Spring IOC

Spring Boot加载

​ Spring的IOC即控制反转,核心即将类的创建交给Spring工厂.Spring会扫描@MapperScan()指定的地址,将其中所有交给Spring容器管理的类(@Component,@Service,@Controller,@@Configuration等...)以Bean的形式放到Spring工厂.当需要某个类的时候,直接通过@Resource或者@Autowired即可完成类实例的装配.如果没有指定@MapperScan(),默认扫描启动类下所有包及子包.

1.启动类

@MapperScan("com.trevis.sharding.mapper")
@SpringBootApplication
public class ShardingApplication {

    public static void main(String[] args) {
        SpringApplication.run(ShardingApplication.class, args);
    }
}

2.进入SpringApplication.Java构造函数初始化SpringApplication对象后调用run()方法;

public SpringApplication(ResourceLoader resourceLoader, Class... primarySources) {
        this.resourceLoader = resourceLoader;
        Assert.notNull(primarySources, "PrimarySources must not be null");
        this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
        this.webApplicationType = WebApplicationType.deduceFromClasspath();
        setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
        setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
        this.mainApplicationClass = deduceMainApplicationClass();
    }

public static ConfigurableApplicationContext run(Class[] primarySources, String[] args) {
        return new SpringApplication(primarySources).run(args);
    }

3.这里的返回值是ConfigurableApplicationContext,即返回应用上下文.在这里完成Bean的装配

• Stopwatch: Spring计时器
• SpringApplicationRunListeners: 监听器
• ApplicationArguments: main方法启动时携带的参数,args大多数时候都是空的
• Banner: 启动banner图
• context = createApplicationContext(): 创建应用上下文
• prepareContext(): 将主类信息加载到Spring容器
• refreshContext(): 将扫描到的需要Sping管理的类加载到IOC容器

public ConfigurableApplicationContext run(String... args) {
   StopWatch stopWatch = new StopWatch();
   stopWatch.start();
   ConfigurableApplicationContext context = null;
   Collection exceptionReporters = new ArrayList<>();
   configureHeadlessProperty();
   SpringApplicationRunListeners listeners = getRunListeners(args);
   listeners.starting();
   try {
      ApplicationArguments applicationArguments = new DefaultApplicationArguments(args);
      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;
}

根据初始化构造函数时的webApplicationType创建上下文.这里应该是SERVLET容器.

protected ConfigurableApplicationContext createApplicationContext() {
   Class contextClass = this.applicationContextClass;
   if (contextClass == null) {
      try {
         switch (this.webApplicationType) {
         case SERVLET:
            contextClass = Class.forName(DEFAULT_SERVLET_WEB_CONTEXT_CLASS);
            break;
         case REACTIVE:
            contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
            break;
         default:
            contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
         }
      }
      catch (ClassNotFoundException ex) {
         throw new IllegalStateException(
               "Unable create a default ApplicationContext, please specify an ApplicationContextClass", ex);
      }
   }
   return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}

获取context,根据webApplicationType通过反射加载如下类.这里并没有关于Bean工厂的创建,我们去他的父类寻找.如图(略模糊),GenericApplicationContext是Bean工厂的实现类.

在GenericApplicationContext找到了beanFactory;

private final DefaultListableBeanFactory beanFactory;

@Nullable
private ResourceLoader resourceLoader;

private boolean customClassLoader = false;

private final AtomicBoolean refreshed = new AtomicBoolean();


/**
 * Create a new GenericApplicationContext.
 * @see #registerBeanDefinition
 * @see #refresh
 */
public GenericApplicationContext() {
   this.beanFactory = new DefaultListableBeanFactory();
}

4.完成Bean的注册

从上下文拿到Bean工厂

ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();

spring容器默认覆盖相同bean

if (beanFactory instanceof DefaultListableBeanFactory) {
   ((DefaultListableBeanFactory) beanFactory)
         .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
}

延迟加载,默认false

if (this.lazyInitialization) {
   context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
}

private void prepareContext(ConfigurableApplicationContext context, ConfigurableEnvironment environment,
      SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments, Banner printedBanner) {
   context.setEnvironment(environment);
   postProcessApplicationContext(context);
   applyInitializers(context);
   listeners.contextPrepared(context);
   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);
   }
   if (this.lazyInitialization) {
      context.addBeanFactoryPostProcessor(new LazyInitializationBeanFactoryPostProcessor());
   }
   // Load the sources
   Set