Spring 加載多個xml配置文件的原理分析
示例
先給出兩個Bean的配置文件:
spring-configlication.xml:
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:aop="http://www.springframework.org/schema/aop"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd
http://www.springframework.org/schema/aop
http://www.springframework.org/schema/aop/spring-aop.xsd">
<bean id="person" class="com.john.aop.Person">
</bean>
<bean id="ChineseFemaleSinger" class="com.john.beanFactory.Singer" abstract="true" >
<property name="country" value="中國"/>
<property name="gender" value="女"/>
</bean>
</beans>
spring-config-instance-factory.xml
<?xml version="1.0" encoding="UTF-8"?>
<beans xmlns="http://www.springframework.org/schema/beans"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns:context="http://www.springframework.org/schema/context"
xmlns:aop="http://www.springframework.org/schema/aop"
xsi:schemaLocation="http://www.springframework.org/schema/beans
http://www.springframework.org/schema/beans/spring-beans.xsd
http://www.springframework.org/schema/context
http://www.springframework.org/schema/context/spring-context.xsd
http://www.springframework.org/schema/aop
http://www.springframework.org/schema/aop/spring-aop.xsd">
<bean id="carFactory" class="com.john.domain.CarFactory" />
<!--實例工廠方法創(chuàng)建bean-->
<bean id="instanceCar" factory-bean="carFactory" factory-method="createCar">
<constructor-arg ref="brand"/>
</bean>
<bean id="brand" class="com.john.domain.Brand" />
</beans>
java示例代碼
public class ConfigLocationsDemo {
public static void main(String[] args) {
ClassPathXmlApplicationContext applicationContext = new ClassPathXmlApplicationContext();
applicationContext.setConfigLocations("spring-configlocation.xml","spring-config-instance-factory.xml");
applicationContext.refresh();
String[] beanNames = applicationContext.getBeanDefinitionNames();
for (String beanName : beanNames) {
System.out.println(beanName);
}
}
}
這樣我們就會在控制臺打印出兩個配置文件中所有的Bean.
person ChineseFemaleSinger carFactory instanceCar brand Process finished with exit code 0
實現(xiàn)
AbstractRefreshableConfigApplicationContext
從類的名字推導出這是一個帶刷新功能并且?guī)渲霉δ艿膽蒙舷挛摹?/p>
/**
* Set the config locations for this application context.
* <p>If not set, the implementation may use a default as appropriate.
*/
public void setConfigLocations(@Nullable String... locations) {
if (locations != null) {
this.configLocations = new String[locations.length];
for (int i = 0; i < locations.length; i++) {
this.configLocations[i] = resolvePath(locations[i]).trim();
}
}
else {
this.configLocations = null;
}
}
這個方法很好理解,首先根據(jù)傳入配置文件路徑字符串數(shù)組遍歷,并且里面調(diào)用了resolvePath方法解析占位符。那么我們要想下了,這里只做了解析占位符并且把字符串賦值給configLocations變量,那必然肯定會在什么時候去讀取這個路徑下的文件并加載bean吧?會不會是在應用上下文調(diào)用refresh方法的時候去加載呢?帶著思考我們來到了應用上下文的refresh方法。
AbstractApplicationContext
@Override
public void refresh() throws BeansException, IllegalStateException {
synchronized (this.startupShutdownMonitor) {
// Tell the subclass to refresh the internal bean factory.
//告訴子類刷新 內(nèi)部BeanFactory
//https://www.iteye.com/blog/rkdu2-163-com-2003638
//內(nèi)部會加載bean定義
ConfigurableListableBeanFactory beanFactory = obtainFreshBeanFactory();
}
}
/**
* Tell the subclass to refresh the internal bean factory.
* @return the fresh BeanFactory instance
* @see #refreshBeanFactory()
* @see #getBeanFactory()
*/
//得到刷新過的beanFactory
protected ConfigurableListableBeanFactory obtainFreshBeanFactory() {
//抽象類AbstractRefreshableApplicationContext
//里面會加載bean定義
//todo 加載bean定義
refreshBeanFactory();
//如果beanFactory為null 會報錯
return getBeanFactory();
}
/**
* Subclasses must implement this method to perform the actual configuration load.
* The method is invoked by {@link #refresh()} before any other initialization work.
* <p>A subclass will either create a new bean factory and hold a reference to it,
* or return a single BeanFactory instance that it holds. In the latter case, it will
* usually throw an IllegalStateException if refreshing the context more than once.
* @throws BeansException if initialization of the bean factory failed
* @throws IllegalStateException if already initialized and multiple refresh
* attempts are not supported
*/
//AbstractRefreshableApplicationContext 實現(xiàn)了此方法
//GenericApplicationContext 實現(xiàn)了此方法
protected abstract void refreshBeanFactory() throws BeansException, IllegalStateException;
我們看到refreshBeanFactory的第一句注釋就提到了Subclasses must implement this method to perform the actual configuration load,意思就是子類必須實現(xiàn)此方法來完成最終的配置加載,那實現(xiàn)此方法的Spring內(nèi)部默認有兩個類,AbstractRefreshableApplicationContext和GenericApplicationContext,這里我們就關心AbstractRefreshableApplicationContext:
AbstractRefreshableApplicationContext
我們要時刻記得上面的AbstractRefreshableConfigApplicationContext類是繼承于AbstractRefreshableApplicationContext的,到這里我們給張類關系圖以便加深理解:

/**
* This implementation performs an actual refresh of this context's underlying
* bean factory, shutting down the previous bean factory (if any) and
* initializing a fresh bean factory for the next phase of the context's lifecycle.
*/
@Override
protected final void refreshBeanFactory() throws BeansException {
//判斷beanFactory 是否為空
if (hasBeanFactory()) {
destroyBeans();
closeBeanFactory(); //設置beanFactory = null
}
try {
DefaultListableBeanFactory beanFactory = createBeanFactory();
//加載Bean定義
//todo AbstractXmlApplicationContext 子類實現(xiàn) 放入beandefinitionMap中
loadBeanDefinitions(beanFactory);
}
catch (IOException ex) {
throw new ApplicationContextException("I/O error parsing bean definition source for " + getDisplayName(), ex);
}
}
這里就看到了前篇文章提到一個很重要的方法loadBeanDefinitions,我們再拿出來回顧下加深理解:
/**
* Load bean definitions into the given bean factory, typically through
* delegating to one or more bean definition readers.
* @param beanFactory the bean factory to load bean definitions into
* @throws BeansException if parsing of the bean definitions failed
* @throws IOException if loading of bean definition files failed
* @see org.springframework.beans.factory.support.PropertiesBeanDefinitionReader
* @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
*/
protected abstract void loadBeanDefinitions(DefaultListableBeanFactory beanFactory)
throws BeansException, IOException;
這里因為我們是采用xml配置的,那么肯定是XmlBeanDefinitionReader無疑,我們再回顧下實現(xiàn)此方法的AbstractXmlApplicationContext:
AbstractXmlApplicationContext
/**
* Loads the bean definitions via an XmlBeanDefinitionReader.
* @see org.springframework.beans.factory.xml.XmlBeanDefinitionReader
* @see #initBeanDefinitionReader
* @see #loadBeanDefinitions
*/
//todo 重載了 AbstractRefreshableApplicationContext
@Override
protected void loadBeanDefinitions(DefaultListableBeanFactory beanFactory) throws BeansException, IOException {
//忽略代碼。。
loadBeanDefinitions(beanDefinitionReader);
}
/**
* Load the bean definitions with the given XmlBeanDefinitionReader.
* <p>The lifecycle of the bean factory is handled by the {@link #refreshBeanFactory}
* method; hence this method is just supposed to load and/or register bean definitions.
* @param reader the XmlBeanDefinitionReader to use
* @throws BeansException in case of bean registration errors
* @throws IOException if the required XML document isn't found
* @see #refreshBeanFactory
* @see #getConfigLocations
* @see #getResources
* @see #getResourcePatternResolver
*/
//bean工廠的生命周期由 refreshBeanFactory 方法來處理
//這個方法只是 去加載和注冊 bean定義
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws BeansException, IOException {
//ClassPathXmlApplicationContext
Resource[] configResources = getConfigResources();
if (configResources != null) {
reader.loadBeanDefinitions(configResources);
}
String[] configLocations = getConfigLocations();
if (configLocations != null) {
//抽象AbstractBeanDefinitionReader里去加載
reader.loadBeanDefinitions(configLocations);
}
}
這里我們終于到了這個configLocations的用武之地,它就傳入了XmlBeanDefinitionReader的loadBeanDefinitions方法中。在這里我們也看到了Spring首先會根據(jù)configResources加載BeanDefinition,其次才會去根據(jù)configLocations配置去加載BeanDefinition。到這里我們可以學到Spring中對面向?qū)ο笾蟹庋b,繼承和多態(tài)的運用。下篇文章我們繼續(xù)剖析Spring關于Xml加載Bean定義的點滴。
以上就是Spring 加載多個xml配置文件的原理分析的詳細內(nèi)容,更多關于Spring 加載xml配置文件的資料請關注腳本之家其它相關文章!
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