spring中常用配置文件application.properties源码分析

秒速五厘米 2023-10-02 20:22 16阅读 0赞

spring中常用配置文件application.properties源码分析，这是一个非常重要的启动环节，今天我们通过测试代码结合源码一步步分析其原理。

一、首先看最基础最原始的配置方案：完全 xml 配置

1、xml 核心配置：

2、application.properties 配置文件和实体类

enjoy.name=nandao
    enjoy.password=123

实体类：

@Data
    public class PropertiesBean {
    
        private String name;
    
        private String password;
    }

3、执行测试方法：

@Test
        public void test18() {
            ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext("spring.xml");
            PropertiesBean bean = applicationContext.getBean(PropertiesBean.class);
            System.out.println(bean.getName() + "--" + bean.getPassword());
        }

执行结果如下：

![994ecb8b6c694c24b179857d06c50c2c.png][] 如果没有自定义标签解析的配置打印结果如下：

![65bb3f26b6ba4790819bebf5f85dfb9c.png][]

也就是正常情况下实例化对象之后，对象里面的参数是占位符，推测自定义标签解析配置文件之后，循环去找占位符替换正常的值。

4、从自定义标签入口：

![4919ace88f224aec88fa22a4f3611f36.png][]

点击spring.handers：找到这个spi实现类

![b29f15263a414635adae0f11bbc53a2c.png][]

点击ContextNamespaceHandler类:找到自定义标签对应的实现类PropertyPlaceholderBeanDefinitionParser

![e5edb0f449eb4836a1b73bb5c71b2531.png][]

5、点击 PropertyPlaceholderBeanDefinitionParser 类进入：

class PropertyPlaceholderBeanDefinitionParser extends AbstractPropertyLoadingBeanDefinitionParser {
    
    	private static final String SYSTEM_PROPERTIES_MODE_ATTRIBUTE = "system-properties-mode";
    
    	private static final String SYSTEM_PROPERTIES_MODE_DEFAULT = "ENVIRONMENT";
    
    
    	@Override
    	@SuppressWarnings("deprecation")
    	protected Class<?> getBeanClass(Element element) {
    		// As of Spring 3.1, the default value of system-properties-mode has changed from
    		// 'FALLBACK' to 'ENVIRONMENT'. This latter value indicates that resolution of
    		// placeholders against system properties is a function of the Environment and
    		// its current set of PropertySources.
            //自定义标签调用时会走到这里，返回这个类
    		if (SYSTEM_PROPERTIES_MODE_DEFAULT.equals(element.getAttribute(SYSTEM_PROPERTIES_MODE_ATTRIBUTE))) {
    			return PropertySourcesPlaceholderConfigurer.class;
    		}
    
    		// The user has explicitly specified a value for system-properties-mode: revert to
    		// PropertyPlaceholderConfigurer to ensure backward compatibility with 3.0 and earlier.
    		// This is deprecated; to be removed along with PropertyPlaceholderConfigurer itself.
    		return org.springframework.beans.factory.config.PropertyPlaceholderConfigurer.class;
    	}
    
    	@Override
    	protected void doParse(Element element, ParserContext parserContext, BeanDefinitionBuilder builder) {
    		super.doParse(element, parserContext, builder);
    
    		builder.addPropertyValue("ignoreUnresolvablePlaceholders",
    				Boolean.valueOf(element.getAttribute("ignore-unresolvable")));
    
    		String systemPropertiesModeName = element.getAttribute(SYSTEM_PROPERTIES_MODE_ATTRIBUTE);
    		if (StringUtils.hasLength(systemPropertiesModeName) &&
    				!systemPropertiesModeName.equals(SYSTEM_PROPERTIES_MODE_DEFAULT)) {
    			builder.addPropertyValue("systemPropertiesModeName", "SYSTEM_PROPERTIES_MODE_" + systemPropertiesModeName);
    		}
    
    		if (element.hasAttribute("value-separator")) {
    			builder.addPropertyValue("valueSeparator", element.getAttribute("value-separator"));
    		}
    		if (element.hasAttribute("trim-values")) {
    			builder.addPropertyValue("trimValues", element.getAttribute("trim-values"));
    		}
    		if (element.hasAttribute("null-value")) {
    			builder.addPropertyValue("nullValue", element.getAttribute("null-value"));
    		}
    	}
    
    }

[自定义标签分析][Link 1]

这里我们补充一些自定义标签没有分享到的地方。

![d4b98e02d5674efea022ec44423dea19.png][]

6、进入 AbstractBeanDefinitionParser 类：

@Override
    	@Nullable
    	public final BeanDefinition parse(Element element, ParserContext parserContext) {
            //核心接口点击进入
    		AbstractBeanDefinition definition = parseInternal(element, parserContext);
    		if (definition != null && !parserContext.isNested()) {
    			try {
    				String id = resolveId(element, definition, parserContext);
    				if (!StringUtils.hasText(id)) {
    					parserContext.getReaderContext().error(
    							"Id is required for element '" + parserContext.getDelegate().getLocalName(element)
    									+ "' when used as a top-level tag", element);
    				}
    				String[] aliases = null;
    				if (shouldParseNameAsAliases()) {
    					String name = element.getAttribute(NAME_ATTRIBUTE);
    					if (StringUtils.hasLength(name)) {
    						aliases = StringUtils.trimArrayElements(StringUtils.commaDelimitedListToStringArray(name));
    					}
    				}
    				BeanDefinitionHolder holder = new BeanDefinitionHolder(definition, id, aliases);
    				registerBeanDefinition(holder, parserContext.getRegistry());
    				if (shouldFireEvents()) {
    					BeanComponentDefinition componentDefinition = new BeanComponentDefinition(holder);
    					postProcessComponentDefinition(componentDefinition);
    					parserContext.registerComponent(componentDefinition);
    				}
    			}
    			catch (BeanDefinitionStoreException ex) {
    				String msg = ex.getMessage();
    				parserContext.getReaderContext().error((msg != null ? msg : ex.toString()), element);
    				return null;
    			}
    		}
    		return definition;
    	}

7、钩子接口，子类AbstractSingleBeanDefinitionParser实现：

@Override
    	protected final AbstractBeanDefinition parseInternal(Element element, ParserContext parserContext) {
    		BeanDefinitionBuilder builder = BeanDefinitionBuilder.genericBeanDefinition();
    		String parentName = getParentName(element);
    		if (parentName != null) {
    			builder.getRawBeanDefinition().setParentName(parentName);
    		}//核心接口，点击进入
    		Class<?> beanClass = getBeanClass(element);
    		if (beanClass != null) {
    			builder.getRawBeanDefinition().setBeanClass(beanClass);
    		}
    		else {
    			String beanClassName = getBeanClassName(element);
    			if (beanClassName != null) {
    				builder.getRawBeanDefinition().setBeanClassName(beanClassName);
    			}
    		}
    		builder.getRawBeanDefinition().setSource(parserContext.extractSource(element));
    		BeanDefinition containingBd = parserContext.getContainingBeanDefinition();
    		if (containingBd != null) {
    			// Inner bean definition must receive same scope as containing bean.
    			builder.setScope(containingBd.getScope());
    		}
    		if (parserContext.isDefaultLazyInit()) {
    			// Default-lazy-init applies to custom bean definitions as well.
    			builder.setLazyInit(true);
    		}
    		doParse(element, parserContext, builder);
    		return builder.getBeanDefinition();
    	}

8、点击进入子类接口 PropertyPlaceholderBeanDefinitionParser 的 getBeanClass 方法，也就是SPI初始化的类。

二、第一个环节完成了配置文件的解析和BeanDefinition对象的实例化，那么什么时候把站位符替换成正常的值？从此开始

1、赋值入口

/*
    				 * BeanDefinitionRegistryPostProcessor
    				 * BeanFactoryPostProcessor
    				 * 完成对这两个接口的调用
    				 * */
    				invokeBeanFactoryPostProcessors(beanFactory);

点击：

protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory) {
            //核心入口
    		PostProcessorRegistrationDelegate.invokeBeanFactoryPostProcessors(beanFactory, getBeanFactoryPostProcessors());
    
    		// Detect a LoadTimeWeaver and prepare for weaving, if found in the meantime
    		// (e.g. through an @Bean method registered by ConfigurationClassPostProcessor)
    		if (beanFactory.getTempClassLoader() == null && beanFactory.containsBean(LOAD_TIME_WEAVER_BEAN_NAME)) {
    			beanFactory.addBeanPostProcessor(new LoadTimeWeaverAwareProcessor(beanFactory));
    			beanFactory.setTempClassLoader(new ContextTypeMatchClassLoader(beanFactory.getBeanClassLoader()));
    		}
    	}

2、点击进入：PostProcessorRegistrationDelegate

public static void invokeBeanFactoryPostProcessors(
    			ConfigurableListableBeanFactory beanFactory, List<BeanFactoryPostProcessor> beanFactoryPostProcessors) {
    
    		// Invoke BeanDefinitionRegistryPostProcessors first, if any.
    		Set<String> processedBeans = new HashSet<>();
    
    		if (beanFactory instanceof BeanDefinitionRegistry) {
    			BeanDefinitionRegistry registry = (BeanDefinitionRegistry) beanFactory;
    			List<BeanFactoryPostProcessor> regularPostProcessors = new ArrayList<>();
    			List<BeanDefinitionRegistryPostProcessor> registryProcessors = new ArrayList<>();
    
    			for (BeanFactoryPostProcessor postProcessor : beanFactoryPostProcessors) {
    				if (postProcessor instanceof BeanDefinitionRegistryPostProcessor) {
    					BeanDefinitionRegistryPostProcessor registryProcessor =
    							(BeanDefinitionRegistryPostProcessor) postProcessor;
    					registryProcessor.postProcessBeanDefinitionRegistry(registry);
    					registryProcessors.add(registryProcessor);
    				}
    				else {
    					regularPostProcessors.add(postProcessor);
    				}
    			}
    
    			// Do not initialize FactoryBeans here: We need to leave all regular beans
    			// uninitialized to let the bean factory post-processors apply to them!
    			// Separate between BeanDefinitionRegistryPostProcessors that implement
    			// PriorityOrdered, Ordered, and the rest.
    			List<BeanDefinitionRegistryPostProcessor> currentRegistryProcessors = new ArrayList<>();
    
    			//获取实现了BeanDefinitionRegistryPostProcessor接口的所有类的BeanDefinition对象的beanName
    			// First, invoke the BeanDefinitionRegistryPostProcessors that implement PriorityOrdered.
    			String[] postProcessorNames =
    					beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
    			for (String ppName : postProcessorNames) {
    				if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
    					currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
    					processedBeans.add(ppName);
    				}
    			}
    			//排序
    			sortPostProcessors(currentRegistryProcessors, beanFactory);
    			registryProcessors.addAll(currentRegistryProcessors);
    			//调用过程
    			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
    			currentRegistryProcessors.clear();
    
    			// Next, invoke the BeanDefinitionRegistryPostProcessors that implement Ordered.
    			postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
    			for (String ppName : postProcessorNames) {
    				//判断是否是实现的Ordered接口
    				if (!processedBeans.contains(ppName) && beanFactory.isTypeMatch(ppName, Ordered.class)) {
    					currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
    					processedBeans.add(ppName);
    				}
    			}
    			sortPostProcessors(currentRegistryProcessors, beanFactory);
    			registryProcessors.addAll(currentRegistryProcessors);
    			invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
    			currentRegistryProcessors.clear();
    
    			//没实现排序接口的调用
    			// Finally, invoke all other BeanDefinitionRegistryPostProcessors until no further ones appear.
    			boolean reiterate = true;
    			while (reiterate) {
    				reiterate = false;
    				postProcessorNames = beanFactory.getBeanNamesForType(BeanDefinitionRegistryPostProcessor.class, true, false);
    				for (String ppName : postProcessorNames) {
    					if (!processedBeans.contains(ppName)) {
    						currentRegistryProcessors.add(beanFactory.getBean(ppName, BeanDefinitionRegistryPostProcessor.class));
    						processedBeans.add(ppName);
    						reiterate = true;
    					}
    				}
    				sortPostProcessors(currentRegistryProcessors, beanFactory);
    				registryProcessors.addAll(currentRegistryProcessors);
    				invokeBeanDefinitionRegistryPostProcessors(currentRegistryProcessors, registry);
    				currentRegistryProcessors.clear();
    			}
    
    			//调用postProcessBeanFactory方法，点击调用
    			// Now, invoke the postProcessBeanFactory callback of all processors handled so far.
    			invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);//核心
    			invokeBeanFactoryPostProcessors(regularPostProcessors, beanFactory);
    		}
    
    		else {
    			// Invoke factory processors registered with the context instance.
    			invokeBeanFactoryPostProcessors(beanFactoryPostProcessors, beanFactory);
    		}
    
    		// Do not initialize FactoryBeans here: We need to leave all regular beans
    		// uninitialized to let the bean factory post-processors apply to them!
    		String[] postProcessorNames =
    				beanFactory.getBeanNamesForType(BeanFactoryPostProcessor.class, true, false);
    
    		// Separate between BeanFactoryPostProcessors that implement PriorityOrdered,
    		// Ordered, and the rest.
    		List<BeanFactoryPostProcessor> priorityOrderedPostProcessors = new ArrayList<>();
    		List<String> orderedPostProcessorNames = new ArrayList<>();
    		List<String> nonOrderedPostProcessorNames = new ArrayList<>();
    		for (String ppName : postProcessorNames) {
    			if (processedBeans.contains(ppName)) {
    				// skip - already processed in first phase above
    			}
    			//实现了PriorityOrdered接口的
    			else if (beanFactory.isTypeMatch(ppName, PriorityOrdered.class)) {
    				priorityOrderedPostProcessors.add(beanFactory.getBean(ppName, BeanFactoryPostProcessor.class));
    			}
    			//实现了Ordered接口的
    			else if (beanFactory.isTypeMatch(ppName, Ordered.class)) {
    				orderedPostProcessorNames.add(ppName);
    			}
    			else {
    				//没实现接口的
    				nonOrderedPostProcessorNames.add(ppName);
    			}
    		}
    
    		//排序
    		// First, invoke the BeanFactoryPostProcessors that implement PriorityOrdered.
    		sortPostProcessors(priorityOrderedPostProcessors, beanFactory);
    		//调用
    		invokeBeanFactoryPostProcessors(priorityOrderedPostProcessors, beanFactory);
    
    		// Next, invoke the BeanFactoryPostProcessors that implement Ordered.
    		List<BeanFactoryPostProcessor> orderedPostProcessors = new ArrayList<>(orderedPostProcessorNames.size());
    		for (String postProcessorName : orderedPostProcessorNames) {
    			orderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    		}
    		sortPostProcessors(orderedPostProcessors, beanFactory);
    		invokeBeanFactoryPostProcessors(orderedPostProcessors, beanFactory);
    
    		// Finally, invoke all other BeanFactoryPostProcessors.
    		List<BeanFactoryPostProcessor> nonOrderedPostProcessors = new ArrayList<>(nonOrderedPostProcessorNames.size());
    		for (String postProcessorName : nonOrderedPostProcessorNames) {
    			nonOrderedPostProcessors.add(beanFactory.getBean(postProcessorName, BeanFactoryPostProcessor.class));
    		}
    		invokeBeanFactoryPostProcessors(nonOrderedPostProcessors, beanFactory);
    
    		// Clear cached merged bean definitions since the post-processors might have
    		// modified the original metadata, e.g. replacing placeholders in values...
    		beanFactory.clearMetadataCache();
    	}

3、点击 invokeBeanFactoryPostProcessors(registryProcessors, beanFactory);

private static void invokeBeanFactoryPostProcessors(
    			Collection<? extends BeanFactoryPostProcessor> postProcessors, ConfigurableListableBeanFactory beanFactory) {
    
    		for (BeanFactoryPostProcessor postProcessor : postProcessors) {
    			postProcessor.postProcessBeanFactory(beanFactory);//循环遍历
    		}
    	}

选择：

![1de9a9b11c444621be1564844d518358.png][]

4、点击进入：

/**
    	 * 调用的是这个，新版本参数解析执行的是这里
    	*/
    	@Override
    	public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
    		if (this.propertySources == null) {
    			this.propertySources = new MutablePropertySources();
    			if (this.environment != null) {
    				//把environment对象封装成的PropertySource对象加入到
    				this.propertySources.addLast(
    						//把environment对象封装成PropertySource对象MutablePropertySources中的list中
    					new PropertySource<Environment>(ENVIRONMENT_PROPERTIES_PROPERTY_SOURCE_NAME, this.environment) {
    						@Override
    						@Nullable
    						//source就是environment对象
    						public String getProperty(String key) {
    							return this.source.getProperty(key);
    						}
    					}
    				);
    			}
    			try {
    				//加载本地配置文件中的属性值包装成properties对象后，最终包装成PropertySource对象
    				PropertySource<?> localPropertySource =
    						new PropertiesPropertySource(LOCAL_PROPERTIES_PROPERTY_SOURCE_NAME, mergeProperties());
    				//加入到MutablePropertySources中的list中
    				if (this.localOverride) {
    					this.propertySources.addFirst(localPropertySource);
    				}
    				else {
    					this.propertySources.addLast(localPropertySource);
    				}
    			}
    			catch (IOException ex) {
    				throw new BeanInitializationException("Could not load properties", ex);
    			}
    		}
            //点击进入
    		processProperties(beanFactory, new PropertySourcesPropertyResolver(this.propertySources));
    		this.appliedPropertySources = this.propertySources;
    	}

进入：

protected void processProperties(ConfigurableListableBeanFactory beanFactoryToProcess,
    			final ConfigurablePropertyResolver propertyResolver) throws BeansException {
    
    		//设置占位符的前缀后缀
    		propertyResolver.setPlaceholderPrefix(this.placeholderPrefix);
    		propertyResolver.setPlaceholderSuffix(this.placeholderSuffix);
    		//设分割符 :
    		propertyResolver.setValueSeparator(this.valueSeparator);
    
    		//重点是这个匿名对象 @Value的依赖注入会掉过来
    		StringValueResolver valueResolver = strVal -> {
    			String resolved = (this.ignoreUnresolvablePlaceholders ?
    					propertyResolver.resolvePlaceholders(strVal) :
    					propertyResolver.resolveRequiredPlaceholders(strVal));
    			if (this.trimValues) {
    				resolved = resolved.trim();
    			}
    			return (resolved.equals(this.nullValue) ? null : resolved);
    		};
    		//核心流程。把占位符${xxx}替换成真正的值，点击进入
    		doProcessProperties(beanFactoryToProcess, valueResolver);
    	}

5、点击doProcessProperties(beanFactoryToProcess, valueResolver);方法进入父类， PlaceholderConfigurerSupport

protected void doProcessProperties(ConfigurableListableBeanFactory beanFactoryToProcess,
    			StringValueResolver valueResolver) {
    
    		//beanDefinition的修改者
    		BeanDefinitionVisitor visitor = new BeanDefinitionVisitor(valueResolver);
    
    		//获取所有的beanNames
    		String[] beanNames = beanFactoryToProcess.getBeanDefinitionNames();
    		for (String curName : beanNames) {
    			// Check that we're not parsing our own bean definition,
    			// to avoid failing on unresolvable placeholders in properties file locations.
    			if (!(curName.equals(this.beanName) && beanFactoryToProcess.equals(this.beanFactory))) {
    				//获取BeanDefinition对象
    				BeanDefinition bd = beanFactoryToProcess.getBeanDefinition(curName);
    				try {
    					//修改BeanDefinition中的MutablePropertyValues中的每一个属性值，把属性值有${enjoy.name}修改成真正的参数值，
    					visitor.visitBeanDefinition(bd);
    				}
    				catch (Exception ex) {
    					throw new BeanDefinitionStoreException(bd.getResourceDescription(), curName, ex.getMessage(), ex);
    				}
    			}
    		}
    
    		// New in Spring 2.5: resolve placeholders in alias target names and aliases as well.
    		beanFactoryToProcess.resolveAliases(valueResolver);
    		//把内嵌的Value解析器设置到BeanFactory中..为@Value的依赖注入做准备
    		// New in Spring 3.0: resolve placeholders in embedded values such as annotation attributes.
    		beanFactoryToProcess.addEmbeddedValueResolver(valueResolver);
    	}

6、点击visitor.visitBeanDefinition(bd); 进入BeanDefinitionVisitor

public void visitBeanDefinition(BeanDefinition beanDefinition) {
    		visitParentName(beanDefinition);
    		visitBeanClassName(beanDefinition);
    		visitFactoryBeanName(beanDefinition);
    		visitFactoryMethodName(beanDefinition);
    		visitScope(beanDefinition);
    		//如果BeanDefinition存在属性值，则把占位符替换成真正的属性值
    		if (beanDefinition.hasPropertyValues()) {
    			visitPropertyValues(beanDefinition.getPropertyValues());//点击
    		}
    		//构造函数占位符
    		if (beanDefinition.hasConstructorArgumentValues()) {
    			ConstructorArgumentValues cas = beanDefinition.getConstructorArgumentValues();
    			visitIndexedArgumentValues(cas.getIndexedArgumentValues());
    			visitGenericArgumentValues(cas.getGenericArgumentValues());
    		}
    	}

显示带有占位符的参数：

![c1446b44e44d442c9bab75fa7280fe3b.png][]

点击visitPropertyValues(beanDefinition.getPropertyValues());

protected void visitPropertyValues(MutablePropertyValues pvs) {
    		PropertyValue[] pvArray = pvs.getPropertyValues();
    		for (PropertyValue pv : pvArray) {
    			Object newVal = resolveValue(pv.getValue());//获取配置文件里真正的参数，点击进入
    			if (!ObjectUtils.nullSafeEquals(newVal, pv.getValue())) {
    				pvs.add(pv.getName(), newVal);
    			}
    		}
    	}

参数查看：

![e16c870bb71a465a855f33a354ad1e4a.png][]

点击 resolveValue(pv.getValue()) 进入

@Nullable
    	protected Object resolveValue(@Nullable 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 == null) {
    				return null;
    			}
    			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 == null) {
    				return null;
    			}
    			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);
    		}//来到此处
    		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;
    	}

如图：

![a75bb511de284e82828f2db42f941cbb.png][]

继续  
![9b80ea8c318042b1ad010ee97d0c059e.png][]

![5f000bb4582241e8a000496c2f9fcf2b.png][]

下一个参数：

![32d1fdd9b11e4e6faef52e2b04fe0620.png][]

点击进入：

@Nullable
    	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");
    		}//点击
    		String resolvedValue = this.valueResolver.resolveStringValue(strVal);
    		// Return original String if not modified.
    		return (strVal.equals(resolvedValue) ? strVal : resolvedValue);
    	}

7、来到：PropertyPlaceholderConfigurer

@Override
    		@Nullable
    		public String resolveStringValue(String strVal) throws BeansException {
    			String resolved = this.helper.replacePlaceholders(strVal, this.resolver);
    			if (trimValues) {
    				resolved = resolved.trim();
    			}
    			return (resolved.equals(nullValue) ? null : resolved);
    		}

8，来到 PropertyPlaceholderHelper

public String replacePlaceholders(String value, PlaceholderResolver placeholderResolver) {
    		Assert.notNull(value, "'value' must not be null");
    		return parseStringValue(value, placeholderResolver, null);
    	}

继续

protected String parseStringValue(
    			String value, PlaceholderResolver placeholderResolver, @Nullable Set<String> visitedPlaceholders) {
    
    		int startIndex = value.indexOf(this.placeholderPrefix);
    		if (startIndex == -1) {
    			return value;
    		}
    
    		StringBuilder result = new StringBuilder(value);
    		while (startIndex != -1) {
    			int endIndex = findPlaceholderEndIndex(result, startIndex);
    			if (endIndex != -1) {
    				String placeholder = result.substring(startIndex + this.placeholderPrefix.length(), endIndex);
    				String originalPlaceholder = placeholder;
    				if (visitedPlaceholders == null) {
    					visitedPlaceholders = new HashSet<>(4);
    				}
    				if (!visitedPlaceholders.add(originalPlaceholder)) {
    					throw new IllegalArgumentException(
    							"Circular placeholder reference '" + originalPlaceholder + "' in property definitions");
    				}
    				// Recursive invocation, parsing placeholders contained in the placeholder key.
    				placeholder = parseStringValue(placeholder, placeholderResolver, visitedPlaceholders);
    				// Now obtain the value for the fully resolved key...
    				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) {
    					// Recursive invocation, parsing placeholders contained in the
    					// previously resolved placeholder value.
    					propVal = parseStringValue(propVal, placeholderResolver, visitedPlaceholders);
    					result.replace(startIndex, endIndex + this.placeholderSuffix.length(), propVal);
    					if (logger.isTraceEnabled()) {
    						logger.trace("Resolved placeholder '" + placeholder + "'");
    					}
    					startIndex = result.indexOf(this.placeholderPrefix, startIndex + propVal.length());
    				}
    				else if (this.ignoreUnresolvablePlaceholders) {
    					// Proceed with unprocessed value.
    					startIndex = result.indexOf(this.placeholderPrefix, endIndex + this.placeholderSuffix.length());
    				}
    				else {
    					throw new IllegalArgumentException("Could not resolve placeholder '" +
    							placeholder + "'" + " in value \"" + value + "\"");
    				}
    				visitedPlaceholders.remove(originalPlaceholder);
    			}
    			else {
    				startIndex = -1;
    			}
    		}
    		return result.toString();
    	}

参数如图：

![600aebfa7b5e462ab9eb16545b8c6b61.png][]

三、目前配置文件解析还有另一种解析方式，业务代码注解扫描方式：

1、取代下面配置：

<context:property-placeholder location="classpath:application.properties"/>

2、新的方式：

import org.springframework.context.ResourceLoaderAware;
    import org.springframework.context.annotation.Bean;
    import org.springframework.context.support.PropertySourcesPlaceholderConfigurer;
    import org.springframework.core.io.ResourceLoader;
    import org.springframework.stereotype.Component;
    
    
    @Component
    public class BeanConfig implements ResourceLoaderAware {
    
      private ResourceLoader resourceLoader;
    
        @Bean
        public PropertySourcesPlaceholderConfigurer getPropertySourcesPlaceholderConfigurer() {       
            PropertySourcesPlaceholderConfigurer propertySourcesPlaceholderConfigurer = new PropertySourcesPlaceholderConfigurer();
            
           propertySourcesPlaceholderConfigurer.setLocation(resourceLoader.getResource("application.properties"));
            return propertySourcesPlaceholderConfigurer;
        }
    
        @Override
        public void setResourceLoader(ResourceLoader resourceLoader) {
            this.resourceLoader = resourceLoader;
        }
    }

此时发现，propertySourcesPlaceholderConfigurer 类很熟悉，一目了然！

到此赋值流程结束，链路比较长，大家要详细阅读、认真思考，定会进步很多。

[994ecb8b6c694c24b179857d06c50c2c.png]: https://img-blog.csdnimg.cn/994ecb8b6c694c24b179857d06c50c2c.png
[65bb3f26b6ba4790819bebf5f85dfb9c.png]: https://img-blog.csdnimg.cn/65bb3f26b6ba4790819bebf5f85dfb9c.png
[4919ace88f224aec88fa22a4f3611f36.png]: https://img-blog.csdnimg.cn/4919ace88f224aec88fa22a4f3611f36.png
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[e5edb0f449eb4836a1b73bb5c71b2531.png]: https://img-blog.csdnimg.cn/e5edb0f449eb4836a1b73bb5c71b2531.png
[Link 1]: https://blog.csdn.net/nandao158/article/details/105567997
[d4b98e02d5674efea022ec44423dea19.png]: https://img-blog.csdnimg.cn/d4b98e02d5674efea022ec44423dea19.png
[1de9a9b11c444621be1564844d518358.png]: https://img-blog.csdnimg.cn/1de9a9b11c444621be1564844d518358.png
[c1446b44e44d442c9bab75fa7280fe3b.png]: https://img-blog.csdnimg.cn/c1446b44e44d442c9bab75fa7280fe3b.png
[e16c870bb71a465a855f33a354ad1e4a.png]: https://img-blog.csdnimg.cn/e16c870bb71a465a855f33a354ad1e4a.png
[a75bb511de284e82828f2db42f941cbb.png]: https://img-blog.csdnimg.cn/a75bb511de284e82828f2db42f941cbb.png
[9b80ea8c318042b1ad010ee97d0c059e.png]: https://img-blog.csdnimg.cn/9b80ea8c318042b1ad010ee97d0c059e.png
[5f000bb4582241e8a000496c2f9fcf2b.png]: https://img-blog.csdnimg.cn/5f000bb4582241e8a000496c2f9fcf2b.png
[32d1fdd9b11e4e6faef52e2b04fe0620.png]: https://img-blog.csdnimg.cn/32d1fdd9b11e4e6faef52e2b04fe0620.png
[600aebfa7b5e462ab9eb16545b8c6b61.png]: https://img-blog.csdnimg.cn/600aebfa7b5e462ab9eb16545b8c6b61.png