题：
最近在做公共框架的构建，由于采用了模块化的插件机制，在开发的过程中，发现不同开发人员的spring配置中，出现了两个bean的配置id和实现类名称都一样的情况。
例如有下面的bean类：
package com.XXX.common.test;
public class SameNameBean {
private String beanName ;
public void setBeanName(String beanName) {
this . beanName = beanName;
}
public String test() {
return "Hello " + beanName ;
}
}
和两个xml的配置:
beanContext1.xml:
<? xml version = "1.0" encoding = "UTF-8" ?>
<! DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "/spring-beans.dtd" >
< beans >
< bean id = " testNameBean " class = "com.xxx.common.test.SameNameBean" >
< property name = " beanName " value = "beanContext1" />
</ bean >
</ beans >
beanContext2.xml:
<? xml version = "1.0" encoding = "UTF-8" ?>
<! DOCTYPE beans PUBLIC "-//SPRING//DTD BEAN//EN" "/spring-beans.dtd" >
< beans >
< bean id = " testNameBean " class = "com.xxx.common.test.SameNameBean" >
< property name = " beanName " value = "beanContext2" />
</ bean >
</ beans >
当spring容器初始化时候同时加载这两份配置文件到当前的上下文的时候，代码如下：
public class TestBean {
public static void main(String[] args) {
ClassPathXmlApplicationContext context = new ClassPathXmlApplicationContext(
new String[] { "classpath*:beanContext*.xml" });
//context.setAllowBeanDefinitionOverriding(false);
//context.refresh();
SameNameBean sameNameBean = (SameNameBean) context
.getBean( "testNameBean" );
System. out .println(sameNameBean.test());
}
}
执行结果是：
Hello beanContext2
从结果可以看出，beanContext2.xml的bean的配置覆盖了beanContext1.xml中bean的配置，而且在spring初始化上下文的过程中没有任何的警告。这样如果在项目中定义了两个id同名的bean，并且他们的实现方式类又是不一样的，在项目的业务逻辑看起来就会非常诡异，而且，如果也不利于排除问题。
解决问题：
那么，我们如何来解决这个问题吗？靠程序员自律？绝对不定义重复名称的bean？我觉得这个是不靠谱的，只有通过在程序中引入一种交错机制才能解决这个问题。
首先，我们将上面那段程序的log4j日志打开，看看在spring在初始化的时候面对有两个同名的bean是怎么处理的。
- INFO - Refreshing org.springframework.context.support.ClassPathXmlApplicationContext@aa9835: display name [org.springframework.context.support.ClassPathXmlApplicationContext@aa9835]; startup date [Sat Jun 19 18:23:30 CST 2014]; root of context hierarchy
- INFO - Loading XML bean definitions from class path resource [beanContext1.xml]
- DEBUG - Using JAXP provider [com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderFactoryImpl]
- DEBUG - Found beans DTD [file:///spring-beans.dtd] in classpath: spring-beans.dtd
- DEBUG - Loading bean definitions
- DEBUG - Loaded 1 bean definitions from location pattern [beanContext1.xml]
- INFO - Loading XML bean definitions from class path resource [beanContext2.xml]
- DEBUG - Using JAXP provider [com.sun.org.apache.xerces.internal.jaxp.DocumentBuilderFactoryImpl]
- DEBUG - Found beans DTD [file:///spring-beans.dtd] in classpath: spring-beans.dtd
- DEBUG - Loading bean definitions
- INFO - Overriding bean definition for bean 'testNameBean': replacing [Generic bean: class [com.xxx.common.test.SameNameBean]; scope=singleton; abstract=false; lazyInit=false; autowireMode=0; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=null; factoryMethodName=null; initMethodName=null; destroyMethodName=null; defined in class path resource [beanContext1.xml]] with [Generic bean: class [com.xxx.common.test.SameNameBean]; scope=singleton; abstract=false; lazyInit=false; autowireMode=0; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=null; factoryMethodName=null; initMethodName=null; destroyMethodName=null; defined in class path resource [beanContext2.xml]]
- DEBUG - Loaded 0 bean definitions from location pattern [beanContext2.xml]
- INFO - Bean factory for application context [org.springframework.context.support.ClassPathXmlApplicationContext@aa9835]:org.springframework.beans.factory.support.DefaultListableBeanFactory@1662dc8
- DEBUG - 1 beans defined in org.springframework.context.support.ClassPathXmlApplicationContext@aa9835: display name [org.springframework.context.support.ClassPathXmlApplicationContext@aa9835]; startup date [Sat Jun 19 18:23:30 CST 2014]; root of context hierarchy
- DEBUG - Unable to locate MessageSource with name 'messageSource': using default [org.springframework.context.support.DelegatingMessageSource@1cb25f1]
- DEBUG - Unable to locate ApplicationEventMulticaster with name 'applicationEventMulticaster': using default [org.springframework.context.event.SimpleApplicationEventMulticaster@503429]
- INFO - Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@1662dc8: defining beans [testNameBean]; root of factory hierarchy
- DEBUG - Creating shared instance of singleton bean 'testNameBean'
- DEBUG - Creating instance of bean 'testNameBean'
- DEBUG - Eagerly caching bean 'testNameBean' to allow for resolving potential circular references
- DEBUG - Finished creating instance of bean 'testNameBean'
- DEBUG - Returning cached instance of singleton bean 'testNameBean'
以上日志中标红的是关键，spring在处理有重名的bean的定义的时候原来是使用的覆盖（override）的方式。我们来看看它是如何覆盖的。
在org.springframework.beans.factory.support.DefaultListableBeanFactory这个类中有这样一段代码：
synchronized (this.beanDefinitionMap) {
Object oldBeanDefinition = this.beanDefinitionMap.get(beanName);
if (oldBeanDefinition != null) {
if (!this.allowBeanDefinitionOverriding) {
throw new BeanDefinitionStoreException(beanDefinition
.getResourceDescription(), beanName,
"Cannot register bean definition ["
+ beanDefinition + "] for bean '"
+ beanName + "': There is already ["
+ oldBeanDefinition + "] bound.");
} else {
if (this.logger.isInfoEnabled()) {
this.logger
.info("Overriding bean definition for bean '"
+ beanName + "': replacing ["
+ oldBeanDefinition + "] with ["
+ beanDefinition + "]");
}
}
} else {
this.beanDefinitionNames.add(beanName);
this.frozenBeanDefinitionNames = null;
}
this.beanDefinitionMap.put(beanName, beanDefinition);
resetBeanDefinition(beanName);
}
spring ioc容器在加载bean的过程中会去判断beanName 是否有重复，如果发现重复的话再根据allowBeanDefinitionOverriding 这个成员变量，如果是false的话则抛出BeanDefinitionStoreException 这个异常，如果为true的话就会覆盖这个bean的定义。
所以，解决这个问题的办法就比较简单了，只要将这个allowBeanDefinitionOverriding值在spring初始化的时候设置为false就行了。
在web工程中加载spring容器，一般都会通过加载下面的 listener:
<listener>
<listener-class>org.springframework.web.context.ContextLoaderListener</listener-class>
</listener>
在这个listener中会构造 org.springframework.web.context.ContextLoader 这个构造器来加载bean。所以，只要扩展 ContextLoader 和ContextLoaderListener这两个类就行了，代码如下：
CustomSpringContextLoader：
package com.xxx.itpub.contrl.context;
import javax.servlet.ServletContext;
import org.springframework.web.context.ConfigurableWebApplicationContext;
import org.springframework.web.context.ContextLoader;
import org.springframework.web.context.support.XmlWebApplicationContext;
public class CustomSpringContextLoader extends ContextLoader {
@Override
protected void customizeContext(ServletContext servletContext,
ConfigurableWebApplicationContext applicationContext) {
XmlWebApplicationContext context = (XmlWebApplicationContext) applicationContext;
context.setAllowBeanDefinitionOverriding( false );
}
}
CustomSpringContextLoaderListener ：
package com.xxx.itpub.contrl.listener;
import org.springframework.web.context.ContextLoader;
import org.springframework.web.context.ContextLoaderListener;
import com.eshore.itpub.contrl.context.CustomSpringContextLoader;
public class CustomSpringContextLoaderListener extends ContextLoaderListener {
@Override
protected ContextLoader createContextLoader() {
return new CustomSpringContextLoader();
}
}
最后修改WEB-INF下web.xml 文件，修改listener的配置，如下：
< listener >
< listener-class > com.xxx.itpub.contrl.listener.CustomSpringContextLoaderListener </ listener-class >
</ listener >
设置完就ok了，这样被加载的xml文件中如果再出现名字相同的bean，spring在加载过程中就会抛出下面的异常：
[2014-08-07 19:32:04.329]-[ERROR] org.springframework.web.context.ContextLoader Context initialization failed
org.springframework.beans.factory.parsing.BeanDefinitionParsingException : Configuration problem: Failed to register bean definition with name 'publicDAO'
Offending resource: file [D:\software\dev\apache-tomcat-6.0.16\webapps\itpub_web\WEB-INF\classes\conf\spring\dbContext.xml]; nested exception is org.springframework.beans.factory.BeanDefinitionStoreException : Invalid bean definition with name 'publicDAO' defined in file [D:\software\dev\apache-tomcat-6.0.16\webapps\itpub_web\WEB-INF\classes\conf\spring\dbContext.xml]: Cannot register bean definition [Generic bean: class [com.xxx.itpub.daopub.database.impl.PublicDAOImpl]; scope=; abstract=false; lazyInit=false; autowireMode=0; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=null; factoryMethodName=null; initMethodName=null; destroyMethodName=null; defined in file [D:\software\dev\apache-tomcat-6.0.16\webapps\itpub_web\WEB-INF\classes\conf\spring\dbContext.xml]] for bean 'publicDAO': There is already [Generic bean: class [com.xxx.itpub.daopub.database.impl.PublicDAOImpl]; scope=; abstract=false; lazyInit=false; autowireMode=1; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=null; factoryMethodName=null; initMethodName=null; destroyMethodName=null; defined in file [D:\software\dev\apache-tomcat-6.0.16\webapps\itpub_web\WEB-INF\classes\conf\spring\beansContext.xml]] bound.
at org.springframework.beans.factory.parsing.FailFastProblemReporter.error( FailFastProblemReporter.java:68 )
at org.springframework.beans.factory.parsing.ReaderContext.error( ReaderContext.java:85 )
at org.springframework.beans.factory.parsing.ReaderContext.error( ReaderContext.java:76 )
at org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.processBeanDefinition( DefaultBeanDefinitionDocumentReader.java:320 )
at org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.parseDefaultElement( DefaultBeanDefinitionDocumentReader.java:203 )
at org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.parseBeanDefinitions( DefaultBeanDefinitionDocumentReader.java:182 )
at org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.doRegisterBeanDefinitions( DefaultBeanDefinitionDocumentReader.java:139 )
at org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.registerBeanDefinitions( DefaultBeanDefinitionDocumentReader.java:108 )
at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.registerBeanDefinitions( XmlBeanDefinitionReader.java:493 )
at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.doLoadBeanDefinitions( XmlBeanDefinitionReader.java:390 )
at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions( XmlBeanDefinitionReader.java:334 )
at org.springframework.beans.factory.xml.XmlBeanDefinitionReader.loadBeanDefinitions( XmlBeanDefinitionReader.java:302 )
at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions( AbstractBeanDefinitionReader.java:174 )
at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions( AbstractBeanDefinitionReader.java:209 )
at org.springframework.beans.factory.support.AbstractBeanDefinitionReader.loadBeanDefinitions( AbstractBeanDefinitionReader.java:180 )
at org.springframework.web.context.support.XmlWebApplicationContext.loadBeanDefinitions( XmlWebApplicationContext.java:125 )
at org.springframework.web.context.support.XmlWebApplicationContext.loadBeanDefinitions( XmlWebApplicationContext.java:94 )
at org.springframework.context.support.AbstractRefreshableApplicationContext.refreshBeanFactory( AbstractRefreshableApplicationContext.java:130 )
at org.springframework.context.support.AbstractApplicationContext.obtainFreshBeanFactory( AbstractApplicationContext.java:537 )
at org.springframework.context.support.AbstractApplicationContext.refresh( AbstractApplicationContext.java:451 )
at org.springframework.web.context.ContextLoader.configureAndRefreshWebApplicationContext( ContextLoader.java:389 )
at org.springframework.web.context.ContextLoader.initWebApplicationContext( ContextLoader.java:294 )
at org.springframework.web.context.ContextLoaderListener.contextInitialized( ContextLoaderListener.java:112 )
at org.apache.catalina.core.StandardContext.listenerStart( StandardContext.java:3843 )
at org.apache.catalina.core.StandardContext.start( StandardContext.java:4350 )
at org.apache.catalina.core.ContainerBase.addChildInternal( ContainerBase.java:791 )
at org.apache.catalina.core.ContainerBase.addChild( ContainerBase.java:771 )
at org.apache.catalina.core.StandardHost.addChild( StandardHost.java:525 )
at org.apache.catalina.startup.HostConfig.deployDirectory( HostConfig.java:924 )
at org.apache.catalina.startup.HostConfig.deployDirectories( HostConfig.java:887 )
at org.apache.catalina.startup.HostConfig.deployApps( HostConfig.java:492 )
at org.apache.catalina.startup.HostConfig.start( HostConfig.java:1147 )
at org.apache.catalina.startup.HostConfig.lifecycleEvent( HostConfig.java:311 )
at org.apache.catalina.util.LifecycleSupport.fireLifecycleEvent( LifecycleSupport.java:117 )
at org.apache.catalina.core.ContainerBase.start( ContainerBase.java:1053 )
at org.apache.catalina.core.StandardHost.start( StandardHost.java:719 )
at org.apache.catalina.core.ContainerBase.start( ContainerBase.java:1045 )
at org.apache.catalina.core.StandardEngine.start( StandardEngine.java:443 )
at org.apache.catalina.core.StandardService.start( StandardService.java:516 )
at org.apache.catalina.core.StandardServer.start( StandardServer.java:710 )
at org.apache.catalina.startup.Catalina.start( Catalina.java:578 )
at sun.reflect.NativeMethodAccessorImpl.invoke0( Native Method )
at sun.reflect.NativeMethodAccessorImpl.invoke(Unknown Source)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(Unknown Source)
at java.lang.reflect.Method.invoke(Unknown Source)
at org.apache.catalina.startup.Bootstrap.start( Bootstrap.java:288 )
at org.apache.catalina.startup.Bootstrap.main( Bootstrap.java:413 )
Caused by: org.springframework.beans.factory.BeanDefinitionStoreException : Invalid bean definition with name 'publicDAO' defined in file [D:\software\dev\apache-tomcat-6.0.16\webapps\itpub_web\WEB-INF\classes\conf\spring\dbContext.xml]: Cannot register bean definition [Generic bean: class [com.eshore.itpub.daopub.database.impl.PublicDAOImpl]; scope=; abstract=false; lazyInit=false; autowireMode=0; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=null; factoryMethodName=null; initMethodName=null; destroyMethodName=null; defined in file [D:\software\dev\apache-tomcat-6.0.16\webapps\itpub_web\WEB-INF\classes\conf\spring\dbContext.xml]] for bean 'publicDAO': There is already [Generic bean: class [com.xxx.itpub.daopub.database.impl.PublicDAOImpl]; scope=; abstract=false; lazyInit=false; autowireMode=1; dependencyCheck=0; autowireCandidate=true; primary=false; factoryBeanName=null; factoryMethodName=null; initMethodName=null; destroyMethodName=null; defined in file [D:\software\dev\apache-tomcat-6.0.16\webapps\itpub_web\WEB-INF\classes\conf\spring\beansContext.xml]] bound.
at org.springframework.beans.factory.support.DefaultListableBeanFactory.registerBeanDefinition( DefaultListableBeanFactory.java:657 )
at org.springframework.beans.factory.support.BeanDefinitionReaderUtils.registerBeanDefinition( BeanDefinitionReaderUtils.java:148 )
at org.springframework.beans.factory.xml.DefaultBeanDefinitionDocumentReader.processBeanDefinition( DefaultBeanDefinitionDocumentReader.java:317 )
... 43 more
2014-8-7 19:32:04 org.apache.catalina.core.StandardContext listenerStart
严重: Exception sending context initialized event to listener instance of class com.eshore.itpub.contrl.listener.CustomSpringContextLoaderListener
org.springframework.beans.factory.parsing.BeanDefinitionParsingException : Configuration problem: Failed to register bean definition with name 'publicDAO'
此时根据异常信息，去除掉同名的id之后，就可以了。
对于自动识别Autowired的同样有效。
