引言
在我之前写的文章中有详细的分析过Spring的启动过程，如果大家有深入阅读过Spring Framework的核心源码，那么阅读Spring Boot的源码相信会更加轻松。个人觉得其实Spring Boot 特别核心的东西其实比较少，其核心仍然是Spring Framework
启动入口
还是一步到位，直接看源码
public ConfigurableApplicationContext run(String... args) {
// 统计启动时间
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
// 设置 java.awt.headless 参数
configureHeadlessProperty();
// 获取监听器
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
configureIgnoreBeanInfo(environment);
Banner printedBanner = printBanner(environment);
// 创建 context容器
context = createApplicationContext();
exceptionReporters = getSpringFactoriesInstances(
SpringBootExceptionReporter.class,
new Class[] { ConfigurableApplicationContext.class }, context);
// 准备容器
prepareContext(context, environment, listeners, applicationArguments,
printedBanner);
// 刷新容器
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;
}
- createApplicationContext
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);
}
}
// 这里会引入一些BeanFactoryProcess，比如 ConfigurationClassPostProcessor 解析Configuration注解的
return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}
注: 引入的BeanFactoryProcess 的逻辑在DEFAULT_SERVLET_WEB_CONTEXT_CLASS的构造方法中
// 看下 AnnotationConfigServletWebServerApplicationContext 的构造方法
public AnnotationConfigServletWebServerApplicationContext() {
// 相当于xml中配置了 <context:annotation-config>
this.reader = new AnnotatedBeanDefinitionReader(this);
// 相当于xml中配置了 <context:component-scan>
this.scanner = new ClassPathBeanDefinitionScanner(this);
}
我们在看下 AnnotatedBeanDefinitionReader 的构造方法
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry) {
this(registry, getOrCreateEnvironment(registry));
}
/**
* Create a new {@code AnnotatedBeanDefinitionReader} for the given registry and using
* the given {@link Environment}.
* @param registry the {@code BeanFactory} to load bean definitions into,
* in the form of a {@code BeanDefinitionRegistry}
* @param environment the {@code Environment} to use when evaluating bean definition
* profiles.
* @since 3.1
*/
public AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry, Environment environment) {
Assert.notNull(registry, "BeanDefinitionRegistry must not be null");
Assert.notNull(environment, "Environment must not be null");
this.registry = registry;
this.conditionEvaluator = new ConditionEvaluator(registry, environment, null);
// 在这里 注册了一堆的 BeanFactoryProcess
AnnotationConfigUtils.registerAnnotationConfigProcessors(this.registry);
}
下面主要prepareContext和refreshContext方法
- prepareContext
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
context.getBeanFactory().registerSingleton("springApplicationArguments",
applicationArguments);
if (printedBanner != null) {
context.getBeanFactory().registerSingleton("springBootBanner", printedBanner);
}
// Load the sources
Set<Object> sources = getAllSources();
Assert.notEmpty(sources, "Sources must not be empty");
// 这里引入了 启动类
load(context, sources.toArray(new Object[0]));
listeners.contextLoaded(context);
}
注： 这里的主要作用就是引入了启动类，加入到 BeanFactory中
- refreshContext
- 后面其实 就是 Spring 统一的一套了
- 可以看我的之前写的 Spring 源码解析系列
总结
Springboot的核心在于自动配置 快速集成 。一些原本需要在Spring xml文件配置的东西，Spring 只需要一个注解就帮我们都做了。不过前文也都说了，核心还是 Spring Framework。
Spring 系列
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