Package org.springframework.context.support

Class AbstractApplicationContext

java.lang.Object
org.springframework.core.io.DefaultResourceLoader
org.springframework.context.support.AbstractApplicationContext
All Implemented Interfaces:
Closeable, AutoCloseable, BeanFactory, HierarchicalBeanFactory, ListableBeanFactory, ApplicationContext, ApplicationEventPublisher, ConfigurableApplicationContext, Lifecycle, MessageSource, EnvironmentCapable, ResourceLoader, ResourcePatternResolver
Direct Known Subclasses:
AbstractRefreshableApplicationContext, GenericApplicationContext
public abstract class AbstractApplicationContext extends DefaultResourceLoader implements ConfigurableApplicationContext
Abstract implementation of the ApplicationContext interface. Doesn't mandate the type of storage used for configuration; simply implements common context functionality. Uses the Template Method design pattern, requiring concrete subclasses to implement abstract methods.

In contrast to a plain BeanFactory, an ApplicationContext is supposed to detect special beans defined in its internal bean factory: Therefore, this class automatically registers BeanFactoryPostProcessors, BeanPostProcessors, and ApplicationListeners which are defined as beans in the context.

A MessageSource may also be supplied as a bean in the context, with the name "messageSource"; otherwise, message resolution is delegated to the parent context. Furthermore, a multicaster for application events can be supplied as an "applicationEventMulticaster" bean of type ApplicationEventMulticaster in the context; otherwise, a default multicaster of type SimpleApplicationEventMulticaster will be used.

Implements resource loading by extending DefaultResourceLoader. Consequently treats non-URL resource paths as class path resources (supporting full class path resource names that include the package path, e.g. "mypackage/myresource.dat"), unless the DefaultResourceLoader.getResourceByPath(java.lang.String) method is overridden in a subclass.

Since:
January 21, 2001
Author:
Rod Johnson, Juergen Hoeller, Mark Fisher, Stephane Nicoll, Sam Brannen, Sebastien Deleuze, Brian Clozel
See Also:

  • Field Details

  • Constructor Details

    • AbstractApplicationContext

      public AbstractApplicationContext()
      Create a new AbstractApplicationContext with no parent.

    • AbstractApplicationContext

      public AbstractApplicationContext(@Nullable ApplicationContext parent)
      Create a new AbstractApplicationContext with the given parent context.
      Parameters:
      parent - the parent context

  • Method Details

    • setId

      public void setId(String id)
      Set the unique id of this application context.

      Default is the object id of the context instance, or the name of the context bean if the context is itself defined as a bean.

      Specified by:
      setId in interface ConfigurableApplicationContext
      Parameters:
      id - the unique id of the context

    • getId

      public String getId()
      Description copied from interface: ApplicationContext
      Return the unique id of this application context.
      Specified by:
      getId in interface ApplicationContext
      Returns:
      the unique id of the context, or null if none

    • getApplicationName

      public String getApplicationName()
      Description copied from interface: ApplicationContext
      Return a name for the deployed application that this context belongs to.
      Specified by:
      getApplicationName in interface ApplicationContext
      Returns:
      a name for the deployed application, or the empty String by default

    • setDisplayName

      public void setDisplayName(String displayName)
      Set a friendly name for this context. Typically done during initialization of concrete context implementations.

      Default is the object id of the context instance.

    • getDisplayName

      public String getDisplayName()
      Return a friendly name for this context.
      Specified by:
      getDisplayName in interface ApplicationContext
      Returns:
      a display name for this context (never null)

    • getParent

      @Nullable public ApplicationContext getParent()
      Return the parent context, or null if there is no parent (that is, this context is the root of the context hierarchy).
      Specified by:
      getParent in interface ApplicationContext
      Returns:
      the parent context, or null if there is no parent

    • setEnvironment

      public void setEnvironment(ConfigurableEnvironment environment)
      Set the Environment for this application context.

      Default value is determined by createEnvironment(). Replacing the default with this method is one option but configuration through getEnvironment() should also be considered. In either case, such modifications should be performed before refresh().

      Specified by:
      setEnvironment in interface ConfigurableApplicationContext
      Parameters:
      environment - the new environment
      See Also:

    • getEnvironment

      public ConfigurableEnvironment getEnvironment()
      Return the Environment for this application context in configurable form, allowing for further customization.

      If none specified, a default environment will be initialized via createEnvironment().

      Specified by:
      getEnvironment in interface ConfigurableApplicationContext
      Specified by:
      getEnvironment in interface EnvironmentCapable

    • createEnvironment

      protected ConfigurableEnvironment createEnvironment()
      Create and return a new StandardEnvironment.

      Subclasses may override this method in order to supply a custom ConfigurableEnvironment implementation.

    • getAutowireCapableBeanFactory

      public AutowireCapableBeanFactory getAutowireCapableBeanFactory() throws IllegalStateException
      Return this context's internal bean factory as AutowireCapableBeanFactory, if already available.
      Specified by:
      getAutowireCapableBeanFactory in interface ApplicationContext
      Returns:
      the AutowireCapableBeanFactory for this context
      Throws:
      IllegalStateException - if the context does not support the AutowireCapableBeanFactory interface, or does not hold an autowire-capable bean factory yet (e.g. if refresh() has never been called), or if the context has been closed already
      See Also:

    • getStartupDate

      public long getStartupDate()
      Return the timestamp (ms) when this context was first loaded.
      Specified by:
      getStartupDate in interface ApplicationContext
      Returns:
      the timestamp (ms) when this context was first loaded

    • publishEvent

      public void publishEvent(ApplicationEvent event)
      Publish the given event to all listeners.

      Note: Listeners get initialized after the MessageSource, to be able to access it within listener implementations. Thus, MessageSource implementations cannot publish events.

      Specified by:
      publishEvent in interface ApplicationEventPublisher
      Parameters:
      event - the event to publish (may be application-specific or a standard framework event)
      See Also:

    • publishEvent

      public void publishEvent(Object event)
      Publish the given event to all listeners.

      Note: Listeners get initialized after the MessageSource, to be able to access it within listener implementations. Thus, MessageSource implementations cannot publish events.

      Specified by:
      publishEvent in interface ApplicationEventPublisher
      Parameters:
      event - the event to publish (may be an ApplicationEvent or a payload object to be turned into a PayloadApplicationEvent)
      See Also:

    • publishEvent

      protected void publishEvent(Object event, @Nullable ResolvableType eventType)
      Publish the given event to all listeners.
      Parameters:
      event - the event to publish (may be an ApplicationEvent or a payload object to be turned into a PayloadApplicationEvent)
      eventType - the resolved event type, if known
      Since:
      4.2

    • setApplicationStartup

      public void setApplicationStartup(ApplicationStartup applicationStartup)
      Description copied from interface: ConfigurableApplicationContext
      Set the ApplicationStartup for this application context.

      This allows the application context to record metrics during startup.

      Specified by:
      setApplicationStartup in interface ConfigurableApplicationContext
      Parameters:
      applicationStartup - the new context event factory

    • getApplicationStartup

      public ApplicationStartup getApplicationStartup()
      Description copied from interface: ConfigurableApplicationContext
      Return the ApplicationStartup for this application context.
      Specified by:
      getApplicationStartup in interface ConfigurableApplicationContext

    • getResourcePatternResolver

      protected ResourcePatternResolver getResourcePatternResolver()
      Return the ResourcePatternResolver to use for resolving location patterns into Resource instances. Default is a PathMatchingResourcePatternResolver, supporting Ant-style location patterns.

      Can be overridden in subclasses, for extended resolution strategies, for example in a web environment.

      Do not call this when needing to resolve a location pattern. Call the context's getResources method instead, which will delegate to the ResourcePatternResolver.

      Returns:
      the ResourcePatternResolver for this context
      See Also:

    • setParent

      public void setParent(@Nullable ApplicationContext parent)
      Set the parent of this application context.

      The parent environment is merged with this (child) application context environment if the parent is non-null and its environment is an instance of ConfigurableEnvironment.

      Specified by:
      setParent in interface ConfigurableApplicationContext
      Parameters:
      parent - the parent context
      See Also:

    • addBeanFactoryPostProcessor

      public void addBeanFactoryPostProcessor(BeanFactoryPostProcessor postProcessor)
      Description copied from interface: ConfigurableApplicationContext
      Add a new BeanFactoryPostProcessor that will get applied to the internal bean factory of this application context on refresh, before any of the bean definitions get evaluated. To be invoked during context configuration.
      Specified by:
      addBeanFactoryPostProcessor in interface ConfigurableApplicationContext
      Parameters:
      postProcessor - the factory processor to register

    • getBeanFactoryPostProcessors

      public List<BeanFactoryPostProcessor> getBeanFactoryPostProcessors()
      Return the list of BeanFactoryPostProcessors that will get applied to the internal BeanFactory.

    • addApplicationListener

      public void addApplicationListener(ApplicationListener<?> listener)
      Description copied from interface: ConfigurableApplicationContext
      Add a new ApplicationListener that will be notified on context events such as context refresh and context shutdown.

      Note that any ApplicationListener registered here will be applied on refresh if the context is not active yet, or on the fly with the current event multicaster in case of a context that is already active.

      Specified by:
      addApplicationListener in interface ConfigurableApplicationContext
      Parameters:
      listener - the ApplicationListener to register
      See Also:

    • removeApplicationListener

      public void removeApplicationListener(ApplicationListener<?> listener)
      Description copied from interface: ConfigurableApplicationContext
      Remove the given ApplicationListener from this context's set of listeners, assuming it got registered via ConfigurableApplicationContext.addApplicationListener(org.springframework.context.ApplicationListener<?>) before.
      Specified by:
      removeApplicationListener in interface ConfigurableApplicationContext
      Parameters:
      listener - the ApplicationListener to deregister

    • getApplicationListeners

      public Collection<ApplicationListener<?>> getApplicationListeners()
      Return the list of statically specified ApplicationListeners.

    • refresh

      public void refresh() throws BeansException, IllegalStateException
      Description copied from interface: ConfigurableApplicationContext
      Load or refresh the persistent representation of the configuration, which might be from Java-based configuration, an XML file, a properties file, a relational database schema, or some other format.

      As this is a startup method, it should destroy already created singletons if it fails, to avoid dangling resources. In other words, after invocation of this method, either all or no singletons at all should be instantiated.

      Specified by:
      refresh in interface ConfigurableApplicationContext
      Throws:
      BeansException - if the bean factory could not be initialized
      IllegalStateException - if already initialized and multiple refresh attempts are not supported

    • prepareRefresh

      protected void prepareRefresh()
      Prepare this context for refreshing, setting its startup date and active flag as well as performing any initialization of property sources.

    • initPropertySources

      protected void initPropertySources()

      Replace any stub property sources with actual instances.

      See Also:

    • obtainFreshBeanFactory

      protected ConfigurableListableBeanFactory obtainFreshBeanFactory()
      Tell the subclass to refresh the internal bean factory.
      Returns:
      the fresh BeanFactory instance
      See Also:

    • prepareBeanFactory

      protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory)
      Configure the factory's standard context characteristics, such as the context's ClassLoader and post-processors.
      Parameters:
      beanFactory - the BeanFactory to configure

    • postProcessBeanFactory

      protected void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory)
      Modify the application context's internal bean factory after its standard initialization. All bean definitions will have been loaded, but no beans will have been instantiated yet. This allows for registering special BeanPostProcessors etc in certain ApplicationContext implementations.
      Parameters:
      beanFactory - the bean factory used by the application context

    • invokeBeanFactoryPostProcessors

      protected void invokeBeanFactoryPostProcessors(ConfigurableListableBeanFactory beanFactory)
      Instantiate and invoke all registered BeanFactoryPostProcessor beans, respecting explicit order if given.

      Must be called before singleton instantiation.

    • registerBeanPostProcessors

      protected void registerBeanPostProcessors(ConfigurableListableBeanFactory beanFactory)
      Instantiate and register all BeanPostProcessor beans, respecting explicit order if given.

      Must be called before any instantiation of application beans.

    • initMessageSource

      protected void initMessageSource()
      Initialize the MessageSource. Use parent's if none defined in this context.

    • initApplicationEventMulticaster

      protected void initApplicationEventMulticaster()
      Initialize the ApplicationEventMulticaster. Uses SimpleApplicationEventMulticaster if none defined in the context.
      See Also:

    • initLifecycleProcessor

      protected void initLifecycleProcessor()
      Initialize the LifecycleProcessor. Uses DefaultLifecycleProcessor if none defined in the context.
      See Also:

    • onRefresh

      protected void onRefresh() throws BeansException
      Template method which can be overridden to add context-specific refresh work. Called on initialization of special beans, before instantiation of singletons.

      This implementation is empty.

      Throws:
      BeansException - in case of errors
      See Also:

    • registerListeners

      protected void registerListeners()
      Add beans that implement ApplicationListener as listeners. Doesn't affect other listeners, which can be added without being beans.

    • finishBeanFactoryInitialization

      protected void finishBeanFactoryInitialization(ConfigurableListableBeanFactory beanFactory)
      Finish the initialization of this context's bean factory, initializing all remaining singleton beans.

    • finishRefresh

      protected void finishRefresh()
      Finish the refresh of this context, invoking the LifecycleProcessor's onRefresh() method and publishing the ContextRefreshedEvent.

    • cancelRefresh

      protected void cancelRefresh(BeansException ex)
      Cancel this context's refresh attempt, resetting the active flag after an exception got thrown.
      Parameters:
      ex - the exception that led to the cancellation

    • resetCommonCaches

      protected void resetCommonCaches()
      Reset Spring's common reflection metadata caches, in particular the ReflectionUtils, AnnotationUtils, ResolvableType and CachedIntrospectionResults caches.
      Since:
      4.2
      See Also:

    • registerShutdownHook

      public void registerShutdownHook()
      Register a shutdown hook named SpringContextShutdownHook with the JVM runtime, closing this context on JVM shutdown unless it has already been closed at that time.

      Delegates to doClose() for the actual closing procedure.

      Specified by:
      registerShutdownHook in interface ConfigurableApplicationContext
      See Also:

    • close

      public void close()
      Close this application context, destroying all beans in its bean factory.

      Delegates to doClose() for the actual closing procedure. Also removes a JVM shutdown hook, if registered, as it's not needed anymore.

      Specified by:
      close in interface AutoCloseable
      Specified by:
      close in interface Closeable
      Specified by:
      close in interface ConfigurableApplicationContext
      See Also:

    • doClose

      protected void doClose()
      Actually performs context closing: publishes a ContextClosedEvent and destroys the singletons in the bean factory of this application context.

      Called by both close() and a JVM shutdown hook, if any.

      See Also:

    • destroyBeans

      protected void destroyBeans()
      Template method for destroying all beans that this context manages. The default implementation destroy all cached singletons in this context, invoking DisposableBean.destroy() and/or the specified "destroy-method".

      Can be overridden to add context-specific bean destruction steps right before or right after standard singleton destruction, while the context's BeanFactory is still active.

      See Also:

    • onClose

      protected void onClose()
      Template method which can be overridden to add context-specific shutdown work. The default implementation is empty.

      Called at the end of doClose()'s shutdown procedure, after this context's BeanFactory has been closed. If custom shutdown logic needs to execute while the BeanFactory is still active, override the destroyBeans() method instead.

    • isActive

      public boolean isActive()
      Description copied from interface: ConfigurableApplicationContext
      Determine whether this application context is active, that is, whether it has been refreshed at least once and has not been closed yet.
      Specified by:
      isActive in interface ConfigurableApplicationContext
      Returns:
      whether the context is still active
      See Also:

    • assertBeanFactoryActive

      protected void assertBeanFactoryActive()
      Assert that this context's BeanFactory is currently active, throwing an IllegalStateException if it isn't.

      Invoked by all BeanFactory delegation methods that depend on an active context, i.e. in particular all bean accessor methods.

      The default implementation checks the 'active' status of this context overall. May be overridden for more specific checks, or for a no-op if getBeanFactory() itself throws an exception in such a case.

    • getBean

      public Object getBean(String name) throws BeansException
      Description copied from interface: BeanFactory
      Return an instance, which may be shared or independent, of the specified bean.

      This method allows a Spring BeanFactory to be used as a replacement for the Singleton or Prototype design pattern. Callers may retain references to returned objects in the case of Singleton beans.

      Translates aliases back to the corresponding canonical bean name.

      Will ask the parent factory if the bean cannot be found in this factory instance.

      Specified by:
      getBean in interface BeanFactory
      Parameters:
      name - the name of the bean to retrieve
      Returns:
      an instance of the bean
      Throws:
      NoSuchBeanDefinitionException - if there is no bean with the specified name
      BeansException - if the bean could not be obtained

    • getBean

      public <T> T getBean(String name, Class<T> requiredType) throws BeansException
      Description copied from interface: BeanFactory
      Return an instance, which may be shared or independent, of the specified bean.

      Behaves the same as BeanFactory.getBean(String), but provides a measure of type safety by throwing a BeanNotOfRequiredTypeException if the bean is not of the required type. This means that ClassCastException can't be thrown on casting the result correctly, as can happen with BeanFactory.getBean(String).

      Translates aliases back to the corresponding canonical bean name.

      Will ask the parent factory if the bean cannot be found in this factory instance.

      Specified by:
      getBean in interface BeanFactory
      Parameters:
      name - the name of the bean to retrieve
      requiredType - type the bean must match; can be an interface or superclass
      Returns:
      an instance of the bean
      Throws:
      NoSuchBeanDefinitionException - if there is no such bean definition
      BeanNotOfRequiredTypeException - if the bean is not of the required type
      BeansException - if the bean could not be created

    • getBean

      public Object getBean(String name, Object... args) throws BeansException
      Description copied from interface: BeanFactory
      Return an instance, which may be shared or independent, of the specified bean.

      Allows for specifying explicit constructor arguments / factory method arguments, overriding the specified default arguments (if any) in the bean definition.

      Specified by:
      getBean in interface BeanFactory
      Parameters:
      name - the name of the bean to retrieve
      args - arguments to use when creating a bean instance using explicit arguments (only applied when creating a new instance as opposed to retrieving an existing one)
      Returns:
      an instance of the bean
      Throws:
      NoSuchBeanDefinitionException - if there is no such bean definition
      BeanDefinitionStoreException - if arguments have been given but the affected bean isn't a prototype
      BeansException - if the bean could not be created

    • getBean

      public <T> T getBean(Class<T> requiredType) throws BeansException
      Description copied from interface: BeanFactory
      Return the bean instance that uniquely matches the given object type, if any.

      This method goes into ListableBeanFactory by-type lookup territory but may also be translated into a conventional by-name lookup based on the name of the given type. For more extensive retrieval operations across sets of beans, use ListableBeanFactory and/or BeanFactoryUtils.

      Specified by:
      getBean in interface BeanFactory
      Parameters:
      requiredType - type the bean must match; can be an interface or superclass
      Returns:
      an instance of the single bean matching the required type
      Throws:
      NoSuchBeanDefinitionException - if no bean of the given type was found
      NoUniqueBeanDefinitionException - if more than one bean of the given type was found
      BeansException - if the bean could not be created
      See Also:

    • getBean

      public <T> T getBean(Class<T> requiredType, Object... args) throws BeansException
      Description copied from interface: BeanFactory
      Return an instance, which may be shared or independent, of the specified bean.

      Allows for specifying explicit constructor arguments / factory method arguments, overriding the specified default arguments (if any) in the bean definition.

      This method goes into ListableBeanFactory by-type lookup territory but may also be translated into a conventional by-name lookup based on the name of the given type. For more extensive retrieval operations across sets of beans, use ListableBeanFactory and/or BeanFactoryUtils.

      Specified by:
      getBean in interface BeanFactory
      Parameters:
      requiredType - type the bean must match; can be an interface or superclass
      args - arguments to use when creating a bean instance using explicit arguments (only applied when creating a new instance as opposed to retrieving an existing one)
      Returns:
      an instance of the bean
      Throws:
      NoSuchBeanDefinitionException - if there is no such bean definition
      BeanDefinitionStoreException - if arguments have been given but the affected bean isn't a prototype
      BeansException - if the bean could not be created

    • getBeanProvider

      public <T> ObjectProvider<T> getBeanProvider(Class<T> requiredType)
      Description copied from interface: BeanFactory
      Return a provider for the specified bean, allowing for lazy on-demand retrieval of instances, including availability and uniqueness options.

      For matching a generic type, consider BeanFactory.getBeanProvider(ResolvableType).

      Specified by:
      getBeanProvider in interface BeanFactory
      Parameters:
      requiredType - type the bean must match; can be an interface or superclass
      Returns:
      a corresponding provider handle
      See Also:

    • getBeanProvider

      public <T> ObjectProvider<T> getBeanProvider(ResolvableType requiredType)
      Description copied from interface: BeanFactory
      Return a provider for the specified bean, allowing for lazy on-demand retrieval of instances, including availability and uniqueness options. This variant allows for specifying a generic type to match, similar to reflective injection points with generic type declarations in method/constructor parameters.

      Note that collections of beans are not supported here, in contrast to reflective injection points. For programmatically retrieving a list of beans matching a specific type, specify the actual bean type as an argument here and subsequently use ObjectProvider.orderedStream() or its lazy streaming/iteration options.

      Also, generics matching is strict here, as per the Java assignment rules. For lenient fallback matching with unchecked semantics (similar to the ´unchecked´ Java compiler warning), consider calling BeanFactory.getBeanProvider(Class) with the raw type as a second step if no full generic match is available with this variant.

      Specified by:
      getBeanProvider in interface BeanFactory
      Parameters:
      requiredType - type the bean must match; can be a generic type declaration
      Returns:
      a corresponding provider handle
      See Also:

    • containsBean

      public boolean containsBean(String name)
      Description copied from interface: BeanFactory
      Does this bean factory contain a bean definition or externally registered singleton instance with the given name?

      If the given name is an alias, it will be translated back to the corresponding canonical bean name.

      If this factory is hierarchical, will ask any parent factory if the bean cannot be found in this factory instance.

      If a bean definition or singleton instance matching the given name is found, this method will return true whether the named bean definition is concrete or abstract, lazy or eager, in scope or not. Therefore, note that a true return value from this method does not necessarily indicate that BeanFactory.getBean(java.lang.String) will be able to obtain an instance for the same name.

      Specified by:
      containsBean in interface BeanFactory
      Parameters:
      name - the name of the bean to query
      Returns:
      whether a bean with the given name is present

    • isSingleton

      public boolean isSingleton(String name) throws NoSuchBeanDefinitionException
      Description copied from interface: BeanFactory
      Is this bean a shared singleton? That is, will BeanFactory.getBean(java.lang.String) always return the same instance?

      Note: This method returning false does not clearly indicate independent instances. It indicates non-singleton instances, which may correspond to a scoped bean as well. Use the BeanFactory.isPrototype(java.lang.String) operation to explicitly check for independent instances.

      Translates aliases back to the corresponding canonical bean name.

      Will ask the parent factory if the bean cannot be found in this factory instance.

      Specified by:
      isSingleton in interface BeanFactory
      Parameters:
      name - the name of the bean to query
      Returns:
      whether this bean corresponds to a singleton instance
      Throws:
      NoSuchBeanDefinitionException - if there is no bean with the given name
      See Also:

    • isPrototype

      public boolean isPrototype(String name) throws NoSuchBeanDefinitionException
      Description copied from interface: BeanFactory
      Is this bean a prototype? That is, will BeanFactory.getBean(java.lang.String) always return independent instances?

      Note: This method returning false does not clearly indicate a singleton object. It indicates non-independent instances, which may correspond to a scoped bean as well. Use the BeanFactory.isSingleton(java.lang.String) operation to explicitly check for a shared singleton instance.

      Translates aliases back to the corresponding canonical bean name.

      Will ask the parent factory if the bean cannot be found in this factory instance.

      Specified by:
      isPrototype in interface BeanFactory
      Parameters:
      name - the name of the bean to query
      Returns:
      whether this bean will always deliver independent instances
      Throws:
      NoSuchBeanDefinitionException - if there is no bean with the given name
      See Also:

    • isTypeMatch

      public boolean isTypeMatch(String name, ResolvableType typeToMatch) throws NoSuchBeanDefinitionException
      Description copied from interface: BeanFactory
      Check whether the bean with the given name matches the specified type. More specifically, check whether a BeanFactory.getBean(java.lang.String) call for the given name would return an object that is assignable to the specified target type.

      Translates aliases back to the corresponding canonical bean name.

      Will ask the parent factory if the bean cannot be found in this factory instance.

      Specified by:
      isTypeMatch in interface BeanFactory
      Parameters:
      name - the name of the bean to query
      typeToMatch - the type to match against (as a ResolvableType)
      Returns:
      true if the bean type matches, false if it doesn't match or cannot be determined yet
      Throws:
      NoSuchBeanDefinitionException - if there is no bean with the given name
      See Also:

    • isTypeMatch

      public boolean isTypeMatch(String name, Class<?> typeToMatch) throws NoSuchBeanDefinitionException
      Description copied from interface: BeanFactory
      Check whether the bean with the given name matches the specified type. More specifically, check whether a BeanFactory.getBean(java.lang.String) call for the given name would return an object that is assignable to the specified target type.

      Translates aliases back to the corresponding canonical bean name.

      Will ask the parent factory if the bean cannot be found in this factory instance.

      Specified by:
      isTypeMatch in interface BeanFactory
      Parameters:
      name - the name of the bean to query
      typeToMatch - the type to match against (as a Class)
      Returns:
      true if the bean type matches, false if it doesn't match or cannot be determined yet
      Throws:
      NoSuchBeanDefinitionException - if there is no bean with the given name
      See Also:

    • getType

      @Nullable public Class<?> getType(String name) throws NoSuchBeanDefinitionException
      Description copied from interface: BeanFactory
      Determine the type of the bean with the given name. More specifically, determine the type of object that BeanFactory.getBean(java.lang.String) would return for the given name.

      For a FactoryBean, return the type of object that the FactoryBean creates, as exposed by FactoryBean.getObjectType(). This may lead to the initialization of a previously uninitialized FactoryBean (see BeanFactory.getType(String, boolean)).

      Translates aliases back to the corresponding canonical bean name.

      Will ask the parent factory if the bean cannot be found in this factory instance.

      Specified by:
      getType in interface BeanFactory
      Parameters:
      name - the name of the bean to query
      Returns:
      the type of the bean, or null if not determinable
      Throws:
      NoSuchBeanDefinitionException - if there is no bean with the given name
      See Also:

    • getType

      @Nullable public Class<?> getType(String name, boolean allowFactoryBeanInit) throws NoSuchBeanDefinitionException
      Description copied from interface: BeanFactory
      Determine the type of the bean with the given name. More specifically, determine the type of object that BeanFactory.getBean(java.lang.String) would return for the given name.

      For a FactoryBean, return the type of object that the FactoryBean creates, as exposed by FactoryBean.getObjectType(). Depending on the allowFactoryBeanInit flag, this may lead to the initialization of a previously uninitialized FactoryBean if no early type information is available.

      Translates aliases back to the corresponding canonical bean name.

      Will ask the parent factory if the bean cannot be found in this factory instance.

      Specified by:
      getType in interface BeanFactory
      Parameters:
      name - the name of the bean to query
      allowFactoryBeanInit - whether a FactoryBean may get initialized just for the purpose of determining its object type
      Returns:
      the type of the bean, or null if not determinable
      Throws:
      NoSuchBeanDefinitionException - if there is no bean with the given name
      See Also:

    • getAliases

      public String[] getAliases(String name)
      Description copied from interface: BeanFactory
      Return the aliases for the given bean name, if any.

      All of those aliases point to the same bean when used in a BeanFactory.getBean(java.lang.String) call.

      If the given name is an alias, the corresponding original bean name and other aliases (if any) will be returned, with the original bean name being the first element in the array.

      Will ask the parent factory if the bean cannot be found in this factory instance.

      Specified by:
      getAliases in interface BeanFactory
      Parameters:
      name - the bean name to check for aliases
      Returns:
      the aliases, or an empty array if none
      See Also:

    • containsBeanDefinition

      public boolean containsBeanDefinition(String beanName)
      Description copied from interface: ListableBeanFactory
      Check if this bean factory contains a bean definition with the given name.

      Does not consider any hierarchy this factory may participate in, and ignores any singleton beans that have been registered by other means than bean definitions.

      Specified by:
      containsBeanDefinition in interface ListableBeanFactory
      Parameters:
      beanName - the name of the bean to look for
      Returns:
      if this bean factory contains a bean definition with the given name
      See Also:

    • getBeanDefinitionCount

      public int getBeanDefinitionCount()
      Description copied from interface: ListableBeanFactory
      Return the number of beans defined in the factory.

      Does not consider any hierarchy this factory may participate in, and ignores any singleton beans that have been registered by other means than bean definitions.

      Specified by:
      getBeanDefinitionCount in interface ListableBeanFactory
      Returns:
      the number of beans defined in the factory

    • getBeanDefinitionNames

      public String[] getBeanDefinitionNames()
      Description copied from interface: ListableBeanFactory
      Return the names of all beans defined in this factory.

      Does not consider any hierarchy this factory may participate in, and ignores any singleton beans that have been registered by other means than bean definitions.

      Specified by:
      getBeanDefinitionNames in interface ListableBeanFactory
      Returns:
      the names of all beans defined in this factory, or an empty array if none defined

    • getBeanProvider

      public <T> ObjectProvider<T> getBeanProvider(Class<T> requiredType, boolean allowEagerInit)
      Description copied from interface: ListableBeanFactory
      Return a provider for the specified bean, allowing for lazy on-demand retrieval of instances, including availability and uniqueness options.
      Specified by:
      getBeanProvider in interface ListableBeanFactory
      Parameters:
      requiredType - type the bean must match; can be an interface or superclass
      allowEagerInit - whether stream-based access may initialize lazy-init singletons and objects created by FactoryBeans (or by factory methods with a "factory-bean" reference) for the type check
      Returns:
      a corresponding provider handle
      See Also:

    • getBeanProvider

      public <T> ObjectProvider<T> getBeanProvider(ResolvableType requiredType, boolean allowEagerInit)
      Description copied from interface: ListableBeanFactory
      Return a provider for the specified bean, allowing for lazy on-demand retrieval of instances, including availability and uniqueness options.
      Specified by:
      getBeanProvider in interface ListableBeanFactory
      Parameters:
      requiredType - type the bean must match; can be a generic type declaration. Note that collection types are not supported here, in contrast to reflective injection points. For programmatically retrieving a list of beans matching a specific type, specify the actual bean type as an argument here and subsequently use ObjectProvider.orderedStream() or its lazy streaming/iteration options.
      allowEagerInit - whether stream-based access may initialize lazy-init singletons and objects created by FactoryBeans (or by factory methods with a "factory-bean" reference) for the type check
      Returns:
      a corresponding provider handle
      See Also:

    • getBeanNamesForType

      public String[] getBeanNamesForType(ResolvableType type)
      Description copied from interface: ListableBeanFactory
      Return the names of beans matching the given type (including subclasses), judging from either bean definitions or the value of getObjectType in the case of FactoryBeans.

      NOTE: This method introspects top-level beans only. It does not check nested beans which might match the specified type as well.

      Does consider objects created by FactoryBeans, which means that FactoryBeans will get initialized. If the object created by the FactoryBean doesn't match, the raw FactoryBean itself will be matched against the type.

      Does not consider any hierarchy this factory may participate in. Use BeanFactoryUtils' beanNamesForTypeIncludingAncestors to include beans in ancestor factories too.

      Note: Does not ignore singleton beans that have been registered by other means than bean definitions.

      This version of getBeanNamesForType matches all kinds of beans, be it singletons, prototypes, or FactoryBeans. In most implementations, the result will be the same as for getBeanNamesForType(type, true, true).

      Bean names returned by this method should always return bean names in the order of definition in the backend configuration, as far as possible.

      Specified by:
      getBeanNamesForType in interface ListableBeanFactory
      Parameters:
      type - the generically typed class or interface to match
      Returns:
      the names of beans (or objects created by FactoryBeans) matching the given object type (including subclasses), or an empty array if none
      See Also:

    • getBeanNamesForType

      public String[] getBeanNamesForType(ResolvableType type, boolean includeNonSingletons, boolean allowEagerInit)
      Description copied from interface: ListableBeanFactory
      Return the names of beans matching the given type (including subclasses), judging from either bean definitions or the value of getObjectType in the case of FactoryBeans.

      NOTE: This method introspects top-level beans only. It does not check nested beans which might match the specified type as well.

      Does consider objects created by FactoryBeans if the "allowEagerInit" flag is set, which means that FactoryBeans will get initialized. If the object created by the FactoryBean doesn't match, the raw FactoryBean itself will be matched against the type. If "allowEagerInit" is not set, only raw FactoryBeans will be checked (which doesn't require initialization of each FactoryBean).

      Does not consider any hierarchy this factory may participate in. Use BeanFactoryUtils' beanNamesForTypeIncludingAncestors to include beans in ancestor factories too.

      Note: Does not ignore singleton beans that have been registered by other means than bean definitions.

      Bean names returned by this method should always return bean names in the order of definition in the backend configuration, as far as possible.

      Specified by:
      getBeanNamesForType in interface ListableBeanFactory
      Parameters:
      type - the generically typed class or interface to match
      includeNonSingletons - whether to include prototype or scoped beans too or just singletons (also applies to FactoryBeans)
      allowEagerInit - whether to initialize lazy-init singletons and objects created by FactoryBeans (or by factory methods with a "factory-bean" reference) for the type check. Note that FactoryBeans need to be eagerly initialized to determine their type: So be aware that passing in "true" for this flag will initialize FactoryBeans and "factory-bean" references.
      Returns:
      the names of beans (or objects created by FactoryBeans) matching the given object type (including subclasses), or an empty array if none
      See Also:

    • getBeanNamesForType

      public String[] getBeanNamesForType(@Nullable Class<?> type)
      Description copied from interface: ListableBeanFactory
      Return the names of beans matching the given type (including subclasses), judging from either bean definitions or the value of getObjectType in the case of FactoryBeans.

      NOTE: This method introspects top-level beans only. It does not check nested beans which might match the specified type as well.

      Does consider objects created by FactoryBeans, which means that FactoryBeans will get initialized. If the object created by the FactoryBean doesn't match, the raw FactoryBean itself will be matched against the type.

      Does not consider any hierarchy this factory may participate in. Use BeanFactoryUtils' beanNamesForTypeIncludingAncestors to include beans in ancestor factories too.

      Note: Does not ignore singleton beans that have been registered by other means than bean definitions.

      This version of getBeanNamesForType matches all kinds of beans, be it singletons, prototypes, or FactoryBeans. In most implementations, the result will be the same as for getBeanNamesForType(type, true, true).

      Bean names returned by this method should always return bean names in the order of definition in the backend configuration, as far as possible.

      Specified by:
      getBeanNamesForType in interface ListableBeanFactory
      Parameters:
      type - the class or interface to match, or null for all bean names
      Returns:
      the names of beans (or objects created by FactoryBeans) matching the given object type (including subclasses), or an empty array if none
      See Also:

    • getBeanNamesForType

      public String[] getBeanNamesForType(@Nullable Class<?> type, boolean includeNonSingletons, boolean allowEagerInit)
      Description copied from interface: ListableBeanFactory
      Return the names of beans matching the given type (including subclasses), judging from either bean definitions or the value of getObjectType in the case of FactoryBeans.

      NOTE: This method introspects top-level beans only. It does not check nested beans which might match the specified type as well.

      Does consider objects created by FactoryBeans if the "allowEagerInit" flag is set, which means that FactoryBeans will get initialized. If the object created by the FactoryBean doesn't match, the raw FactoryBean itself will be matched against the type. If "allowEagerInit" is not set, only raw FactoryBeans will be checked (which doesn't require initialization of each FactoryBean).

      Does not consider any hierarchy this factory may participate in. Use BeanFactoryUtils' beanNamesForTypeIncludingAncestors to include beans in ancestor factories too.

      Note: Does not ignore singleton beans that have been registered by other means than bean definitions.

      Bean names returned by this method should always return bean names in the order of definition in the backend configuration, as far as possible.

      Specified by:
      getBeanNamesForType in interface ListableBeanFactory
      Parameters:
      type - the class or interface to match, or null for all bean names
      includeNonSingletons - whether to include prototype or scoped beans too or just singletons (also applies to FactoryBeans)
      allowEagerInit - whether to initialize lazy-init singletons and objects created by FactoryBeans (or by factory methods with a "factory-bean" reference) for the type check. Note that FactoryBeans need to be eagerly initialized to determine their type: So be aware that passing in "true" for this flag will initialize FactoryBeans and "factory-bean" references.
      Returns:
      the names of beans (or objects created by FactoryBeans) matching the given object type (including subclasses), or an empty array if none
      See Also:

    • getBeansOfType

      public <T> Map<String,T> getBeansOfType(@Nullable Class<T> type) throws BeansException
      Description copied from interface: ListableBeanFactory
      Return the bean instances that match the given object type (including subclasses), judging from either bean definitions or the value of getObjectType in the case of FactoryBeans.

      NOTE: This method introspects top-level beans only. It does not check nested beans which might match the specified type as well.

      Does consider objects created by FactoryBeans, which means that FactoryBeans will get initialized. If the object created by the FactoryBean doesn't match, the raw FactoryBean itself will be matched against the type.

      Does not consider any hierarchy this factory may participate in. Use BeanFactoryUtils' beansOfTypeIncludingAncestors to include beans in ancestor factories too.

      Note: Does not ignore singleton beans that have been registered by other means than bean definitions.

      This version of getBeansOfType matches all kinds of beans, be it singletons, prototypes, or FactoryBeans. In most implementations, the result will be the same as for getBeansOfType(type, true, true).

      The Map returned by this method should always return bean names and corresponding bean instances in the order of definition in the backend configuration, as far as possible.

      Specified by:
      getBeansOfType in interface ListableBeanFactory
      Parameters:
      type - the class or interface to match, or null for all concrete beans
      Returns:
      a Map with the matching beans, containing the bean names as keys and the corresponding bean instances as values
      Throws:
      BeansException - if a bean could not be created
      See Also:

    • getBeansOfType

      public <T> Map<String,T> getBeansOfType(@Nullable Class<T> type, boolean includeNonSingletons, boolean allowEagerInit) throws BeansException
      Description copied from interface: ListableBeanFactory
      Return the bean instances that match the given object type (including subclasses), judging from either bean definitions or the value of getObjectType in the case of FactoryBeans.

      NOTE: This method introspects top-level beans only. It does not check nested beans which might match the specified type as well.

      Does consider objects created by FactoryBeans if the "allowEagerInit" flag is set, which means that FactoryBeans will get initialized. If the object created by the FactoryBean doesn't match, the raw FactoryBean itself will be matched against the type. If "allowEagerInit" is not set, only raw FactoryBeans will be checked (which doesn't require initialization of each FactoryBean).

      Does not consider any hierarchy this factory may participate in. Use BeanFactoryUtils' beansOfTypeIncludingAncestors to include beans in ancestor factories too.

      Note: Does not ignore singleton beans that have been registered by other means than bean definitions.

      The Map returned by this method should always return bean names and corresponding bean instances in the order of definition in the backend configuration, as far as possible.

      Specified by:
      getBeansOfType in interface ListableBeanFactory
      Parameters:
      type - the class or interface to match, or null for all concrete beans
      includeNonSingletons - whether to include prototype or scoped beans too or just singletons (also applies to FactoryBeans)
      allowEagerInit - whether to initialize lazy-init singletons and objects created by FactoryBeans (or by factory methods with a "factory-bean" reference) for the type check. Note that FactoryBeans need to be eagerly initialized to determine their type: So be aware that passing in "true" for this flag will initialize FactoryBeans and "factory-bean" references.
      Returns:
      a Map with the matching beans, containing the bean names as keys and the corresponding bean instances as values
      Throws:
      BeansException - if a bean could not be created
      See Also:

    • getBeanNamesForAnnotation

      public String[] getBeanNamesForAnnotation(Class<? extends Annotation> annotationType)
      Description copied from interface: ListableBeanFactory
      Find all names of beans which are annotated with the supplied Annotation type, without creating corresponding bean instances yet.

      Note that this method considers objects created by FactoryBeans, which means that FactoryBeans will get initialized in order to determine their object type.

      Specified by:
      getBeanNamesForAnnotation in interface ListableBeanFactory
      Parameters:
      annotationType - the type of annotation to look for (at class, interface or factory method level of the specified bean)
      Returns:
      the names of all matching beans
      See Also:

    • getBeansWithAnnotation

      public Map<String,Object> getBeansWithAnnotation(Class<? extends Annotation> annotationType) throws BeansException
      Description copied from interface: ListableBeanFactory
      Find all beans which are annotated with the supplied Annotation type, returning a Map of bean names with corresponding bean instances.

      Note that this method considers objects created by FactoryBeans, which means that FactoryBeans will get initialized in order to determine their object type.

      Specified by:
      getBeansWithAnnotation in interface ListableBeanFactory
      Parameters:
      annotationType - the type of annotation to look for (at class, interface or factory method level of the specified bean)
      Returns:
      a Map with the matching beans, containing the bean names as keys and the corresponding bean instances as values
      Throws:
      BeansException - if a bean could not be created
      See Also:

    • findAnnotationOnBean

      @Nullable public <A extends Annotation> A findAnnotationOnBean(String beanName, Class<A> annotationType) throws NoSuchBeanDefinitionException
      Description copied from interface: ListableBeanFactory
      Find an Annotation of annotationType on the specified bean, traversing its interfaces and superclasses if no annotation can be found on the given class itself, as well as checking the bean's factory method (if any).
      Specified by:
      findAnnotationOnBean in interface ListableBeanFactory
      Parameters:
      beanName - the name of the bean to look for annotations on
      annotationType - the type of annotation to look for (at class, interface or factory method level of the specified bean)
      Returns:
      the annotation of the given type if found, or null otherwise
      Throws:
      NoSuchBeanDefinitionException - if there is no bean with the given name
      See Also:

    • findAnnotationOnBean

      @Nullable public <A extends Annotation> A findAnnotationOnBean(String beanName, Class<A> annotationType, boolean allowFactoryBeanInit) throws NoSuchBeanDefinitionException
      Description copied from interface: ListableBeanFactory
      Find an Annotation of annotationType on the specified bean, traversing its interfaces and superclasses if no annotation can be found on the given class itself, as well as checking the bean's factory method (if any).
      Specified by:
      findAnnotationOnBean in interface ListableBeanFactory
      Parameters:
      beanName - the name of the bean to look for annotations on
      annotationType - the type of annotation to look for (at class, interface or factory method level of the specified bean)
      allowFactoryBeanInit - whether a FactoryBean may get initialized just for the purpose of determining its object type
      Returns:
      the annotation of the given type if found, or null otherwise
      Throws:
      NoSuchBeanDefinitionException - if there is no bean with the given name
      See Also:

    • getParentBeanFactory

      @Nullable public BeanFactory getParentBeanFactory()
      Description copied from interface: HierarchicalBeanFactory
      Return the parent bean factory, or null if there is none.
      Specified by:
      getParentBeanFactory in interface HierarchicalBeanFactory

    • containsLocalBean

      public boolean containsLocalBean(String name)
      Description copied from interface: HierarchicalBeanFactory
      Return whether the local bean factory contains a bean of the given name, ignoring beans defined in ancestor contexts.

      This is an alternative to containsBean, ignoring a bean of the given name from an ancestor bean factory.

      Specified by:
      containsLocalBean in interface HierarchicalBeanFactory
      Parameters:
      name - the name of the bean to query
      Returns:
      whether a bean with the given name is defined in the local factory
      See Also:

    • getInternalParentBeanFactory

      @Nullable protected BeanFactory getInternalParentBeanFactory()
      Return the internal bean factory of the parent context if it implements ConfigurableApplicationContext; else, return the parent context itself.
      See Also:

    • getMessage

      public String getMessage(String code, @Nullable Object[] args, @Nullable String defaultMessage, Locale locale)
      Description copied from interface: MessageSource
      Try to resolve the message. Return default message if no message was found.
      Specified by:
      getMessage in interface MessageSource
      Parameters:
      code - the message code to look up, e.g. 'calculator.noRateSet'. MessageSource users are encouraged to base message names on qualified class or package names, avoiding potential conflicts and ensuring maximum clarity.
      args - an array of arguments that will be filled in for params within the message (params look like "{0}", "{1,date}", "{2,time}" within a message), or null if none
      defaultMessage - a default message to return if the lookup fails
      locale - the locale in which to do the lookup
      Returns:
      the resolved message if the lookup was successful, otherwise the default message passed as a parameter (which may be null)
      See Also:

    • getMessage

      public String getMessage(String code, @Nullable Object[] args, Locale locale) throws NoSuchMessageException
      Description copied from interface: MessageSource
      Try to resolve the message. Treat as an error if the message can't be found.
      Specified by:
      getMessage in interface MessageSource
      Parameters:
      code - the message code to look up, e.g. 'calculator.noRateSet'. MessageSource users are encouraged to base message names on qualified class or package names, avoiding potential conflicts and ensuring maximum clarity.
      args - an array of arguments that will be filled in for params within the message (params look like "{0}", "{1,date}", "{2,time}" within a message), or null if none
      locale - the locale in which to do the lookup
      Returns:
      the resolved message (never null)
      Throws:
      NoSuchMessageException - if no corresponding message was found
      See Also:

    • getMessage

      public String getMessage(MessageSourceResolvable resolvable, Locale locale) throws NoSuchMessageException
      Description copied from interface: MessageSource
      Try to resolve the message using all the attributes contained within the MessageSourceResolvable argument that was passed in.

      NOTE: We must throw a NoSuchMessageException on this method since at the time of calling this method we aren't able to determine if the defaultMessage property of the resolvable is null or not.

      Specified by:
      getMessage in interface MessageSource
      Parameters:
      resolvable - the value object storing attributes required to resolve a message (may include a default message)
      locale - the locale in which to do the lookup
      Returns:
      the resolved message (never null since even a MessageSourceResolvable-provided default message needs to be non-null)
      Throws:
      NoSuchMessageException - if no corresponding message was found (and no default message was provided by the MessageSourceResolvable)
      See Also:

    • getInternalParentMessageSource

      @Nullable protected MessageSource getInternalParentMessageSource()
      Return the internal message source of the parent context if it is an AbstractApplicationContext too; else, return the parent context itself.

    • getResources

      public Resource[] getResources(String locationPattern) throws IOException
      Description copied from interface: ResourcePatternResolver
      Resolve the given location pattern into Resource objects.

      Overlapping resource entries that point to the same physical resource should be avoided, as far as possible. The result should have set semantics.

      Specified by:
      getResources in interface ResourcePatternResolver
      Parameters:
      locationPattern - the location pattern to resolve
      Returns:
      the corresponding Resource objects
      Throws:
      IOException - in case of I/O errors

    • start

      public void start()
      Description copied from interface: Lifecycle
      Start this component.

      Should not throw an exception if the component is already running.

      In the case of a container, this will propagate the start signal to all components that apply.

      Specified by:
      start in interface Lifecycle
      See Also:

    • stop

      public void stop()
      Description copied from interface: Lifecycle
      Stop this component, typically in a synchronous fashion, such that the component is fully stopped upon return of this method. Consider implementing SmartLifecycle and its stop(Runnable) variant when asynchronous stop behavior is necessary.

      Note that this stop notification is not guaranteed to come before destruction: On regular shutdown, Lifecycle beans will first receive a stop notification before the general destruction callbacks are being propagated; however, on hot refresh during a context's lifetime or on aborted refresh attempts, a given bean's destroy method will be called without any consideration of stop signals upfront.

      Should not throw an exception if the component is not running (not started yet).

      In the case of a container, this will propagate the stop signal to all components that apply.

      Specified by:
      stop in interface Lifecycle
      See Also:

    • isRunning

      public boolean isRunning()
      Description copied from interface: Lifecycle
      Check whether this component is currently running.

      In the case of a container, this will return true only if all components that apply are currently running.

      Specified by:
      isRunning in interface Lifecycle
      Returns:
      whether the component is currently running

    • refreshBeanFactory

      protected abstract void refreshBeanFactory() throws BeansException, IllegalStateException
      Subclasses must implement this method to perform the actual configuration load. The method is invoked by refresh() before any other initialization work.

      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
      IllegalStateException - if already initialized and multiple refresh attempts are not supported

    • closeBeanFactory

      protected abstract void closeBeanFactory()
      Subclasses must implement this method to release their internal bean factory. This method gets invoked by close() after all other shutdown work.

      Should never throw an exception but rather log shutdown failures.

    • getBeanFactory

      public abstract ConfigurableListableBeanFactory getBeanFactory() throws IllegalStateException
      Subclasses must return their internal bean factory here. They should implement the lookup efficiently, so that it can be called repeatedly without a performance penalty.

      Note: Subclasses should check whether the context is still active before returning the internal bean factory. The internal factory should generally be considered unavailable once the context has been closed.

      Specified by:
      getBeanFactory in interface ConfigurableApplicationContext
      Returns:
      this application context's internal bean factory (never null)
      Throws:
      IllegalStateException - if the context does not hold an internal bean factory yet (usually if refresh() has never been called) or if the context has been closed already
      See Also:

    • toString

      public String toString()
      Return information about this context.
      Overrides:
      toString in class Object