springboot加载bean过程探索

springboot一般通过以下main方法来启动项目

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

查看源码发现加载的主要逻辑写在了

ConfigurableApplicationContext org.springframework.boot.SpringApplication.run(String... args)这个方法里面

具体逻辑如下：

/**
     * Run the Spring application, creating and refreshing a new
     * {@link ApplicationContext}.
     * @param args the application arguments (usually passed from a Java main method)
     * @return a running {@link 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);
            //1.创建容器
            context = createApplicationContext();
            exceptionReporters = getSpringFactoriesInstances(
                    SpringBootExceptionReporter.class,
                    new Class[] { ConfigurableApplicationContext.class }, context);
            //2.把bean装载进容器context中去
            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;
    }

下面重点讲"把bean装载进容器context中去"的这个方法prepareContext(context, environment, listeners, applicationArguments, printedBanner)的逻辑

方法的代码实现逻辑如下:

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
        ConfigurableListableBeanFactory beanFactory = context.getBeanFactory();
        beanFactory.registerSingleton("springApplicationArguments", applicationArguments);
        if (printedBanner != null) {
            beanFactory.registerSingleton("springBootBanner", printedBanner);
        }
        if (beanFactory instanceof DefaultListableBeanFactory) {
            ((DefaultListableBeanFactory) beanFactory)
                    .setAllowBeanDefinitionOverriding(this.allowBeanDefinitionOverriding);
        }
        // Load the sources 也就要加载的声明配置的类，这里是声明了@SpringBootApplication的DemoApplication
        Set<Object> sources = getAllSources();
        Assert.notEmpty(sources, "Sources must not be empty");
        //把声明了@SpringBootApplication的类加载进容器的具体实现
        load(context, sources.toArray(new Object[0]));
        listeners.contextLoaded(context);
    }

load方法的具体实现：

/**
     * Load beans into the application context.
     * @param context the context to load beans into
     * @param sources the sources to load
     */
    protected void load(ApplicationContext context, Object[] sources) {
        if (logger.isDebugEnabled()) {
            logger.debug(
                    "Loading source " + StringUtils.arrayToCommaDelimitedString(sources));
        }
        //这个BeanDefinationLoader的实现类为org.springframework.boot.BeanDefinitionLoader,为springboot自定义的一个beanDefination的加载器，专门用来加载配置声明的类的

        BeanDefinitionLoader loader = createBeanDefinitionLoader(
                getBeanDefinitionRegistry(context), sources);
        if (this.beanNameGenerator != null) {
            loader.setBeanNameGenerator(this.beanNameGenerator);
        }
        if (this.resourceLoader != null) {
            loader.setResourceLoader(this.resourceLoader);
        }
        if (this.environment != null) {
            loader.setEnvironment(this.environment);
        }
        //org.springframework.boot.BeanDefinitionLoader把beanDefination加载进spring的BeanDefinationRegistry中的方法

     loader.load();

 }

以下为org.springframework.boot.BeanDefinitionLoader的loan方法实现逻辑:

private int load(Class<?> source) {
        if (isGroovyPresent()
                && GroovyBeanDefinitionSource.class.isAssignableFrom(source)) {
            // Any GroovyLoaders added in beans{} DSL can contribute beans here
            GroovyBeanDefinitionSource loader = BeanUtils.instantiateClass(source,
                    GroovyBeanDefinitionSource.class);
            load(loader);
        }
        if (isComponent(source)) {
            //通过org.springframework.context.annotation.AnnotatedBeanDefinitionReader.AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry)来注册注解扫描的类定义

        this.annotatedReader.register(source);
        return 1;
        }
        return 0;
    }

org.springframework.context.annotation.AnnotatedBeanDefinitionReader的作用是啥呢?来看看

AnnotatedBeanDefinitionReader类的注释:

/**
 * Convenient adapter for programmatic registration of annotated bean classes.
 * This is an alternative to {@link ClassPathBeanDefinitionScanner}, applying
 * the same resolution of annotations but for explicitly registered classes only.
 *
 * @author Juergen Hoeller
 * @author Chris Beams
 * @author Sam Brannen
 * @author Phillip Webb
 * @since 3.0
 * @see AnnotationConfigApplicationContext#register
 */
public class AnnotatedBeanDefinitionReader

意思就是:

用于声明bean类的编程注册的方便的适配器，
这是ClassPathBeanDefinitionsCanner的替代方法，应用
声明类解析，但仅限于显式注册的类。