原文地址：http://www.cnphp6.com/archives/85639

Spring配置文件：

<context:property-placeholder?location="classpath:/settings.properties"?/> <context:property-placeholder?location="classpath:/conf.properties"/>

settings.properties

redis.masterName=mymaster

conf.properties

home.abroad=1

測試類：

@Component public?class?PropertyPlaceHolderTest?{@Value("${redis.masterName}")String?masterName;@Value("${home.abroad}")int?homeAbroad;public?static?void?main(String[]?args)?{ApplicationContext?ctx?=?new?ClassPathXmlApplicationContext("classpath:applicationContext-test.xml");PropertyPlaceHolderTest?bean?=?ctx.getBean(PropertyPlaceHolderTest.class);System.out.println(ToStringBuilder.reflectionToString(bean));} }

執行上述測試類 報錯：

Caused?by:?java.lang.IllegalArgumentException:?Could?not?resolve?placeholder?'home.abroad'?in?string?value?[${home.abroad}]at?org.springframework.util.PropertyPlaceholderHelper.parseStringValue(PropertyPlaceholderHelper.java:173)at?org.springframework.util.PropertyPlaceholderHelper.replacePlaceholders(PropertyPlaceholderHelper.java:125)at?org.springframework.core.env.AbstractPropertyResolver.doResolvePlaceholders(AbstractPropertyResolver.java:151)at?org.springframework.core.env.AbstractPropertyResolver.resolveRequiredPlaceholders(AbstractPropertyResolver.java:142)at?org.springframework.context.support.PropertySourcesPlaceholderConfigurer$2.resolveStringValue(PropertySourcesPlaceholderConfigurer.java:169)at?org.springframework.beans.factory.support.AbstractBeanFactory.resolveEmbeddedValue(AbstractBeanFactory.java:748)at?org.springframework.beans.factory.support.DefaultListableBeanFactory.doResolveDependency(DefaultListableBeanFactory.java:745)at?org.springframework.beans.factory.support.DefaultListableBeanFactory.resolveDependency(DefaultListableBeanFactory.java:735)at?org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor$AutowiredFieldElement.inject(AutowiredAnnotationBeanPostProcessor.java:478)...?15?more

?

為什么只能解析出第一個property-placeholder配置中的key？第二個property-placeholder配置文件中的key是被忽略了嗎？

但明明日志顯示兩個配置文件均被成功解析了啊。

INFO??org.springframework.context.support.PropertySourcesPlaceholderConfigurer??Loading?properties?file?from?class?path?resource?[settings.properties] INFO??org.springframework.context.support.PropertySourcesPlaceholderConfigurer??Loading?properties?file?from?class?path?resource?[conf.properties]

那到底是什么原因呢？只有分析源代碼了。發現一旦解析配置文件后會將其封裝到一個PropertySourcesPropertyResolver對象中，如下所示：

//所屬類：PropertySourcesPlaceholderConfigurer @Override public?void?postProcessBeanFactory(ConfigurableListableBeanFactory?beanFactory)?throws?BeansException?{????????//......???this.processProperties(beanFactory,?new?PropertySourcesPropertyResolver(this.propertySources)); }

再創建一個StringValueResolver對象，實際使用上面的PropertySourcesPropertyResolver對象來解析占位符中的字符串。

//所屬類：PropertySourcesPlaceholderConfigurer protected?void?processProperties(ConfigurableListableBeanFactory?beanFactoryToProcess,final?ConfigurablePropertyResolver?propertyResolver)?throws?BeansException?{//......StringValueResolver?valueResolver?=?new?StringValueResolver()?{public?String?resolveStringValue(String?strVal)?{String?resolved?=?ignoreUnresolvablePlaceholders??propertyResolver.resolvePlaceholders(strVal)?:propertyResolver.resolveRequiredPlaceholders(strVal);return?(resolved.equals(nullValue)???null?:?resolved);}};doProcessProperties(beanFactoryToProcess,?valueResolver);}

最后將此StringValueResolver對象放入到一個List中，

//所屬類：AbstractBeanFactory public?void?addEmbeddedValueResolver(StringValueResolver?valueResolver)?{Assert.notNull(valueResolver,?"StringValueResolver?must?not?be?null");this.embeddedValueResolvers.add(valueResolver);}

當自動注入@Value標注的字段時，

DEBUG?org.springframework.beans.factory.annotation.InjectionMetadata??Processing?injected?method?of?bean?'propertyPlaceHolderTest':?AutowiredFieldElement?for?int?com.tcl.test.PropertyPlaceHolderTest.homeAbroad

需要解析@Value中的占位符中的內容了，涉及到源碼是：

//所屬類：AbstractBeanFactory public?String?resolveEmbeddedValue(String?value)?{String?result?=?value;for?(StringValueResolver?resolver?:?this.embeddedValueResolvers)?{result?=?resolver.resolveStringValue(result);}return?result;}

從之前描述可知this.embeddedValueResolvers中有兩個valueResolver對象（分別對應兩個context:property-placeholder元素），于是先取出第一個valueResolver（對應settings.properties）來解析${home.abroad}，而它是配置在conf.poperties中的，肯定解析不到，于是就報錯了，見源代碼：

//所屬的類與方法：PropertyPlaceholderHelper.parseStringValue if?(propVal?!=?null)?{//...... } 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?+?"]"); }

?

但明明才遍歷了List中第一個valueResolver對象呢，后面的那個可以成功解析啊。錯誤拋的也太急了點吧。

Spring肯定也考慮了這一點，從上面的源代碼也可以看出，只要設置了ignoreUnresolvablePlaceholders為true的話，就不會走最后的else分支了。

修改Spring配置，顯式指定第一個context:property-placeholder元素ignore-unresolvable屬性為true，如下所示：

<context:property-placeholder?location="classpath:/settings.properties"?ignore-unresolvable="true"/> <context:property-placeholder?location="classpath:/conf.properties"/>

這時就不會報錯了，${home.abroad}也能被成功解析了。見輸出：

com.tcl.test.PropertyPlaceHolderTest@2f949a6b[masterName=mymaster,homeAbroad=1]

當然正常情況下沒必要配置成兩個或多個context:property-placeholder，完全可以用一個context:property-placeholder來指定多個配置文件，如下所示：

<context:property-placeholder?location="classpath:/settings.properties,/conf.properties"?/>

轉載于:https://www.cnblogs.com/davidwang456/p/5735452.html

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