springboot源码解析-管中窥豹系列之bean如何生成？（十四）

一、前言

• Springboot源码解析是一件大工程，逐行逐句的去研究代码，会很枯燥，也不容易坚持下去。
• 我们不追求大而全，而是试着每次去研究一个小知识点，最终聚沙成塔，这就是我们的springboot源码管中窥豹系列。

二、bean如何生成？

• 我们之前介绍了beanDefinition的结构： springboot源码解析-管中窥豹系列之BeanDefinition（八）
• 我们之前也介绍了BeanPostProcessor和BeanFactoryPostProcessor
• 我们也介绍了自动装配，各种使用getBean的调用
• 有两个核心问题：beanDefinition是什么时候加载进springcontext容器的？又是如何生成bean的？
• 我们上一节解决了第一个问题：beanDefinition是什么时候加载？
• 我们这一节解决第二个问题：如何生成bean？

三、源码分析

进入到main方法：

public static void main(String[] args) throws Exception {
    SpringApplication.run(MyServerApplication.class, args);
}

从main方法进入到run方法：

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;
}

再从run方法进到refreshContext(context)里面的refresh:

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);

            // Last step: publish corresponding event.
            finishRefresh();
        }

        catch (BeansException ex) {
            if (logger.isWarnEnabled()) {
                logger.warn("Exception encountered during context initialization - " +
                        "cancelling refresh attempt: " + 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();
        }
    }
}

这次我们看这个方法：finishBeanFactoryInitialization(beanFactory)

protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
    // Initialize conversion service for this context.
    if (beanFactory.containsBean(CONVERSION_SERVICE_BEAN_NAME) &&
            beanFactory.isTypeMatch(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class)) {
        beanFactory.setConversionService(
                beanFactory.getBean(CONVERSION_SERVICE_BEAN_NAME, ConversionService.class));
    }

    // Register a default embedded value resolver if no bean post-processor
    // (such as a PropertyPlaceholderConfigurer bean) registered any before:
    // at this point, primarily for resolution in annotation attribute values.
    if (!beanFactory.hasEmbeddedValueResolver()) {
        beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
    }

    // Initialize LoadTimeWeaverAware beans early to allow for registering their transformers early.
    String[] weaverAwareNames = beanFactory.getBeanNamesForType(LoadTimeWeaverAware.class, false, false);
    for (String weaverAwareName : weaverAwareNames) {
        getBean(weaverAwareName);
    }

    // Stop using the temporary ClassLoader for type matching.
    beanFactory.setTempClassLoader(null);

    // Allow for caching all bean definition metadata, not expecting further changes.
    beanFactory.freezeConfiguration();

    // Instantiate all remaining (non-lazy-init) singletons.
    beanFactory.preInstantiateSingletons();
}

核心方法在最后一句：beanFactory.preInstantiateSingletons()

public void preInstantiateSingletons() throws BeansException {
    if (logger.isTraceEnabled()) {
        logger.trace("Pre-instantiating singletons in " + this);
    }

    // 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();
            }
        }
    }
}

• 重点看第一个for循环
• 对所有的BeanDefinition，非静态，非懒加载，并且是单例，就执行getBean(beanName)
• 先忽略FactoryBean，我们后面再说
• 我们看看getBean(beanName)

@Override
public Object getBean(String name) throws BeansException {
    return doGetBean(name, null, null, false);
}

protected <T> T doGetBean(final String name, @Nullable final Class<T> requiredType,
        @Nullable final Object[] args, boolean typeCheckOnly) throws BeansException {

    final String beanName = transformedBeanName(name);
    Object bean;

    // Eagerly check singleton cache for manually registered singletons.
    Object sharedInstance = getSingleton(beanName);
    if (sharedInstance != null && args == null) {
        if (logger.isTraceEnabled()) {
            if (isSingletonCurrentlyInCreation(beanName)) {
                logger.trace("Returning eagerly cached instance of singleton bean '" + beanName +
                        "' that is not fully initialized yet - a consequence of a circular reference");
            }
            else {
                logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
            }
        }
        bean = getObjectForBeanInstance(sharedInstance, name, beanName, null);
    }

    else {
        // Fail if we're already creating this bean instance:
        // We're assumably within a circular reference.
        if (isPrototypeCurrentlyInCreation(beanName)) {
            throw new BeanCurrentlyInCreationException(beanName);
        }

        // Check if bean definition exists in this factory.
        BeanFactory parentBeanFactory = getParentBeanFactory();
        if (parentBeanFactory != null && !containsBeanDefinition(beanName)) {
            // Not found -> check parent.
            String nameToLookup = originalBeanName(name);
            if (parentBeanFactory instanceof AbstractBeanFactory) {
                return ((AbstractBeanFactory) parentBeanFactory).doGetBean(
                        nameToLookup, requiredType, args, typeCheckOnly);
            }
            else if (args != null) {
                // Delegation to parent with explicit args.
                return (T) parentBeanFactory.getBean(nameToLookup, args);
            }
            else if (requiredType != null) {
                // No args -> delegate to standard getBean method.
                return parentBeanFactory.getBean(nameToLookup, requiredType);
            }
            else {
                return (T) parentBeanFactory.getBean(nameToLookup);
            }
        }

        if (!typeCheckOnly) {
            markBeanAsCreated(beanName);
        }

        try {
            final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName);
            checkMergedBeanDefinition(mbd, beanName, args);

            // Guarantee initialization of beans that the current bean depends on.
            String[] dependsOn = mbd.getDependsOn();
            if (dependsOn != null) {
                for (String dep : dependsOn) {
                    if (isDependent(beanName, dep)) {
                        throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                                "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
                    }
                    registerDependentBean(dep, beanName);
                    try {
                        getBean(dep);
                    }
                    catch (NoSuchBeanDefinitionException ex) {
                        throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                                "'" + beanName + "' depends on missing bean '" + dep + "'", ex);
                    }
                }
            }

            // Create bean instance.
            if (mbd.isSingleton()) {
                sharedInstance = getSingleton(beanName, () -> {
                    try {
                        return createBean(beanName, mbd, args);
                    }
                    catch (BeansException ex) {
                        // Explicitly remove instance from singleton cache: It might have been put there
                        // eagerly by the creation process, to allow for circular reference resolution.
                        // Also remove any beans that received a temporary reference to the bean.
                        destroySingleton(beanName);
                        throw ex;
                    }
                });
                bean = getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
            }

            else if (mbd.isPrototype()) {
                // It's a prototype -> create a new instance.
                Object prototypeInstance = null;
                try {
                    beforePrototypeCreation(beanName);
                    prototypeInstance = createBean(beanName, mbd, args);
                }
                finally {
                    afterPrototypeCreation(beanName);
                }
                bean = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
            }

            else {
                String scopeName = mbd.getScope();
                final Scope scope = this.scopes.get(scopeName);
                if (scope == null) {
                    throw new IllegalStateException("No Scope registered for scope name '" + scopeName + "'");
                }
                try {
                    Object scopedInstance = scope.get(beanName, () -> {
                        beforePrototypeCreation(beanName);
                        try {
                            return createBean(beanName, mbd, args);
                        }
                        finally {
                            afterPrototypeCreation(beanName);
                        }
                    });
                    bean = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
                }
                catch (IllegalStateException ex) {
                    throw new BeanCreationException(beanName,
                            "Scope '" + scopeName + "' is not active for the current thread; consider " +
                            "defining a scoped proxy for this bean if you intend to refer to it from a singleton",
                            ex);
                }
            }
        }
        catch (BeansException ex) {
            cleanupAfterBeanCreationFailure(beanName);
            throw ex;
        }
    }

    // Check if required type matches the type of the actual bean instance.
    if (requiredType != null && !requiredType.isInstance(bean)) {
        try {
            T convertedBean = getTypeConverter().convertIfNecessary(bean, requiredType);
            if (convertedBean == null) {
                throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
            }
            return convertedBean;
        }
        catch (TypeMismatchException ex) {
            if (logger.isTraceEnabled()) {
                logger.trace("Failed to convert bean '" + name + "' to required type '" +
                        ClassUtils.getQualifiedName(requiredType) + "'", ex);
            }
            throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
        }
    }
    return (T) bean;
}

• 方法比较长，我们一点点看
• Object sharedInstance = getSingleton(beanName);
• 先看看能不能拿到sharedInstance，这部分的bean是手动插入的bean
• 没拿到，则执行else部分
• 最重要的是这一句： createBean(beanName, mbd, args)

protected Object createBean(String beanName, RootBeanDefinition mbd, @Nullable Object[] args)
        throws BeanCreationException {

    if (logger.isTraceEnabled()) {
        logger.trace("Creating instance of bean '" + beanName + "'");
    }
    RootBeanDefinition mbdToUse = mbd;

    // Make sure bean class is actually resolved at this point, and
    // clone the bean definition in case of a dynamically resolved Class
    // which cannot be stored in the shared merged bean definition.
    Class<?> resolvedClass = resolveBeanClass(mbd, beanName);
    if (resolvedClass != null && !mbd.hasBeanClass() && mbd.getBeanClassName() != null) {
        mbdToUse = new RootBeanDefinition(mbd);
        mbdToUse.setBeanClass(resolvedClass);
    }

    // Prepare method overrides.
    try {
        mbdToUse.prepareMethodOverrides();
    }
    catch (BeanDefinitionValidationException ex) {
        throw new BeanDefinitionStoreException(mbdToUse.getResourceDescription(),
                beanName, "Validation of method overrides failed", ex);
    }

    try {
        // Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
        Object bean = resolveBeforeInstantiation(beanName, mbdToUse);
        if (bean != null) {
            return bean;
        }
    }
    catch (Throwable ex) {
        throw new BeanCreationException(mbdToUse.getResourceDescription(), beanName,
                "BeanPostProcessor before instantiation of bean failed", ex);
    }

    try {
        Object beanInstance = doCreateBean(beanName, mbdToUse, args);
        if (logger.isTraceEnabled()) {
            logger.trace("Finished creating instance of bean '" + beanName + "'");
        }
        return beanInstance;
    }
    catch (BeanCreationException | ImplicitlyAppearedSingletonException ex) {
        // A previously detected exception with proper bean creation context already,
        // or illegal singleton state to be communicated up to DefaultSingletonBeanRegistry.
        throw ex;
    }
    catch (Throwable ex) {
        throw new BeanCreationException(
                mbdToUse.getResourceDescription(), beanName, "Unexpected exception during bean creation", ex);
    }
}

细枝末节先不看，进入到doCreateBean(beanName, mbdToUse, args)

protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final @Nullable Object[] args)
        throws BeanCreationException {

    // Instantiate the bean.
    BeanWrapper instanceWrapper = null;
    if (mbd.isSingleton()) {
        instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
    }
    if (instanceWrapper == null) {
        instanceWrapper = createBeanInstance(beanName, mbd, args);
    }
    final Object bean = instanceWrapper.getWrappedInstance();
    Class<?> beanType = instanceWrapper.getWrappedClass();
    if (beanType != NullBean.class) {
        mbd.resolvedTargetType = beanType;
    }

    // Allow post-processors to modify the merged bean definition.
    synchronized (mbd.postProcessingLock) {
        if (!mbd.postProcessed) {
            try {
                applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
            }
            catch (Throwable ex) {
                throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                        "Post-processing of merged bean definition failed", ex);
            }
            mbd.postProcessed = true;
        }
    }

    // Eagerly cache singletons to be able to resolve circular references
    // even when triggered by lifecycle interfaces like BeanFactoryAware.
    boolean earlySingletonExposure = (mbd.isSingleton() && this.allowCircularReferences &&
            isSingletonCurrentlyInCreation(beanName));
    if (earlySingletonExposure) {
        if (logger.isTraceEnabled()) {
            logger.trace("Eagerly caching bean '" + beanName +
                    "' to allow for resolving potential circular references");
        }
        addSingletonFactory(beanName, () -> getEarlyBeanReference(beanName, mbd, bean));
    }

    // Initialize the bean instance.
    Object exposedObject = bean;
    try {
        populateBean(beanName, mbd, instanceWrapper);
        exposedObject = initializeBean(beanName, exposedObject, mbd);
    }
    catch (Throwable ex) {
        if (ex instanceof BeanCreationException && beanName.equals(((BeanCreationException) ex).getBeanName())) {
            throw (BeanCreationException) ex;
        }
        else {
            throw new BeanCreationException(
                    mbd.getResourceDescription(), beanName, "Initialization of bean failed", ex);
        }
    }

    if (earlySingletonExposure) {
        Object earlySingletonReference = getSingleton(beanName, false);
        if (earlySingletonReference != null) {
            if (exposedObject == bean) {
                exposedObject = earlySingletonReference;
            }
            else if (!this.allowRawInjectionDespiteWrapping && hasDependentBean(beanName)) {
                String[] dependentBeans = getDependentBeans(beanName);
                Set<String> actualDependentBeans = new LinkedHashSet<>(dependentBeans.length);
                for (String dependentBean : dependentBeans) {
                    if (!removeSingletonIfCreatedForTypeCheckOnly(dependentBean)) {
                        actualDependentBeans.add(dependentBean);
                    }
                }
                if (!actualDependentBeans.isEmpty()) {
                    throw new BeanCurrentlyInCreationException(beanName,
                            "Bean with name '" + beanName + "' has been injected into other beans [" +
                            StringUtils.collectionToCommaDelimitedString(actualDependentBeans) +
                            "] in its raw version as part of a circular reference, but has eventually been " +
                            "wrapped. This means that said other beans do not use the final version of the " +
                            "bean. This is often the result of over-eager type matching - consider using " +
                            "'getBeanNamesForType' with the 'allowEagerInit' flag turned off, for example.");
                }
            }
        }
    }

    // Register bean as disposable.
    try {
        registerDisposableBeanIfNecessary(beanName, bean, mbd);
    }
    catch (BeanDefinitionValidationException ex) {
        throw new BeanCreationException(
                mbd.getResourceDescription(), beanName, "Invalid destruction signature", ex);
    }

    return exposedObject;
}

还是看核心方法：instanceWrapper = createBeanInstance(beanName, mbd, args)

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
    // Make sure bean class is actually resolved at this point.
    Class<?> beanClass = resolveBeanClass(mbd, beanName);

    if (beanClass != null && !Modifier.isPublic(beanClass.getModifiers()) && !mbd.isNonPublicAccessAllowed()) {
        throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                "Bean class isn't public, and non-public access not allowed: " + beanClass.getName());
    }

    Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
    if (instanceSupplier != null) {
        return obtainFromSupplier(instanceSupplier, beanName);
    }

    if (mbd.getFactoryMethodName() != null) {
        return instantiateUsingFactoryMethod(beanName, mbd, args);
    }

    // Shortcut when re-creating the same bean...
    boolean resolved = false;
    boolean autowireNecessary = false;
    if (args == null) {
        synchronized (mbd.constructorArgumentLock) {
            if (mbd.resolvedConstructorOrFactoryMethod != null) {
                resolved = true;
                autowireNecessary = mbd.constructorArgumentsResolved;
            }
        }
    }
    if (resolved) {
        if (autowireNecessary) {
            return autowireConstructor(beanName, mbd, null, null);
        }
        else {
            return instantiateBean(beanName, mbd);
        }
    }

    // Candidate constructors for autowiring?
    Constructor<?>[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
    if (ctors != null || mbd.getResolvedAutowireMode() == AUTOWIRE_CONSTRUCTOR ||
            mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args)) {
        return autowireConstructor(beanName, mbd, ctors, args);
    }

    // Preferred constructors for default construction?
    ctors = mbd.getPreferredConstructors();
    if (ctors != null) {
        return autowireConstructor(beanName, mbd, ctors, null);
    }

    // No special handling: simply use no-arg constructor.
    return instantiateBean(beanName, mbd);
}

看最后一行：instantiateBean(beanName, mbd)

protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
    try {
        Object beanInstance;
        final BeanFactory parent = this;
        if (System.getSecurityManager() != null) {
            beanInstance = AccessController.doPrivileged((PrivilegedAction<Object>) () ->
                    getInstantiationStrategy().instantiate(mbd, beanName, parent),
                    getAccessControlContext());
        }
        else {
            beanInstance = getInstantiationStrategy().instantiate(mbd, beanName, parent);
        }
        BeanWrapper bw = new BeanWrapperImpl(beanInstance);
        initBeanWrapper(bw);
        return bw;
    }
    catch (Throwable ex) {
        throw new BeanCreationException(
                mbd.getResourceDescription(), beanName, "Instantiation of bean failed", ex);
    }
}

进入这个方法：getInstantiationStrategy().instantiate(mbd, beanName, parent)

// SimpleInstantiationStrategy.class

public Object instantiate(RootBeanDefinition bd, @Nullable String beanName, BeanFactory owner) {
    // Don't override the class with CGLIB if no overrides.
    if (!bd.hasMethodOverrides()) {
        Constructor<?> constructorToUse;
        synchronized (bd.constructorArgumentLock) {
            constructorToUse = (Constructor<?>) bd.resolvedConstructorOrFactoryMethod;
            if (constructorToUse == null) {
                final Class<?> clazz = bd.getBeanClass();
                if (clazz.isInterface()) {
                    throw new BeanInstantiationException(clazz, "Specified class is an interface");
                }
                try {
                    if (System.getSecurityManager() != null) {
                        constructorToUse = AccessController.doPrivileged(
                                (PrivilegedExceptionAction<Constructor<?>>) clazz::getDeclaredConstructor);
                    }
                    else {
                        constructorToUse = clazz.getDeclaredConstructor();
                    }
                    bd.resolvedConstructorOrFactoryMethod = constructorToUse;
                }
                catch (Throwable ex) {
                    throw new BeanInstantiationException(clazz, "No default constructor found", ex);
                }
            }
        }
        return BeanUtils.instantiateClass(constructorToUse);
    }
    else {
        // Must generate CGLIB subclass.
        return instantiateWithMethodInjection(bd, beanName, owner);
    }
}

看看BeanUtils.instantiateClass(constructorToUse)

public static <T> T instantiateClass(Constructor<T> ctor, Object... args) throws BeanInstantiationException {
    Assert.notNull(ctor, "Constructor must not be null");
    try {
        ReflectionUtils.makeAccessible(ctor);
        if (KotlinDetector.isKotlinReflectPresent() && KotlinDetector.isKotlinType(ctor.getDeclaringClass())) {
            return KotlinDelegate.instantiateClass(ctor, args);
        }
        else {
            Class<?>[] parameterTypes = ctor.getParameterTypes();
            Assert.isTrue(args.length <= parameterTypes.length, "Can't specify more arguments than constructor parameters");
            Object[] argsWithDefaultValues = new Object[args.length];
            for (int i = 0 ; i < args.length; i++) {
                if (args[i] == null) {
                    Class<?> parameterType = parameterTypes[i];
                    argsWithDefaultValues[i] = (parameterType.isPrimitive() ? DEFAULT_TYPE_VALUES.get(parameterType) : null);
                }
                else {
                    argsWithDefaultValues[i] = args[i];
                }
            }
            return ctor.newInstance(argsWithDefaultValues);
        }
    }
    catch (InstantiationException ex) {
        throw new BeanInstantiationException(ctor, "Is it an abstract class?", ex);
    }
    catch (IllegalAccessException ex) {
        throw new BeanInstantiationException(ctor, "Is the constructor accessible?", ex);
    }
    catch (IllegalArgumentException ex) {
        throw new BeanInstantiationException(ctor, "Illegal arguments for constructor", ex);
    }
    catch (InvocationTargetException ex) {
        throw new BeanInstantiationException(ctor, "Constructor threw exception", ex.getTargetException());
    }
}

• 到此，找到终点了，利用构造函数通过反射生产bean

目录

springboot源码解析-管中窥豹系列之总体结构（一）

springboot源码解析-管中窥豹系列之项目类型（二）

springboot源码解析-管中窥豹系列之Runner（三）

springboot源码解析-管中窥豹系列之Initializer（四）

springboot源码解析-管中窥豹系列之排序（五）

springboot源码解析-管中窥豹系列之aware（六）

springboot源码解析-管中窥豹系列之web服务器（七）

springboot源码解析-管中窥豹系列之BeanDefinition（八）

springboot源码解析-管中窥豹系列之自动装配（九）

springboot源码解析-管中窥豹系列之EnableXXX（十）

springboot源码解析-管中窥豹系列之BeanFactoryPostProcessor（十一）

springboot源码解析-管中窥豹系列之BeanPostProcessor（十二）

springboot源码解析-管中窥豹系列之BeanDefine如何加载（十三）

springboot源码解析-管中窥豹系列之bean如何生成？（十四）

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