SSM框架搭建及源码解析--bean的初始化及依赖注入(四)

深碍√TFBOYSˉ_ 2022-06-13 04:26 74阅读 0赞

[spring][]容器会在启动的过程中创建bean的实例,在创建实例的过程中会把@Autowired注解的属性都去找到相应类注入。   
现在来分析一下bean的初始化和依赖注入   
refresh()中的finishBeanFactoryInitialization()方法就是初始化整个beanFactory注册的bean   
finishBeanFactoryInitialization()中preInstantiateSingletons()部分代码

for (String beanName : beanNames) {
                RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName);
                if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
                    if (isFactoryBean(beanName)) {
                        final FactoryBean<?> factory = (FactoryBean<?>) getBean(FACTORY_BEAN_PREFIX + beanName);
                        boolean isEagerInit;
                        if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
                            isEagerInit = AccessController.doPrivileged(new PrivilegedAction<Boolean>() {
                                @Override
                                public Boolean run() {
                                    return ((SmartFactoryBean<?>) factory).isEagerInit();
                                }
                            }, getAccessControlContext());
                        }
                        else {
                            isEagerInit = (factory instanceof SmartFactoryBean &&
                                    ((SmartFactoryBean<?>) factory).isEagerInit());
                        }
                        if (isEagerInit) {
                            getBean(beanName);
                        }
                    }
                    else {
                        getBean(beanName);
                    }
                }
            }
     
      
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循环beanDefinitionNames中的beanName调用getBean()

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) {
                    //如果缓存中存在
                            ···
            }
    
            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)) {
                    //如果存在父级容器，则去父级容器中获取
                }
    
                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 dependsOnBean : dependsOn) {
                            if (isDependent(beanName, dependsOnBean)) {
                                throw new BeanCreationException(mbd.getResourceDescription(), beanName,
                                        "Circular depends-on relationship between '" + beanName + "' and '" + dependsOnBean + "'");
                            }
                            registerDependentBean(dependsOnBean, beanName);
                            getBean(dependsOnBean);
                        }
                    }
    
                    // Create bean instance.
                    // 如果是单例
                    if (mbd.isSingleton()) {
                        sharedInstance = getSingleton(beanName, new ObjectFactory<Object>() {
                            @Override
                            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);
                    }
                    // 如果是原型
                    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, new ObjectFactory<Object>() {
                                @Override
                                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);
                        }
                    }
                }
                catch (BeansException ex) {
                    cleanupAfterBeanCreationFailure(beanName);
                    throw ex;
                }
            }
     
      
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如果没有在缓存中获取，都会调用到createBean()中的doCreateBean()   
其中最重要的两句是

//创建bean的实例
    instanceWrapper = createBeanInstance(beanName, mbd, args);
    //注入bean中的属性
    populateBean(beanName, mbd, instanceWrapper);
     
      
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bean实例创建是通过反射调用Constructor.newInstance()来创建实例的   
注入是在创建实例后,populateBean()方法调用BeanPostProcessor的实现类AutowiredAnnotationBeanPostProcessor

if (hasInstAwareBpps) {
                    for (BeanPostProcessor bp : getBeanPostProcessors()) {
                        if (bp instanceof InstantiationAwareBeanPostProcessor) {
                            InstantiationAwareBeanPostProcessor ibp = (InstantiationAwareBeanPostProcessor) bp;
                            pvs = ibp.postProcessPropertyValues(pvs, filteredPds, bw.getWrappedInstance(), beanName);
                            if (pvs == null) {
                                return;
                            }
                        }
                    }
                }
     
      
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@Override
        public PropertyValues postProcessPropertyValues(
                PropertyValues pvs, PropertyDescriptor[] pds, Object bean, String beanName) throws BeansException {
    
            InjectionMetadata metadata = findAutowiringMetadata(beanName, bean.getClass(), pvs);
            try {
                metadata.inject(bean, beanName, pvs);
            }
            catch (Throwable ex) {
                throw new BeanCreationException(beanName, "Injection of autowired dependencies failed", ex);
            }
            return pvs;
        }
     
      
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public void inject(Object target, String beanName, PropertyValues pvs) throws Throwable {
            Collection<InjectedElement> elementsToIterate =
                    (this.checkedElements != null ? this.checkedElements : this.injectedElements);
            if (!elementsToIterate.isEmpty()) {
                boolean debug = logger.isDebugEnabled();
                for (InjectedElement element : elementsToIterate) {
                    if (debug) {
                        logger.debug("Processing injected element of bean '" + beanName + "': " + element);
                    }
                    element.inject(target, beanName, pvs);
                }
            }
        }
     
      
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inject()方法中解决依赖

beanFactory.resolveDependency(desc, beanName, autowiredBeanNames, typeConverter);
     
      
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//如果是数组
    if (type.isArray()) { ···· Map<String, Object> matchingBeans = findAutowireCandidates(beanName, componentType, targetDesc); ··· //如果是集合 }else if (Collection.class.isAssignableFrom(type) && type.isInterface()) { ··· Map<String, Object> matchingBeans = findAutowireCandidates(beanName, elementType, targetDesc); ··· //如果是Map }else if (Map.class.isAssignableFrom(type) && type.isInterface()) { ··· Map<String, Object> matchingBeans = findAutowireCandidates(beanName, valueType, targetDesc); ··· }else { ··· Map<String, Object> matchingBeans = findAutowireCandidates(beanName, type, descriptor); ··· }
     
      
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findAutowireCandidates()方法中会去调用getBean获取

for (String candidateName : candidateNames) {
                if (!isSelfReference(beanName, candidateName) && isAutowireCandidate(candidateName, descriptor)) {
                    result.put(candidateName, getBean(candidateName));
                }
            }
     
      
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如果有@Autowired注解会去获取该属性的getBean方法，如此递归解决依赖。

[spring]: http://lib.csdn.net/base/javaee