概述
随着微服务的兴起，Spring-Boot的被越来越多的公司喜爱。然后出去面试时候，总会被面试官问起，看过Spring-Boot源码吗，接下来就分析下Spring-Boot源码。
源码分析
首先是启动类：
@SpringBootApplication
public class DemoApplication {
public static void main(String[] args) {
//为入口
SpringApplication.run(DemoApplication.class, args);
}
}
在调用之前自定义该实例：
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
this.resourceLoader = resourceLoader;
Assert.notNull(primarySources, "PrimarySources must not be null");
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
// 判断工程的类型（REACTIVE、NONE、SERVLET）
this.webApplicationType = WebApplicationType.deduceFromClasspath();
//获取ApplicationContextInitializer，也是在这里开始首次加载spring.factories文件
setInitializers((Collection) getSpringFactoriesInstances(
ApplicationContextInitializer.class));
//获取监听器，这里是第二次加载spring.factories文件
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
this.mainApplicationClass = deduceMainApplicationClass();
}
deduceFromClasspath()方法
static WebApplicationType deduceFromClasspath() {
if (ClassUtils.isPresent(WEBFLUX_INDICATOR_CLASS, null)
&& !ClassUtils.isPresent(WEBMVC_INDICATOR_CLASS, null)
&& !ClassUtils.isPresent(JERSEY_INDICATOR_CLASS, null)) {
return WebApplicationType.REACTIVE;
}
for (String className : SERVLET_INDICATOR_CLASSES) {
if (!ClassUtils.isPresent(className, null)) {
return WebApplicationType.NONE;
}
}
return WebApplicationType.SERVLET;
}
ApplicationContextInitializer是spring组件spring-context组件中的一个接口，主要是spring ioc容器刷新之前的一个回调接口，用于处于自定义逻辑。
基于SPI扩展，去加载spring.factories文件中的实现类：
setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class));
image.png
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
image.png
//拿到工厂实例
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = getClassLoader();
// Use names and ensure unique to protect against duplicates
Set<String> names = new LinkedHashSet<>(
SpringFactoriesLoader.loadFactoryNames(type, classLoader));
List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
classLoader, args, names);
AnnotationAwareOrderComparator.sort(instances);
return instances;
}
image.png
接下来看一下run方法：
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
//第一步：获取并启动监听器
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
//第二步：构造容器环境
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
//设置需要忽略的bean
configureIgnoreBeanInfo(environment);
Banner printedBanner = printBanner(environment);
//第三步：创建容器
context = createApplicationContext();
//第四步：实例化SpringBootExceptionReporter.class，用来支持报告关于启动的错误
exceptionReporters = getSpringFactoriesInstances(
SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
//第五步：准备容器
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
//第六步：刷新容器
refreshContext(context);
//第七步：刷新容器后的扩展接口
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;
}
第一步：获取并启动监听器
第二步：构造容器环境
第三步：创建容器
第四步：实例化SpringBootExceptionReporter.class，用来支持报告关于启动的错误
第五步：准备容器
第六步：刷新容器
第七步：刷新容器后的扩展接口
主要以上七步。
未完待续
