springboot源码学习笔记之springboot启动流程
| 人称: | 露哥 |
| QQ: | 408365330 |
| N01.编程就是验证学习的最好方式 | |
| N02.为了挣钱所以编程，为了挣大钱所以写好代码，为了写好代码所以学习 | |
| N03.好好学习天天编程 | |
springboot启动代码如下：
SpringApplication.run(SpringBootApp.class, args);
SpringApplication静态方法run分析
实际调用的是SpringApplication实例方法run因此我们分两步分别分析SpringApplication构造函数和实例方法run
1.springApplication构造方法
public SpringApplication(Class<?>... primarySources) {
this(null, primarySources);
}
public SpringApplication(ResourceLoader resourceLoader, Class<?>... primarySources) {
this.resourceLoader = resourceLoader;
Assert.notNull(primarySources, "PrimarySources must not be null");
this.primarySources = new LinkedHashSet<>(Arrays.asList(primarySources));
this.webApplicationType = deduceWebApplicationType();
setInitializers((Collection) getSpringFactoriesInstances(
ApplicationContextInitializer.class));
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
this.mainApplicationClass = deduceMainApplicationClass();
}
可以看到真正的调用方法是第二个构造函数；
- 第一步：设置 primarySources
- 第二步：设置webApplicationType 也就是web类型
public enum WebApplicationType {
/**
* The application should not run as a web application and should not start an
* embedded web server.
*/
NONE,
/**
* The application should run as a servlet-based web application and should start an
* embedded servlet web server.
*/
SERVLET,
/**
* The application should run as a reactive web application and should start an
* embedded reactive web server.
*/
REACTIVE
}
默认的web类型是SERVLET 也就是基础servlet类型web,会启动一个嵌入式servlet web服务器
- 第三步：设置初始化器
通过读取“META-INF/spring.factories” 文件获取 ApplicationContextInitializer子类实例；看到这里我们可以通过了解这个特性实现自己的ApplicationContextInitializer初始化器，在此基础上做自己的事情
通过spring-boot的jar包中的spring.factories文件可以看到其中有下面内容
# Application Context Initializers
org.springframework.context.ApplicationContextInitializer=\
org.springframework.boot.context.ConfigurationWarningsApplicationContextInitializer,\
org.springframework.boot.context.ContextIdApplicationContextInitializer,\
org.springframework.boot.context.config.DelegatingApplicationContextInitializer,\
org.springframework.boot.web.context.ServerPortInfoApplicationContextInitializer
由此可以看出spring boot程序默认至少设置了四个初始化器
- 第四步： 设置监听器ApplicationListener
也是通过读取“META-INF/spring.factories” 文件获取ApplicationListener，我们再去spring-boot的源码中可以看到spring.factories中配置的listerner 达到9个
# Application Listeners
org.springframework.context.ApplicationListener=\
org.springframework.boot.ClearCachesApplicationListener,\
org.springframework.boot.builder.ParentContextCloserApplicationListener,\
org.springframework.boot.context.FileEncodingApplicationListener,\
org.springframework.boot.context.config.AnsiOutputApplicationListener,\
org.springframework.boot.context.config.ConfigFileApplicationListener,\
org.springframework.boot.context.config.DelegatingApplicationListener,\
org.springframework.boot.context.logging.ClasspathLoggingApplicationListener,\
org.springframework.boot.context.logging.LoggingApplicationListener,\
org.springframework.boot.liquibase.LiquibaseServiceLocatorApplicationListener
宗上所述，再构建我的项目时候可以通过spring.factories的方式做很多有意义的事情
2.springApplication的实例方法run
首先看下面源码
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();//设置headless模式，设置SystemProperty java.awt.headless默认设置为true
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);//准备环境
configureIgnoreBeanInfo(environment);
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, 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;
}
执行流程
以下是重点说明
- 1.SpringApplicationRunListeners获取
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
通过从spring.factories中获取实现了SpringApplicationRunListener接口的类实例，此处我们知道实现类是EventPublishingRunListener
- 2.启动过程
prepareContext(context, environment, listeners, applicationArguments,printedBanner);//准备Context
refreshContext(context);//Context
afterRefresh(context, applicationArguments);//完成Context刷新后
以上代码体现context的处理过程;充分理解这个过程能很好的利用springboot的特性和context的初始化过程
- 2.1prepareContext准备
此方法中准备context加载环境，例如资源Resources和日志配置 - 2.2refreshContext刷新
此方法刷新context通过各种途径去加载bean(扫描包通过注解加载bean……)；查看源码我们能知道根据webtype 使用的是AnnotationConfigServletWebServerApplicationContext 作为context的；
