SpringBoot深入理解 -- @AliasFor注解的作用
SpringBoot源碼解析 -- SpringBoot啟動過程
SpringBoot源碼解析 -- AutoConfigure的實現(xiàn)原理
SpringBoot源碼解析 -- @ComponentScan的實現(xiàn)原理
SpringBoot源碼解析 -- @Value,@Autowired實現(xiàn)原理
SpringBoot源碼解析 -- Tomcat诊胞，SpringMVC啟動
SpringBoot源碼解析 -- Logging怎爵，Environment啟動
源碼分析基于spring boot 2.1
本文通過閱讀源碼栏饮，分析SpringBoot的啟動過程局服。
先看一個例子
@SpringBootApplication
public class MyApplication {
public static void main(String[] args) {
SpringApplication.run(MyApplication.class, args); // #1
}
}
例子很簡單，本文主要關(guān)注三個問題
- SpringApplication#run方法的作用
- SpringApplication#run方法中MyApplication.class參數(shù)的作用
- SpringApplication#run方法中args參數(shù)的作用
SpringApplication#run
public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
return new SpringApplication(primarySources).run(args);
}
先構(gòu)造SpringApplication實例浊竟，再調(diào)用run方法
SpringApplication#構(gòu)造方法
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
this.resourceLoader = resourceLoader;
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources)); // #1
this.webApplicationType = WebApplicationType.deduceFromClasspath(); //#2
setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class)); //#3
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)); //#4
this.mainApplicationClass = deduceMainApplicationClass(); // #5
}
#1 設(shè)置SpringApplication#primarySources怨喘，注意這里primarySources參數(shù)就是run方法的第一個參數(shù)
#2 判斷當(dāng)前應(yīng)用是JAVA應(yīng)用津畸，SERVLET應(yīng)用或REACTIVE應(yīng)用。
#3 加載spring.factories中配置的ApplicationContextInitializer實現(xiàn)類必怜，將結(jié)果存放到SpringApplication#initializers
#4 加載spring.factories中配置的ApplicationListener實現(xiàn)類洼畅，將結(jié)果存放到SpringApplication#listeners
#5 獲取main方法所在Class
SpringApplication#getSpringFactoriesInstances -> SpringFactoriesLoader#loadSpringFactories
private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
MultiValueMap<String, String> result = cache.get(classLoader);
if (result != null) {
return result;
}
try {
Enumeration<URL> urls = (classLoader != null ?
classLoader.getResources(FACTORIES_RESOURCE_LOCATION) :
ClassLoader.getSystemResources(FACTORIES_RESOURCE_LOCATION)); //#1
result = new LinkedMultiValueMap<>();
while (urls.hasMoreElements()) {
URL url = urls.nextElement();
UrlResource resource = new UrlResource(url);
Properties properties = PropertiesLoaderUtils.loadProperties(resource); //#2
for (Map.Entry<?, ?> entry : properties.entrySet()) {
String factoryClassName = ((String) entry.getKey()).trim();
for (String factoryName : StringUtils.commaDelimitedListToStringArray((String) entry.getValue())) {
result.add(factoryClassName, factoryName.trim()); //#3
}
}
}
cache.put(classLoader, result);
return result;
}
catch (IOException ex) {
throw new IllegalArgumentException("Unable to load factories from location [" +
FACTORIES_RESOURCE_LOCATION + "]", ex);
}
}
#1 FACTORIES_RESOURCE_LOCATION就是字符串"META-INF/spring.factories"，這里讀取jar中META-INF/spring.factories文件內(nèi)容
#2 加載spring.factories文件（格式為Properties）
#3 讀取Properties內(nèi)容棚赔，緩存結(jié)果
spring.factories格式為
# Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener
key為spring擴(kuò)展接口（或聲明功能的注解），value為對應(yīng)的功能實現(xiàn)類的列表
SpringApplication#run
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch(); // #1
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty(); // #2
SpringApplicationRunListeners listeners = getRunListeners(args); // #3
listeners.starting(); // #4
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(args); // #5
ConfigurableEnvironment environment = prepareEnvironment(listeners, applicationArguments); // #6
configureIgnoreBeanInfo(environment); // #7
Banner printedBanner = printBanner(environment);
context = createApplicationContext(); // #8
exceptionReporters = getSpringFactoriesInstances(SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
prepareContext(context, environment, listeners, applicationArguments, printedBanner); // #9
refreshContext(context); // #10
afterRefresh(context, applicationArguments); // #11
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass).logStarted(getApplicationLog(), stopWatch);
}
listeners.started(context); // #12
callRunners(context, applicationArguments); // #13
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, listeners);
throw new IllegalStateException(ex);
}
try {
listeners.running(context); // #14
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, null);
throw new IllegalStateException(ex);
}
return context;
}
#1 開始計時（計算初始化需要花費多少時間）
#2 配置java.awt.headless
#3 獲取spring.factories中配置的SpringApplicationRunListener實現(xiàn)類
SpringApplicationRunListeners是SpringApplicationRunListener的組合徘郭，SpringApplicationRunListener是SpringBoot中新增接口靠益，通過它來間接調(diào)用 ApplicationListener。
該接口實現(xiàn)類為EventPublishingRunListener残揉，他的構(gòu)造方法中需傳入SpringApplication胧后，并獲取SpringApplication#listeners屬性。
SpringApplicationRunListener組件很重要抱环，SpringBoot中很多擴(kuò)展也是通過listerner實現(xiàn)的壳快，如日志系統(tǒng)的啟動
#4 發(fā)送ApplicationStartedEvent事件
#5 命令行參數(shù)處理
#6 構(gòu)建Environment
#7 處理spring.beaninfo.ignore配置
#8 創(chuàng)建ApplicationContext
#9 prepareContext
#10 refreshContext
#11 afterRefresh，預(yù)留擴(kuò)展方法
#12 發(fā)送ApplicationStartedEvent事件
#13 運行ApplicationRunner镇草，CommandLineRunner
#14 發(fā)送ApplicationReadyEvent事件
SpringApplication#prepareEnvironment
private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments) {
ConfigurableEnvironment environment = getOrCreateEnvironment(); // #1
configureEnvironment(environment, applicationArguments.getSourceArgs()); // #2
ConfigurationPropertySources.attach(environment);
listeners.environmentPrepared(environment); // #3
bindToSpringApplication(environment);
if (!this.isCustomEnvironment) {
environment = new EnvironmentConverter(getClassLoader()).convertEnvironmentIfNecessary(environment,
deduceEnvironmentClass());
}
ConfigurationPropertySources.attach(environment);
return environment;
}
#1 創(chuàng)建一個Environment
#2 將SpringApplication#run中的可變參數(shù)列表傳遞給Environment
回到文章開頭說的第3個問題眶痰，關(guān)于MyApplication#run中的args參數(shù)
我們在啟動SpringBoot時，可以添加命令行參數(shù)梯啤，如java -jar MyApplication.jar --spring.profiles.active=dev
命令行參數(shù)--spring.profiles.active=dev會傳遞給main方法竖伯，main方法中需要將其傳遞給SpringApplication#run方法，
這里將命令行參數(shù)添加Environment中因宇，作為一個PropertySource七婴。
必須在main方法中將args參數(shù)傳給SpringApplication#run方法，否則會造成命令行的參數(shù)失效察滑。
#3 發(fā)送ApplicationEnvironmentPreparedEvent事件
SpringApplication#createApplicationContext
protected ConfigurableApplicationContext createApplicationContext() {
Class<?> contextClass = this.applicationContextClass;
if (contextClass == null) {
try {
switch (this.webApplicationType) {
case SERVLET:
contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS); // #1
break;
case REACTIVE:
contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS); // #2
break;
default:
contextClass = Class.forName(DEFAULT_CONTEXT_CLASS); // #3
}
}
catch (ClassNotFoundException ex) {
throw new IllegalStateException(
"Unable create a default ApplicationContext, " + "please specify an ApplicationContextClass",
ex);
}
}
return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass); // #4
}
#1 SERVLET應(yīng)用打厘，選擇AnnotationConfigServletWebServerApplicationContext
#2 REACTIVE應(yīng)用，選擇AnnotationConfigReactiveWebServerApplicationContext
#3 JAVA應(yīng)用贺辰，選擇AnnotationConfigApplicationContext
#4 構(gòu)造對應(yīng)的Spring Context
AnnotationConfigServletWebServerApplicationContext#構(gòu)造方法 -> AnnotatedBeanDefinitionReader#構(gòu)造方法 ->
AnnotationConfigUtils#registerAnnotationConfigProcessors
這里注冊一些實現(xiàn)SpringBoot功能必須的PostProcessor
public static Set<BeanDefinitionHolder> registerAnnotationConfigProcessors(
BeanDefinitionRegistry registry, @Nullable Object source) {
DefaultListableBeanFactory beanFactory = unwrapDefaultListableBeanFactory(registry);
if (beanFactory != null) {
if (!(beanFactory.getDependencyComparator() instanceof AnnotationAwareOrderComparator)) {
beanFactory.setDependencyComparator(AnnotationAwareOrderComparator.INSTANCE);
}
if (!(beanFactory.getAutowireCandidateResolver() instanceof ContextAnnotationAutowireCandidateResolver)) {
beanFactory.setAutowireCandidateResolver(new ContextAnnotationAutowireCandidateResolver());
}
}
Set<BeanDefinitionHolder> beanDefs = new LinkedHashSet<>(8);
if (!registry.containsBeanDefinition(CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(ConfigurationClassPostProcessor.class); //#1
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, CONFIGURATION_ANNOTATION_PROCESSOR_BEAN_NAME));
}
if (!registry.containsBeanDefinition(AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME)) {
RootBeanDefinition def = new RootBeanDefinition(AutowiredAnnotationBeanPostProcessor.class); //#2
def.setSource(source);
beanDefs.add(registerPostProcessor(registry, def, AUTOWIRED_ANNOTATION_PROCESSOR_BEAN_NAME));
}
...
return beanDefs;
}
#1 注冊ConfigurationClassPostProcessor户盯，該P(yáng)ostProcessor處理@Configuration等注解
#2 注冊AutowiredAnnotationBeanPostProcessor，該P(yáng)ostProcessor處理@Value魂爪，@Autowired等注解
SpringApplication#prepareContext
private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment,
SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
context.setEnvironment(environment);
postProcessApplicationContext(context);
applyInitializers(context); //#1
listeners.contextPrepared(context); //#2
if (this.logStartupInfo) {
logStartupInfo(context.getParent() == null);
logStartupProfileInfo(context);
}
// Add boot specific singleton beans
ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
if (printedBanner != null) {
beanFactory.registerSingleton("springBootBanner", printedBanner);
}
if (beanFactory instanceof DefaultListableBeanFactory) {
((DefaultListableBeanFactory) beanFactory)
.setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
}
// Load the sources
Set<Object> sources = getAllSources();
Assert.notEmpty(sources, "Sources must not be empty");
load(context, sources.toArray(new Object[0])); //#3
listeners.contextLoaded(context); //#4
}
#1 調(diào)用ApplicationContextInitializer#initialize
#2 調(diào)用SpringApplicationRunListener#contextPrepared方法
#3 getAllSources獲取primarySources以及所有的PropertySource先舷，并解析為BeanDefinition注冊到Spring上下文中（后面要使用）
PropertySource（屬性源）用于Environment重新獲取配置屬性。
primarySources就是SpringApplication#run方法的第一個參數(shù)
回到文章開頭第2個問題滓侍，
通過SpringApplication#run方法的MyApplication.class參數(shù)蒋川，這里將MyApplication的BeanDefinition注冊到Spring上下文中，后面Spring就是可以獲取MyApplication上的@SpringBootApplication等注解了撩笆。
#4 發(fā)送ApplicationContextInitializedEvent事件
SpringApplication#refreshContext
之前spring源碼解析的文章已經(jīng)說過refreshContext操作了捺球。
SpringApplication#callRunners
private void callRunners(ApplicationContext context, ApplicationArguments args) {
List<Object> runners = new ArrayList<>();
runners.addAll(context.getBeansOfType(ApplicationRunner.class).values()); // #1
runners.addAll(context.getBeansOfType(CommandLineRunner.class).values());
AnnotationAwareOrderComparator.sort(runners);
for (Object runner : new LinkedHashSet<>(runners)) { // #2
if (runner instanceof ApplicationRunner) {
callRunner((ApplicationRunner) runner, args);
}
if (runner instanceof CommandLineRunner) {
callRunner((CommandLineRunner) runner, args);
}
}
}
#1 獲取ApplicationRunner和CommandLineRunner
#2 調(diào)用對應(yīng)的run方法
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