SpringBoot2.0之SpringApplication源码分析

柔情只为你懂 2021-11-13 23:01 305阅读 0赞

***此源码分析针对于SpringBoot的2.0.1.RELEASE版本***

##### 一、首先我们先看到启动类中 #####

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDgyNjM0OQ_size_16_color_FFFFFF_t_70]

##### 二、点击进入SpringApplication的run方法 #####

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDgyNjM0OQ_size_16_color_FFFFFF_t_70 1]  
由此可以看出SpringApplication.run(AppWeiXin.class, args);实际上是返回的有对象的。即ConfigurableApplicationContext

##### 三、继续进入run方法 #####

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDgyNjM0OQ_size_16_color_FFFFFF_t_70 2]  
由此我们可以知道

ConfigurableApplicationContext run = SpringApplication.run(AppWeiXin.class, args);
    //其实就等于
    ConfigurableApplicationContext run = new SpringApplication(AppWeiXin.class).run(args);

##### 四、继续进入SpringApplication #####

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDgyNjM0OQ_size_16_color_FFFFFF_t_70 3]  
可以知道，SpringApplication的有参构造方法再次调用了它的重载有参构造方法

##### 五、然后我们看到上面大红框中的this.webApplicationType = deduceWebApplicationType();，进入deduceWebApplicationType方法 #####

![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDgyNjM0OQ_size_16_color_FFFFFF_t_70 4]  
点击进入ClassUtil.isPresent方法中，同时进入REACTIVE\_WEB\_ENVIRONMENT\_CLASS等几个常量中，我们可以知道deduceWebApplicationType就是判断是否为web应用，通过classLoader判断是否加载的有以下三个类

public static final String DEFAULT_REACTIVE_WEB_CONTEXT_CLASS = "org.springframework."
    			+ "boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext";
    
    	private static final String REACTIVE_WEB_ENVIRONMENT_CLASS = "org.springframework."
    			+ "web.reactive.DispatcherHandler";
    
    	private static final String MVC_WEB_ENVIRONMENT_CLASS = "org.springframework."
    			+ "web.servlet.DispatcherServlet";

然后我进入WebApplicationType中，看到NONE,SERVLET,REACTIVE三种枚举常量，查看[官方文档][Link 1]官方文档可知：  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDgyNjM0OQ_size_16_color_FFFFFF_t_70 5]

##### 六、看到四中的setInitializers((Collection)getSpringFactoriesInstances(ApplicationContextInitializer.class)); #####

我们可以先看(Collection)getSpringFactoriesInstances(ApplicationContextInitializer.class)，它其实就是从类路径下找到META-INF/spring.factories配置的所有ApplicationContextInitializer；然后再将其保存到List<ApplicationListener<?>>中  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDgyNjM0OQ_size_16_color_FFFFFF_t_70 6]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDgyNjM0OQ_size_16_color_FFFFFF_t_70 7]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDgyNjM0OQ_size_16_color_FFFFFF_t_70 8]  
![在这里插入图片描述][watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3dlaXhpbl80MDgyNjM0OQ_size_16_color_FFFFFF_t_70 9]

##### 七、看到四中的setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));，原理同六 #####

它是从类路径下找到META-INF/spring.factories配置的所有ApplicationListener

##### 八、然后获取Main函数主类 #####

this.mainApplicationClass = deduceMainApplicationClass();

##### 九、SpringBoot的run方法说明 #####

public ConfigurableApplicationContext run(String... args) { 
     // 构造一个任务执行观察器
       StopWatch stopWatch = new StopWatch();
    // 开始执行，记录开始时间
       stopWatch.start();
    // 声明IOC容器
       ConfigurableApplicationContext context = null;
       Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
       configureHeadlessProperty();
    // 获取SpringApplicationRunListeners，内部只有一个EventPublishingRunListener
       SpringApplicationRunListeners listeners = getRunListeners(args);
        //回调所有的获取SpringApplicationRunListener.starting()方法
     listeners.starting();
       try { 
      // 构造一个应用程序参数持有类
          ApplicationArguments applicationArguments = new DefaultApplicationArguments(
                args);
      // 参数环境配置
          ConfigurableEnvironment environment = prepareEnvironment(listeners,
                applicationArguments);
          configureIgnoreBeanInfo(environment);
    // 打印启动信息
          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, listeners, exceptionReporters, ex);
          throw new IllegalStateException(ex);
       }
       listeners.running(context);
       return context;
    }

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[Link 1]: https://docs.spring.io/spring-boot/docs/current/api/org/springframework/boot/WebApplicationType.html
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