spring boot 源码解析 启动流程
spring boot 源码解析 启动流程
在面试过程中经常被问到过spring boot的启动流程,今天就翻一下源码整体看一下;
首先,新建一个启动类,可以看到是首先调用的SpringApplication的静态方法run
@SpringBootApplication
public class SourceReadApplillcation {
public static void main(String[] args) {
SpringApplication.run(SourceReadApplillcation.class,args);
}
}
- 这里传入启动类的class,然后调用SpringApplication的构造函数new一个实例,接着调用run方法;
public static ConfigurableApplicationContext run(Class<?> primarySource,
String... args) {
return run(new Class<?>[] { primarySource }, args);
}
public static ConfigurableApplicationContext run(Class<?>[] primarySources,
String[] args) {
return new SpringApplication(primarySources).run(args);
}
public SpringApplication(Class<?>... primarySources) {
this(null, primarySources);
}
@SuppressWarnings({ "unchecked", "rawtypes" })
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
this.resourceLoader = resourceLoader;
Assert.notNull(primarySources, "PrimarySources must not be null");
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
//推断web应用类型;
this.webApplicationType = WebApplicationType.deduceFromClasspath();
//设置初始化器,从META-INF/spring.factories读取ApplicationContextInitializer
//配置的值,读取详情后续研究
setInitializers((Collection) getSpringFactoriesInstances(
ApplicationContextInitializer.class));
//设置监听器,同上,读取ApplicationListener配置的值
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
//设置应用main启动类
this.mainApplicationClass = deduceMainApplicationClass();
}
负责启动SpringBoot的主要方法
public ConfigurableApplicationContext run(String... args) {
//计时器,主要为了统计消耗时间
StopWatch stopWatch = new StopWatch();
stopWatch.start();
//初始化应用上下文和异常报告集合
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
//设置java.awt.headless模式为true
onfigureHeadlessProperty();
//设置并启动META-INF/spring.factories下SpringApplicationRunListener配置的监听器
//这里为EventPublishingRunListener,会通过反射调用其构造函数进行初始化
//并将一开始设置的监听器保存到AbstractApplicationEventMulticaster的
//内部类ListenerRetriever中,详情后续
SpringApplicationRunListeners listeners = getRunListeners(args);
//触发监听器开始启动事件
listeners.starting();
try {
//初始化应用参数,例如启动设置的命令行参数等,可以通过这个类获取
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
//准备运行环境
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
configureIgnoreBeanInfo(environment);
//打印banner
Banner printedBanner = printBanner(environment);
//创建上下文,Springboot默认为AnnotationConfigApplicationContext
context = createApplicationContext();
//准备异常报告
exceptionReporters = getSpringFactoriesInstances(
SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
//准备上下文
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
//刷新上下文
refreshContext(context);
//上下文刷新后置处理(空方法)
afterRefresh(context, applicationArguments);
//计时统计结束
stopWatch.stop();
if (this.logStartupInfo) {
new StartupInfoLogger(this.mainApplicationClass)
.logStarted(getApplicationLog(), stopWatch);
}
//触发启动完成事件
listeners.started(context);
callRunners(context, applicationArguments);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, listeners);
throw new IllegalStateException(ex);
}
try {
//触发运行事件
listeners.running(context);
}
catch (Throwable ex) {
handleRunFailure(context, ex, exceptionReporters, null);
throw new IllegalStateException(ex);
}
return context;
}
整个启动流程大体就是这样,先有一个整体的概念,其中实现细节很庞杂,后续逐一研究