Context confusion - Spring instantiating singleton beans twice

Question

I'm doing my Spring configuration programatically. I'm not getting the injection results I'm expecting so I looked at logs and for some reason Spring is generating my singleton beans twice.

I get this in Tomcat start-up logs

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>

Is this normal behavior?

This is my Application Context

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

This is my Servlet Context

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

And my Servlet Initializer class called 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("/");
}

This is my full Tomcat start-up log:

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

Answer 1

Singleton guarantees single instance inside Spring container. That mean that you could have as many singleton instances as there are containers (even if they use the same JVM class loader). See The singleton scope and this answer for Singleton Design Pattern vs. Singleton Bean

In your case you're instantiating two contexts - rootContext and servletContext and that were log statements are coming from.

If you want to have single instance of every singleton - you could merge these two contexts.

---

Small java class which illustrates such behavior(apologies for weird code formatting - wanted to make it more concise ):

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 {}