上下文混乱 - Spring 实例化单例 Bean 两次

Question

我正在以编程方式配置Spring。我没有得到我期望的注入结果，所以我查看了日志，发现Spring生成了两个单例bean。

在Tomcat启动日志中，我看到了以下内容：

INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@74b1128c: defining beans <LIST OF BEANS>

...little further

INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@61de76d0: defining beans <SAME LIST OF BEANS>

这是正常的行为吗？

这是我的应用程序上下文。

@Configuration
@EnableTransactionManagement
@ComponentScan(basePackages = {"com.application.shiro",
                   "com.business.dao.impl", 
                   "com.business.services"})
public class AppRootContext {    
    /* Beans */
}

这是我的Servlet上下文

@Configuration
@EnableWebMvc
@ComponentScan(basePackages = {"com.application.controllers"})
public class AppServletContext extends WebMvcConfigurerAdapter {
    /* Beans */
}

我的Servlet初始化类名为BidAppInitializer

@Override
public void onStartup(ServletContext container) throws ServletException {
    AnnotationConfigWebApplicationContext rootContext = new AnnotationConfigWebApplicationContext();
    rootContext.register(AppRootContext.class);

    container.addListener(new ContextLoaderListener(rootContext));

    AnnotationConfigWebApplicationContext servletContext = new AnnotationConfigWebApplicationContext();
    servletContext.register(AppServletContext.class);

    ServletRegistration.Dynamic appServlet = container.addServlet("bidapp", new DispatcherServlet(servletContext));
    appServlet.setLoadOnStartup(1);
    appServlet.addMapping("/");
}

这是我的完整Tomcat启动日志：

Feb 26, 2013 11:32:21 PM org.apache.catalina.core.AprLifecycleListener init
INFO: The APR based Apache Tomcat Native library which allows optimal performance in production environments was not found on the java.library.path: C:\Program Files\Java\jre7\bin;C:\Windows\Sun\Java\bin;C:\Windows\system32;C:\Windows;C:\Program Files (x86)\NVIDIA Corporation\PhysX\Common;C:\Windows\system32;C:\Windows;C:\Windows\System32\Wbem;C:\Windows\System32\WindowsPowerShell\v1.0\;C:\Program Files\MATLAB\R2010b\runtime\win64;C:\Program Files\MATLAB\R2010b\bin;C:\Users\Soto\Desktop\android-sdk-windows\tools;C:\Program Files (x86)\Common Files\Teleca Shared;C:\Program Files\TortoiseSVN\bin;C:\Program Files (x86)\QuickTime\QTSystem\;C:\Program Files\TortoiseHg\;C:\MinGW\bin;C:\Program Files\nodejs\; C:\PostgreSQL\9.2\bin\;C:\Program Files\MySQL\MySQL Server 5.5\bin;C:\MySQL\MySQL Server 5.5\bin;C:\Ruby193\bin;C:\Program Files (x86)\SSH Communications Security\SSH Secure Shell;C:\Users\Soto\Desktop\android-sdk-windows\tools;C:\MinGW\bin;C:\Users\Soto\AppData\Roaming\npm\;C:\apache-maven-3.0.4\bin;C:\Program Files\Java\jdk1.7.0_02\bin;C:\PostgreSQL\9.2\bin;.
Feb 26, 2013 11:32:21 PM org.apache.tomcat.util.digester.SetPropertiesRule begin
WARNING: [SetPropertiesRule]{Server/Service/Engine/Host/Context} Setting property 'source' to 'org.eclipse.jst.j2ee.server:BidApp' did not find a matching property.
Feb 26, 2013 11:32:21 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["http-bio-8080"]
Feb 26, 2013 11:32:21 PM org.apache.coyote.AbstractProtocol init
INFO: Initializing ProtocolHandler ["ajp-bio-8009"]
Feb 26, 2013 11:32:21 PM org.apache.catalina.startup.Catalina load
INFO: Initialization processed in 824 ms
Feb 26, 2013 11:32:21 PM org.apache.catalina.core.StandardService startInternal
INFO: Starting service Catalina
Feb 26, 2013 11:32:21 PM org.apache.catalina.core.StandardEngine startInternal
INFO: Starting Servlet Engine: Apache Tomcat/7.0.22
Feb 26, 2013 11:32:29 PM org.apache.catalina.core.ApplicationContext log
INFO: Spring WebApplicationInitializers detected on classpath: [com.bidapp.bootstrap.BidAppInitializer@60515c64]
Feb 26, 2013 11:32:32 PM org.apache.catalina.core.ApplicationContext log
INFO: Initializing Spring root WebApplicationContext
Feb 26, 2013 11:32:32 PM org.springframework.web.context.ContextLoader initWebApplicationContext
INFO: Root WebApplicationContext: initialization started
Feb 26, 2013 11:32:32 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing Root WebApplicationContext: startup date [Tue Feb 26 23:32:32 EST 2013]; root of context hierarchy
Feb 26, 2013 11:32:33 PM org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider registerDefaultFilters
INFO: JSR-330 'javax.inject.Named' annotation found and supported for component scanning
Feb 26, 2013 11:32:33 PM org.springframework.web.context.support.AnnotationConfigWebApplicationContext loadBeanDefinitions
INFO: Registering annotated classes: [class com.bidapp.bootstrap.AppRootContext]
Feb 26, 2013 11:32:33 PM org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider registerDefaultFilters
INFO: JSR-330 'javax.inject.Named' annotation found and supported for component scanning
Feb 26, 2013 11:32:36 PM org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor <init>
INFO: JSR-330 'javax.inject.Inject' annotation found and supported for autowiring

SDASD <--- Logged by my Root Context class constructor

Feb 26, 2013 11:33:49 PM org.springframework.context.support.AbstractApplicationContext$BeanPostProcessorChecker postProcessAfterInitialization
INFO: Bean 'appRootContext' of type [class com.bidapp.bootstrap.AppRootContext$$EnhancerByCGLIB$$84ad5432] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
Feb 26, 2013 11:33:52 PM org.springframework.context.support.AbstractApplicationContext$BeanPostProcessorChecker postProcessAfterInitialization
INFO: Bean 'proxyAsyncConfiguration' of type [class org.springframework.scheduling.annotation.ProxyAsyncConfiguration$$EnhancerByCGLIB$$f08c92c2] is not eligible for getting processed by all BeanPostProcessors (for example: not eligible for auto-proxying)
Feb 26, 2013 11:33:54 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@6393d737: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.annotation.internalPersistenceAnnotationProcessor,appRootContext,org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor#0,accountActivationDaoHibernateImpl,accountDao,auctionDaoHibernateImpl,categoryDao,accountService,emailService,org.springframework.aop.config.internalAutoProxyCreator,proxyTransactionManagementConfiguration,org.springframework.transaction.config.internalTransactionAdvisor,transactionAttributeSource,transactionInterceptor,proxyAsyncConfiguration,org.springframework.context.annotation.internalAsyncAnnotationProcessor,securityManager,credentialsMatcher,sessionFactory,transactionManager,hibernateRealm,lifecycleBeanPostProcessor,webTemplateResolver,emailTemplateResolver,templateEngine,shiroFilter,taskExecutor,dataSource,mailSender,viewResolver]; root of factory hierarchy
Feb 26, 2013 11:33:56 PM com.mchange.v2.log.MLog <clinit>
INFO: MLog clients using java 1.4+ standard logging.
Feb 26, 2013 11:33:56 PM com.mchange.v2.c3p0.C3P0Registry banner
INFO: Initializing c3p0-0.9.1 [built 16-January-2007 14:46:42; debug? true; trace: 10]
Feb 26, 2013 11:34:45 PM com.mchange.v2.c3p0.impl.AbstractPoolBackedDataSource getPoolManager
INFO: Initializing c3p0 pool... com.mchange.v2.c3p0.ComboPooledDataSource [ acquireIncrement -> 10, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, dataSourceName -> 1hge15x8t76zmwq1uj2ed9|6cfb984, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> com.mysql.jdbc.Driver, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> 1hge15x8t76zmwq1uj2ed9|6cfb984, idleConnectionTestPeriod -> 0, initialPoolSize -> 3, jdbcUrl -> jdbc:mysql://localhost:3306/bidapp, lastAcquisitionFailureDefaultUser -> null, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 1800, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 20, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 5, numHelperThreads -> 3, numThreadsAwaitingCheckoutDefaultUser -> 0, preferredTestQuery -> null, properties -> {user=******, password=******}, propertyCycle -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false ]
Feb 26, 2013 11:35:33 PM org.springframework.orm.hibernate4.HibernateTransactionManager afterPropertiesSet
INFO: Using DataSource [com.mchange.v2.c3p0.ComboPooledDataSource [ acquireIncrement -> 10, acquireRetryAttempts -> 30, acquireRetryDelay -> 1000, autoCommitOnClose -> false, automaticTestTable -> null, breakAfterAcquireFailure -> false, checkoutTimeout -> 0, connectionCustomizerClassName -> null, connectionTesterClassName -> com.mchange.v2.c3p0.impl.DefaultConnectionTester, dataSourceName -> 1hge15x8t76zmwq1uj2ed9|6cfb984, debugUnreturnedConnectionStackTraces -> false, description -> null, driverClass -> com.mysql.jdbc.Driver, factoryClassLocation -> null, forceIgnoreUnresolvedTransactions -> false, identityToken -> 1hge15x8t76zmwq1uj2ed9|6cfb984, idleConnectionTestPeriod -> 0, initialPoolSize -> 3, jdbcUrl -> jdbc:mysql://localhost:3306/bidapp, lastAcquisitionFailureDefaultUser -> null, maxAdministrativeTaskTime -> 0, maxConnectionAge -> 0, maxIdleTime -> 1800, maxIdleTimeExcessConnections -> 0, maxPoolSize -> 20, maxStatements -> 0, maxStatementsPerConnection -> 0, minPoolSize -> 5, numHelperThreads -> 3, numThreadsAwaitingCheckoutDefaultUser -> 0, preferredTestQuery -> null, properties -> {user=******, password=******}, propertyCycle -> 0, testConnectionOnCheckin -> false, testConnectionOnCheckout -> false, unreturnedConnectionTimeout -> 0, usesTraditionalReflectiveProxies -> false ]] of Hibernate SessionFactory for HibernateTransactionManager
Feb 26, 2013 11:35:36 PM org.springframework.web.context.ContextLoader initWebApplicationContext
INFO: Root WebApplicationContext: initialization completed in 183726 ms
Feb 26, 2013 11:35:36 PM org.apache.catalina.core.ApplicationContext log
INFO: Initializing Spring FrameworkServlet 'bidapp'
Feb 26, 2013 11:35:36 PM org.springframework.web.servlet.FrameworkServlet initServletBean
INFO: FrameworkServlet 'bidapp': initialization started
Feb 26, 2013 11:35:36 PM org.springframework.context.support.AbstractApplicationContext prepareRefresh
INFO: Refreshing WebApplicationContext for namespace 'bidapp-servlet': startup date [Tue Feb 26 23:35:36 EST 2013]; parent: Root WebApplicationContext
Feb 26, 2013 11:35:36 PM org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider registerDefaultFilters
INFO: JSR-330 'javax.inject.Named' annotation found and supported for component scanning
Feb 26, 2013 11:35:36 PM org.springframework.web.context.support.AnnotationConfigWebApplicationContext loadBeanDefinitions
INFO: Registering annotated classes: [class com.bidapp.bootstrap.AppServletContext]
Feb 26, 2013 11:35:37 PM org.springframework.context.annotation.ClassPathScanningCandidateComponentProvider registerDefaultFilters
INFO: JSR-330 'javax.inject.Named' annotation found and supported for component scanning
Feb 26, 2013 11:35:40 PM org.springframework.beans.factory.annotation.AutowiredAnnotationBeanPostProcessor <init>
INFO: JSR-330 'javax.inject.Inject' annotation found and supported for autowiring
Feb 26, 2013 11:35:42 PM org.springframework.beans.factory.support.DefaultListableBeanFactory preInstantiateSingletons
INFO: Pre-instantiating singletons in org.springframework.beans.factory.support.DefaultListableBeanFactory@2c8ff601: defining beans [org.springframework.context.annotation.internalConfigurationAnnotationProcessor,org.springframework.context.annotation.internalAutowiredAnnotationProcessor,org.springframework.context.annotation.internalRequiredAnnotationProcessor,org.springframework.context.annotation.internalCommonAnnotationProcessor,org.springframework.context.annotation.internalPersistenceAnnotationProcessor,appServletContext,org.springframework.context.annotation.ConfigurationClassPostProcessor$ImportAwareBeanPostProcessor#0,accountController,auctionController,indexPagesController,delegatingWebMvcConfiguration,requestMappingHandlerMapping,viewControllerHandlerMapping,beanNameHandlerMapping,resourceHandlerMapping,defaultServletHandlerMapping,requestMappingHandlerAdapter,mvcConversionService,mvcValidator,httpRequestHandlerAdapter,simpleControllerHandlerAdapter,handlerExceptionResolver]; parent: org.springframework.beans.factory.support.DefaultListableBeanFactory@6393d737
Feb 26, 2013 11:35:52 PM org.springframework.web.servlet.handler.AbstractHandlerMethodMapping registerHandlerMethod
...Controller handler method mappings

- Sotirios Delimanolis

---

看起来在你的Tomcat日志中，那些bean列表实际上并不是完全相同的bean列表，特别是类似于auctionController这样的类，它们只被实例化一次。 - Terrell Plotzki

你是绝对正确的。Derp。 - Sotirios Delimanolis

Answer 1

单例模式保证Spring容器内只有一个实例。这意味着，您可以有与容器数量相同的singleton实例（即使它们使用相同的JVM类加载器）。请参见The singleton scope和此答案Singleton Design Pattern vs. Singleton Bean。

在您的情况下，您正在实例化两个上下文——rootContext和servletContext，并且从那里获取日志语句。

如果您想要每个单例的单个实例，则可以合并这两个上下文。

---

这是一个小的Java类，用于说明这种行为（对于奇怪的代码格式化表示歉意 - 希望能更简洁明了）：

package singleton;

import java.util.UUID;

import org.springframework.context.annotation.AnnotationConfigApplicationContext;
import org.springframework.context.annotation.ComponentScan;
import org.springframework.context.annotation.Configuration;
import org.springframework.stereotype.Component;

public class AppMain {

    public static void main(String[] args) {
        final AnnotationConfigApplicationContext rootContext = new AnnotationConfigApplicationContext();
        rootContext.register(AppRootContext.class);
        rootContext.refresh();

        final AnnotationConfigApplicationContext servletContext = new AnnotationConfigApplicationContext();
        servletContext.register(AppServletContext.class);
        servletContext.refresh();

        final Singleton one = (Singleton) rootContext.getBean("singleton");
        final Singleton andAnotherOne = (Singleton) servletContext.getBean("singleton");

        System.out.println("Singletons are " + (one.ID.equals(andAnotherOne.ID) ? "equal" : "different"));
    }
}

@Component
class Singleton {public String ID = UUID.randomUUID().toString();}

@Configuration
@ComponentScan(basePackages = { "singleton" })
class AppRootContext {}

@Configuration
@ComponentScan(basePackages = { "singleton" })
class AppServletContext {}

- Petro Semeniuk

---

我想补充一点，容器本质上是ClassLoader实例，因此单例在ClassLoader内得到了尊重。 - Andrew Alcock

通常情况下是这样的，但在这种情况下，两个容器都是在同一个线程中使用默认构造函数实例化的，并且将使用相同的类加载器（Thread.getContextClassLoader()）。这种行为是从DefaultResourceLoader继承而来的。也就是说，即使Spring容器共享相同的类加载器，您仍将获得多个Spring单例实例。 - Petro Semeniuk

抱歉，我的表述不够清晰。GoF Singleton 的实现将在 ClassLoader 中的所有容器中成为单例，但您是正确的，使用 singleton scope 每个容器只能获得一个对象。对此我感到抱歉。 - Andrew Alcock

啊，抱歉，你是对的。我以为你指的是“另一个”单例模式。这个“bean作用域”和“GoF设计模式”的区别有时候真的很令人困惑。 - Petro Semeniuk

Answer 2

有两种类型的上下文，一种是根上下文，另一种是Web应用程序上下文。

如果在WebAppInitalizer中扩展了AbstractAnnotationConfigDispatcherServletInitializer类，请确保您覆盖以下方法，并确保类定义不会在两个方法中重复出现。

@Override protected Class[] getServletConfigClasses() { return new Class[] { MvcConfig.class}; }

@Override
protected Class<?>[] getRootConfigClasses() {
    return new Class[] {RooTContextAppConfig.class };
}

- Rahul Tokase