springboot加載bean過程探索

springboot一般通過以下main方法來啟動項目

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

查看源碼發現加載的主要邏輯寫在了

ConfigurableApplicationContext org. springframework. boot. SpringApplication.run( String... args)這個方法里面

具體邏輯如下：

/**
     * 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.創建容器
            context = createApplicationContext();
            exceptionReporters = getSpringFactoriesInstances(
                    SpringBootExceptionReporter.class,
                    new Class[] { ConfigurableApplicationContext.class }, context);
            //2.把bean裝載進容器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;
    }

 

下面重點講"把bean裝載進容器context中去"的這個方法prepareContext(context, environment, listeners, applicationArguments, printedBanner)的邏輯

 方法的代碼實現邏輯如下:

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 也就要加載的聲明配置的類，這里是聲明了@SpringBootApplication的DemoApplication
        Set<Object> sources = getAllSources();
        Assert.notEmpty(sources, "Sources must not be empty");
        //把聲明了@SpringBootApplication的類加載進容器的具體實現
        load(context, sources.toArray(new Object[0]));
        listeners.contextLoaded(context);
    }

 

load方法的具體實現：

/**
     * 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));
        }
        //這個BeanDefinationLoader的實現類為org.springframework.boot.BeanDefinitionLoader,為springboot自定義的一個beanDefination的加載器，專門用來加載配置聲明的類的

 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加載進spring的BeanDefinationRegistry中的方法

 loader.load();

 }

 

以下為org.springframework.boot.BeanDefinitionLoader的loan方法實現邏輯:

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)) {
            //通過org.springframework.context.annotation.AnnotatedBeanDefinitionReader.AnnotatedBeanDefinitionReader(BeanDefinitionRegistry registry)來注冊注解掃描的類定義

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

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

AnnotatedBeanDefinitionReader類的注釋:

/**
 * 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:

用於聲明bean類的編程注冊的方便的適配器，
這是ClassPathBeanDefinitionsCanner的替代方法，應用
聲明類解析，但僅限於顯式注冊的類。