SpringBoot源码分析

Springboot源码分析

1、SpringApplication初始化

从run()方法进入，可以看到Springboot起首创建了SpringApplication，然后调用SpringApplication的run()方法。

1. public static ConfigurableApplicationContext run(Class<?>[] primarySources, String[] args) {
2.     return (new SpringApplication(primarySources)).run(args);
3. }

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创建SpringApplication，起首要执行它的构造方法。

1. //SpringApplication.class
2. public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
3.     this.sources = new LinkedHashSet();
4.     this.bannerMode = Mode.CONSOLE;
5.     this.logStartupInfo = true;
6.     this.addCommandLineProperties = true;
7.     this.addConversionService = true;
8.     this.headless = true;
9.     this.registerShutdownHook = true;
10.     this.additionalProfiles = new HashSet();
11.     this.isCustomEnvironment = false;
12.     this.lazyInitialization = false;
13.     this.resourceLoader = resourceLoader;
14.     Assert.notNull(primarySources, "PrimarySources must not be null");
15.     this.primarySources = new LinkedHashSet(Arrays.asList(primarySources));
16.     //webApplication类型一般是servlet
17.     this.webApplicationType = WebApplicationType.deduceFromClasspath();
18.    //设置初始化器，加载spring.factories文件中的ApplicationContextInitializer
19.     this.setInitializers(this.getSpringFactoriesInstances(ApplicationContextInitializer.class));
20.     //设置监听器，加载spring.factories文件中的ApplicationListener
21.     this.setListeners(this.getSpringFactoriesInstances(ApplicationListener.class));
22.     //启动类的类型，我们的是com.example.demo.DemoApplication
23.     this.mainApplicationClass = this.deduceMainApplicationClass();
24. }

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1.1 & 1.2 设置初始化器和监听器

上面的setInitializers和setListeners去初始化spring.factories文件中对应的类，然后放入ArrayList中。比如这些：

1. org.springframework.context.ApplicationContextInitializer=\
2. org.springframework.boot.autoconfigure.SharedMetadataReaderFactoryContextInitializer,\
3. org.springframework.boot.autoconfigure.logging.ConditionEvaluationReportLoggingListener
5. # Application Listeners
6. org.springframework.context.ApplicationListener=\
7. org.springframework.boot.autoconfigure.BackgroundPreinitializer

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1.2.1 getSpringFactoriesInstances

在getSpringFactoriesInstances()方法中，springboot起首去所有spring.factories找到对应的类，然后通过反射创建类的实例。

1. //SpringApplication.class
2. private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
3.     return this.getSpringFactoriesInstances(type, new Class[0]);
4. }
6. private <T> Collection<T> getSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, Object... args) {
7.     ClassLoader classLoader = this.getClassLoader();
8.     //获取spring.factories中对应类的类名，以ApplicationListenser为例，springboot会去文件中找到所有ApplicationListener对应的类，放入Set中。
9.     Set<String> names = new LinkedHashSet(SpringFactoriesLoader.loadFactoryNames(type, classLoader));
10.     //反射创建类的实例对象，放到List中返回
11.     List<T> instances = this.createSpringFactoriesInstances(type, parameterTypes, classLoader, args, names);
12.     AnnotationAwareOrderComparator.sort(instances);
13.     return instances;
14. }
16. private <T> List<T> createSpringFactoriesInstances(Class<T> type, Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args, Set<String> names) {
17.     List<T> instances = new ArrayList(names.size());
18.     Iterator var7 = names.iterator();
20.     while(var7.hasNext()) {
21.         String name = (String)var7.next();
23.         try {
24.             //获取类信息
25.             Class<?> instanceClass = ClassUtils.forName(name, classLoader);
26.             Assert.isAssignable(type, instanceClass);
27.             //获取构造器
28.             Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
29.             //创建实例
30.             T instance = BeanUtils.instantiateClass(constructor, args);
31.             instances.add(instance);
32.         } catch (Throwable var12) {
33.             throw new IllegalArgumentException("Cannot instantiate " + type + " : " + name, var12);
34.         }
35.     }
37.     return instances;
38. }

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1.2.2 loadFactoryNames()

进入SpringFactoriesLoader.loadFactoryNames(type, classLoader)看一下，这里还是以ApplicationListener为例，这时的type是org.springframework.context.ApplicationListener，classLoader是AppClassLoader。

1. //SpringFactoriesLoader.class
2. public static List<String> loadFactoryNames(Class<?> factoryType, @Nullable ClassLoader classLoader) {
3.     String factoryTypeName = factoryType.getName();
4.     return (List)loadSpringFactories(classLoader).getOrDefault(factoryTypeName, Collections.emptyList());
5. }
7. private static Map<String, List<String>> loadSpringFactories(@Nullable ClassLoader classLoader) {
8.     MultiValueMap<String, String> result = (MultiValueMap)cache.get(classLoader);
9.     if (result != null) {
10.         return result;
11.     } else {
12.         try {
13.             Enumeration<URL> urls = classLoader != null ? classLoader.getResources("META-INF/spring.factories") : ClassLoader.getSystemResources("META-INF/spring.factories");
14.             MultiValueMap<String, String> result = new LinkedMultiValueMap();
16.             while(urls.hasMoreElements()) {
17.                 URL url = (URL)urls.nextElement();
18.                 UrlResource resource = new UrlResource(url);
19.                 Properties properties = PropertiesLoaderUtils.loadProperties(resource);
20.                 Iterator var6 = properties.entrySet().iterator();
22.                 while(var6.hasNext()) {
23.                     Map.Entry<?, ?> entry = (Map.Entry)var6.next();
24.                     String factoryTypeName = ((String)entry.getKey()).trim();
25.                     String[] var9 = StringUtils.commaDelimitedListToStringArray((String)entry.getValue());
26.                     int var10 = var9.length;
28.                     for(int var11 = 0; var11 < var10; ++var11) {
29.                         String factoryImplementationName = var9[var11];
30.                         result.add(factoryTypeName, factoryImplementationName.trim());
31.                     }
32.                 }
33.             }
35.             cache.put(classLoader, result);
36.             return result;
37.         } catch (IOException var13) {
38.             throw new IllegalArgumentException("Unable to load factories from location [META-INF/spring.factories]", var13);
39.         }
40.     }
41. }

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loadSpringFactories()方法会遍历所有的spring.factories文件，把所有的类的名字生存到map中，然后调用getOrDefault()方法就可以获取到所有的ApplicationListner对应的类名了。

SpringApplication初始化完了，接下来该执行run()方法了
2、SpringApplication执行run()方法

1. //SpringApplication.class
2. public ConfigurableApplicationContext run(String... args) {
3.     StopWatch stopWatch = new StopWatch();
4.     stopWatch.start();
5.     //这里是Spring的上下文
6.     ConfigurableApplicationContext context = null;
7.     Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList();
8.     this.configureHeadlessProperty();
9.     //获取运行监听器，获取到的是EventPublishingRunListener，这是springboot的启动监听器
10.     SpringApplicationRunListeners listeners = this.getRunListeners(args);
11.     //启动监听器
12.     listeners.starting();
14.     Collection exceptionReporters;
15.     try {
16.         ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
17.         //2.1 准备环境
18.         ConfigurableEnvironment environment = this.prepareEnvironment(listeners, applicationArguments);
19.         this.configureIgnoreBeanInfo(environment);
20.         //Banner打印类
21.         Banner printedBanner = this.printBanner(environment);
22.         //2.2 创建应用上下文
23.         context = this.createApplicationContext();
24.         exceptionReporters = this.getSpringFactoriesInstances(SpringBootExceptionReporter.class, new Class[]{ConfigurableApplicationContext.class}, context);
25.         //2.3 准备上下文
26.         this.prepareContext(context, environment, listeners, applicationArguments, printedBanner);
27.         //2.4 刷新上下文
28.         this.refreshContext(context);
29.         //刷新上下文后置处理
30.         this.afterRefresh(context, applicationArguments);
31.         stopWatch.stop();
32.         if (this.logStartupInfo) {
33.             (new StartupInfoLogger(this.mainApplicationClass)).logStarted(this.getApplicationLog(), stopWatch);
34.         }
35.                 //发布上下文启动完成事件
36.         listeners.started(context);
37.         this.callRunners(context, applicationArguments);
38.     } catch (Throwable var10) {
39.         this.handleRunFailure(context, var10, exceptionReporters, listeners);
40.         throw new IllegalStateException(var10);
41.     }
43.     try {
44.         listeners.running(context);
45.         return context;
46.     } catch (Throwable var9) {
47.         this.handleRunFailure(context, var9, exceptionReporters, (SpringApplicationRunListeners)null);
48.         throw new IllegalStateException(var9);
49.     }
50. }

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2.1 prepareEnvironment()准备环境

1. //SpringApplication.class
2. private ConfigurableEnvironment prepareEnvironment(SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) {
3.     //根据前面推断的webApplicationType创建对应的环境，servlet对应的是StandardServletEnvironment()
4.     ConfigurableEnvironment environment = this.getOrCreateEnvironment();
5.     //根据参数配置环境，包括命令行参数，启动类传入的参数
6.     this.configureEnvironment((ConfigurableEnvironment)environment, applicationArguments.getSourceArgs());
7.     ConfigurationPropertySources.attach((Environment)environment);
8.     //执行完这个，配置文件中的配置进行就被加载到环境中了
9.     listeners.environmentPrepared((ConfigurableEnvironment)environment);
10.     //环境和SpringApplication绑定起来
11.     this.bindToSpringApplication((ConfigurableEnvironment)environment);
12.     if (!this.isCustomEnvironment) {
13.         environment = (new EnvironmentConverter(this.getClassLoader())).convertEnvironmentIfNecessary((ConfigurableEnvironment)environment, this.deduceEnvironmentClass());
14.     }
16.     ConfigurationPropertySources.attach((Environment)environment);
17.     return (ConfigurableEnvironment)environment;
18. }

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2.1.1 根据参数配置环境configureEnvironment()

1. //SpringApplication.class
2. protected void configureEnvironment(ConfigurableEnvironment environment, String[] args) {
3.     if (this.addConversionService) {
4.         ConversionService conversionService = ApplicationConversionService.getSharedInstance();
5.         environment.setConversionService((ConfigurableConversionService)conversionService);
6.     }
7.         //配置命令行中的参数
8.     this.configurePropertySources(environment, args);
9.     //激活相应的配置文件，例如application.propertires或者application-dev.properties等
10.     this.configureProfiles(environment, args);
11. }

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如果我启动的dev环境，执行完上面的代码后环境中是这样的

2.1.2 listeners.environmentPrepared()

执行完这句代码后，配置文件中的信息就被加载到环境中了，如下图。具体怎么做到的还没看懂

2.2 创建应用上下文createApplicationContext()

1. //SpringApplication.class
2. protected ConfigurableApplicationContext createApplicationContext() {
3.     Class<?> contextClass = this.applicationContextClass;
4.     if (contextClass == null) {
5.         try {
6.             switch (this.webApplicationType) {
7.                 case SERVLET:
8.                     contextClass = Class.forName("org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext");
9.                     break;
10.                 case REACTIVE:
11.                     contextClass = Class.forName("org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext");
12.                     break;
13.                 default:
14.                     contextClass = Class.forName("org.springframework.context.annotation.AnnotationConfigApplicationContext");
15.             }
16.         } catch (ClassNotFoundException var3) {
17.             throw new IllegalStateException("Unable create a default ApplicationContext, please specify an ApplicationContextClass", var3);
18.         }
19.     }
21.     return (ConfigurableApplicationContext)BeanUtils.instantiateClass(contextClass);
22. }

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这个函数也是根据前面的webApplicationType创建应用上下文，servlet对应的是AnnotationConfigServletWebServerApplicationContext，当初始化完这个类时，其实也会创建一个IOC容器beanFactory，如下图所示。这是因为AnnotationConfigServletWebServerApplicationContext会继承GenericApplicationContext，当执行完这个类的构造函数，会创建一个DefaultListableBeanFactory()的beanFactory，这个就是IOC容器。

2.3 准备上下文prepareContext()

1. //SpringApplication.class
2. private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment, SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
3.     //设置上下文环境
4.     context.setEnvironment(environment);
5.     this.postProcessApplicationContext(context);
6.     //初始化所有的ApplicationContextInitializer
7.     this.applyInitializers(context);
8.     //发布上下文准备完成事件
9.     listeners.contextPrepared(context);
10.     if (this.logStartupInfo) {
11.         this.logStartupInfo(context.getParent() == null);
12.         this.logStartupProfileInfo(context);
13.     }
14.     //获取IOC容器beanFactory
15.     ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
16.     //将springApplicationArguments和springBootBanner注册成单例
17.     beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
18.     if (printedBanner != null) {
19.         beanFactory.registerSingleton("springBootBanner", printedBanner);
20.     }
22.     if (beanFactory instanceof DefaultListableBeanFactory) {
23.         ((DefaultListableBeanFactory)beanFactory).setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
24.     }
26.     if (this.lazyInitialization) {
27.         context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
28.     }
29.         //2.3.1 获取资源，其中primarySources就是我们定义的启动类DemoApplication
30.     Set<Object> sources = this.getAllSources();
31.     Assert.notEmpty(sources, "Sources must not be empty");
32.     //2.3.2 加载启动类，注入IOC容器
33.     this.load(context, sources.toArray(new Object[0]));
34.     //发布完成加载事件
35.     listeners.contextLoaded(context);
36. }

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2.3.1 & 2.3.2 获取启动类，注入IOC容器

当执行完getAllSources()，可以获取到启动类DemoApplication

重点看load()方法，进入load()。

1. //SpringApplication.class
2. protected void load(ApplicationContext context, Object[] sources) {
3.     if (logger.isDebugEnabled()) {
4.         logger.debug("Loading source " + StringUtils.arrayToCommaDelimitedString(sources));
5.     }
6.         //创建BeanDefinitionLoader
7.     BeanDefinitionLoader loader = this.createBeanDefinitionLoader(this.getBeanDefinitionRegistry(context), sources);
8.     if (this.beanNameGenerator != null) {
9.         loader.setBeanNameGenerator(this.beanNameGenerator);
10.     }
12.     if (this.resourceLoader != null) {
13.         loader.setResourceLoader(this.resourceLoader);
14.     }
16.     if (this.environment != null) {
17.         loader.setEnvironment(this.environment);
18.     }
19.         //加载启动类
20.     loader.load();
21. }

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其中getBeanDefinitionRegistry(context)方法会将之前的上下文context强转成BeanDefinitionRegistry，他们之间的继承关系很复杂，可以转换成不同的类完成不同的方法。createBeanDefinitionLoader()方法创建了一个BeanDefinitionLoader()，点进去看看。

1. //BeanDefinitionLoader.class
2. BeanDefinitionLoader(BeanDefinitionRegistry registry, Object... sources) {
3.     Assert.notNull(registry, "Registry must not be null");
4.     Assert.notEmpty(sources, "Sources must not be empty");
5.     this.sources = sources;
6.     //注解形式的Bean阅读器
7.     this.annotatedReader = new AnnotatedBeanDefinitionReader(registry);
8.     //xml形式的Bean阅读器
9.     this.xmlReader = new XmlBeanDefinitionReader(registry);
10.     if (this.isGroovyPresent()) {
11.         this.groovyReader = new GroovyBeanDefinitionReader(registry);
12.     }
13.         //类路径扫描器
14.     this.scanner = new ClassPathBeanDefinitionScanner(registry);
15.     this.scanner.addExcludeFilter(new ClassExcludeFilter(sources));
16. }

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一直跟进load()。

1. //BeanDefinitionLoader.class
2. private int load(Class<?> source) {
3.     if (this.isGroovyPresent() && GroovyBeanDefinitionSource.class.isAssignableFrom(source)) {
4.         GroovyBeanDefinitionSource loader = (GroovyBeanDefinitionSource)BeanUtils.instantiateClass(source, GroovyBeanDefinitionSource.class);
5.         this.load(loader);
6.     }
7.         //启动类会走进这里
8.     if (this.isEligible(source)) {
9.         //将启动类注册进beanDefinitionMap
10.         this.annotatedReader.register(new Class[]{source});
11.         return 1;
12.     } else {
13.         return 0;
14.     }
15. }

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进入register()方法。
[code]//AnnotatedBeanDefinitionReader.classpublic void register(Class... componentClasses) {    Class[] var2 = componentClasses;    int var3 = componentClasses.length;    for(int var4 = 0; var4 < var3; ++var4) {        Class componentClass = var2[var4];        this.registerBean(componentClass);    }}public void registerBean(Class beanClass) {    this.doRegisterBean(beanClass, (String)null, (Class[])null, (Supplier)null, (BeanDefinitionCustomizer[])null);}private  void doRegisterBean(Class beanClass, @Nullable String name, @Nullable Class