Spring源码分析-BeanFactoryPostProcessors 应用之 PropertyPlaceholderConfigurer

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BeanFactoryPostProcessors

介绍

BeanFactoryPostProcessors完整定义:

/**
 * Allows for custom modification of an application context's bean definitions,
 * adapting the bean property values of the context's underlying bean factory.
 * @see BeanPostProcessor
 * @see PropertyResourceConfigurer
 */
public interface BeanFactoryPostProcessor {

	/**
	 * Modify the application context's internal bean factory after its standard
	 * initialization. All bean definitions will have been loaded, but no beans
	 * will have been instantiated yet. This allows for overriding or adding
	 * properties even to eager-initializing beans.
	 * @param beanFactory the bean factory used by the application context
	 * @throws org.springframework.beans.BeansException in case of errors
	 */
	void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException;

}

咱们知道spring最大优势就是其可扩展性,BeanFactoryPostProcessor接口就是spring中提供给咱们用于扩展的一个地方。咱们看该接口上的javadoc其实很是的详细,这也是咱们看spring源码的一个技巧，就是看一个类是干吗的必定要先通读其注释。

结合接口上的注释大体描述下BeanFactoryPostProcessor：
容许用户经过修改applicationContext 中的bean定义(就是xml中定义的bean的信息即:BeanDefinition是和xml有一对一的配置，好比是不是单利，以及propert 属性的赋值等)
来调整applicationContext中bean工厂中bean属性值。

也就是说执行到BeanFactoryPostProcessor时所有的BeanDefinition定义已经加载好了可是bean实例尚未被建立,咱们能够修补或者覆盖bean属性值。

咱们能够看一下ApplicationContext中BeanFactoryPostProcessor的调用位置来印证是否如此

下面是ApplicationContext核心代码：

public void refresh() throws BeansException, IllegalStateException {
		synchronized (this.startupShutdownMonitor) {
			// Prepare this context for refreshing.
			prepareRefresh();

			
			//获取beanFactory实例
			ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

		
	     	prepareBeanFactory(beanFactory);

			try {
			 
				postProcessBeanFactory(beanFactory);

				//这里正是咱们的BeanFactoryPostProcessor执行的位置
				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.
				//建立非懒加载的全部单例  这里是真正建立bean实例的地方
				finishBeanFactoryInitialization(beanFactory);

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

			catch (BeansException ex) {
				// Destroy already created singletons to avoid dangling resources.
				destroyBeans();

				// Reset 'active' flag.
				cancelRefresh(ex);

				// Propagate exception to caller.
				throw ex;
			}
		}
	}

通过

ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();

			// Prepare the bean factory for use in this context.
			prepareBeanFactory(beanFactory);

这两步咱们已经拿到了beanFactory实例,也就是每个bean对应的BeanDefinition已经加载好了。下面才是执行invokeBeanFactoryPostProcessors(beanFactory)，也就印证了咱们上面的结论。 下面咱们经过一个BeanFactoryPostProcessor的典型应用PropertyPlaceholderConfigurer来详细讲解BeanFactoryPostProcessor执行原理

PropertyPlaceholderConfigurer

简单使用的例子

PropertyPlaceholderConfigurer相信你们都使用过,咱们在配置bean的属性可使用占位符来赋值，而后经过调整properties文件中对应的属性值来修改。看一个使用PropertyPlaceholderConfigurer简单的例子:

public class Student {
    
        private String name;
    
        private Integer age;
    
        public String getName() {
            return name;
        }
    
        public void setName(String name) {
            this.name = name;
        }
    
        public Integer getAge() {
            return age;
        }
    
        public void setAge(Integer age) {
            this.age = age;
        }
    }

    <bean class="com.yalunwang.Student" id="student">
        <property name="name" value="${student.name}"></property>
        <property name="age" value="${student.age}"></property>
    </bean>

    <bean class="org.springframework.beans.factory.config.PropertyPlaceholderConfigurer">
        <property name="location" value="classpath:bean.properties"></property>
    </bean>

bean.properties配置文件:

student.name=anan
    student.age=2

单元测试:

@Test
    public void test_ioc_app(){
        ApplicationContext ac = new ClassPathXmlApplicationContext("spring-ioc.xml");

        Student student =(Student) ac.getBean("student");

        System.out.println("name: "+student.getName());
        System.out.println("age: "+student.getAge());
    }

输出结果一切正常:

name: anan
age: 2

源码分析

先看一下PropertyPlaceholderConfigurer的类继承图:

能够看到PropertyPlaceholderConfigurer实现了BeanFactoryPostProcessor和 PriorityOrdered。

咱们接着对上面的 invokeBeanFactoryPostProcessors(beanFactory)继续进行分析:

/**
	 * Instantiate and invoke all registered BeanFactoryPostProcessor beans,
	 * respecting explicit order if given.
	 * 实例化并调用全部已注册的BeanFactoryPostProcessor Bean，
     * 若是继承了Order接口按顺序执行
	 * <p>Must be called before singleton instantiation.
	 */
	protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
		// Invoke BeanDefinitionRegistryPostProcessors first, if any.
		Set<String> processedBeans = new HashSet<String>();
		//若是是beanFactory实现了BeanDefinitionRegistry
		if (beanFactory instanceof BeanDefinitionRegistry) {
			BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
			List<BeanFactoryPostProcessor> regularPostProcessors = new LinkedList<BeanFactoryPostProcessor>();
			List<BeanDefinitionRegistryPostProcessor> registryPostProcessors =
					new LinkedList<BeanDefinitionRegistryPostProcessor>();
		    //遍历硬编码设置的beanFactory后置处理器			
			for (BeanFactoryPostProcessor postProcessor : getBeanFactoryPostProcessors()) {
			    //若是是BeanDefinitionRegistryPostProcessor类型先执行postProcessBeanDefinitionRegistry方法再将其添加到registryPostProcessors集合中进行后续postProcessBeanFactory方法的执行
				if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
					BeanDefinitionRegistryPostProcessor registryPostProcessor =
							(BeanDefinitionRegistryPostProcessor) postProcessor;
					registryPostProcessor.postProcessBeanDefinitionRegistry(registry);
					registryPostProcessors.add(registryPostProcessor);
				}
				else {
				    //同理将正常的beanFactory后置处理器添加到regularPostProcessors集合中进行后续postProcessBeanFactory方法的执行
					regularPostProcessors.add(postProcessor);
				}
			}
			//找出配置的BeanDefinitionRegistryPostProcessor后置处理器	
			Map<String, BeanDefinitionRegistryPostProcessor> beanMap =
					beanFactory.getBeansOfType(BeanDefinitionRegistryPostProcessor.class, true, false);
			List<BeanDefinitionRegistryPostProcessor> registryPostProcessorBeans =
					new ArrayList<BeanDefinitionRegistryPostProcessor>(beanMap.values());
			OrderComparator.sort(registryPostProcessorBeans);
			//执行BeanDefinitionRegistryPostProcessor后置处理器的postProcessBeanDefinitionRegistry方法
			for (BeanDefinitionRegistryPostProcessor postProcessor : registryPostProcessorBeans) {
				postProcessor.postProcessBeanDefinitionRegistry(registry);
			}
			//执行上面添加的beanFactory后置处理器的集合里的方法
			invokeBeanFactoryPostProcessors(registryPostProcessors, beanFactory);
			invokeBeanFactoryPostProcessors(registryPostProcessorBeans, beanFactory);
			invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
			//处理后的添加到集合里 防止后面重复执行
			processedBeans.addAll(beanMap.keySet());
		}
		else {
			// Invoke factory processors registered with the context instance.
			invokeBeanFactoryPostProcessors(getBeanFactoryPostProcessors(), beanFactory);
		}

	
		//获取配置的BeanFactoryPostProcessor
		//如下按实现了 PriorityOrdered  Ordered 没有继承 三种进行优先级排序执行 
		String[] postProcessorNames =
				beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
        
     	List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
		List<String> orderedPostProcessorNames = new ArrayList<String>();
		List<String> nonOrderedPostProcessorNames = new ArrayList<String>();
		for (String ppName : postProcessorNames) {
		    //这个就是上面记录的若是已经处理了配置的BeanFactoryPostProcessors就跳过
			if (processedBeans.contains(ppName)) {
				// skip - already processed in first phase above
			}
			else if (isTypeMatch(ppName, PriorityOrdered.class)) {
				priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
			}
			else if (isTypeMatch(ppName, Ordered.class)) {
				orderedPostProcessorNames.add(ppName);
			}
			else {
				nonOrderedPostProcessorNames.add(ppName);
			}
		}

		// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
		OrderComparator.sort(priorityOrderedPostProcessors);
		//上面咱们说了PropertyPlaceholderConfigurer 实现了BeanFactoryPostProcessor和 PriorityOrdered,因此会在这一步执行调用
		invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

		// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
		List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
		for (String postProcessorName : orderedPostProcessorNames) {
			orderedPostProcessors.add(getBean(postProcessorName, BeanFactoryPostProcessor.class));
		}
		OrderComparator.sort(orderedPostProcessors);
		invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);

		// Finally, invoke all other BeanFactoryPostProcessors.
		List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<BeanFactoryPostProcessor>();
		for (String postProcessorName : nonOrderedPostProcessorNames) {
			nonOrderedPostProcessors.add(getBean(postProcessorName, BeanFactoryPostProcessor.class));
		}
		invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
	}

上面主要的执行逻辑我都添加了中文注释方便你们理解。 总结一下改方法主要作的事情:

1. 先判断若是beanFactory是BeanDefinitionRegistry类型的话就添加对BeanDefinitionRegistryPostProcessor类型的调用,BeanDefinitionRegistryPostProcessor接口是BeanFactoryPostProcessor的子接口,BeanDefinitionRegistryPostProcessor的做用是方便咱们能够手动注册bean交给spring来管理,能够经过扩展其惟一的方法(void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry registry) throws BeansException;) 来注册bean到spring里，这个不是本次分析的重点后面再举例讲解。
2. 先对硬编码配置的BeanFactoryPostProcessor进行处理 若是是BeanDefinitionRegistryPostProcessor类型会进行postProcessBeanDefinitionRegistry调用和postProcessBeanFactory调用,若是不是则只进行postProcessBeanFactory调用。
3. 再对配置的BeanDefinitionRegistryPostProcessor进行处理(postProcessBeanDefinitionRegistry调用和postProcessBeanFactory调用)
4. 最后对配置BeanFactoryPostProcessor的进行处理会按 PriorityOrdered/Ordered/没有继承任何排序接口 三种进行优先级排序执行postProcessBeanFactory调用。其中咱们的PropertyPlaceholderConfigurer 实现了BeanFactoryPostProcessor和 PriorityOrdered,因此会在这一步执行调用 invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

• ** 咱们继续进行分析：**

invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);

会执行PropertyPlaceholderConfigurer父类PropertyResourceConfigurer中的方法

/**
	 * {@linkplain #mergeProperties Merge}, {@linkplain #convertProperties convert} and
	 * {@linkplain #processProperties process} properties against the given bean factory.
	 * @throws BeanInitializationException if any properties cannot be loaded
	 */
	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
		try {
			Properties mergedProps = mergeProperties();

			// Convert the merged properties, if necessary.
			convertProperties(mergedProps);

			// Let the subclass process the properties.
			processProperties(beanFactory, mergedProps);
		}
		catch (IOException ex) {
			throw new BeanInitializationException("Could not load properties", ex);
		}
	}

mergeProperties()方法会先将 <property name="location" value="classpath:bean.properties"></property> 配置的properties加载到mergedProps里 后面调用** processProperties(beanFactory, mergedProps)**;进行处理

• processProperties(beanFactory, mergedProps)分析

protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess, Properties props)
			throws BeansException {

		StringValueResolver valueResolver = new PlaceholderResolvingStringValueResolver(props);

		this.doProcessProperties(beanFactoryToProcess, valueResolver);
	}

这里只有两行代码,第一行是建立StringValueResolver实例(用于替换占位符的真正方法) 咱们跨过千山万水终于要到立刻要进行占位符替换了，继续分析

protected void doProcessProperties(ConfigurableListableBeanFactory beanFactoryToProcess,
			StringValueResolver valueResolver) {
       
        
        //将建立的valueResolver设置到BeanDefinitionVisitor里 用于最终替换逻辑 (替换占位符为对应properties里配置的值)
		BeanDefinitionVisitor visitor = new BeanDefinitionVisitor(valueResolver);
        //拿出ioc容器里注册的beans
		String[] beanNames = beanFactoryToProcess.getBeanDefinitionNames();
		for (String curName : beanNames) {
			
			//排除掉当前beanName也就是 PropertyPlaceholderConfigurer Bean 且beanFactoryToProcess必须是当前容器
			if (!(curName.equals(this.beanName) && beanFactoryToProcess.equals(this.beanFactory))) {
			    //获取一个bean对应的bean定义
				BeanDefinition bd = beanFactoryToProcess.getBeanDefinition(curName);
				try {
				    //进行bean定义元数据的替换操做
					visitor.visitBeanDefinition(bd);
				}
				catch (Exception ex) {
					throw new BeanDefinitionStoreException(bd.getResourceDescription(), curName, ex.getMessage());
				}
			}
		}

		// New in Spring 2.5: resolve placeholders in alias target names and aliases as well.
		beanFactoryToProcess.resolveAliases(valueResolver);

		// New in Spring 3.0: resolve placeholders in embedded values such as annotation attributes.
		beanFactoryToProcess.addEmbeddedValueResolver(valueResolver);
	}

上面我已经使用中文注释写的很清楚了接着进行分析

• visitor.visitBeanDefinition(bd);

public void visitBeanDefinition(BeanDefinition beanDefinition) {
		visitParentName(beanDefinition);
		visitBeanClassName(beanDefinition);
		visitFactoryBeanName(beanDefinition);
		visitFactoryMethodName(beanDefinition);
		visitScope(beanDefinition);
		visitPropertyValues(beanDefinition.getPropertyValues());
		ConstructorArgumentValues cas = beanDefinition.getConstructorArgumentValues();
		visitIndexedArgumentValues(cas.getIndexedArgumentValues());
		visitGenericArgumentValues(cas.getGenericArgumentValues());
	}

这里能够对应 bean的parentName beanClassName property等进行替换操做咱们这里只关注属性的替换操做

• visitPropertyValues(beanDefinition.getPropertyValues());

protected void visitPropertyValues(MutablePropertyValues pvs) {
		PropertyValue[] pvArray = pvs.getPropertyValues();
		for (PropertyValue pv : pvArray) {
			Object newVal = resolveValue(pv.getValue());
			if (!ObjectUtils.nullSafeEquals(newVal, pv.getValue())) {
				pvs.add(pv.getName(), newVal);
			}
		}
	}

• Object newVal = resolveValue(pv.getValue());

@SuppressWarnings("rawtypes")
	protected Object resolveValue(Object value) {
		if (value instanceof BeanDefinition) {
			visitBeanDefinition((BeanDefinition) value);
		}
		else if (value instanceof BeanDefinitionHolder) {
			visitBeanDefinition(((BeanDefinitionHolder) value).getBeanDefinition());
		}
		else if (value instanceof RuntimeBeanReference) {
			RuntimeBeanReference ref = (RuntimeBeanReference) value;
			String newBeanName = resolveStringValue(ref.getBeanName());
			if (!newBeanName.equals(ref.getBeanName())) {
				return new RuntimeBeanReference(newBeanName);
			}
		}
		else if (value instanceof RuntimeBeanNameReference) {
			RuntimeBeanNameReference ref = (RuntimeBeanNameReference) value;
			String newBeanName = resolveStringValue(ref.getBeanName());
			if (!newBeanName.equals(ref.getBeanName())) {
				return new RuntimeBeanNameReference(newBeanName);
			}
		}
		else if (value instanceof Object[]) {
			visitArray((Object[]) value);
		}
		else if (value instanceof List) {
			visitList((List) value);
		}
		else if (value instanceof Set) {
			visitSet((Set) value);
		}
		else if (value instanceof Map) {
			visitMap((Map) value);
		}
		else if (value instanceof TypedStringValue) {
			TypedStringValue typedStringValue = (TypedStringValue) value;
			String stringValue = typedStringValue.getValue();
			if (stringValue != null) {
				String visitedString = resolveStringValue(stringValue);
				typedStringValue.setValue(visitedString);
			}
		}
		else if (value instanceof String) {
			return resolveStringValue((String) value);
		}
		return value;
	}

这里有不少类型,是由于spring支持不少类型的配置好比property的值咱们能够配置为ref=xxxbean那么value就是RuntimeBeanReference类型, 若是配置

<list>
                <value>343</value>
                <value>45</value>
            </list>

那么value就是List类型等等。这里咱们例子中配置的类型是TypedStringValue，那么执行

else if (value instanceof TypedStringValue) {
			TypedStringValue typedStringValue = (TypedStringValue) value;
			//这里拿到的值是原始的带有占位符的好比例子里就是${student.name}、${student.age}这种
			String stringValue = typedStringValue.getValue();
			if (stringValue != null) {
			    //这一步就是去进行替换
				String visitedString = resolveStringValue(stringValue);
				typedStringValue.setValue(visitedString);
			}
		}

• String visitedString = resolveStringValue(stringValue);

/**
	 * Resolve the given String value, for example parsing placeholders.
	 * @param strVal the original String value
	 * @return the resolved String value
	 */
	protected String resolveStringValue(String strVal) {
		if (this.valueResolver == null) {
			throw new IllegalStateException("No StringValueResolver specified - pass a resolver " +
					"object into the constructor or override the 'resolveStringValue' method");
		}
		//调用咱们以前传进来的valueResolver也就是上面 (BeanDefinitionVisitor visitor = new BeanDefinitionVisitor(valueResolver); 这里传进来的) 进行替换操做
		String resolvedValue = this.valueResolver.resolveStringValue(strVal);
		// Return original String if not modified.
		return (strVal.equals(resolvedValue) ? strVal : resolvedValue);
	}

valueResolver其实就是PlaceholderResolvingStringValueResolver实例,它又委托PropertyPlaceholderHelper进行操做

也就是

/**
	 * Replaces all placeholders of format {@code ${name}} with the value returned
	 * from the supplied {@link PlaceholderResolver}.
	 * @param value the value containing the placeholders to be replaced.
	 * @param placeholderResolver the {@code PlaceholderResolver} to use for replacement.
	 * @return the supplied value with placeholders replaced inline.
	 */
	public String replacePlaceholders(String value, PlaceholderResolver placeholderResolver) {
		Assert.notNull(value, "Argument 'value' must not be null.");
		return parseStringValue(value, placeholderResolver, new HashSet<String>());
	}

	protected String parseStringValue(
			String strVal, PlaceholderResolver placeholderResolver, Set<String> visitedPlaceholders) {

		StringBuilder buf = new StringBuilder(strVal);

		int startIndex = strVal.indexOf(this.placeholderPrefix);
		while (startIndex != -1) {
			int endIndex = findPlaceholderEndIndex(buf, startIndex);
			if (endIndex != -1) {
			    //将ex. ${student.name} 转成 student.name
				String placeholder = buf.substring(startIndex + this.placeholderPrefix.length(), endIndex);
				String originalPlaceholder = placeholder;
				if (!visitedPlaceholders.add(originalPlaceholder)) {
					throw new IllegalArgumentException(
							"Circular placeholder reference '" + originalPlaceholder + "' in property definitions");
				}
				// 递归调用直到没有占位符
				placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders);
				// 获取properties配置文件对应的值  就是获取student.name 对应在 properties里的值
				String propVal = placeholderResolver.resolvePlaceholder(placeholder);
				if (propVal == null && this.valueSeparator != null) {
					int separatorIndex = placeholder.indexOf(this.valueSeparator);
					if (separatorIndex != -1) {
						String actualPlaceholder = placeholder.substring(0, separatorIndex);
						String defaultValue = placeholder.substring(separatorIndex + this.valueSeparator.length());
						propVal = placeholderResolver.resolvePlaceholder(actualPlaceholder);
						if (propVal == null) {
							propVal = defaultValue;
						}
					}
				}
				if (propVal != null) {
				    //再次递归调用 确保最后的值没有占位符
					propVal = parseStringValue(propVal, placeholderResolver, visitedPlaceholders);
					//将原先的StringBuff的原始值替换为拿到的值
					buf.replace(startIndex, endIndex + this.placeholderSuffix.length(), propVal);
					if (logger.isTraceEnabled()) {
						logger.trace("Resolved placeholder '" + placeholder + "'");
					}
					//这里由于已经替换成真正的值 拿不到占位符(${)因此值就是-1 会跳出循环返回
					startIndex = buf.indexOf(this.placeholderPrefix, startIndex + propVal.length());
				}
				else if (this.ignoreUnresolvablePlaceholders) {
					// Proceed with unprocessed value.
					startIndex = buf.indexOf(this.placeholderPrefix, endIndex + this.placeholderSuffix.length());
				}
				else {
					throw new IllegalArgumentException("Could not resolve placeholder '" +
							placeholder + "'" + " in string value \"" + strVal + "\"");
				}
				visitedPlaceholders.remove(originalPlaceholder);
			}
			else {
				startIndex = -1;
			}
		}

		return buf.toString();
	}

该方法是真正替换的操做所在,改方法已经添加中文注释应该很好理解了，总结就是作了一下两件事: 1.首先会将ex. ${student.name} 转成 student.name 2.将student.name经过 tring propVal = placeholderResolver.resolvePlaceholder(placeholder);获取真正的值而后返回。

protected String resolvePlaceholder(String placeholder, Properties props, int systemPropertiesMode) {
		String propVal = null;
		if (systemPropertiesMode == SYSTEM_PROPERTIES_MODE_OVERRIDE) {
			propVal = resolveSystemProperty(placeholder);
		}
		if (propVal == null) {
			propVal = resolvePlaceholder(placeholder, props);
		}
		if (propVal == null && systemPropertiesMode == SYSTEM_PROPERTIES_MODE_FALLBACK) {
			propVal = resolveSystemProperty(placeholder);
		}
		return propVal;
	}

该方法就比较简单了就是根据不一样的模式作处理,systemPropertiesMode默认是SYSTEM_PROPERTIES_MODE_FALLBACK

1. 若是systemPropertiesMode = SYSTEM_PROPERTIES_MODE_OVERRIDE 是指 系统配置文件优先级大于咱们的配置文件。
2. 拿不到或者配置不等于SYSTEM_PROPERTIES_MODE_OVERRIDE 就去咱们配置文件里进行获取
3. 若是还获取不到且若是systemPropertiesMode=SYSTEM_PROPERTIES_MODE_FALLBACK就再尝试去系统文件里查找。

结论

通过以上各个步骤最终BeanDefinition里的parentName beanClassName property中的占位符都会被咱们propertis配置文件中对应的值所替换掉，这就为后续实例化bean后作bean实例属性填充时作好了准备。 咱们再进行 Student student =(Student) ac.getBean("student"); 时就能够正常打印对应的值了。

看源码的一点分享tip

• 看源码可能会比较枯燥,坚持很重要,若是看一遍是懵的那就是歇一歇再继续多看几遍这样慢慢就会找到感受
• 看的过程当中必定要写例子进行调试,而后再继续反复看慢慢就会明白其中的含义
• 看源码能够看某一个核心类的继承图,以及javadoc。还能够尝试画出核心的时序图，这些都能对咱们看懂源码起到事半功倍的做用。

联系我

• 个人我的博客: http://yalunwang.com
• 个人github: https://github.com/yalunwang
• 个人博客园：https://www.cnblogs.com/yalunwang/

至此本篇源码分析就结束了,后续继续spring源码分析的文章。加油！！！

原文出处：https://www.cnblogs.com/yalunwang/p/12380985.html