spring ioc 源码解析（二）

末蓝、 2022-09-21 05:32 187阅读 0赞

### spring创建bean原理 ###

#### 1. 获取bean实例，下面通过final RootBeanDefinition mbd = getMergedLocalBeanDefinition(beanName)从beanDefinitionMap缓存中获取BeanDefinition结果 ####

public Object getBean(String name) throws BeansException {
            return doGetBean(name, null, null, false);
        }
    
            /** * Return an instance, which may be shared or independent, of the specified bean. * @param name the name of the bean to retrieve * @param requiredType the required type of the bean to retrieve * @param args arguments to use if creating a prototype using explicit arguments to a * static factory method. It is invalid to use a non-null args value in any other case. * @param typeCheckOnly whether the instance is obtained for a type check, * not for actual use * @return an instance of the bean * @throws BeansException if the bean could not be created */
        @SuppressWarnings("unchecked")
        protected <T> T doGetBean(
                final String name, final Class<T> requiredType, 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.isDebugEnabled()) {
                    if (isSingletonCurrentlyInCreation(beanName)) {
                        logger.debug("Returning eagerly cached instance of singleton bean '" + beanName +
                                "' that is not fully initialized yet - a consequence of a circular reference");
                    }
                    else {
                        logger.debug("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 (args != null) {
                        // Delegation to parent with explicit args.
                        return (T) parentBeanFactory.getBean(nameToLookup, args);
                    }
                    else {
                        // No args -> delegate to standard getBean method.
                        return parentBeanFactory.getBean(nameToLookup, requiredType);
                    }
                }
    
                if (!typeCheckOnly) {
                    markBeanAsCreated(beanName);
                }
    
                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 dependsOnBean : dependsOn) {
                        getBean(dependsOnBean);
                        registerDependentBean(dependsOnBean, beanName);
                    }
                }
    
                // Create bean instance.
                if (mbd.isSingleton()) {
                    sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
                        public Object getObject() throws BeansException {
                            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 '" + scopeName + "'");
                    }
                    try {
                        Object scopedInstance = scope.get(beanName, new ObjectFactory<Object>() {
                            public Object getObject() throws BeansException {
                                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);
                    }
                }
            }
    
            // Check if required type matches the type of the actual bean instance.
            if (requiredType != null && bean != null && !requiredType.isAssignableFrom(bean.getClass())) {
                try {
                    return getTypeConverter().convertIfNecessary(bean, requiredType);
                }
                catch (TypeMismatchException ex) {
                    if (logger.isDebugEnabled()) {
                        logger.debug("Failed to convert bean '" + name + "' to required type [" +
                                ClassUtils.getQualifiedName(requiredType) + "]", ex);
                    }
                    throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
                }
            }
            return (T) bean;
        }

#### 2. 从加载xml生成的beanDefinitionMap中获取BeanDefinition结果 ####

protected RootBeanDefinition getMergedLocalBeanDefinition(String beanName) throws BeansException {
            // Quick check on the concurrent map first, with minimal locking.
            RootBeanDefinition mbd = this.mergedBeanDefinitions.get(beanName);
            if (mbd != null) {
                return mbd;
            }
            return getMergedBeanDefinition(beanName, getBeanDefinition(beanName));
        }
    
        public BeanDefinition getBeanDefinition(String beanName) throws NoSuchBeanDefinitionException {
            BeanDefinition bd = this.beanDefinitionMap.get(beanName);
            if (bd == null) {
                if (this.logger.isTraceEnabled()) {
                    this.logger.trace("No bean named '" + beanName + "' found in " + this);
                }
                throw new NoSuchBeanDefinitionException(beanName);
            }
            return bd;
        }

#### 3. 通过内部调用doCreateBean()方法创建bean实例 ####

protected Object createBean(final String beanName, final RootBeanDefinition mbd, final Object[] args)
                throws BeanCreationException {
    
            if (logger.isDebugEnabled()) {
                logger.debug("Creating instance of bean '" + beanName + "'");
            }
            // Make sure bean class is actually resolved at this point.
            resolveBeanClass(mbd, beanName);
    
            // Prepare method overrides.
            try {
                mbd.prepareMethodOverrides();
            }
            catch (BeanDefinitionValidationException ex) {
                throw new BeanDefinitionStoreException(mbd.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, mbd);
                if (bean != null) {
                    return bean;
                }
            }
            catch (Throwable ex) {
                throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                        "BeanPostProcessor before instantiation of bean failed", ex);
            }
    
            Object beanInstance = doCreateBean(beanName, mbd, args);
            if (logger.isDebugEnabled()) {
                logger.debug("Finished creating instance of bean '" + beanName + "'");
            }
            return beanInstance;
        }

#### 4. 通过内部调用createBeanInstance方法创建bean实例 ####

/** * Actually create the specified bean. Pre-creation processing has already happened * at this point, e.g. checking {@code postProcessBeforeInstantiation} callbacks. * <p>Differentiates between default bean instantiation, use of a * factory method, and autowiring a constructor. * @param beanName the name of the bean * @param mbd the merged bean definition for the bean * @param args arguments to use if creating a prototype using explicit arguments to a * static factory method. This parameter must be {@code null} except in this case. * @return a new instance of the bean * @throws BeanCreationException if the bean could not be created * @see #instantiateBean * @see #instantiateUsingFactoryMethod * @see #autowireConstructor */
        protected Object doCreateBean(final String beanName, final RootBeanDefinition mbd, final Object[] args) {
            // 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 != null ? instanceWrapper.getWrappedInstance() : null);
            Class<?> beanType = (instanceWrapper != null ? instanceWrapper.getWrappedClass() : null);
    
            // Allow post-processors to modify the merged bean definition.
            synchronized (mbd.postProcessingLock) {
                if (!mbd.postProcessed) {
                    applyMergedBeanDefinitionPostProcessors(mbd, beanType, beanName);
                    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.isDebugEnabled()) {
                    logger.debug("Eagerly caching bean '" + beanName +
                            "' to allow for resolving potential circular references");
                }
                addSingletonFactory(beanName, new ObjectFactory() {
                    public Object getObject() throws BeansException {
                        return getEarlyBeanReference(beanName, mbd, bean);
                    }
                });
            }
    
            // Initialize the bean instance.
            Object exposedObject = bean;
            try {
                populateBean(beanName, mbd, instanceWrapper);
                if (exposedObject != null) {
                    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<String>(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 " +
                                    "'getBeanNamesOfType' 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;
        }

#### 5. 真正创建bean实例 ####

protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, 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());
            }
            //如果工厂方法不为空时，使用工厂方法创建实例
            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) {
                    // 构造函数自动注入
                    return autowireConstructor(beanName, mbd, null, null);
                }
                else {
                    // 使用默认构造函数构造
                    return instantiateBean(beanName, mbd);
                }
            }
    
            // Need to determine the constructor...
            Constructor[] ctors = determineConstructorsFromBeanPostProcessors(beanClass, beanName);
            if (ctors != null ||
                    mbd.getResolvedAutowireMode() == RootBeanDefinition.AUTOWIRE_CONSTRUCTOR ||
                    mbd.hasConstructorArgumentValues() || !ObjectUtils.isEmpty(args))  {
                return autowireConstructor(beanName, mbd, ctors, args);
            }
    
            // No special handling: simply use no-arg constructor.
            // 使用默认构造函数构造
            return instantiateBean(beanName, mbd);
        }

#### 6. 通过默认constructor创建bean ####

/** * Instantiate the given bean using its default constructor. * @param beanName the name of the bean * @param mbd the bean definition for the bean * @return BeanWrapper for the new instance */
        protected BeanWrapper instantiateBean(final String beanName, final RootBeanDefinition mbd) {
            try {
                Object beanInstance;
                final BeanFactory parent = this;
                if (System.getSecurityManager() != null) {
                    beanInstance = AccessController.doPrivileged(new PrivilegedAction<Object>() {
                        public Object run() {
                            return 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);
            }
        }

#### 7. 获取Constructor ####

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

#### 8. 真正使用ctor.newInstance(args);创建bean实例 ####

public static <T> T instantiateClass(Constructor<T> ctor, Object... args) throws BeanInstantiationException {
            Assert.notNull(ctor, "Constructor must not be null");
            try {
                ReflectionUtils.makeAccessible(ctor);
                return ctor.newInstance(args);
            }
            catch (InstantiationException ex) {
                throw new BeanInstantiationException(ctor.getDeclaringClass(),
                        "Is it an abstract class?", ex);
            }
            catch (IllegalAccessException ex) {
                throw new BeanInstantiationException(ctor.getDeclaringClass(),
                        "Is the constructor accessible?", ex);
            }
            catch (IllegalArgumentException ex) {
                throw new BeanInstantiationException(ctor.getDeclaringClass(),
                        "Illegal arguments for constructor", ex);
            }
            catch (InvocationTargetException ex) {
                throw new BeanInstantiationException(ctor.getDeclaringClass(),
                        "Constructor threw exception", ex.getTargetException());
            }
        }