【源码解析】聊聊SpringBean是如何初始化和创建

我们知道通过类进行修复不同的属性,比如单例、原型等,而具体的流程是怎么样的呢,这一篇我们开始从源码的视角分析以下。

刷新方法

在刷新容器中有一个方法,其实就是 Bean创建的过程。

	finishBeanFactoryInitialization(beanFactory);

finishBeanFactoryInitialization

	protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory) {
		// 给工厂设置好 ConversionService【负责类型转换的组件服务】, 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));
		}

		// 注册一个默认的值解析器("${}")  ;Register a default embedded value resolver if no BeanFactoryPostProcessor
		// (such as a PropertySourcesPlaceholderConfigurer bean) registered any before:
		// at this point, primarily for resolution in annotation attribute values.
		if (!beanFactory.hasEmbeddedValueResolver()) {
			beanFactory.addEmbeddedValueResolver(strVal -> getEnvironment().resolvePlaceholders(strVal));
		}

		// LoadTimeWeaverAware;aspectj:加载时织入功能【aop】。 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); //从容器中获取组件,有则直接获取,没则进行创建
		}

		// 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.
		//初始化所有的非懒加载的单实例Bean
		beanFactory.preInstantiateSingletons(); //这里是重点
	}

而BeanFactory中 preInstantiateSingletons是初始化所有的bean对象的核心流程。

	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);

		// 创建出所有的单实例Bean;Trigger initialization of all non-lazy singleton beans...
		for (String beanName : beanNames) {
			RootBeanDefinition bd = getMergedLocalBeanDefinition(beanName); //开始解析文件的时候每一个bean标签被解析封装成一个BeanDefinition
			if (!bd.isAbstract() && bd.isSingleton() && !bd.isLazyInit()) {
				if (isFactoryBean(beanName)) { //如果是FactoryBean则执行下面逻辑
					Object bean = getBean(FACTORY_BEAN_PREFIX + beanName); //得到HelloFactory
					if (bean instanceof FactoryBean) {
						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 { //不是FactoryBean则执行这个,普通的单实例非懒加载bean的创建
					getBean(beanName); //核心流程
				}
			}
		}

		// 触发 post-initialization 逻辑;  Trigger post-initialization callback for all applicable beans...
		for (String beanName : beanNames) {
			Object singletonInstance = getSingleton(beanName);
			if (singletonInstance instanceof SmartInitializingSingleton) {
				StartupStep smartInitialize = this.getApplicationStartup().start("spring.beans.smart-initialize")
						.tag("beanName", beanName);
				SmartInitializingSingleton smartSingleton = (SmartInitializingSingleton) singletonInstance;
				if (System.getSecurityManager() != null) {
					AccessController.doPrivileged((PrivilegedAction<Object>) () -> {
						smartSingleton.afterSingletonsInstantiated();
						return null;
					}, getAccessControlContext());
				}
				else {
					smartSingleton.afterSingletonsInstantiated();
				}
				smartInitialize.end();
			}
		}
	}

而这里通过去遍历所有的bean去进行创建,显示判断是isFactoryBean 还是普通bean。显然我们创建的是普通的bean对象。

doGetBean

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

		String beanName = transformedBeanName(name); //转换Bean名字
		Object beanInstance;

		// 先检查单实例bean的缓存 Eagerly check singleton cache for manually registered singletons.
		Object sharedInstance = getSingleton(beanName); //检查缓存中有没有,如果是第一次获取肯定是没有的
		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 + "'");
				}
			}
			beanInstance = getObjectForBeanInstance(sharedInstance, name, beanName, null);
		}

		else { //默认第一次获取组件都会进入else环节
			// Fail if we're already creating this bean instance:
			// We're assumably within a circular reference.
			if (isPrototypeCurrentlyInCreation(beanName)) {
				throw new BeanCurrentlyInCreationException(beanName);
			}

			// 拿到整个beanFactory的父工厂;看父工厂没有,从父工厂先尝试获取组件; Check if bean definition exists in this factory.
			BeanFactory parentBeanFactory = getParentBeanFactory();
			if (parentBeanFactory != null && !containsBeanDefinition(beanName)) { //以下开始从父工厂获取组件
				// 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); //标记当前beanName的bean已经被创建
			}

			StartupStep beanCreation = this.applicationStartup.start("spring.beans.instantiate")
					.tag("beanName", name);
			try {
				if (requiredType != null) {
					beanCreation.tag("beanType", requiredType::toString);
				}
				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) { //看当前Bean有没有依赖其他Bean
						if (isDependent(beanName, dep)) {
							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
									"Circular depends-on relationship between '" + beanName + "' and '" + dep + "'");
						}
						registerDependentBean(dep, beanName);
						try {
							getBean(dep); //依赖了其他bean,就先获取其他的哪些bean
						}
						catch (NoSuchBeanDefinitionException ex) {
							throw new BeanCreationException(mbd.getResourceDescription(), beanName,
									"'" + beanName + "' depends on missing bean '" + dep + "'", ex);
						}
					}
				}

				// 创建bean的实例;Create bean instance.
				if (mbd.isSingleton()) {
					sharedInstance = getSingleton(beanName, () -> {
						try {
							return createBean(beanName, mbd, args);  //创建bean对象的实例
						}
						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;
						}
					}); //看当前bean是否是FactoryBean
					beanInstance = 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);
					}
					beanInstance = getObjectForBeanInstance(prototypeInstance, name, beanName, mbd);
				}

				else {
					String scopeName = mbd.getScope();
					if (!StringUtils.hasLength(scopeName)) {
						throw new IllegalStateException("No scope name defined for bean ´" + beanName + "'");
					}
					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);
							}
						});
						beanInstance = getObjectForBeanInstance(scopedInstance, name, beanName, mbd);
					}
					catch (IllegalStateException ex) {
						throw new ScopeNotActiveException(beanName, scopeName, ex);
					}
				}
			}
			catch (BeansException ex) {
				beanCreation.tag("exception", ex.getClass().toString());
				beanCreation.tag("message", String.valueOf(ex.getMessage()));
				cleanupAfterBeanCreationFailure(beanName);
				throw ex;
			}
			finally {
				beanCreation.end();
			}
		}
		//转Object为Bean的T类型
		return adaptBeanInstance(name, beanInstance, requiredType);
	}

这里的核心流程其实是先从Bean工厂是否获取到,如果没有的话判断具体的Bean类型,是单例、原型、还是其他。而单例Bean获取的时候,其实使用了双检查锁。

	protected Object getSingleton(String beanName, boolean allowEarlyReference) {
		//先检查单例缓存池,获取当前对象  Quick check for existing instance without full singleton lock
		Object singletonObject = this.singletonObjects.get(beanName); //一级缓存
		if (singletonObject == null && isSingletonCurrentlyInCreation(beanName)) { //如果当前bean正在创建过程中,而且缓存中没有则继续
			singletonObject = this.earlySingletonObjects.get(beanName); //二级
			if (singletonObject == null && allowEarlyReference) {
				synchronized (this.singletonObjects) {
					// Consistent creation of early reference within full singleton lock
					singletonObject = this.singletonObjects.get(beanName);
					if (singletonObject == null) {
						singletonObject = this.earlySingletonObjects.get(beanName);
						if (singletonObject == null) {
							ObjectFactory<?> singletonFactory = this.singletonFactories.get(beanName); //三级
							if (singletonFactory != null) {
								singletonObject = singletonFactory.getObject();
								this.earlySingletonObjects.put(beanName, singletonObject);
								this.singletonFactories.remove(beanName);
							}
						}
					}
				}
			}
		}
		return singletonObject;
	}

createdBean

	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 {
			//(即使AOP的BeanPostProcessor都不会珍惜这个机会) 提前给我们一个机会,去返回组件的代理对象。 Give BeanPostProcessors a chance to return a proxy instead of the target bean instance.
			//AOP核心流程
			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 { //Spring真正自己创建对象
			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);
		}
	}

实例化的前置处理

	protected Object resolveBeforeInstantiation(String beanName, RootBeanDefinition mbd) {
		Object bean = null;
		if (!Boolean.FALSE.equals(mbd.beforeInstantiationResolved)) {
			// Make sure bean class is actually resolved at this point.
			if (!mbd.isSynthetic() && hasInstantiationAwareBeanPostProcessors()) {
				Class<?> targetType = determineTargetType(beanName, mbd);
				if (targetType != null) {
					bean = applyBeanPostProcessorsBeforeInstantiation(targetType, beanName);
					if (bean != null) {
						bean = applyBeanPostProcessorsAfterInitialization(bean, beanName);
					}
				}
			}
			mbd.beforeInstantiationResolved = (bean != null);
		}
		return bean;
	}

这个方法核心就在于 applyBeanPostProcessorsBeforeInstantiation() 和 applyBeanPostProcessorsAfterInitialization() 两个方法,before 为实例化前的后处理器应用,after 为实例化后的后处理器应用,由于本文的主题是创建 bean,关于 Bean 的增强处理后也就是AOP 单独开一篇讲解。

创建Bean

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

		// Instantiate the bean.
		BeanWrapper instanceWrapper = null;
		if (mbd.isSingleton()) { //是否单例的
			instanceWrapper = this.factoryBeanInstanceCache.remove(beanName);
		}
		if (instanceWrapper == null) {
			//创建Bean的实例,默认使用无参构造器创建的对象,组件的原始对象就创建了
			instanceWrapper = createBeanInstance(beanName, mbd, args);
		}
		Object bean = instanceWrapper.getWrappedInstance();
		Class<?> beanType = instanceWrapper.getWrappedClass();
		if (beanType != NullBean.class) {
			mbd.resolvedTargetType = beanType;
		}

		//允许 后置处理器 再来修改下beanDefinition;MergedBeanDefinitionPostProcessor.postProcessMergedBeanDefinition;;   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;
			}
		}

		// 提前暴露单实例。专门来解决循环引用问题;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)); //三级缓存中的Bean也会被后置处理来增强,
		}

		// Initialize the bean instance.
		Object exposedObject = bean;
		try {
			populateBean(beanName, mbd, instanceWrapper); //给创建好的对象每个属性进行赋值,@Autowired发生在这里 数据填充
			exposedObject = initializeBean(beanName, exposedObject, mbd);//初始化bean
		}
		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);
			}
		}
		//早期单实例暴露
		if (earlySingletonExposure) {
			Object earlySingletonReference = getSingleton(beanName, false); //检查早期缓存中是否存在这个组件
			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;
	}

大概流程如下:
createBeanInstance() 实例化 bean
populateBean() 属性填充
循环依赖的处理
initializeBean() 初始化 bean

createBeanInstance

	protected BeanWrapper createBeanInstance(String beanName, RootBeanDefinition mbd, @Nullable Object[] args) {
		//获取Bean的类型  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());
		}
		//定义Bean的示例提供者
		Supplier<?> instanceSupplier = mbd.getInstanceSupplier();
		if (instanceSupplier != null) {
			return obtainFromSupplier(instanceSupplier, beanName);
		}
		//@Bean等可能会调用此方法进行创建出来
		if (mbd.getFactoryMethodName() != null) {
			return instantiateUsingFactoryMethod(beanName, mbd, args);
		}

		//快速创建? 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);
			}
		}

		//后置处理器有机会在这里决定当前bean用哪个构造器?SmartInstantiationAwareBeanPostProcessor.determineCandidateConstructors()   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); //构造器方式的自动注入与对象创建
		}

		//使用默认的自己设置的高优先级的构造器  Preferred constructors for default construction?
		ctors = mbd.getPreferredConstructors();
		if (ctors != null) {
			return autowireConstructor(beanName, mbd, ctors, null);
		}

		// 默认使用无参构造器为当前组件创建对象;No special handling: simply use no-arg constructor.
		return instantiateBean(beanName, mbd);
	}

实例化策略

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

具体在实例化的时候,并没有直接利用反射进行创建对象,而是通过不同的方式,比如Cglib或者Spring的工具类进行反射的。

请添加图片描述
至此,整个bean的初始化和创建过程就完成了。

其实整体上来说,就是先创建BeanFacotry,然后在创建Bean对象,但是Bean对象因为有AOP、事务等功能处理,所以就有很多的前后处理器进行增强对象。

本文来自互联网用户投稿,该文观点仅代表作者本人,不代表本站立场。本站仅提供信息存储空间服务,不拥有所有权,不承担相关法律责任。如若转载,请注明出处:http://www.mfbz.cn/a/118582.html

如若内容造成侵权/违法违规/事实不符,请联系我们进行投诉反馈qq邮箱809451989@qq.com,一经查实,立即删除!

相关文章

图像切分:将一张长图片切分为指定长宽的多张图片

1.需求 比如有一张很长的图片其大小为宽度779&#xff0c;高度为122552&#xff0c;那我想把图片切分为779乘以1280的格式。 步骤如下&#xff1a; 使用图像处理库&#xff08;如PIL或OpenCV&#xff09;加载原始图片。确定子图片的宽度和高度。计算原始图片的宽度和高度&am…

Java —— 类和对象(一)

目录 1. 面向对象的初步认知 1.1 什么是面向对象 1.2 面向对象与面向过程 2. 类定义和使用 2.1 认识类 2.2 类的定义格式 3. 类的实例化(如何产生对象) 3.1 什么是实例化 3.2 访问对象的成员 3.3 类和对象的说明 4. this引用 4.1 为什么要有this引用 4.2 什么是this引用 4.3 th…

硕鼠——视频下载利器

相信很多做自媒体、剪辑的同志们&#xff0c;经常会遇到一个棘手的问题&#xff1a;剪辑的素材从何而来。诸如很多高燃混剪的视频&#xff0c;往往需要多个影视作品中的原画来进行二次创作&#xff0c;可是这些视频素材从何而来呢&#xff1f; 有小伙伴们提出&#xff0c;通过录…

功率放大器主要特点是什么

功率放大器是一种常见的电子设备&#xff0c;用于放大输入信号的电压。它在各种领域中都有广泛的应用&#xff0c;包括音频放大、通信系统、仪器仪表等。功率放大器具有以下主要特点&#xff1a; 功率放大器具有高放大增益。其主要功能是将输入信号的电压放大到所需的输出电压水…

什么是商业?什么是企业?什么又是竞争呢?

博主从商了&#xff0c;读了一些关于商业企业跟竞争的关系的书跟文章&#xff0c;突然就有点感受想分享一下&#xff0c;请诸位佬讨论一下&#xff0c;听取一下各位佬的意见&#xff0c;学习一下各位的宝贵经验。 百度百科是这样解释商业企业跟竞争的 商业是以买卖方式使商品流…

优雅设计之美:实现Vue应用程序的时尚布局

前言 页面布局是减少代码重复和创建可维护且具有专业外观的应用程序的基本模式。如果使用的是Nuxt&#xff0c;则可以提供开箱即用的优雅解决方案。然而&#xff0c;令人遗憾的是&#xff0c;在Vue中&#xff0c;这些问题并未得到官方文档的解决。 经过多次尝试&#xff0c;小…

stable-diffusion-webui安装Wav2Lip

常见错误 1.错误&#xff1a;Torch is not able to use GPU; add --skip-torch-cuda-test to COMMANDLINE_ARGS variable to disable this check 修改代码&#xff1a; launch_utils.py 删除三个地方&#xff1a;

简单工厂VS工厂方法

工厂方法模式–制造细节无需知 前面介绍过简单工厂模式&#xff0c;简单工厂模式只是最基本的创建实例相关的设计模式。在真实情况下&#xff0c;有更多复杂的情况需要处理。简单工厂生成实例的类&#xff0c;知道了太多的细节&#xff0c;这就导致这个类很容易出现难维护、灵…

windows环境下安装Java过程(免登录Oracle官网下载java)

下载路径 oracle官网&#xff1a; java下载路径 Oracle共享账号可下载JDK&#xff1a; 指路 安装流程 执行下载后的jdk的可执行文件一路next下去&#xff0c; 可以自定义安装路径添加环境变量&#xff0c; 两个地方需要添加 在cmd中输入java -version 进行验证&#xff0c;…

IOC容器创建bean实例的4种方式

&#x1f388;个人公众号:&#x1f388; :✨✨✨ 可为编程✨ &#x1f35f;&#x1f35f; &#x1f511;个人信条:&#x1f511; 知足知不足 有为有不为 为与不为皆为可为&#x1f335; &#x1f349;本篇简介:&#x1f349; 本篇记录IOC容器创建bean实例的4种方式&#xff0c;…

关于 HTML 的一切:初学者指南

HTML 代表超文本标记语言&#xff0c;是用于创建网页和 Web 应用程序的标准语言。 本指南将全面介绍 HTML&#xff0c;涵盖从基本语法和语义到更高级功能的所有内容。 我的目标是用简单的术语解释 HTML&#xff0c;以便即使没有编码经验的人也能学习如何使用 HTML 构建网页。…

PostCSS通过px2rem插件和lib-flexible将px单位转换为rem(root em)单位实现大屏适配

目录 文档postcss中使用postcss-plugin-px2rem安装postcss-plugin-px2rem示例默认配置 webpack中使用postcss-plugin-px2rem项目结构安装依赖文件内容 大屏适配参考文章 文档 类似的插件 postcss-plugin-px2rem https://www.npmjs.com/package/postcss-plugin-px2remhttps://g…

Go invalid memory address or nil pointer dereference错误 空指针问题

Go 指针声明后赋值&#xff0c;出现 panic: runtime error: invalid memory address or nil pointer dereference&#xff0c;这种是内存地址错误。 首先我们要了解指针&#xff0c;指针地址在 Go 中 * 代表取指针地址中存的值&#xff0c;& 代表取一个值的地址对于指针&am…

JVM 各个参数详解

在一些规模稍大的应用中&#xff0c;Java虚拟机&#xff08;JVM&#xff09;的内存设置尤为重要&#xff0c;想在项目中取得好的效率&#xff0c;GC&#xff08;垃圾回收&#xff09;的设置是第一步。 PermGen space&#xff1a;全称是Permanent Generation space.就是说是永久…

PDF文件解析

一、PDF文件介绍 PDF是英文Portable Document Format缩写&#xff0c;就是可移植的意思&#xff0c;它是以PostScript语言图象模型为基础&#xff0c;无论在哪种打印机上都可保证精确的颜色和准确的打印效果&#xff0c;PostScript咱也不懂&#xff0c;估计和SVG的原理差不多吧…

k8s提交spark应用消费kafka数据写入elasticsearch7

一、k8s集群环境 k8s 1.23版本&#xff0c;三个节点&#xff0c;容器运行时使用docker。 spark版本时3.3.3 k8s部署单节点的zookeeper、kafka、elasticsearch7 二、spark源码 https://download.csdn.net/download/TT1024167802/88509398 命令行提交方式 /opt/module/spark…

14:00面试,14:06就出来了,问的问题有点变态。。。。。。

从小厂出来&#xff0c;没想到在另一家公司又寄了。 到这家公司开始上班&#xff0c;加班是每天必不可少的&#xff0c;看在钱给的比较多的份上&#xff0c;就不太计较了。没想到5月一纸通知&#xff0c;所有人不准加班&#xff0c;加班费不仅没有了&#xff0c;薪资还要降40%…

pytorch3D Windows下安装经验总结

一、说明及准备工作 最近在安装pytorch3D的时候遇到了很多问题&#xff0c;查了很多博客&#xff0c;但发现讲的都不太全&#xff0c;所以特将自己的及收集到的安装过程经验总结如下。我是在Anaconda中虚拟环境下安装的。 1.1准备工作 官方安装教程如下&#xff1a;https://…

Docker Tomcat 搭建文件服务器

本文基于openwrt上进行。 步骤 1: 安装 Docker 如果尚未安装Docker&#xff0c;首先需要安装Docker。根据你的操作系统&#xff0c;参考Docker官方文档来完成安装, 这里不做详细介绍。 步骤 2: 拉去docker Tomcat镜像 进入openwrt管理界面&#xff0c;docker选项中 拉取最新…

Java 设计模式——外观模式

目录 1.概述2.结构3.实现3.1.子系统类3.2.外观类3.3.测试 4.优缺点5.使用场景6.源码解析 1.概述 &#xff08;1&#xff09;有些人可能炒过股票&#xff0c;但其实大部分人都不太懂&#xff0c;这种没有足够了解证券知识的情况下做股票是很容易亏钱的&#xff0c;刚开始炒股肯…
最新文章