i = 0; i < candidates.length; i++) {
if (!skip[i]) {//匹配-》不跳過-》添加進result
result.add(candidates[i]);
}
}
if (logger.isTraceEnabled()) {
int numberFiltered = configurations.size() - result.size();
logger.trace("Filtered " + numberFiltered + " auto configuration class in "
+ TimeUnit.NANOSECONDS.toMillis(System.nanoTime() - startTime)
+ " ms");
}
return new ArrayList<String>(result);
}
2.2 SpringApplication .run()靜態(tài)方法
SpringApplication.run
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
FailureAnalyzers analyzers = null;
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);//1.獲取監(jiān)聽器
listeners.starting();-->啟動！
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
ConfigurableEnvironment environment = prepareEnvironment(listeners,//2.準備好環(huán)境，觸發(fā)ApplicationEnvironmentPreparedEvent事件
applicationArguments);
Banner printedBanner = printBanner(environment);//打印啟動提示字符，默認spring的字符圖
context = createApplicationContext();//實例化一個可配置應(yīng)用上下文
analyzers = new FailureAnalyzers(context);
prepareContext(context, environment, listeners, applicationArguments,//3.準備上下文
printedBanner);
refreshContext(context);//4.刷新上下文
afterRefresh(context, applicationArguments);//5.刷新上下文后
listeners.finished(context, null);--關(guān)閉！
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
}
return context;
}
catch (Throwable ex) {
handleRunFailure(context, listeners, analyzers, ex);
throw new IllegalStateException(ex);
}
}
1. getRunListeners 獲取監(jiān)聽器（ SpringApplicationRunListeners ）
實際是 SpringApplicationRunListener 類
private SpringApplicationRunListeners getRunListeners(String[] args) {
Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances(
SpringApplicationRunListener.class, types, this, args));
}
private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type) {
return getSpringFactoriesInstances(type, new Class<?>[] {});
}
private <T> Collection<? extends T> getSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
// 使用Set確保的字符串的唯一性
Set<String> names = new LinkedHashSet<String>(
SpringFactoriesLoader.loadFactoryNames(type, classLoader));// 1.載入工廠名稱集合
List<T> instances = createSpringFactoriesInstances(type, parameterTypes,// 2.創(chuàng)建工廠實例
classLoader, args, names);
AnnotationAwareOrderComparator.sort(instances);// 排序
return instances;
}
1.1 載入工廠名稱（loadFactoryNames）
當前類的類加載器從 META-INF/spring.factories 文件中獲取SpringApplicationRunListener類的配置
public static List<String> loadFactoryNames(Class<?> factoryClass, ClassLoader classLoader) {
String factoryClassName = factoryClass.getName();
try {
Enumeration<URL> urls = (classLoader != null ? classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION));
List<String> result = new ArrayList<String>();
while (urls.hasMoreElements()) {
URL url = urls.nextElement();
Properties properties = PropertiesLoaderUtils.loadProperties(new UrlResource(url));
String factoryClassNames = properties.getProperty(factoryClassName);
result.addAll(Arrays.asList(StringUtils.commaDelimitedListToStringArray(factoryClassNames)));
}
return result;
}
catch (IOException ex) {
throw new IllegalArgumentException("Unable to load [" + factoryClass.getName() +
"] factories from location [" + FACTORIES_RESOURCE_LOCATION + "]", ex);
}
}
上圖，獲取到工廠類名后，下面來看看META-INF/spring.factories中定義了啥：
# PropertySource Loaders org.springframework.boot.env.PropertySourceLoader=\ org.springframework.boot.env.PropertiesPropertySourceLoader,\ org.springframework.boot.env.YamlPropertySourceLoader # Run Listeners 這里呢，看這里?。。?！ org.springframework.boot.SpringApplicationRunListener=\ org.springframework.boot.context.event.EventPublishingRunListener # Application Context Initializers org.springframework.context.ApplicationContextInitializer=\ org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\ org.springframework.boot.context.ContextIdApplicationContextInitializer,\ org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\ org.springframework.boot.context.embedded.ServerPortInfoApplicationContextInitializer # Application Listeners org.springframework.context.ApplicationListener=\ org.springframework.boot.ClearCachesApplicationListener,\ org.springframework.boot.builder.ParentContextCloserApplicationListener,\ org.springframework.boot.context.FileEncodingApplicationListener,\ org.springframework.boot.context.config.AnsiOutputApplicationListener,\ org.springframework.boot.context.config.ConfigFileApplicationListener,\ org.springframework.boot.context.config.DelegatingApplicationListener,\ org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener,\ org.springframework.boot.logging.ClasspathLoggingApplicationListener,\ org.springframework.boot.logging.LoggingApplicationListener # Environment Post Processors org.springframework.boot.env.EnvironmentPostProcessor=\ org.springframework.boot.cloud.CloudFoundryVcapEnvironmentPostProcessor,\ org.springframework.boot.env.SpringApplicationJsonEnvironmentPostProcessor # Failure Analyzers org.springframework.boot.diagnostics.FailureAnalyzer=\ org.springframework.boot.diagnostics.analyzer.BeanCurrentlyInCreationFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.BeanNotOfRequiredTypeFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.BindFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.ConnectorStartFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.NoUniqueBeanDefinitionFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.PortInUseFailureAnalyzer,\ org.springframework.boot.diagnostics.analyzer.ValidationExceptionFailureAnalyzer # FailureAnalysisReporters org.springframework.boot.diagnostics.FailureAnalysisReporter=\ org.springframework.boot.diagnostics.LoggingFailureAnalysisReporter
哇，都是些類全名稱，且key都是接口，value都是實現(xiàn)類。我們根據(jù)key=“ org.springframework.boot.SpringApplicationRunListener ”查詢得到實現(xiàn)類value=" org.springframework.boot.context.event.EventPublishingRunListener" 事件發(fā)布啟動監(jiān)聽器 ， 一猜也知道肯定要用” 反射 ”根據(jù)類名獲取類實例，下面很快得到驗證...
1.2 創(chuàng)建spring工廠實例（createSpringFactoriesInstances）
根據(jù)第一步得到的Set<String> names（SpringApplicationRunListener的唯一實現(xiàn)類 EventPublishingRunListener ）生成" 事件發(fā)布啟動監(jiān)聽器 " 工廠實例
@SuppressWarnings("unchecked")
private <T> List<T> createSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args,
Set<String> names) {
List<T> instances = new ArrayList<T>(names.size());
for (String name : names) {
try {
Class<?> instanceClass = ClassUtils.forName(name, classLoader);// 利用反射獲取類
Assert.isAssignable(type, instanceClass);
Constructor<?> constructor = instanceClass
.getDeclaredConstructor(parameterTypes);// 得到構(gòu)造器
T instance = (T) BeanUtils.instantiateClass(constructor, args);// 根據(jù)構(gòu)造器和參數(shù)構(gòu)造實例
instances.add(instance);
}
catch (Throwable ex) {
throw new IllegalArgumentException(
"Cannot instantiate " + type + " : " + name, ex);
}
}
return instances;
}
準備上下文
private void prepareContext(ConfigurableApplicationContext context,
ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments, Banner printedBanner) {
context.setEnvironment(environment);
postProcessApplicationContext(context);//單例一個BeanNameGenerator，把ResourceLoader設(shè)置進應(yīng)用上下文
applyInitializers(context);//執(zhí)行初始化器
listeners.contextPrepared(context);// 監(jiān)聽器執(zhí)行上下文"已準備好"方法
if (this.logStartupInfo) {
logStartupInfo(context.getParent() == null);
logStartupProfileInfo(context);
}
// 添加spring boot特殊單例bean
context.getBeanFactory().registerSingleton("springApplicationArguments",
applicationArguments);
if (printedBanner != null) {
context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
}
// 載入資源
Set<Object> sources = getSources();
Assert.notEmpty(sources, "Sources must not be empty");
load(context, sources.toArray(new Object[sources.size()]));
listeners.contextLoaded(context);// 監(jiān)聽器執(zhí)行"上下文已加載"方法
}
刷新上下文
private void refreshContext(ConfigurableApplicationContext context) {
refresh(context);//核心類
if (this.registerShutdownHook) {
try {
context.registerShutdownHook();//注冊關(guān)閉鉤子，容器關(guān)閉時執(zhí)行
}
catch (AccessControlException ex) {
// Not allowed in some environments.
}
}
}
protected void refresh(ApplicationContext applicationContext) {
Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
((AbstractApplicationContext) applicationContext).refresh();
}
最終執(zhí)行的是AbstractApplicationContext抽象類的 refresh 方法。
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
//準備刷新的上下文環(huán)境，例如對系統(tǒng)屬性或者環(huán)境變量進行準備及驗證。
prepareRefresh();
//啟動子類的refreshBeanFactory方法.解析xml
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
//為BeanFactory配置容器特性，例如類加載器、事件處理器等.
prepareBeanFactory(beanFactory);
try {
//設(shè)置BeanFactory的后置處理. 空方法，留給子類拓展用。
postProcessBeanFactory(beanFactory);
//調(diào)用BeanFactory的后處理器, 這些后處理器是在Bean定義中向容器注冊的.
invokeBeanFactoryPostProcessors(beanFactory);
//注冊Bean的后處理器, 在Bean創(chuàng)建過程中調(diào)用.
registerBeanPostProcessors(beanFactory);
//初始化上下文中的消息源，即不同語言的消息體進行國際化處理
initMessageSource();
//初始化ApplicationEventMulticaster bean,應(yīng)用事件廣播器
initApplicationEventMulticaster();
//初始化其它特殊的Bean， 空方法，留給子類拓展用。
onRefresh();
//檢查并向容器注冊監(jiān)聽器Bean
registerListeners();
//實例化所有剩余的(non-lazy-init) 單例Bean.
finishBeanFactoryInitialization(beanFactory);
//發(fā)布容器事件, 結(jié)束refresh過程.
finishRefresh();
}
catch (BeansException ex) {
if (logger.isWarnEnabled()) {
logger.warn("Exception encountered during context initialization - " +
"cancelling refresh attempt: " + ex);
}
//銷毀已經(jīng)創(chuàng)建的單例Bean, 以避免資源占用.
destroyBeans();
//取消refresh操作, 重置active標志.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
}
finally {
//重置Spring的核心緩存
resetCommonCaches();
}
}
}
刷新完上下文后
spring boot提供的2個供用戶自己拓展的接口： ApplicationRunner和 CommandLineRunner?？梢栽谌萜鲉油戤吅螅ㄉ舷挛乃⑿潞螅﹫?zhí)行，做一些類似數(shù)據(jù)初始化的操作。
private void callRunners(ApplicationContext context, ApplicationArguments args) {
List<Object> runners = new ArrayList<Object>();
runners.addAll(context.getBeansOfType(ApplicationRunner.class).values());//從上下文中獲取ApplicationRunner類型的bean
runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());//從上下文中獲取CommandLineRunner類型的bean
AnnotationAwareOrderComparator.sort(runners);//排序
for (Object runner : new LinkedHashSet<Object>(runners)) {
if (runner instanceof ApplicationRunner) {
callRunner((ApplicationRunner) runner, args);//執(zhí)行
}
if (runner instanceof CommandLineRunner) {
callRunner((CommandLineRunner) runner, args);
}
}
}
兩個區(qū)別在于入?yún)⒉煌鶕?jù)實際情況自己選擇。
public interface CommandLineRunner {
void run(String... args) throws Exception;
}
public interface ApplicationRunner {
void run(ApplicationArguments args) throws Exception;
}
CommandLineRunner中執(zhí)行參數(shù)是原始的 java啟動類main方法的String[] args字符串數(shù)組參數(shù)； ApplicationRunner中的參數(shù)經(jīng)過處理提供一些方法例如:
List<String> getOptionValues(String name);
根據(jù)名稱獲取值list,java 啟動命令中 --foo=bar --foo=baz，則根據(jù)foo參數(shù)名返回list ["bar", "baz"]
三、總結(jié)
按照前面的分析，Spring-boot容器啟動流程總體可劃分為2部分：
1） 執(zhí)行注解 ：掃描指定范圍下的bean、載入自動配置類對應(yīng)的bean加載到IOC容器。
2）man方法中具體SpringAppliocation.run() ，全流程貫穿SpringApplicationEvent,有6個子類：
ApplicationFailedEvent.class ApplicationPreparedEvent.class ApplicationReadyEvent.class ApplicationStartedEvent.class ApplicationStartingEvent.class SpringApplicationEvent.class
這里用到了很經(jīng)典的 spring事件驅(qū)動模型 ，飛機票： Spring事件驅(qū)動模型和觀察者模式
類圖如下：
如上圖，就是一個經(jīng)典spring 事件驅(qū)動模型，包含3種角色：事件發(fā)布者、事件、監(jiān)聽者。對應(yīng)到spring-boot中就是：
1 .EventPublishingRunListener 這個類封裝了 事件發(fā)布 ，
2. SpringApplicationEvent 是spring-boot中定義的事件（上面說的6種事件），繼承自 ApplicationEvent （spring中定義的）
3. 監(jiān)聽者 spring-boot并沒有實現(xiàn)針對上述6種事件的監(jiān)聽者（我沒找到...）， 這里用戶可以自己實現(xiàn)監(jiān)聽者（上述6種事件）來注入spring boot容器啟動流程，觸發(fā)相應(yīng)的事件。
例如：實現(xiàn)ApplicationListener<ApplicationReadyEvent>這個接口，在容器啟動完畢時最后一步listener.finished時，如果啟動沒有異常，就會執(zhí)行！可以做一些數(shù)據(jù)初始化之類的操作。
總結(jié)
以上所述是小編給大家介紹的spring boot容器啟動的相關(guān)知識，希望對大家有所幫助，如果大家有任何疑問請給我留言，小編會及時回復大家的。在此也非常感謝大家對腳本之家網(wǎng)站的支持！
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