学习过springboot的都知道,在Springboot的main入口函数中调用SpringApplication.run(DemoApplication.class,args)函数便可以启用SpringBoot应用程序,跟踪一下SpringApplication源码可以发现,最终还是调用了SpringApplication的动态run函数。
下面以SpringBoot2.0.3.RELEASE为例简单分析一下运行过程。
SpringApplicatiton部分源码:
1 public static ConfigurableApplicationContext run(Class<?>[] primarySources, 2 String[] args) { 3 //创建springapplication对象,调用函数run(args) 4 return new SpringApplication(primarySources).run(args); 5 }
上面的源码可以发现还是先创建SpringApplication实例,再调用run方法
第一步 分析 SpringApplication构造函数
SpringApplication构造函数代码如下:
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
this.resourceLoader = resourceLoader;
Assert.notNull(primarySources, "PrimarySources must not be null");
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
//1:判断web环境
this.webApplicationType = deduceWebApplicationType();
//2:加载classpath下META-INF/spring.factories中配置的ApplicationContextInitializer
setInitializers((Collection) getSpringFactoriesInstances(
ApplicationContextInitializer.class));
//3:加载classpath下META-INF/spring.factories中配置的ApplicationListener
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
//4:推断main方法所在的类
this.mainApplicationClass = deduceMainApplicationClass();
}
具体逻辑分析:
deduceWebApplicationType(), SpringApplication构造函数中首先初始化应用类型,根据加载相关类路径判断应用类型,具体逻辑如下:
1 private static final String REACTIVE_WEB_ENVIRONMENT_CLASS = "org.springframework."
2 + "web.reactive.DispatcherHandler";
3
4 private static final String MVC_WEB_ENVIRONMENT_CLASS = "org.springframework."
5 + "web.servlet.DispatcherServlet";
6
7 private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet",
8 "org.springframework.web.context.ConfigurableWebApplicationContext" };
9
10
11
12 private WebApplicationType deduceWebApplicationType() {
13 //当类路径中存在REACTIVE_WEB_ENVIRONMENT_CLASS并且不存在MVC_WEB_ENVIRONMENT_CLASS时
14 if (ClassUtils.isPresent(REACTIVE_WEB_ENVIRONMENT_CLASS, null)
15 && !ClassUtils.isPresent(MVC_WEB_ENVIRONMENT_CLASS, null)) {
16 return WebApplicationType.REACTIVE;
17 }
18 //当加载的类路径中不包含WEB_ENVIRONMENT_CLASSES中定义的任何一个类时,返回标准应用()
19 for (String className : WEB_ENVIRONMENT_CLASSES) {
20 if (!ClassUtils.isPresent(className, null)) {22 return WebApplicationType.NONE;
23 }
24 }
25 //加载的类路径中包含了WEB_ENVIRONMENT_CLASSES中定义的所有类型则判断为servlet的web应用
26 return WebApplicationType.SERVLET;
27 }