Getting Spring Application Context

Question

Is there a way to statically globally request a copy of the ApplicationContext in a Spring application   Assuming the main class starts up and initializes the application context  does it need to pass that down through the call stack to any classes that need it  or is there a way for a class to ask for the previously created context    Which I assume has to be a singleton

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Please note that  the below code will create new application context instead of using the already loaded one   private static final ApplicationContext context                   new ClassPathXmlApplicationContext  beans xml      Also note that beans xml should be part of src main resources means in war it is part of WEB INF classes  where as the real application will be loaded through applicationContext xml mentioned at Web xml    lt context-param gt       lt param-name gt contextConfigLocation lt  param-name gt       lt param-value gt META-INF spring applicationContext xml lt  param-value gt   lt  context-param gt    It is difficult to mention applicationContext xml path in ClassPathXmlApplicationContext constructor  ClassPathXmlApplicationContext  META-INF spring applicationContext xml   wont be able to locate the file   So it is better to use existing applicationContext by using annotations    Component public class OperatorRequestHandlerFactory        public static ApplicationContext context        Autowired     public void setApplicationContext ApplicationContext applicationContext            context   applicationContext

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Even after adding  Autowire if your class is not a RestController or Configuration Class  the applicationContext object was coming as null  Tried Creating new class with below and it is working fine   Component public class SpringContext implements ApplicationContextAware      private static ApplicationContext applicationContext       Override     public void setApplicationContext ApplicationContext applicationContext  throws       BeansException       this applicationContext applicationContext           you can then implement a getter method in the same class as per your need like getting the Implemented class reference by      applicationContext getBean String serviceName Interface Class

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If you use a web-app there is also another way to access the application context without using singletons by using a servletfilter and a ThreadLocal  In the filter you can access the application context using WebApplicationContextUtils and store either the application context or the needed beans in the TheadLocal    Caution  if you forget to unset the ThreadLocal you will get nasty problems when trying to undeploy the application  Thus  you should set it and immediately start a try that unsets the ThreadLocal in the finally-part   Of course  this still uses a singleton  the ThreadLocal  But the actual beans do not need to be anymore  The can even be request-scoped  and this solution also works if you have multiple WARs in an Application with the libaries in the EAR  Still  you might consider this use of ThreadLocal as bad as the use of plain singletons   -   Perhaps Spring already provides a similar solution  I did not find one  but I don t know for sure

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I know this question is answered  but I would like to share the Kotlin code I did to retrieve the Spring Context    I am not a specialist  so I am open to critics  reviews and advices   https   gist github com edpichler 9e22309a86b97dbd4cb1ffe011aa69dd  package com company web spring  import com company jpa spring MyBusinessAppConfig import org springframework beans factory annotation Autowired import org springframework context ApplicationContext import org springframework context annotation AnnotationConfigApplicationContext import org springframework context annotation ComponentScan import org springframework context annotation Configuration import org springframework context annotation Import import org springframework stereotype Component import org springframework web context ContextLoader import org springframework web context WebApplicationContext import org springframework web context support WebApplicationContextUtils import javax servlet http HttpServlet   Configuration  Import value    MyBusinessAppConfig  class    ComponentScan basePackageClasses     SpringUtils  class   open class WebAppConfig                Singleton object to create  only if necessary   return and reuse a Spring Application Context        When you instantiates a class by yourself  spring context does not autowire its properties  but you can wire by yourself     This class helps to find a context or create a new one  so you can wire properties inside objects that are not    created by Spring  e g   Servlets  usually created by the web server         Sometimes a SpringContext is created inside jUnit tests  or in the application server  or just manually  Independent    where it was created  I recommend you to configure your spring configuration to scan this SpringUtils package  so the  springAppContext     property will be used and autowired at the SpringUtils object the start of your spring context  and you will have just one instance of spring context public available       Ps  Even if your spring configuration doesn t include the SpringUtils  Component  it will works tto  but it will create a second Spring Context o your application       Component object SpringUtils            var springAppContext  ApplicationContext    null      Autowired     set value            field   value                         Tries to find and reuse the Application Spring Context  If none found  creates one and save for reuse          return returns a Spring Context              fun ctx    ApplicationContext           if  springAppContext   null                println  achou               return springAppContext as ApplicationContext                       springcontext not autowired  Trying to find on the thread            val webContext   ContextLoader getCurrentWebApplicationContext           if  webContext    null                springAppContext   webContext              println  achou no servidor               return springAppContext as WebApplicationContext                     println  nao achou  vai criar             None spring context found  Start creating a new one            val applicationContext   AnnotationConfigApplicationContext   WebAppConfig  class java              saving the context for reusing next time         springAppContext   applicationContext         return applicationContext                        return a Spring context of the WebApplication          param createNewWhenNotFound when true  creates a new Spring Context to return  when no one found in the ServletContext          param httpServlet the  WebServlet              fun ctx httpServlet  HttpServlet  createNewWhenNotFound  Boolean   ApplicationContext           try               val webContext   WebApplicationContextUtils findWebApplicationContext httpServlet servletContext              if  webContext    null                    return webContext                           if  createNewWhenNotFound                      creates a new one                 return ctx                 else                   throw NullPointerException  Cannot found a Spring Application Context                            catch  er  IllegalStateException               if  createNewWhenNotFound                      creates a new one                 return ctx                             throw er                      Now  a spring context is publicly available  being able to call the same method independent of the context  junit tests  beans  manually instantiated classes  like on this Java Servlet    WebServlet name    MyWebHook   value     WebHook   public class MyWebServlet extends HttpServlet         private MyBean byBean               SpringUtils INSTANCE ctx this  true  getBean MyBean class         public MyWebServlet

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Approach 1  You can inject ApplicationContext by implementing ApplicationContextAware interface  Reference link    Component public class ApplicationContextProvider implements ApplicationContextAware        private ApplicationContext applicationContext       public ApplicationContext getApplicationContext             return applicationContext              Override     public void setApplicationContext ApplicationContext applicationContext  throws BeansException           this applicationContext   applicationContext            Approach 2  Autowire Application context in any of spring managed beans    Component public class SpringBean      Autowired   private ApplicationContext appContext      Reference link

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Here s a nice way  not mine  the original reference is here  http   sujitpal blogspot com 2007 03 accessing-spring-beans-from-legacy-code html  I ve used this approach and it works fine  Basically it s a simple bean that holds a  static  reference to the application context  By referencing it in the spring config it s initialized    Take a look at the original ref  it s very clear

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Before you implement any of the other suggestions  ask yourself these questions      Why am I trying to get the ApplicationContext  Am I effectively using the ApplicationContext as a service locator  Can I avoid accessing the ApplicationContext at all    The answers to these questions are easier in certain types of applications  Web apps  for example  than they are in others  but are worth asking anyway   Accessing the ApplicationContext does kind of violate the whole dependency injection principle  but sometimes you ve not got much choice

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Note that by storing any state from the current ApplicationContext  or the ApplicationContext itself in a static variable - for example using the singleton pattern - you will make your tests unstable and unpredictable if you re using Spring-test  This is because Spring-test caches and reuses application contexts in the same JVM  For example    Test A run and it is annotated with  ContextConfiguration   classpath foo xml      Test B run and it is annotated with  ContextConfiguration   classpath foo xml    classpath bar xml   Test C run and it is annotated with  ContextConfiguration   classpath foo xml      When Test A runs  an ApplicationContext is created  and any beans implemeting ApplicationContextAware or autowiring ApplicationContext might write to the static variable   When Test B runs the same thing happens  and the static variable now points to Test B s ApplicationContext  When Test C runs  no beans are created as the TestContext  and herein the ApplicationContext  from Test A is resused  Now you got a static variable pointing to another ApplicationContext than the one currently holding the beans for your test

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SpringApplicationContext java  import org springframework beans BeansException  import org springframework context ApplicationContext  import org springframework context ApplicationContextAware          Wrapper to always return a reference to the Spring Application  Context from    within non-Spring enabled beans  Unlike Spring MVC s  WebApplicationContextUtils    we do not need a reference to the Servlet context for this  All we need is    for this bean to be initialized during application startup      public class SpringApplicationContext implements  ApplicationContextAware      private static ApplicationContext CONTEXT              This method is called from within the ApplicationContext once it is       done starting up  it will stick a reference to itself into this bean       param context a reference to the ApplicationContext         public void setApplicationContext ApplicationContext context  throws BeansException       CONTEXT   context                  This is about the same as context getBean  beanName    except it has its      own static handle to the Spring context  so calling this method statically      will give access to the beans by name in the Spring application context       As in the context getBean  beanName   call  the caller must cast to the      appropriate target class  If the bean does not exist  then a Runtime error      will be thrown        param beanName the name of the bean to get        return an Object reference to the named bean          public static Object getBean String beanName        return CONTEXT getBean beanName           Source  http   sujitpal blogspot de 2007 03 accessing-spring-beans-from-legacy-code html

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Do autowire in Spring bean as below      Autowired   private ApplicationContext appContext   you will the applicationcontext object

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There are many way to get application context in Spring application  Those are given bellow    Via ApplicationContextAware   import org springframework beans BeansException  import org springframework context ApplicationContext  import org springframework context ApplicationContextAware   public class AppContextProvider implements ApplicationContextAware    private ApplicationContext applicationContext    Override public void setApplicationContext ApplicationContext applicationContext  throws BeansException       this applicationContext   applicationContext         Here setApplicationContext ApplicationContext applicationContext  method you will get the applicationContext     ApplicationContextAware       Interface to be implemented by any object that wishes to be notified   of the ApplicationContext that it runs in  Implementing this interface   makes sense for example when an object requires access to a set of   collaborating beans     Via Autowired    Autowired private ApplicationContext applicationContext     Here  Autowired keyword will provide the applicationContext  Autowired has some problem  It will create problem during unit-testing

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If the object that needs access to the container is a bean in the container  just implement the BeanFactoryAware or ApplicationContextAware interfaces   If an object outside the container needs access to the container  I ve used a standard GoF singleton pattern for the spring container  That way  you only have one singleton in your application  the rest are all singleton beans in the container

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Not sure how useful this will be  but you can also get the context when you initialize the app  This is the soonest you can get the context  even before an  Autowire     SpringBootApplication public class Application extends SpringBootServletInitializer       private static ApplicationContext context          I believe this only runs during an embedded Tomcat with  mvn spring-boot run           I don t believe it runs when deploying to Tomcat on AWS      public static void main String   args            context   SpringApplication run Application class  args           DataSource dataSource   context getBean javax sql DataSource class           Logger getLogger  Application   info  DATASOURCE       dataSource

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Take a look at ContextSingletonBeanFactoryLocator   It provides static accessors to get hold of Spring s contexts  assuming they have been registered in certain ways     It s not pretty  and more complex than perhaps you d like  but it works

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I believe you could use SingletonBeanFactoryLocator  The beanRefFactory xml file would hold the actual applicationContext  It would go something like this    lt bean id  mainContext  class  org springframework context support ClassPathXmlApplicationContext  gt        lt constructor-arg gt           lt list gt               lt value gt    applicationContext xml lt  value gt           lt  list gt        lt  constructor-arg gt    lt  bean gt    And the code to get a bean from the applicationcontext from whereever would be something like this   BeanFactoryLocator bfl   SingletonBeanFactoryLocator getInstance    BeanFactoryReference bf   bfl useBeanFactory  mainContext    SomeService someService    SomeService  bf getFactory   getBean  someService      The Spring team discourage the use of this class and yadayada  but it has suited me well where I have used it

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You can implement ApplicationContextAware or just use  Autowired   public class SpringBean      Autowired   private ApplicationContext appContext      SpringBean will have ApplicationContext injected  within which this bean is instantiated  For example if you have web application with a pretty standard contexts hierarchy   main application context  lt -  child  MVC context   and SpringBean is declared within main context  it will have main context injected  otherwise  if it s declared within MVC context  it will have MVC context injected

[java] Getting Spring Application Context

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