In spring, if a bean implements ApplicationContextAware, then it is able to access the applicationContext. Therefore it is able to get other beans.
e.g.
public class SpringContextUtil implements ApplicationContextAware {
private static ApplicationContext applicationContext;
public void setApplicationContext(ApplicationContext context) throws BeansException {
applicationContext = context;
}
public static ApplicationContext getApplicationContext() {
return applicationContext;
}
}
Then SpringContextUtil.getApplicationContext.getBean("name") can get the bean "name".
To do this, we should put this SpringContextUtil inside the applications.xml, e.g.
<bean class="com.util.SpringContextUtil" />
Here the bean SpringContextUtil doesn't include the property applicationContext. I guess when spring bean initialize, this property is set. But how is this done? How does the method setApplicationContext get called?
When spring instantiates beans, it looks for a couple of interfaces like ApplicationContextAware and InitializingBean. If they are found, the methods are invoked. E.g. (very simplified)
Class<?> beanClass = beanDefinition.getClass();
Object bean = beanClass.newInstance();
if (bean instanceof ApplicationContextAware) {
((ApplicationContextAware) bean).setApplicationContext(ctx);
}
Note that in newer version it may be better to use annotations, rather than implementing spring-specific interfaces. Now you can simply use:
#Inject // or #Autowired
private ApplicationContext ctx;
Spring source code to explain how ApplicationContextAware work
when you use ApplicationContext context = new ClassPathXmlApplicationContext("applicationContext.xml");
In AbstractApplicationContext class,the refresh() method have the following code:
// Prepare the bean factory for use in this context.
prepareBeanFactory(beanFactory);
enter this method,beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this)); will add ApplicationContextAwareProcessor to AbstractrBeanFactory.
protected void prepareBeanFactory(ConfigurableListableBeanFactory beanFactory) {
// Tell the internal bean factory to use the context's class loader etc.
beanFactory.setBeanClassLoader(getClassLoader());
beanFactory.setBeanExpressionResolver(new StandardBeanExpressionResolver(beanFactory.getBeanClassLoader()));
beanFactory.addPropertyEditorRegistrar(new ResourceEditorRegistrar(this, getEnvironment()));
// Configure the bean factory with context callbacks.
beanFactory.addBeanPostProcessor(new ApplicationContextAwareProcessor(this));
...........
When spring initialize bean in AbstractAutowireCapableBeanFactory,
in method initializeBean,call applyBeanPostProcessorsBeforeInitialization to implement the bean post process. the process include inject the applicationContext.
#Override
public Object applyBeanPostProcessorsBeforeInitialization(Object existingBean, String beanName)
throws BeansException {
Object result = existingBean;
for (BeanPostProcessor beanProcessor : getBeanPostProcessors()) {
result = beanProcessor.postProcessBeforeInitialization(result, beanName);
if (result == null) {
return result;
}
}
return result;
}
when BeanPostProcessor implement Objectto execute the postProcessBeforeInitialization method,for example ApplicationContextAwareProcessor that added before.
private void invokeAwareInterfaces(Object bean) {
if (bean instanceof Aware) {
if (bean instanceof EnvironmentAware) {
((EnvironmentAware) bean).setEnvironment(this.applicationContext.getEnvironment());
}
if (bean instanceof EmbeddedValueResolverAware) {
((EmbeddedValueResolverAware) bean).setEmbeddedValueResolver(
new EmbeddedValueResolver(this.applicationContext.getBeanFactory()));
}
if (bean instanceof ResourceLoaderAware) {
((ResourceLoaderAware) bean).setResourceLoader(this.applicationContext);
}
if (bean instanceof ApplicationEventPublisherAware) {
((ApplicationEventPublisherAware) bean).setApplicationEventPublisher(this.applicationContext);
}
if (bean instanceof MessageSourceAware) {
((MessageSourceAware) bean).setMessageSource(this.applicationContext);
}
if (bean instanceof ApplicationContextAware) {
((ApplicationContextAware) bean).setApplicationContext(this.applicationContext);
}
}
}
Interface to be implemented by any object that wishes to be notified of the ApplicationContext that it runs in.
above is excerpted from the Spring doc website https://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/context/ApplicationContextAware.html.
So, it seemed to be invoked when Spring container has started, if you want to do something at that time.
It just has one method to set the context, so you will get the context and do something to sth now already in context I think.
ApplicationContextAware Interface ,the current application context, through which you can invoke the spring container services. We can get current applicationContext instance injected by below method in the class
public void setApplicationContext(ApplicationContext context) throws BeansException.
Related
On application close, each singleton bean is destroyed by DefaultListableBeanFactory.destroySingletons().
If the bean has a public void no-arg method called shutdown, then it will be invoked.
I have some 3rd party beans, all of which implement a certain interface, let's call it DoNotDestroy, that I do not want Spring to destroy.
I can specify a blank string destroy method on each bean, like so:
#Bean(destroyMethod = "")
public MyBean myBean() {
return new MyBean();
}
However, I would prefer to somehow configure Spring to not destroy any beans that implement DoNotDestroy. Is there a good way to do this?
Rather than blanking out the destroy method in each #Bean method, I can implement a BeanFactoryPostProcessor to do the same thing:
#Component
public class DoNotDestroyPostProcessor implements BeanFactoryPostProcessor {
private final Logger log = LoggerFactory.getLogger(DoNotDestroyPostProcessor.class);
#Override
public void postProcessBeanFactory(ConfigurableListableBeanFactory beanFactory) throws BeansException {
String[] doNotDestroys = beanFactory.getBeanNamesForType(DoNotDestroy.class);
for (String doNotDestroy : doNotDestroys) {
BeanDefinition bean = beanFactory.getBeanDefinition(doNotDestroy);
log.info("Don't destroy bean {} {}", bean.getFactoryMethodName(), bean.getDestroyMethodName());
bean.setDestroyMethodName("");
}
}
}
This avoids the problem of someone adding a bean and forgetting to blank out the destroy method.
I have a Spring 3.0.7 application, in which I have to initialize some beans in Java rather than xml. I'm trying to figure out why the beans I initialize can't be retrieved from the application context.
When the below code executes, I get "org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'beanName' is defined" when I call beanFactory.getBean("beanName").
public class BeanToCreateBeans implements ApplicationContextAware {
#Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
AutowireCapableBeanFactory beanFactory = applicationContext.getAutowireCapableBeanFactory();
BeanObject bean = new BeanObject();
beanFactory.initializeBean(bean, "beanName");
System.out.println("bean in the application: " + beanFactory.getBean("beanName"));
}
}
Why can't the bean be retrieved after creating it? I need to be able to create the bean and add it to the application context.
Update: As the answer states, my code isn't actually registering the bean, which answers the question I posed. So, in order to make my code work the way I wanted, it looks like:
public class BeanToCreateBeans implements BeanDefinitionRegistryPostProcessor, ApplicationContextAware {
private ApplicationContext applicationContext;
#Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry bdr) throws BeansException {
BeanDefinition definition = new RootBeanDefinition(BeanObject.class);
bdr.registerBeanDefinition("beanName", definition);
AutowireCapableBeanFactory beanFactory = applicationContext.getAutowireCapableBeanFactory();
BeanObject bean = new BeanObject();
beanFactory.initializeBean(bean, "beanName");
System.out.println("bean in the application: " + beanFactory.getBean("beanName"));
}
#Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
this.applicationContext = applicationContext;
}
}
AutowireCapableBeanFactory#initializeBean(Object, String) doesn't add a bean to a context or bean factory. The javadoc states
Initialize the given raw bean, applying factory callbacks such as
setBeanName and setBeanFactory, also applying all bean post processors
(including ones which might wrap the given raw bean).
It basically just processes the object you pass to it as if it was a bean initialized as part of the ApplicationContext. Notice that the method returns an Object, the result of the initialization.
Returns:
the bean instance to use, either the original or a wrapped one
I am developing a SpringBoot project and I want to get the bean by its name using applicationContext. I have tried many solution from web but could not succeed. My Requirement is that I have a controller
ControllerA
and inside the controller I have a method getBean(String className). I want to get instance of registered bean. I have hibernate entities and I want to get an instance of the bean by passing the name of class only in getBean method.
Please help if someone know the solution.
You can Autowire the ApplicationContext, either as a field
#Autowired
private ApplicationContext context;
or a method
#Autowired
public void context(ApplicationContext context) { this.context = context; }
Finally use
context.getBean(SomeClass.class)
You can use ApplicationContextAware.
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.
There are a few methods for obtaining a reference to the application context. You can implement ApplicationContextAware as in the following example:
package hello;
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
#Component
public class ApplicationContextProvider implements ApplicationContextAware {
private ApplicationContext applicationContext;
#Override
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
this.applicationContext = applicationContext;
}
public ApplicationContext getContext() {
return applicationContext;
}
}
Update:
When Spring instantiates beans, it looks for ApplicationContextAware implementations, If they are found, the setApplicationContext() methods will be invoked.
In this way, Spring is setting current applicationcontext.
Code snippet from Spring's source code:
private void invokeAwareInterfaces(Object bean) {
.....
.....
if (bean instanceof ApplicationContextAware) {
((ApplicationContextAware)bean).setApplicationContext(this.applicationContext);
}
}
Once you get the reference to Application context, you get fetch the bean whichever you want by using getBean().
actually you want to get the object from the Spring engine, where the engine already maintaining the object of your required class at that starting of the spring application(Initialization of the Spring engine).Now the thing is you just have to get that object to a reference.
in a service class
#Autowired
private ApplicationContext context;
SomeClass sc = (SomeClass)context.getBean(SomeClass.class);
now in the reference of the sc you are having the object.
Hope explained well. If any doubt please let me know.
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 to get the bean. Like:
applicationContext.getBean(String serviceName,Interface.Class)
Using SpringApplication.run(Class<?> primarySource, String... arg) worked for me. E.g.:
#SpringBootApplication
public class YourApplication {
public static void main(String[] args) {
ConfigurableApplicationContext context = SpringApplication.run(YourApplication.class, args);
}
}
As an alternative approach you can use ConfigurableApplicationContext to get bean of any class which is annotated with #Component, #Repository or #Service.
Let's say you want to get a bean of the class BaseComponent :
#Service
public class BaseComponent {
public String getMessage() {
return "hello world";
}
}
Now you can use ConfigurableApplicationContext to get the bean:
#Component
public class DemoComponent {
#Autowired
ConfigurableApplicationContext applicationContext;
public BaseComponent getBeanOfBaseComponent() {
return applicationContext.getBean(BaseComponent.class);
}
}
You can use the ApplicationContextAware class that can provide the application context.
public class ApplicationContextProvider implements ApplicationContextAware {
private static ApplicationContext ctx = null;
public static ApplicationContext getApplicationContext() {
return ctx;
}
#Override
public void setApplicationContext(final ApplicationContext ctx) throws BeansException {
ApplicationContextProvider.ctx = ctx;
}
/**
* Tries to autowire the specified instance of the class if one of the specified
* beans which need to be autowired are null.
*
* #param classToAutowire the instance of the class which holds #Autowire
* annotations
* #param beansToAutowireInClass the beans which have the #Autowire annotation
* in the specified {#classToAutowire}
*/
public static void autowire(Object classToAutowire, Object... beansToAutowireInClass) {
for (Object bean : beansToAutowireInClass) {
if (bean == null) {
ctx.getAutowireCapableBeanFactory().autowireBean(classToAutowire);
}
}
}
}
If you are inside of Spring bean (in this case #Controller bean) you shouldn't use Spring context instance at all. Just autowire className bean directly.
BTW, avoid using field injection as it's considered as bad practice.
One API method I use when I'm not sure what the bean name is org.springframework.beans.factory.ListableBeanFactory#getBeanNamesForType(java.lang.Class<?>). I simple pass it the class type and it retrieves a list of beans for me. You can be as specific or general as you'd like to retrieve all the beans associated with that type and its subtypes, example
#Autowired
ApplicationContext ctx
...
SomeController controller = ctx.getBeanNamesForType(SomeController)
Easy way in configration class call the BEAN annoted method . Yes u heard it right---- :P calling SpringBoot #Bean annoted method return the same bean from config .I was trying to call a logout in #predestroy method in config class from a bean and direcltly called the method to get the same bean .
P.S. : I added debug in the #bean annotated method but it didn't entered the method even when i called it.Sure to blame -----> Spring Magic <----
You can use ServiceLocatorFactoryBean. First you need to create an interface for your class
public interface YourClassFactory {
YourClass getClassByName(String name);
}
Then you have to create a config file for ServiceLocatorBean
#Configuration
#Component
public class ServiceLocatorFactoryBeanConfig {
#Bean
public ServiceLocatorFactoryBean serviceLocatorBean(){
ServiceLocatorFactoryBean bean = new ServiceLocatorFactoryBean();
bean.setServiceLocatorInterface(YourClassFactory.class);
return bean;
}
}
Now you can find your class by name like that
#Autowired
private YourClassfactory factory;
YourClass getYourClass(String name){
return factory.getClassByName(name);
}
Just use:
org.springframework.beans.factory.BeanFactory#getBean(java.lang.Class)
Example:
#Component
public class Example {
#Autowired
private ApplicationContext context;
public MyService getMyServiceBean() {
return context.getBean(MyService.class);
}
// your code uses getMyServiceBean()
}
I have all of my DAO's as beans in my applicationContext. Now this works great for autowiring these objects into my controllers to make database calls. However, given that I have embedded objects within some of my POJO's (Example: User class has list of pendingsurvey objects, list of appointment objects, etc) and don't want to grab these embedded objects when I grab the main object (Example: In a page with a list of users I don't need to know their pendingsurveys or appointments), I had set it up so that if the embedded object is null, go to the database to get the data. However, apparently #Autowire doesn't work in this case because the POJO's are not a Spring controlled object or something.
So question now is, how can I get a bean from applicationContext to use in my POJO's? I'm not that good with Spring so specific instructions would be greatly appreciated..
I've tried this but it gives me a bunch of injection dependency errors:
/* applicationContext.xml */
<bean id="userDao" class="UserDao" scope="singleton">
<property name="connectionWrapper" ref="connectionWrapper" />
</bean>
/* User.java - I tried putting in constructor and in the getter for userDao */
ApplicationContext ctx = AppContext.getApplicationContext('applicationContext.xml');
UserDao userDao = (UserDao) ctx.getBean("userDao");
Got it to work, same concept as Ric Jafe's answer but different implementation of it (Source: http://blog.jdevelop.eu/?p=154):
Made this class:
public class ApplicationContextProvider implements ApplicationContextAware {
private static ApplicationContext ctx = null;
public static ApplicationContext getApplicationContext() {
return ctx;
}
public void setApplicationContext(ApplicationContext ctx) throws BeansException {
// Assign the ApplicationContext into a static method
this.ctx = ctx;
}
}
Added this line into applicationContext.xml:
<bean id="applicationContextProvider" class="org.ApplicationContextProvider"></bean>
Called it in my POJO with:
ApplicationContext applicationContext = ApplicationContextProvider.getApplicationContext();
if (applicationContext != null && applicationContext.containsBean("keyName")) {
object = (Object) applicationContext.getBean("keyName");
}
Thanks for all the help guys.
When you load a context like that you are creating a new context, a copy of what was created when the application loaded. To access the same context that your application is using, you have several options, documented here: http://mythinkpond.wordpress.com/2010/03/22/spring-application-context/
For ease of access I'll copy/paste the one that most likely you want to use:
public class MyClass implements ApplicationContextAware {
static final long serialVersionUID = 02L;
ApplicationContext applicationContext = null;
public void doSomething(){
if (applicationContext != null && applicationContext.containsBean("accessKeys")){
MyBean beanA = (MyBean) applicationContext.getBean("mybean");
//Do something with this AccessBean
}
return null;
}
#Override
public void setApplicationContext(final ApplicationContext applicationContext) throws BeansException {
System.out.println("setting context");
this.applicationContext = applicationContext;
}
}
Notice the implements ApplicationContext.
This tells the Spring framework you need the Application Context in this class.. So it autowires it to the applicationContext variable. For this to happen you also need the setter method. Then you can just use it and get your beans. Good coffee :)
P.S. - If you need the context in other classes, you can pass the applicationContext variable to them or use the same method. This way you only have 1 context at all times, containing your beans.
I am using Spring 3 and Hibernate 4
How can I use the following in a non ManagedBean
#Inject
EmployeeService employeeService
Or if I would want to access DAO method I have to make that a ManagedBean as
#Named("mymanagedbean")
#ViewAccessScoped
I have a few Converter class and in order to access DAO service methods I had to use that as ManagedBean even though they are not ManagedBeans.
What is the best approach to call DAO service methods?
Thanks
You will need to implement the Spring interface ApplicationContextAware and then set the ApplicationContext. Then you need provide static methods to get the bean instance.
public class SpringApplicationContext implements ApplicationContextAware {
private static ApplicationContext CONTEXT;
public void setApplicationContext(ApplicationContext context)
throws BeansException {
CONTEXT = context;
}
public static Object getBean(String beanName) { ...}
public static <T> T getBean(Class<T> arg0) {...}
Then in your non-managed bean you can call SpringApplicationContext.getBean method by passing in EmployeeService.class as the argument or the bean name as the argument.
If you want to keep your Converter class clean and use dependency injection (which is highly recommended in order to be able the test the class easily) instead of the class pulling in its dependencies manually, you can use Spring's ability to configure a pre-existing object created outside of the application context. See the related section in Spring's reference documentation here.
Here is a working example (pertinent to zagyi's answer). Application uses Spring Roo and therefore aspectj.
#FacesConverter("example.entity.converter")
#Configurable
public class EntityConverter implements Converter {
#Resource
MyDAO dao;
#Override
public Object getAsObject(FacesContext context, UIComponent component,
String value) {
Entity obj;
try {
obj = dao.getEntity(Long.valueOf(value));
} catch( NumberFormatException e ) {
throw new ConverterException( message );
}
return obj;
}
#Override
public String getAsString(FacesContext context, UIComponent component,
Object value) {
Entity obj = (Entity) value;
return (obj != null) ? obj.getId().toString() : "";
}
}
The dao class
#Repository("myDAO")
public class MyDAOImpl implements MyDAO {
...
}
I have managed to get the DAO method in Converter without #Inject using the following and in EmployeeService class which implements Interface I have defined as #Service(value="employeeService")
EmployeeService employeeService =
(EmployeeService)facesContext.getApplication().getELResolver().
getValue(facesContext.getELContext(), null,
"employeeService");