Spring beanid 同名覆盖问题解决

转载至：http://blog.csdn.net/linuxerlin/article/details/38778761

问题：

   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。