Spring Boot 2.0系列文章(七):SpringApplication 深入探索

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转载请务必注明原创地址为:http://www.54tianzhisheng.cn/2018/04/30/springboot_SpringApplication/

前言

在 Spring Boot 项目的启动类中常见代码如下:

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@SpringBootApplication
public class SpringbotApplication {
public static void main(String[] args) {
SpringApplication.run(SpringbotApplication.class, args);
}
}

其中也就两个比较引人注意的地方:

  • @SpringBootApplication
  • SpringApplication.run()

对于第一个注解 @SpringBootApplication,我已经在博客 Spring Boot 2.0系列文章(六):Spring Boot 2.0中SpringBootApplication注解详解 中详细的讲解了。接下来就是深入探究第二个了 SpringApplication.run()

换个姿势

上面的姿势太简单了,只一行代码就完事了。

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SpringApplication.run(SpringbotApplication.class, args);

其实是支持做一些个性化的设置,接下来我们换个姿势瞧瞧:

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@SpringBootApplication
public class SpringbotApplication {
public static void main(String[] args) {
SpringApplication app = new SpringApplication(SpringbotApplication.class);
// 自定义应用程序的配置
//app.setXxx()
app.run(args)
}
}

没错,就是通过一个构造函数,然后设置相关的属性,从而达到定制化服务。有哪些属性呢?

SpringApplicationFileds

属性对应的 get/set 方法

springapplication_getset

看到没,还很多呢!

举个例子:你想把 Spring Boot 项目的默认 Banner 换成你自己的,就需要在这里如下:

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public static void main(String[] args) {
// SpringApplication.run(Springboot2Application.class, args);
SpringApplication application = new SpringApplication(Springboot2Application.class);
application.setBanner((environment, sourceClass, out) -> {
//这里打印一个logo
System.out.println(" _ _ _\n" +
" | | (_) | |\n" +
" ____| |__ _ ___ | |__ ___ _ __ __ _\n" +
"|_ /| '_ \\ | |/ __|| '_ \\ / _ \\| '_ \\ / _` |\n" +
" / / | | | || |\\__ \\| | | || __/| | | || (_| |\n" +
"/___||_| |_||_||___/|_| |_| \\___||_| |_| \\__, |\n" +
" __/ |\n" +
" |___/\n");
});
application.setBannerMode(Banner.Mode.CONSOLE);
//你还可以干其他的定制化初始设置
application.run(args);
}

现在重启项目,你就会发现,控制台的 logo 已经换成你自己的了。

banner

当然了,你可能会觉得这样写有点复杂,嗯嗯,确实,这样硬编码在代码里确实不太友好。你还可以在src/main/resources路径下新建一个banner.txt文件,banner.txt中填写好需要打印的字符串内容即可。

从该类中可以看到在 Spring Boot 2 中引入了个新的 WebApplicationType 和 WebEnvironment。

springapplication-002

webapplicationtype

springapplication-003

确实,这也是 Spring Boot 2 中比较大的特性,它是支持响应式编程的。我之前在文章 Spring Boot 2.0系列文章(二):Spring Boot 2.0 新特性详解 中也介绍过,以后有机会会介绍它的,这里我先卖个关子。

SpringApplication 初始化

SpringApplication.run() 的实现才是我们要深入探究的主角,该方法代码如下:

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//静态方法,可用于使用默认配置运行 SpringApplication
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);
}

在这个静态方法中,创建 SpringApplication 对象,并调用该对象的 run 方法。

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public SpringApplication(Class<?>... primarySources) {
this(null, primarySources);
}
//创建一个 SpringApplication 实例,应用上下文会根据指定的主要资源加载 beans ,实例在调用 run 方法之前可以定制化
@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));
this.webApplicationType = deduceWebApplicationType();
setInitializers((Collection) getSpringFactoriesInstances(
ApplicationContextInitializer.class));
setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class));
this.mainApplicationClass = deduceMainApplicationClass();
}

首先是进入单个参数的构造方法,然后进入两参数的构造方法(ResourceLoader 为 null),然后进行初始化。

1、deduceWebApplicationType() : 推断应用的类型 ,创建的是一个 SERVLET 应用还是 REACTIVE应用或者是 NONE

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private static final String REACTIVE_WEB_ENVIRONMENT_CLASS = "org.springframework.web.reactive.DispatcherHandler";
private static final String MVC_WEB_ENVIRONMENT_CLASS = "org.springframework.web.servlet.DispatcherServlet";
private static final String[] WEB_ENVIRONMENT_CLASSES = { "javax.servlet.Servlet",
"org.springframework.web.context.ConfigurableWebApplicationContext" };

private WebApplicationType deduceWebApplicationType() {
if (ClassUtils.isPresent(REACTIVE_WEB_ENVIRONMENT_CLASS, null)
&& !ClassUtils.isPresent(MVC_WEB_ENVIRONMENT_CLASS, null)) {
return WebApplicationType.REACTIVE; //该程序是 REACTIVE 程序
}
for (String className : WEB_ENVIRONMENT_CLASSES) {
if (!ClassUtils.isPresent(className, null)) {
return WebApplicationType.NONE; //该程序为 NONE
}
}
return WebApplicationType.SERVLET; //默认返回是 SERVLET 程序
}

2、setInitializers((Collection) getSpringFactoriesInstances(ApplicationContextInitializer.class)):初始化 classpath 下的所有的可用的 ApplicationContextInitializer。

1)、getSpringFactoriesInstances()

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private <T> Collection<T> getSpringFactoriesInstances(Class<T> type) {
return getSpringFactoriesInstances(type, new Class<?>[] {});
}
//获取所有的 Spring 工厂实例
private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
// Use names and ensure unique to protect against duplicates
Set<String> names = new LinkedHashSet<>(SpringFactoriesLoader.loadFactoryNames(type, classLoader)); //获取所有 Spring Factories 的名字
List<T> instances = createSpringFactoriesInstances(type, parameterTypes,
classLoader, args, names);
AnnotationAwareOrderComparator.sort(instances); //Spring 工厂实例排序
return instances;
}
//根据读取到的名字创建对象(Spring 工厂实例)
private <T> List<T> createSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, ClassLoader classLoader, Object[] args, Set<String> names) {
List<T> instances = new ArrayList<>(names.size());
for (String name : names) {
try {
Class<?> instanceClass = ClassUtils.forName(name, classLoader);
Assert.isAssignable(type, instanceClass);
Constructor<?> constructor = instanceClass.getDeclaredConstructor(parameterTypes);
T instance = (T) BeanUtils.instantiateClass(constructor, args);
instances.add(instance);
}
catch (Throwable ex) {
throw new IllegalArgumentException(
"Cannot instantiate " + type + " : " + name, ex);
}
}
return instances;
}

上面的 SpringFactoriesLoader.loadFactoryNames() ,是从 META-INF/spring.factories 的资源文件中,读取 key 为org.springframework.context.ApplicationContextInitializer 的 value。

springfactoriesloader

而 spring.factories 的部分内容如下:

2018-05-01_22-21-20

可以看到,最近的得到的,是 ConfigurationWarningsApplicationContextInitializer,ContextIdApplicationContextInitializer,DelegatingApplicationContextInitializer,ServerPortInfoApplicationContextInitializer 这四个类的名字。

2)、setInitializers():

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public void setInitializers(
Collection<? extends ApplicationContextInitializer<?>> initializers) {
this.initializers = new ArrayList<>();
this.initializers.addAll(initializers);
}

所以,这里 setInitializers() 所得到的成员变量 initializers 就被初始化为ConfigurationWarningsApplicationContextInitializer,ContextIdApplicationContextInitializer,DelegatingApplicationContextInitializer,ServerPortInfoApplicationContextInitializer 这四个类的对象组成的 list。

3、setListeners((Collection) getSpringFactoriesInstances(ApplicationListener.class)):初始化 classpath 下的所有的可用的 ApplicationListener。

1)、getSpringFactoriesInstances() 和上面的类似,但是它是从 META-INF/spring.factories 的资源文件中,获取到 key 为 org.springframework.context.ApplicationListener 的 value。

2018-05-01_22-33-56

2)、setListeners():

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public void setListeners(Collection<? extends ApplicationListener<?>> listeners) {
this.listeners = new ArrayList<>();
this.listeners.addAll(listeners);
}

所以,这里 setListeners() 所得到的成员变量 listeners 就被初始化为 ClearCachesApplicationListener,ParentContextCloserApplicationListener,FileEncodingApplicationListener,AnsiOutputApplicationListener ,ConfigFileApplicationListener,DelegatingApplicationListener,ClasspathLoggingApplicationListener,LoggingApplicationListener,LiquibaseServiceLocatorApplicationListener 这九个类的对象组成的 list。

4、deduceMainApplicationClass() :根据调用栈,推断出 main 方法的类名

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private Class<?> deduceMainApplicationClass() {
try {
StackTraceElement[] stackTrace = new RuntimeException().getStackTrace();
for (StackTraceElement stackTraceElement : stackTrace) {
if ("main".equals(stackTraceElement.getMethodName())) {
return Class.forName(stackTraceElement.getClassName());
}
}
}
catch (ClassNotFoundException ex) {
// Swallow and continue
}
return null;
}

run 方法背后的秘密

上面看完了构造方法后,已经初始化了一个 SpringApplication 对象,接下来调用其 run 方法,代码如下:

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//运行 Spring 应用程序,创建并刷新一个新的 ApplicationContext
public ConfigurableApplicationContext run(String... args) {
StopWatch stopWatch = new StopWatch();
stopWatch.start();
ConfigurableApplicationContext context = null;
Collection<SpringBootExceptionReporter> exceptionReporters = new ArrayList<>();
configureHeadlessProperty();
SpringApplicationRunListeners listeners = getRunListeners(args);
listeners.starting();
try {
ApplicationArguments applicationArguments = new DefaultApplicationArguments(
args);
ConfigurableEnvironment environment = prepareEnvironment(listeners,
applicationArguments);
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;
}

可变个数参数 args 即是我们整个应用程序的入口 main 方法的参数。StopWatch 是来自 org.springframework.util 的工具类,可以用来方便的记录程序的运行时间。

再来看看 1.5.12 与 2.0.1 版本的 run 方法 有什么不一样的地方?

difference-1.5-2.0

接下来好好分析上面新版本(2.0.1)的 run 方法的代码并配合比较旧版本(1.5.12)。

1、configureHeadlessProperty():设置 headless 模式

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private static final String SYSTEM_PROPERTY_JAVA_AWT_HEADLESS = "java.awt.headless";
private boolean headless = true;

private void configureHeadlessProperty() {
System.setProperty(SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, System.getProperty(
SYSTEM_PROPERTY_JAVA_AWT_HEADLESS, Boolean.toString(this.headless)));
}

实际上是就是设置系统属性 java.awt.headless,该属性会被设置为 true。

2、getRunListeners():加载 SpringApplicationRunListener 对象

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 //TODO:  xxx
SpringApplicationRunListeners listeners = getRunListeners(args);//初始化监听器
listeners.starting();
try {
prepareContext(context, environment, listeners, applicationArguments, printedBanner);
refreshContext(context);
afterRefresh(context, applicationArguments);
listeners.started(context);
callRunners(context, applicationArguments);
}
try {
listeners.running(context);
}

private SpringApplicationRunListeners getRunListeners(String[] args) {
Class<?>[] types = new Class<?>[] { SpringApplication.class, String[].class };
return new SpringApplicationRunListeners(logger, getSpringFactoriesInstances(
SpringApplicationRunListener.class, types, this, args));
}

上面的 getRunListeners() 中也利用 SpringFactoriesLoader 加载 META-INF/spring.factories 中 key 为 SpringApplicationRunListener 的值,然后再将获取到的值作为参数传递到 SpringApplicationRunListeners 的构造方法中去创建对象。

2018-05-02_23-11-01

3、new DefaultApplicationArguments(args) :获取启动时传入参数 args(main 方法传进来的参数) 并初始化为 ApplicationArguments 对象。

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public DefaultApplicationArguments(String[] args) {
Assert.notNull(args, "Args must not be null");
this.source = new Source(args);
this.args = args;
}

4、prepareEnvironment(listeners, applicationArguments):根据 listeners 和 applicationArguments 配置SpringBoot 应用的环境。

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private ConfigurableEnvironment prepareEnvironment(
SpringApplicationRunListeners listeners, ApplicationArguments applicationArguments) {
// Create and configure the environment
ConfigurableEnvironment environment = getOrCreateEnvironment();
configureEnvironment(environment, applicationArguments.getSourceArgs());
listeners.environmentPrepared(environment);
bindToSpringApplication(environment);
if (this.webApplicationType == WebApplicationType.NONE) {
environment = new EnvironmentConverter(getClassLoader())
.convertToStandardEnvironmentIfNecessary(environment);
}
ConfigurationPropertySources.attach(environment);
return environment;
}
//如果 environment 不为空,直接 get 到,否则创建
private ConfigurableEnvironment getOrCreateEnvironment() {
if (this.environment != null) {
return this.environment;
}
if (this.webApplicationType == WebApplicationType.SERVLET) {
return new StandardServletEnvironment();
}
return new StandardEnvironment();
}
//配置环境
protected void configureEnvironment(ConfigurableEnvironment environment,String[] args) {
configurePropertySources(environment, args);//配置要使用的PropertySources
configureProfiles(environment, args);//配置要使用的Profiles
}
//将环境绑定到 SpringApplication
protected void bindToSpringApplication(ConfigurableEnvironment environment) {
try {
Binder.get(environment).bind("spring.main", Bindable.ofInstance(this));
}
catch (Exception ex) {
throw new IllegalStateException("Cannot bind to SpringApplication", ex);
}
}

5、configureIgnoreBeanInfo(environment):根据环境信息配置要忽略的 bean 信息

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public static final String IGNORE_BEANINFO_PROPERTY_NAME = "spring.beaninfo.ignore";

private void configureIgnoreBeanInfo(ConfigurableEnvironment environment) {
if (System.getProperty(
CachedIntrospectionResults.IGNORE_BEANINFO_PROPERTY_NAME) == null) {
Boolean ignore = environment.getProperty("spring.beaninfo.ignore",
Boolean.class, Boolean.TRUE);
System.setProperty(CachedIntrospectionResults.IGNORE_BEANINFO_PROPERTY_NAME,
ignore.toString());
}
}

6、printBanner(environment):打印标志,上面我已经说过了。

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private Banner printBanner(ConfigurableEnvironment environment) {
if (this.bannerMode == Banner.Mode.OFF) { //如果设置为 off,不打印 Banner
return null;
}
ResourceLoader resourceLoader = this.resourceLoader != null ? this.resourceLoader
: new DefaultResourceLoader(getClassLoader());
SpringApplicationBannerPrinter bannerPrinter = new SpringApplicationBannerPrinter(
resourceLoader, this.banner);
if (this.bannerMode == Mode.LOG) {
return bannerPrinter.print(environment, this.mainApplicationClass, logger);
}
return bannerPrinter.print(environment, this.mainApplicationClass, System.out);
}

7、createApplicationContext():根据应用类型来确定该 Spring Boot 项目应该创建什么类型的 ApplicationContext ,默认情况下,如果没有明确设置的应用程序上下文或应用程序上下文类,该方法会在返回合适的默认值。

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public static final String DEFAULT_WEB_CONTEXT_CLASS = "org.springframework.boot.web.servlet.context.AnnotationConfigServletWebServerApplicationContext";
public static final String DEFAULT_REACTIVE_WEB_CONTEXT_CLASS = "org.springframework.boot.web.reactive.context.AnnotationConfigReactiveWebServerApplicationContext";
public static final String DEFAULT_CONTEXT_CLASS = "org.springframework.context.annotation.AnnotationConfigApplicationContext";

protected ConfigurableApplicationContext createApplicationContext() {
Class<?> contextClass = this.applicationContextClass;
if (contextClass == null) {
try {
switch (this.webApplicationType) { //根据应用程序的类型来初始化容器
case SERVLET: //servlet 应用程序
contextClass = Class.forName(DEFAULT_WEB_CONTEXT_CLASS);
break;
case REACTIVE: //reactive 应用程序
contextClass = Class.forName(DEFAULT_REACTIVE_WEB_CONTEXT_CLASS);
break;
default: //默认
contextClass = Class.forName(DEFAULT_CONTEXT_CLASS);
}
} catch (ClassNotFoundException ex) {
throw new IllegalStateException(
"Unable create a default ApplicationContext,please specify an ApplicationContextClass",ex);
}
}
//最后通过Spring的工具类 BeanUtils 初始化容器类 bean
return (ConfigurableApplicationContext) BeanUtils.instantiateClass(contextClass);
}

来看看在 1.5.12 中是怎么样的?

createApplicationContext

8、exceptionReporters = getSpringFactoriesInstances( SpringBootExceptionReporter.class, new Class[] { ConfigurableApplicationContext.class }, context)

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private <T> Collection<T> getSpringFactoriesInstances(Class<T> type,
Class<?>[] parameterTypes, Object... args) {
ClassLoader classLoader = Thread.currentThread().getContextClassLoader();
// 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);//根据类型 key 为 SpringBootExceptionReporter 去加载
AnnotationAwareOrderComparator.sort(instances);//对实例排序
return instances;
}

这里也是通过 SpringFactoriesLoader 加载 META-INF/spring.factories 中 key 为 SpringBootExceptionReporter 的全类名的 value 值。

springbootexception

9、prepareContext(context, environment, listeners, applicationArguments, printedBanner):完成整个容器的创建与启动以及 bean 的注入功能。

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//装配 Context
private void prepareContext(ConfigurableApplicationContext context,
ConfigurableEnvironment environment, SpringApplicationRunListeners listeners,
ApplicationArguments applicationArguments, Banner printedBanner) {
//将之前准备好的 environment 设置给创建好的 ApplicationContext 使用
context.setEnvironment(environment);
//1、
postProcessApplicationContext(context);
//2、
applyInitializers(context);
listeners.contextPrepared(context);
if (this.logStartupInfo) {//启动日志
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");
//3、
load(context, sources.toArray(new Object[0]));
listeners.contextLoaded(context);
}

1)、postProcessApplicationContext(context)

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public static final String CONFIGURATION_BEAN_NAME_GENERATOR = "org.springframework.context.annotation.internalConfigurationBeanNameGenerator";

protected void postProcessApplicationContext(ConfigurableApplicationContext context) {
if (this.beanNameGenerator != null) {
context.getBeanFactory().registerSingleton(
AnnotationConfigUtils.CONFIGURATION_BEAN_NAME_GENERATOR,
this.beanNameGenerator);
}
if (this.resourceLoader != null) {
if (context instanceof GenericApplicationContext) {
((GenericApplicationContext) context)
.setResourceLoader(this.resourceLoader);
}
if (context instanceof DefaultResourceLoader) {
((DefaultResourceLoader) context)
.setClassLoader(this.resourceLoader.getClassLoader());
}
}
}

该方法对 context 进行了预设置,设置了 ResourceLoader 和 ClassLoader,并向 bean 工厂中添加了一个beanNameGenerator 。

2)、applyInitializers(context)

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protected void applyInitializers(ConfigurableApplicationContext context) {
for (ApplicationContextInitializer initializer : getInitializers()) {
Class<?> requiredType = GenericTypeResolver.resolveTypeArgument(
initializer.getClass(), ApplicationContextInitializer.class);
Assert.isInstanceOf(requiredType, context, "Unable to call initializer.");
initializer.initialize(context);
}
}

在刷新之前将任何 ApplicationContextInitializer 应用于上下文

3)、load(context, sources.toArray(new Object[0]))

主要是加载各种 beans 到 ApplicationContext 对象中。

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protected void load(ApplicationContext context, Object[] sources) {
BeanDefinitionLoader loader = createBeanDefinitionLoader( //2
getBeanDefinitionRegistry(context), sources);// 1
if (this.beanNameGenerator != null) {
loader.setBeanNameGenerator(this.beanNameGenerator);
}
if (this.resourceLoader != null) {
loader.setResourceLoader(this.resourceLoader);
}
if (this.environment != null) {
loader.setEnvironment(this.environment);
}
loader.load();//3
}

(1)、getBeanDefinitionRegistry(context)

获取 bean 定义注册表

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private BeanDefinitionRegistry getBeanDefinitionRegistry(ApplicationContext context) {
if (context instanceof BeanDefinitionRegistry) {
return (BeanDefinitionRegistry) context;
}
if (context instanceof AbstractApplicationContext) {
return (BeanDefinitionRegistry) ((AbstractApplicationContext) context)
.getBeanFactory();
}
throw new IllegalStateException("Could not locate BeanDefinitionRegistry");
}

(2)、createBeanDefinitionLoader()

通过 BeanDefinitionLoader 的构造方法把参数(注册表、资源)传进去,然后创建 BeanDefinitionLoader。

(3)、load()

把资源全部加载。

10、refreshContext(context)

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private void refreshContext(ConfigurableApplicationContext context) {
refresh(context);//1
if (this.registerShutdownHook) {
try {
context.registerShutdownHook();
}
catch (AccessControlException ex) {
// Not allowed in some environments.
}
}
}
//刷新底层的 ApplicationContext
protected void refresh(ApplicationContext applicationContext) {
Assert.isInstanceOf(AbstractApplicationContext.class, applicationContext);
((AbstractApplicationContext) applicationContext).refresh();
}

refreshContext(context) 方法又调用了 refresh(context)。在调用了 refresh(context) 方法之后,调用了 registerShutdownHook 方法。继续看它的 refresh 方法:

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public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Prepare this context for refreshing.
prepareRefresh();
// Tell the subclass to refresh the internal bean factory.
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
try {
// Allows post-processing of the bean factory in context subclasses.
postProcessBeanFactory(beanFactory);
// Invoke factory processors registered as beans in the context.
invokeBeanFactoryPostProcessors(beanFactory);
// Register bean processors that intercept bean creation.
registerBeanPostProcessors(beanFactory);
// Initialize message source for this context.
initMessageSource();
// Initialize event multicaster for this context.
initApplicationEventMulticaster();
// Initialize other special beans in specific context subclasses.
onRefresh();
// Check for listener beans and register them.
registerListeners();
// Instantiate all remaining (non-lazy-init) singletons.
finishBeanFactoryInitialization(beanFactory); //1
// Last step: publish corresponding event.
finishRefresh();
} catch (BeansException ex) {
。。。
// Destroy already created singletons to avoid dangling resources.
destroyBeans();
// Reset 'active' flag.
cancelRefresh(ex);
// Propagate exception to caller.
throw ex;
} finally {
// Reset common introspection caches in Spring's core, since we
// might not ever need metadata for singleton beans anymore...
resetCommonCaches();
}
}
}

到这里,我们就看见重点了,仔细看上的注释,正在做各种初始化工作,而今天我们关注的重点就是方法 finishBeanFactoryInitialization(beanFactory)。该方法进行了非懒加载 beans 的初始化工作。现在我们进入该方法内部,一探究竟。

finishbeanFactoryini

看上图方法中的最后一步,调用了 beanFactory 的 preInstantiateSingletons() 方法。此处的 beanFactory 是哪个类的实例对象呢?

2018-05-02_16-17-50

可以看到 ConfigurableListableBeanFactory 接口的实现类只有 DefaultListableBeanFactory,我们看下实现类中的 preInstantiateSingletons 方法是怎么做的。

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public void preInstantiateSingletons() throws BeansException {
// Iterate over a copy to allow for init methods which in turn register new bean definitions.
// While this may not be part of the regular factory bootstrap, it does otherwise work fine.
List<String> beanNames = new ArrayList<>(this.beanDefinitionNames);

// Trigger initialization of all non-lazy singleton beans...
for (String beanName : beanNames) {
RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
if (isFactoryBean(beanName)) {
Object bean = getBean(FACTORY_BEAN_PREFIX + beanName);
if (bean instanceof FactoryBean) {
final FactoryBean<?> factory = (FactoryBean<?>) bean;
boolean isEagerInit;
if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean){
isEagerInit = AccessController.doPrivileged((PrivilegedAction<Boolean>)
((SmartFactoryBean<?>) factory)::isEagerInit, getAccessControlContext());
} else {
isEagerInit = (factory instanceof SmartFactoryBean &&
((SmartFactoryBean<?>) factory).isEagerInit());
}
if (isEagerInit) {
getBean(beanName);
}
}
} else {
getBean(beanName);
}
}
}

// Trigger post-initialization callback for all applicable beans...
for (String beanName : beanNames) {
Object singletonInstance = getSingleton(beanName);
if (singletonInstance instanceof SmartInitializingSingleton) {
final SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
if (System.getSecurityManager() != null) {
AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
smartSingleton.afterSingletonsInstantiated();
return null;
}, getAccessControlContext());
} else {
smartSingleton.afterSingletonsInstantiated();
}
}
}
}

从上面的代码中可以看到很多调用了 getBean(beanName) 方法,跟踪此方法进去后,最终发现 getBean 调用了AbstractBeanFactory 类的 doGetBean(xxx) 方法,doGetBean(xxx) 方法中有这么一段代码:

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但是 createBean() 方法并没有得到实现,实现类在 AbstractAutowireCapableBeanFactory 中。这才是创建 bean 的核心方法。

createBean

不知不觉,代码看的越来越深,感觉思维都差点回不去 run 方法了,切回大脑的上下文线程到 run 方法去。

11、afterRefresh(context, applicationArguments):在上下文刷新后调用该方法,其内部没有做任何操作。

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发现没做任何操作了之后,就觉得有点奇怪,所以把当前版本和 1.5.12 对比了下,发现:

afterRefresh

在 1.5.12 中的 afterRefresh() 方法中调用了 callRunners() 方法,但是在 2.0.1 版本中的 run 方法中调用了 callRunners () 方法:

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这里不得不说 SpringApplicationRunListeners 在 2.0.1 中的改变:

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可以发现在 run 方法中,SpringApplicationRunListeners 监听器的状态花生了变化,这也是通过对比不同版本的代码才知道的区别,所以说我们看源码需要多对比着看。

so,我们来看下这个 SpringApplicationRunListener 这个接口:

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started 状态:The context has been refreshed and the application has started but CommandLineRunner and ApplicationRunner have not been called

running 状态:Called immediately before the run method finishes, when the application context has been refreshed and all CommandLineRunner and ApplicationRunners have been called.

相关文章

1、Spring Boot 2.0系列文章(一):Spring Boot 2.0 迁移指南

2、Spring Boot 2.0系列文章(二):Spring Boot 2.0 新特性详解

3、Spring Boot 2.0系列文章(三):Spring Boot 2.0 配置改变

4、Spring Boot 2.0系列文章(四):Spring Boot 2.0 源码阅读环境搭建

5、Spring Boot 2.0系列文章(五):Spring Boot 2.0 项目源码结构预览

6、Spring Boot 2.0系列文章(六):Spring boot 2.0 中 SpringBootApplication 注解详解

7、Spring Boot 2.0系列文章(七):SpringApplication 深入探索

总结

本文从源码级别分析了 Spring Boot 应用程序的启动过程,着重看了 SpringApplication 类中的构造函数的初始化和其 run 方法内部实现,并把涉及到的流程代码都过了一遍。

感悟:有时候跟代码跟着跟着,发现越陷越深,好难跳出来!后面还需多向别人请教阅读源码的技巧!

最后

虽然源码很难,但随着不断的探索,源码在你面前将会一览无遗,享受这种探索后的成就感!加油!骚年!

自己本人能力有限,源码看的不多,上面如有不对的还请留言交流。

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文章目录
  1. 1. 关注我
  2. 2. 前言
  3. 3. 换个姿势
  4. 4. SpringApplication 初始化
  5. 5. run 方法背后的秘密
  6. 6. 相关文章
  7. 7. 总结
  8. 8. 最后
,