I'm pretty new to the Spring Framework, I've been playing around with it and putting a few samples apps together for the purposes of evaluating Spring MVC for use in an upcoming company project. So far I really like what I see in Spring MVC, seems very easy to use and encourages you to write classes that are very unit test-friendly.
Just as an exercise, I'm writing a main method for one of my sample/test projects. One thing I'm unclear about is the exact differences between BeanFactory and ApplicationContext - which is appropriate to use in which conditions?
I understand that ApplicationContext extends BeanFactory, but if I'm just writing a simple main method, do I need the extra functionality that ApplicationContext provides? And just exactly what kind of extra functionality does ApplicationContext provide?
In addition to answering "which should I use in a main() method", are there any standards or guidelines as far as which implementation I should use in such a scenario? Should my main() method be written to depend on the bean/application configuration to be in XML format - is that a safe assumption, or am I locking the user into something specific?
And does this answer change in a web environment - if any of my classes needed to be aware of Spring, are they more likely to need ApplicationContext?
Thanks for any help. I know a lot of these questions are probably answered in the reference manual, but I'm having a hard time finding a clear breakdown of these two interfaces and the pros/cons of each without reading thru the manual with a fine-tooth comb.
The spring docs are great on this: 3.8.1. BeanFactory or ApplicationContext?.
They have a table with a comparison, I'll post a snippet:
Bean Factory
Bean instantiation/wiring
Application Context
Bean instantiation/wiring
Automatic BeanPostProcessor registration
Automatic BeanFactoryPostProcessor registration
Convenient MessageSource access (for i18n)
ApplicationEvent publication
So if you need any of the points presented on the Application Context side, you should use ApplicationContext.
Spring provides two kinds of IOC container, one is XMLBeanFactory and other is ApplicationContext.
BeanFactory
ApplicationContext
Annotation support
No
Yes
BeanPostProcessor Registration
Manual
Automatic
Implementation
XMLBeanFactory
ClassPath/FileSystem/WebXmlApplicationContext
Internationalization
No
Yes
Enterprise services
No
Yes
ApplicationEvent publication
No
Yes
FileSystemXmlApplicationContext Beans loaded through the full path.
ClassPathXmlApplicationContext Beans loaded through the CLASSPATH
XMLWebApplicationContext and AnnotationConfigWebApplicationContext beans loaded through the web application context.
AnnotationConfigApplicationContext Loading Spring beans from Annotation based configuration.
example:
ApplicationContext applicationContext = new AnnotationConfigApplicationContext(BeansConfiguration.class);
ApplicationContext is the container initialized by a ContextLoaderListener or ContextLoaderServlet defined in a web.xml and ContextLoaderPlugin defined in struts-config.xml.
Note: XmlBeanFactory is deprecated as of Spring 3.1 in favor of DefaultListableBeanFactory and XmlBeanDefinitionReader.
To me, the primary difference to choose BeanFactory over ApplicationContext seems to be that ApplicationContext will pre-instantiate all of the beans. From the Spring docs:
Spring sets properties and resolves dependencies as late as possible, when the bean is actually created. This means that a Spring container which has loaded correctly can later generate an exception when you request an object if there is a problem creating that object or one of its dependencies. For example, the bean throws an exception as a result of a missing or invalid property. This potentially delayed visibility of some configuration issues is why ApplicationContext implementations by default pre-instantiate singleton beans. At the cost of some upfront time and memory to create these beans before they are actually needed, you discover configuration issues when the ApplicationContext is created, not later. You can still override this default behavior so that singleton beans will lazy-initialize, rather than be pre-instantiated.
Given this, I initially chose BeanFactory for use in integration/performance tests since I didn't want to load the entire application for testing isolated beans. However -- and somebody correct me if I'm wrong -- BeanFactory doesn't support classpath XML configuration. So BeanFactory and ApplicationContext each provide a crucial feature I wanted, but neither did both.
Near as I can tell, the note in the documentation about overriding default instantiation behavior takes place in the configuration, and it's per-bean, so I can't just set the "lazy-init" attribute in the XML file or I'm stuck maintaining a version of it for test and one for deployment.
What I ended up doing was extending ClassPathXmlApplicationContext to lazily load beans for use in tests like so:
public class LazyLoadingXmlApplicationContext extends ClassPathXmlApplicationContext {
public LazyLoadingXmlApplicationContext(String[] configLocations) {
super(configLocations);
}
/**
* Upon loading bean definitions, force beans to be lazy-initialized.
* #see org.springframework.context.support.AbstractXmlApplicationContext#loadBeanDefinitions(org.springframework.beans.factory.xml.XmlBeanDefinitionReader)
*/
#Override
protected void loadBeanDefinitions(XmlBeanDefinitionReader reader) throws IOException {
super.loadBeanDefinitions(reader);
for (String name: reader.getBeanFactory().getBeanDefinitionNames()) {
AbstractBeanDefinition beanDefinition = (AbstractBeanDefinition) reader.getBeanFactory().getBeanDefinition(name);
beanDefinition.setLazyInit(true);
}
}
}
To add onto what Miguel Ping answered, here is another section from the documentation that answers this as well:
Short version: use an ApplicationContext unless you have a really good reason for not doing so. For those of you that are looking for slightly more depth as to the 'but why' of the above recommendation, keep reading.
(posting this for any future Spring novices who might read this question)
ApplicationContext is more preferred way than BeanFactory
In new Spring versions BeanFactory is replaced with ApplicationContext. But still BeanFactory exists for backward compatability
ApplicationContext extends BeanFactory and has the following benefits
it supports internationalization for text messages
it supports event publication to the registered listeners
access to the resources such as URLs and files
ApplicationContext:
It loads spring beans configured in spring configuration file,and manages the life cycle of the spring bean as and WHEN CONTAINER STARTS.It won't wait until getBean("springbeanref") is called.
BeanFactory
It loads spring beans configured in spring configuration file,manages the life cycle of the spring bean when we call the getBean("springbeanref").So when we call the getBean("springbeanref") at the time of spring bean life cycle starts.
I think it's better to always use ApplicationContext, unless you're in a mobile environment like someone else said already. ApplicationContext has more functionality and you definitely want to use the PostProcessors such as RequiredAnnotationBeanPostProcessor, AutowiredAnnotationBeanPostProcessor and CommonAnnotationBeanPostProcessor, which will help you simplify your Spring configuration files, and you can use annotations such as #Required, #PostConstruct, #Resource, etc in your beans.
Even if you don't use all the stuff ApplicationContext offers, it's better to use it anyway, and then later if you decide to use some resource stuff such as messages or post processors, or the other schema to add transactional advices and such, you will already have an ApplicationContext and won't need to change any code.
If you're writing a standalone app, load the ApplicationContext in your main method, using a ClassPathXmlApplicationContext, and get the main bean and invoke its run() (or whatever method) to start your app. If you're writing a web app, use the ContextLoaderListener in web.xml so that it creates the ApplicationContext and you can later get it from the ServletContext, regardless of whether you're using JSP, JSF, JSTL, struts, Tapestry, etc.
Also, remember you can use multiple Spring configuration files and you can either create the ApplicationContext by listing all the files in the constructor (or listing them in the context-param for the ContextLoaderListener), or you can just load a main config file which has import statements. You can import a Spring configuration file into another Spring configuration file by using <import resource="otherfile.xml" /> which is very useful when you programmatically create the ApplicationContext in the main method and load only one Spring config file.
Difference between BeanFactory and ApplicationContext are following:
BeanFactory uses lazy initialization but ApplicationContext uses eager initialization. In case of BeanFactory, bean is created when you call getBeans() method, but bean is created upfront in case of ApplicationContext when the ApplicationContext object is created.
BeanFactory explicitly provide a resource object using syntax but ApplicationContext creates and manages resource objects on its own.
BeanFactory doesnt support internatiolization but ApplicationContext supports internationalization.
With BeanFactory annotation based dependency injection is not supported but annotation based dependency injection is supported in ApplicationContext.
Using BeanFactory:
BeanFactory beanfactory = new XMLBeanFactory(new FileSystemResource("spring.xml"));
Triangle triangle =(Triangle)beanFactory.getBean("triangle");
Using ApplicationContext:
ApplicationContext context = new ClassPathXMLApplicationContext("spring.xml")
Triangle triangle =(Triangle)context.getBean("triangle");
For the most part, ApplicationContext is preferred unless you need to save resources, like on a mobile application.
I'm not sure about depending on XML format, but I'm pretty sure the most common implementations of ApplicationContext are the XML ones such as ClassPathXmlApplicationContext, XmlWebApplicationContext, and FileSystemXmlApplicationContext. Those are the only three I've ever used.
If your developing a web app, it's safe to say you'll need to use XmlWebApplicationContext.
If you want your beans to be aware of Spring, you can have them implement BeanFactoryAware and/or ApplicationContextAware for that, so you can use either BeanFactory or ApplicationContext and choose which interface to implement.
Basically we can create spring container object in two ways
using BeanFactory.
using ApplicationContext.
both are the interfaces,
using implementation classes we can create object for spring container
coming to the differences
BeanFactory :
Does not support the Annotation based dependency Injection.
Doesn't Support I18N.
By default its support Lazy loading.
it doesn't allow configure to multiple configuration files.
ex: BeanFactory context=new XmlBeanFactory(new Resource("applicationContext.xml"));
ApplicationContext
Support Annotation based dependency Injection.-#Autowired, #PreDestroy
Support I18N
Its By default support Aggresive loading.
It allow to configure multiple configuration files.
ex:
ApplicationContext context=new ClasspathXmlApplicationContext("applicationContext.xml");
BeanFactory and ApplicationContext both are ways to get beans from your spring IOC container but still there are some difference.
BeanFactory is the actual container which instantiates, configures, and manages a number of bean's. These beans are typically collaborate with one another, and thus have dependencies between themselves. These dependencies are reflected in the configuration data used by the BeanFactory.
BeanFactory and ApplicationContext both are Java interfaces and ApplicationContext extends BeanFactory. Both of them are configuration using XML configuration files. In short BeanFactory provides basic Inversion of control(IoC) and Dependency Injection (DI) features while ApplicationContext provides advanced features.
A BeanFactory is represented by the interface "org.springframework.beans.factory" Where BeanFactory, for which there are multiple implementations.
ClassPathResource resource = new ClassPathResource("appConfig.xml");
XmlBeanFactory factory = new XmlBeanFactory(resource);
DIFFERENCE
BeanFactory instantiate bean when you call getBean() method while ApplicationContext instantiate Singleton bean when container is started, It doesn't wait for getBean() to be called.
BeanFactory doesn't provide support for internationalization but ApplicationContext provides support for it.
Another difference between BeanFactory vs ApplicationContext is ability to publish event to beans that are registered as listener.
One of the popular implementation of BeanFactory interface is XMLBeanFactory while one of the popular implementation of ApplicationContext interface is ClassPathXmlApplicationContext.
If you are using auto wiring and using BeanFactory than you need to register AutoWiredBeanPostProcessor using API which you can configure in XML if you are using ApplicationContext. In summary BeanFactory is OK for testing and non production use but ApplicationContext is more feature rich container implementation and should be favored over BeanFactory
BeanFactory by default its support Lazy loading and ApplicationContext by default support Aggresive loading.
Feature Matrix of Bean Factory vs Application Context sourced from spring docs
Screenshot of features of BeanFacotry and ApplicationContext
a. One difference between bean factory and application context is that former only instantiate bean when you call getBean() method while ApplicationContext instantiates Singleton bean when the container is started, It doesn't wait for getBean to be called.
b.
ApplicationContext context = new ClassPathXmlApplicationContext("spring.xml");
or
ApplicationContext context = new ClassPathXmlApplicationContext{"spring_dao.xml","spring_service.xml};
You can use one or more xml file depending on your project requirement. As I am here using two xml files i.e. one for configuration details for service classes other for dao classes. Here ClassPathXmlApplicationContext is child of ApplicationContext.
c. BeanFactory Container is basic container, it can only create objects and inject Dependencies. But we can’t attach other services like security, transaction, messaging etc. to provide all the services we have to use ApplicationContext Container.
d. BeanFactory doesn't provide support for internationalization i.e. i18n but ApplicationContext provides support for it.
e. BeanFactory Container doesn't support the feature of AutoScanning (Support Annotation based dependency Injection), but ApplicationContext Container supports.
f. Beanfactory Container will not create a bean object until the request time. It means Beanfactory Container loads beans lazily. While ApplicationContext Container creates objects of Singleton bean at the time of loading only. It means there is early loading.
g. Beanfactory Container support only two scopes (singleton & prototype) of the beans. But ApplicationContext Container supports all the beans scope.
Refer this doc from Spring Docs:
http://static.springsource.org/spring/docs/3.2.x/spring-framework-reference/html/beans.html#context-introduction-ctx-vs-beanfactory
5.15.1 BeanFactory or ApplicationContext?
Use an ApplicationContext unless you have a good reason for not doing so.
Because the ApplicationContext includes all functionality of the BeanFactory, it is generally recommended over the BeanFactory, except for a few situations such as in an Applet where memory consumption might be critical and a few extra kilobytes might make a difference. However, for most typical enterprise applications and systems, the ApplicationContext is what you will want to use. Spring 2.0 and later makes heavy use of the BeanPostProcessor extension point (to effect proxying and so on). If you use only a plain BeanFactory, a fair amount of support such as transactions and AOP will not take effect, at least not without some extra steps on your part. This situation could be confusing because nothing is actually wrong with the configuration.
ApplicationContext is a big brother of BeanFactory and this would all thing that BeanFactory are provide plus many other things.
In addition to standard org.springframework.beans.factory.BeanFactory lifecycle capabilities, ApplicationContext implementations detect and
invoke ApplicationContextAware beans as well as ResourceLoaderAware, ApplicationEventPublisherAware and MessageSourceAware beans.
In a real-time scenario, the difference between the Spring IOC Core container (BeanFactory) and Advanced J2EE container (ApplicationContext) are as follows.
BeanFactory will create objects for the beans (i.e., for POJO classes) mentioned in the spring.xml file (<bean></bean>) only when you call the .getBean() method, but whereas ApplicationContext creates the objects for all the beans (<bean></bean> if its scope is not explicitly mentioned as "Prototype") configured in the spring.xml while loading the spring.xml file itself.
BeanFactory: (Lazy container because it creates the objects for the beans only when you explicitly call from the user/main class)
/*
* Using core Container - Lazy container - Because it creates the bean objects On-Demand
*/
//creating a resource
Resource r = (Resource) new ClassPathResource("com.spring.resources/spring.xml");
//creating BeanFactory
BeanFactory factory=new XmlBeanFactory(r);
//Getting the bean for the POJO class "HelloWorld.java"
HelloWorld worldObj1 = (HelloWorld) factory.getBean("test");
ApplicationContext: (Eager container because of creating the objects of all singleton beans while loading the spring.xml file itself)
ApplicationContext context = new ClassPathXmlApplicationContext("com/ioc/constructorDI/resources/spring.xml");
Technically, using ApplicationContext is recommended because in real-time applications, the bean objects will be created while the application is getting started in the server itself. This reduces the response time for the user request as the objects are already available to respond.
I need to explain the BeanFactory & ApplicationContext.
BeanFactory: BeanFactory is root interface for accessing the SpringBean Container.There is basic client view of a bean container.
That interface is implemented by the object class that holds the number of beans definitions, and each uniquely identify by the String name
Depending the Bean definition the factory will return the instance that instance may be the instance of contained object or a single shared instance. Which type of instance will be return depends of bean factory configuration.
Normally Bean factory will load the all the all the beans definition, which stored in the configuration source like XML...etc.
BeanFactory is a simplest container providing the basic support for Dependency Injection
Application Context
Application context is a central interface with in the spring application that provide the configuration information to the application. It implements the Bean Factory Interface.
Application context is an advance container its add advance level of enterprise specific functionality such as ability to resolve the textual message from the property file....etc
An ApplicationContext provides:
Bean factory methods for accessing application components. Inherited from ListableBeanFactory.
The ability to load file resources in a generic fashion. Inherited from the ResourceLoader interface.
The ability to publish events to registered listeners. Inherited from the ApplicationEventPublisher interface.
The ability to resolve messages, supporting internationalization. Inherited from the MessageSource interface.
Inheritance from a parent context. Definitions in a descendant context will always take priority. This means, for example, that a single parent context can be used by an entire web application, while each servlet has its own child context that is independent of that of any other servlet.
In addition to standard BeanFactory lifecycle capabilities, ApplicationContext implementations detect and invoke ApplicationContextAware beans as well as ResourceLoaderAware, ApplicationEventPublisherAware and MessageSourceAware beans.
The BeanFactory means spring container which lazily instantiates bean objects after getBean() method is invoked at runtime.
The ApplicationContext means spring framework which eagerly instantiates bean objects during deployment time without or before invoking getBean() method at runtime.
My six cents:
BeanFactory and ApplicationContext both are interfaces where ApplicationContext extends BeanFactory. So ApplicationContext is a child interface and BeanFactory is the parent interface. In other words, ApplicationContext has all the features of BeanFactory and it has some additional features that are not present in BeanFactory.
BeanFactory loads beans on-demand that is Lazy Loading whereas ApplicationContext loads all beans at startup that is Eager Loading.
BeanFactory does not support annotations whereas ApplicationContext supports annotations.
ApplicationContext has additional features that are not present in BeanFactory: Internationalization, Event Publishing, AOP features.
BeanFactory only supports two scopes — Singleton and Prototype whereas ApplicationContext supports all bean scopes.
BeanFactory does not register BeanFactoryPostProcessor and BeanPostProcessor automatically whereas ApplicationContext automatically registers them.
I think it is worth mentioning that since Spring 3, if you want to create a factory, you can also use the #configuration annotation combined with the proper #scope
#Configuration
public class MyFactory {
#Bean
#Scope("prototype")
public MyClass create() {
return new MyClass();
}
}
Your factory should be visible by Spring container using the #ComponentScan annotation or xml configuration
Spring bean scopes article from baeldung site
do use BeanFactory for non-web applications because it supports only Singleton and Prototype bean-scopes.
While ApplicationContext container does support all the bean-scopes so you should use it for web applications.
In summary:
The ApplicationContext includes all functionality of the BeanFactory.
It is generally recommended to use the former.
There are some limited situations such as in a Mobile application, where memory consumption might be critical.
In that scenarios, It can be justifiable to use the more lightweight BeanFactory. However, in the most enterprise applications, the ApplicationContext is what you will want to use.
For more, see my blog post:
Difference between BeanFactory and ApplicationContext in Spring – The java spring blog from the basics
In the example below, is there a way to avoid doing a context.getBean()? All the other beans subsequently used by the testService get autowired. (It is a console application)
public class Test {
private static ITestService testService;
private static ApplicationContext context;
public static void main(String[] args) {
context = new ClassPathXmlApplicationContext(
new String[]{"/META-INF/spring/app-context.xml"});
ITestService testService = context.getBean(ITestService.class);
}
}
I tried adding autowire annotation to ApplicationContext, but it didnt work. Besides how does it know where my app-context.xml is located if I autowire it?
Update: I found what I needed over here
Right, you're missing out a few details here.
Below is a short explanation of how Spring works.
1- The application context is loaded somehow (we will get there soon).
2- After loaded, app context will initialize/create all beans defined. Here is when beans get injected as dependencies. After this Whenever you get a bean back from the app context, that bean is all initialized and ready to go with all the dependencies in place (considering everything went fine).
RE the first step, there are a few way to automate the Spring initialization.
One way is what you are doing, explicitly instantiating one. Other way could be via a context listener in case you're in a web environment, or maybe with the #RunWith. (You can find more here)
In your case, I believe you are looking for using Spring in a (Unit?!?) test environment so you are looking for something like
#RunWith(SpringJUnit4ClassRunner.class)
#ContextConfiguration
public class MyTest {
#Autowired
private ApplicationContext applicationContext;
// class body...
}
further details here
http://docs.spring.io/spring/docs/current/spring-framework-reference/htmlsingle/#testing
You cannot call beans without initializing the application context first.
Secondly in your case Test class should be bean itself to be managed by spring then to autowire ITestService. The purpose of Application context as a container is to manage the bean lifecycle so u need to initialize it first by ClassPathXmlApplicationContextand then it will initialize all beans declared by you in ur xml file. About avoiding the getBean method if you are using servlets for creating web app you can avoid getBean. If not you should handle it manually.
I agree with what #Desorder has said. When I started working with #RunWith(SpringJUnit4ClassRunner.class) and #ContextConfiguration, I used to get my test cases working. But it took me some time to understand how these two are working internally and their default configurations.
If you would like to take some different approach and would like to try without #RunWith and #ContextConfiguration, take a look at the link - TUTORIAL: JUNIT #RULE. With this, you will be very clear which spring xml file locations are provided.
I am developing a spring MVC application. When I try to use AnnotationConfigApplicationContext in my controller class I am getting the following error. I have no idea what this statement exactly means.
#RequestMapping(value = "/generate", method = RequestMethod.POST)
public ModelAndView generateMappingFile(#ModelAttribute Mapping mapping)
{
AnnotationConfigApplicationContext ctx = new AnnotationConfigApplicationContext();
MappingFileGenerator mfg = ctx.getBean(MappingFileGenerator.class);
}
Error Message -->
java.lang.IllegalStateException:org.springframework.context.annotation.AnnotationConfigApplicationContext#116b3c0 has not been refreshed yet
Can someone explain me what went wrong here ? I am using Spring 4.0.1.. I am new to spring mvc.
When you are creating a new instance of an ApplicationContext (regardless which type) you are basically creating new instances of each and every bean configured in that ApplicationContext. That is nice the first time, it might work the second and depending on the amount of beans, the type of beans will crash after that. As the context will never be destroy (until the app crashed and is restarted) you will run into possible memory issues, performance issues, strange transactional problems etc.
A general rule of thumb is to never construct a new instance of an ApplicationContext but to use dependency injection instead.
If you really want access to the ApplicationContext put a field of that type in your controller and put #Autowired on it.
#Controller
public class MyController {
#Autowired
private ApplicationContext ctx;
….
}
Then you can do a lookup for the bean you need in the method. This can be handy if you use the ApplicationContext as a factory for your beans. If all the beans you need are singletons it is better to simply inject the bean you need.
#Controller
public class MyController {
#Autowired
private MappingFileGenerator mfg ;
….
}
Now Spring will inject the MappingFileGenerator and it is available for use in your methods. No need to create a new instance of an ApplicationContext.
More information is in the Spring Reference Guide.
#M.Deinum's comment will get quite a few more upvotes.
Think of creating a new ApplicationContext as instantiating a new (instance of an) application. Do you want to do that every time this (or any other method in said application) is called? No, you don't.
I'm guessing you think you do because you need access to your ApplicationContext in this method. To do that - i.e. to get access to the running application context (rather than creating a new one), you want to do
#Controller // or #Service / #Component / ... : tells Spring that this is a bean, and to inject the specified dependencies
class YourClass {
#Autowired // tells Spring that this object is a dependency should should be injected
ApplicationContext ctx;
#RequestMapping(value = "/generate", method = RequestMethod.POST)
public ModelAndView generateMappingFile(#ModelAttribute Mapping mapping) {
MappingFileGenerator mfg = ctx.getBean(MappingFileGenerator.class);
}
The key here is the Autowired annotation, which tells Spring to inject the annotated object as a dependency.
I highly suggest following the links I've included (for starters), as what you're doing here suggests pretty strongly that you haven't wrapped your head around what DI is and does for you, and until you do, using it is likely to be counterproductive toward it's own ends for you.
In case it helps someone, i was having this issue on a new URL Mapping added to a gradle project, i was missing the first slash of the url and that causing this "illegalstate not refreshed yet" on my tests
My colleagues very often use word "application context". In many articles this collocation used very often too.
My current understanding: application context is single xml file.
But I understand that if I was right, people wouldn't use "application context" instead of configuration xml file.
Can you help me to deal with this issue?
#feak gives a straight answer about the meaning of ApplicationContext in terms of Spring. In short, it is an object that loads the configuration (usually a XML file annotation based) and then Spring will start managing the beans and its benefits:
Beans declared in package
Beans declared by annotations
Constructor and method autowiring
Bean injection
Configuration, .properties and .yaml file loading
etc
To start an application context, you may use one of the following:
Manually load the application context at the beginning of your application. This is done for sample purposes or in standalone applications:
public class Foo {
public static void main(String[] args) {
ApplicationContext context =
new ClassPathXmlApplicationContext("path/to/applicationContext.xml");
//use the context as you wish...
}
}
In case of Java web applications using Spring MVC, the DispatchServlet will load the application context for you, so you only have to create a springapp-servlet.xml file in WEB-INF folder of the application.
Note that an application context is associated to a single configuration (XML based or not). Period.
After understanding this, you could also understand that you can have more than a single application context per application. This is, having two or more ApplicationContexts in the same application. From the last example in the console application, this is easy to check:
public class Foo {
public static void main(String[] args) {
ApplicationContext context =
new ClassPathXmlApplicationContext("path/to/applicationContext.xml");
ApplicationContext context2 =
new ClassPathXmlApplicationContext("path/to/applicationContext.xml");
//use the context as you wish...
}
}
Note that we have two application contexts using the same XML configuration. Can you do this? Yes, you're actually seeing it here. What's the difference, then? The main difference is that Spring beans singleton scopes are singleton per application context, this mean when retrieving a Bar bean that's configured in applicationContext.xml file from context will not be the same as retrieving it from context2, but several retrieves from context will return the same Bar bean instance.
Is this considered a good or bad practice? Neither, it will depend on the problem to be solved (in case of last example, I would say it is a bad practice). Most people would recommend having all your beans configured in a single place (via XML or another) and loaded by a single application context.
Let's understand this in simple words.
The ApplicationContext is the central interface within a Spring application that is used for providing configuration information to the application. It's created when the application starts running.
It provides the entire configuration needed by our application:
Bean Factory - Responsible for creation of java objects called beans. One example is components in the application.
Application listeners - all listeners needed for events.
WebServer information.
Application current environment specific information.
Resource pattern resolver - resource loader with path matcher.
Life cycle Processor.
Class Loader.
Start and shutdown monitor.
Servlet Context.
Reader and Scanner.
Logger
etc.
package com.srmhitter9062.spring;
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
public class ApplicationContextUtils implements ApplicationContextAware {
private static ApplicationContext ctx;
#Override
public void setApplicationContext(ApplicationContext appContext)
throws BeansException {
ctx = appContext;
}
public static ApplicationContext getApplicationContext() {
return ctx;
}
}
We can get some idea about the Application object in below snapshot.
In summary, we can say the Application context is a Configuration object created for application to run.
The applicationContext.xml defines the beans for the "root webapp context". It's a web aware ApplicationContext.
It is used to have beans that are shared between all servlets in a web application.
I hope this is helpful.
I guess that you colleagues meant the loaded spring application context, which allows access to:
configuration of application,
initialized beans,
application events api,
etc
From the javadoc:
Central interface to provide configuration for an application. This is
read-only while the application is running, but may be reloaded if the
implementation supports this.
An ApplicationContext provides: [...]
I'm an end-user of one of my company's products. It is not very suitable for integration into Spring, however I am able to get a handle on the context and retrieve the required bean by name. However, I would still like to know if it was possible to inject a bean into this class, even though the class is not managed by Spring itself.
Clarification: The same application which is managing the lifecycle of some class MyClass, is also managing the lifecycle of the Spring context. Spring does not have any knowledge of the instance of MyClass, and I would like to some how provide the instance to the context, but cannot create the instance in the context itself.
You can do this:
ApplicationContext ctx = ...
YourClass someBeanNotCreatedBySpring = ...
ctx.getAutowireCapableBeanFactory().autowireBeanProperties(
someBeanNotCreatedBySpring,
AutowireCapableBeanFactory.AUTOWIRE_AUTODETECT, true);
You can use #Autowired and so on within YourClass to specify fields to be injected etc.
One way to bring a bean into Spring despite its manufacture being external is to use a helper class marked as a #Configuration bean that has a method (marked with #Bean) that actually makes the instance and hands it back through Spring (which does its property injection and proxy generation at that point).
I'm not quite sure what scope you need; with prototype, you'll get a fresh bean in each place.
#Configuration
public class FooBarMaker {
#Bean(autowire = Autowire.BY_TYPE)
#Scope("prototype")
public FooBar makeAFooBar() {
// You probably need to do some more work in here, I imagine
return new FooBar();
}
}
You can inject properties required for manufacture into the #Configuration bean. (I use this to create instances of an interface where the name of the class to instantiate is defined at runtime.)
suppose that u have the following dependency chain:
A --> B --> C --> x --> y -- > Z
A, B, C are spring managed beans (constructed and manged by spring framework)
x, y are really simple POJOs that constructed by your application, without spring assistance
now if you want that y will get a reference to Z using spring that you need to have a 'handle' to the spring ApplicationContext
one way to do it is to implement ApplicationContextAware interface . In this case I would suggest that either A, B or C will implement this interface and will store the applicationContext reference in a static member.
so lets take Class C for example:
class C implmenets ApplicationContextAware{
public static ApplicationContex ac;
void setApplicationContext(ApplicationContext applicationContext) {
ac = applicationContext;
}
.............
}
now, in class y you should have:
(Z)(C.ac.getBean("classZ")).doSomething()
HTH -- Yonatan
Another way to do this is to us use AspectJ. This is the recommended way of injection Spring beans into non-managed objects that are created with the new operator. See this for details:
http://www.javacodegeeks.com/2011/02/domain-driven-design-spring-aspectj.html
Searching endless combos of autowire inject spring bean into pojo applicationcontextaware beanaware etc circled me back here but this didnt provide a complete enough solution for me.
This is a much better implementation/tutorial of this IMO:
I hope it helps everyone like it finally helped me.
Accessing Spring Beans from outside Spring Context
Be careful that in oldest version of Spring, there is thread-safe problem with bean factory http://jira.springframework.org/browse/SPR-4672
If you want to create an object outside the Spring context, and make that object available for injection into other beans that are in the Spring context, you can follow the steps in this article.
Basically, you create a parent application context and push your external object into this parent context as a singleton. Then you create you main application context (for example, from xml files), with the parent application context as its parent.
Object externalObject = ...
GenericApplicationContext parent = new StaticApplicationContext();
parent.getBeanFactory().registerSingleton( "externalObject", externalObject );
parent.refresh();
ApplicationContext appContext = new ClassPathXmlApplicationContext( ... , parent);
From a Spring configuration class, set a static field on the non-Spring class that needs the beans.
I have an example in my answer to a Liquibase question: https://stackoverflow.com/a/71191546/5499391