Spring源码学习

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Spring容器中Bean的创建

  • 目标：Spring容器中的Bean是如何创建的？为什么能从容器中获取到？

  • 探究过程

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public class Demo {
    public static void main(String[] args) {
        ClassPathXmlApplicationContext app = new ClassPathXmlApplicationContext("applicationContext.xml");
        Student student = (Student)app.getBean("student");
        System.out.println(student);
    }
}
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public ClassPathXmlApplicationContext(String configLocation) throws BeansException {
    this(new String[]{configLocation}, true, (ApplicationContext)null);
}

public ClassPathXmlApplicationContext(String[] configLocations, boolean refresh, @Nullable ApplicationContext parent) throws BeansException {
    super(parent);
    this.setConfigLocations(configLocations);
    if (refresh) {
        //创建对象的方法
        this.refresh();
    }

}

public void refresh() throws BeansException, IllegalStateException {
    synchronized(this.startupShutdownMonitor) {
        this.prepareRefresh();
        ConfigurableListableBeanFactory beanFactory = this.obtainFreshBeanFactory();
        this.prepareBeanFactory(beanFactory);

        try {
            this.postProcessBeanFactory(beanFactory);
            this.invokeBeanFactoryPostProcessors(beanFactory);
            this.registerBeanPostProcessors(beanFactory);
            this.initMessageSource();
            this.initApplicationEventMulticaster();
            this.onRefresh();
            this.registerListeners();
            //创建对象的方法
            this.finishBeanFactoryInitialization(beanFactory);
            this.finishRefresh();
        } catch (BeansException var9) {
            if (this.logger.isWarnEnabled()) {
                this.logger.warn("Exception encountered during context initialization - cancelling refresh attempt: " + var9);
            }

            this.destroyBeans();
            this.cancelRefresh(var9);
            throw var9;
        } finally {
            this.resetCommonCaches();
        }

    }
}

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();
	
    //创建对象的方法
    // Instantiate all remaining (non-lazy-init) singletons.
    beanFactory.preInstantiateSingletons();
}
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public void preInstantiateSingletons() throws BeansException {
    if (this.logger.isTraceEnabled()) {
        this.logger.trace("Pre-instantiating singletons in " + this);
    }

    List<String> beanNames = new ArrayList(this.beanDefinitionNames);
    Iterator var2 = beanNames.iterator();

    while(true) {
        String beanName;
        Object bean;
        do {
            while(true) {
                RootBeanDefinition bd;
                do {
                    do {
                        do {
                            if (!var2.hasNext()) {
                                var2 = beanNames.iterator();

                                while(var2.hasNext()) {
                                    beanName = (String)var2.next();
                                    Object singletonInstance = this.getSingleton(beanName);
                                    if (singletonInstance instanceof SmartInitializingSingleton) {
                                        SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton)singletonInstance;
                                        if (System.getSecurityManager() != null) {
                                            AccessController.doPrivileged(() -> {
                                                smartSingleton.afterSingletonsInstantiated();
                                                return null;
                                            }, this.getAccessControlContext());
                                        } else {
                                            smartSingleton.afterSingletonsInstantiated();
                                        }
                                    }
                                }

                                return;
                            }

                            beanName = (String)var2.next();
                            bd = this.getMergedLocalBeanDefinition(beanName);
                        } while(bd.isAbstract());
                    } while(!bd.isSingleton());
                } while(bd.isLazyInit());

                if (this.isFactoryBean(beanName)) {
                    bean = this.getBean("&" + beanName);
                    break;
                }
				//不是FactoryBean将会调用这里创建
                this.getBean(beanName);
            }
        } while(!(bean instanceof FactoryBean));

        FactoryBean<?> factory = (FactoryBean)bean;
        boolean isEagerInit;
        if (System.getSecurityManager() != null && factory instanceof SmartFactoryBean) {
            SmartFactoryBean var10000 = (SmartFactoryBean)factory;
            ((SmartFactoryBean)factory).getClass();
            isEagerInit = (Boolean)AccessController.doPrivileged(var10000::isEagerInit, this.getAccessControlContext());
        } else {
            isEagerInit = factory instanceof SmartFactoryBean && ((SmartFactoryBean)factory).isEagerInit();
        }

        if (isEagerInit) {
            this.getBean(beanName);
        }
    }
}
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public <T> T getBean(String name, Class<T> requiredType) throws BeansException {
    return this.doGetBean(name, requiredType, (Object[])null, false);
}
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protected <T> T doGetBean(String name, @Nullable Class<T> requiredType, @Nullable Object[] args, boolean typeCheckOnly) throws BeansException {
    String beanName = this.transformedBeanName(name);
    Object sharedInstance = this.getSingleton(beanName);
    Object bean;
    if (sharedInstance != null && args == null) {
        if (this.logger.isTraceEnabled()) {
            if (this.isSingletonCurrentlyInCreation(beanName)) {
                this.logger.trace("Returning eagerly cached instance of singleton bean '" + beanName + "' that is not fully initialized yet - a consequence of a circular reference");
            } else {
                this.logger.trace("Returning cached instance of singleton bean '" + beanName + "'");
            }
        }

        bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, (RootBeanDefinition)null);
    } else {
        if (this.isPrototypeCurrentlyInCreation(beanName)) {
            throw new BeanCurrentlyInCreationException(beanName);
        }

        BeanFactory parentBeanFactory = this.getParentBeanFactory();
        if (parentBeanFactory != null && !this.containsBeanDefinition(beanName)) {
            String nameToLookup = this.originalBeanName(name);
            if (parentBeanFactory instanceof AbstractBeanFactory) {
                return ((AbstractBeanFactory)parentBeanFactory).doGetBean(nameToLookup, requiredType, args, typeCheckOnly);
            }

            if (args != null) {
                return parentBeanFactory.getBean(nameToLookup, args);
            }

            if (requiredType != null) {
                return parentBeanFactory.getBean(nameToLookup, requiredType);
            }

            return parentBeanFactory.getBean(nameToLookup);
        }

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

        try {
            RootBeanDefinition mbd = this.getMergedLocalBeanDefinition(beanName);
            this.checkMergedBeanDefinition(mbd, beanName, args);
            String[] dependsOn = mbd.getDependsOn();
            String[] var11;
            if (dependsOn != null) {
                var11 = dependsOn;
                int var12 = dependsOn.length;

                for(int var13 = 0; var13 < var12; ++var13) {
                    String dep = var11[var13];
                    if (this.isDependent(beanName, dep)) {
                        throw new BeanCreationException(mbd.getResourceDescription(), beanName, "Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
                    }

                    this.registerDependentBean(dep, beanName);

                    try {
                        this.getBean(dep);
                    } catch (NoSuchBeanDefinitionException var24) {
                        throw new BeanCreationException(mbd.getResourceDescription(), beanName, "'" + beanName + "' depends on missing bean '" + dep + "'", var24);
                    }
                }
            }

            if (mbd.isSingleton()) {
                sharedInstance = this.getSingleton(beanName, () -> {
                    try {
                        return this.createBean(beanName, mbd, args);
                    } catch (BeansException var5) {
                        this.destroySingleton(beanName);
                        throw var5;
                    }
                });
                bean = this.getObjectForBeanInstance(sharedInstance, name, beanName, mbd);
            } else if (mbd.isPrototype()) {
                var11 = null;

                Object prototypeInstance;
                try {
                    this.beforePrototypeCreation(beanName);
                    prototypeInstance = this.createBean(beanName, mbd, args);
                } finally {
                    this.afterPrototypeCreation(beanName);
                }

                bean = this.getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
            } else {
                String scopeName = mbd.getScope();
                Scope 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, () -> {
                        this.beforePrototypeCreation(beanName);

                        Object var4;
                        try {
                            var4 = this.createBean(beanName, mbd, args);
                        } finally {
                            this.afterPrototypeCreation(beanName);
                        }

                        return var4;
                    });
                    bean = this.getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
                } catch (IllegalStateException var23) {
                    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", var23);
                }
            }
        } catch (BeansException var26) {
            this.cleanupAfterBeanCreationFailure(beanName);
            throw var26;
        }
    }

    if (requiredType != null && !requiredType.isInstance(bean)) {
        try {
            T convertedBean = this.getTypeConverter().convertIfNecessary(bean, requiredType);
            if (convertedBean == null) {
                throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
            } else {
                return convertedBean;
            }
        } catch (TypeMismatchException var25) {
            if (this.logger.isTraceEnabled()) {
                this.logger.trace("Failed to convert bean '" + name + "' to required type '" + ClassUtils.getQualifiedName(requiredType) + "'", var25);
            }

            throw new BeanNotOfRequiredTypeException(name, requiredType, bean.getClass());
        }
    } else {
        return bean;
    }
}
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public Object getSingleton(String beanName, ObjectFactory<?> singletonFactory) {
    Assert.notNull(beanName, "Bean name must not be null");
    synchronized (this.singletonObjects) {
        Object singletonObject = this.singletonObjects.get(beanName);
        if (singletonObject == null) {
            if (this.singletonsCurrentlyInDestruction) {
                throw new BeanCreationNotAllowedException(beanName,
                                                          "Singleton bean creation not allowed while singletons of this factory are in destruction " +
                                                          "(Do not request a bean from a BeanFactory in a destroy method implementation!)");
            }
            if (logger.isDebugEnabled()) {
                logger.debug("Creating shared instance of singleton bean '" + beanName + "'");
            }
            beforeSingletonCreation(beanName);
            boolean newSingleton = false;
            boolean recordSuppressedExceptions = (this.suppressedExceptions == null);
            if (recordSuppressedExceptions) {
                this.suppressedExceptions = new LinkedHashSet<>();
            }
            try {
                singletonObject = singletonFactory.getObject();
                newSingleton = true;
            }
            catch (IllegalStateException ex) {
                // Has the singleton object implicitly appeared in the meantime ->
                // if yes, proceed with it since the exception indicates that state.
                singletonObject = this.singletonObjects.get(beanName);
                if (singletonObject == null) {
                    throw ex;
                }
            }
            catch (BeanCreationException ex) {
                if (recordSuppressedExceptions) {
                    for (Exception suppressedException : this.suppressedExceptions) {
                        ex.addRelatedCause(suppressedException);
                    }
                }
                throw ex;
            }
            finally {
                if (recordSuppressedExceptions) {
                    this.suppressedExceptions = null;
                }
                afterSingletonCreation(beanName);
            }
            if (newSingleton) {
                addSingleton(beanName, singletonObject);
            }
        }
        return singletonObject;
    }
}
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Student student = (Student)app.getBean("student");

public Object getBean(String name) throws BeansException {
    assertBeanFactoryActive();
    return getBeanFactory().getBean(name);
}

public final ConfigurableListableBeanFactory getBeanFactory() {
    synchronized (this.beanFactoryMonitor) {
        if (this.beanFactory == null) {
            throw new IllegalStateException("BeanFactory not initialized or already closed - " +
                                            "call 'refresh' before accessing beans via the ApplicationContext");
        }
        return this.beanFactory;
    }
}

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

  • 结论：非懒加载的单例实例bean会在容器创建的时候创建，容器内部会创建一个beanFactory，使用beanFactory的doGetBean方法来通过反射进行创建，并且在创建后会把bean放入一个单例bean的Map集合中存储。key就是我们配置的bean的名称。所以我们调用容器的getBean方法来获取对象的时候，其实它也是调用了doGetBean方法。就会从对应的集合中获取到之前创建的对象。
  • 疑问：RootBeanDefinition是什么？是怎么bean名获取对应的RootBeanDefinition对象的；如果是FactoryBean是怎么创建的
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