How to inject ApplicationContext itself - java

I want to inject an ApplicationContext itself to a bean.
Something like
public void setApplicationContext(ApplicationContect context) {
this.context = context;
}
Is that possible in spring?


Previous comments are ok, but I usually prefer:
#Autowired private ApplicationContext applicationContext;


Easy, using the ApplicationContextAware interface.
public class A implements ApplicationContextAware {
private ApplicationContext context;
public void setApplicationContext(ApplicationContext context) {
this.context = context;
}
}
Then in your actual applicationContext you only need to reference your bean.
<bean id="a" class="com.company.A" />


Yes, just implement the ApplicationContextAware -interface.


I saw some comments above about #Autowired not working still. The following may help.
This will not work:
#Route(value = "content", layout = MainView.class)
public class MyLayout extends VerticalLayout implements RouterLayout {
#Autowired private ApplicationContext context;
public MyLayout() {
comps.add(context.getBean(MyComponentA.class)); // context always null :(
}
You must do this:
#Autowired
public MyLayout(ApplicationContext context) {
comps.add(context.getBean(MyComponentA.class)); //context is set :)
}
or this:
#PostConstruct
private void init() {
comps.add(context.getBean(MyComponentA.class)); // context is set :)
}
Also note that Upload is another component that must be set within the scope of #PostConstruct. This was a nightmare for me to figure out. Hope this helps!
I almost forgot to mention that the #Scope annotation may be necessary for your Bean, as seen below. This was the case when using Upload within a Bean because the UI is not instantiate/attached prior to the Bean being created and will cause a Null Reference Exception to be thrown. It won't do so when using #Route, but will when using #Component - so the latter is not an option and if #Route is not viable, then I would recommend using #Configuration class to create the bean with the prototype scope.
#Configuration
public class MyConfig {
#Bean
#Scope(value = ConfigurableBeanFactory.SCOPE_PROTOTYPE, proxyMode = ScopedProxyMode.TARGET_CLASS)
public MyComponentA getMyBean() {
return new MyComponentA();
}
}


Special solution: get Spring beans from any (non Spring) classes
#Component
public class SpringContext {
private static ApplicationContext applicationContext;
#Autowired
private void setApplicationContext(ApplicationContext ctx) {
applicationContext = ctx;
}
public static <T> T getBean(Class<T> componentClass) {
return applicationContext.getBean(componentClass);
}
}

Related

Cannot getBean after adding #Component above Class

I cannot get the bean by adding #Component on it.
I have created a class as below for getting bean in cases where instances are not injected by #autowired.
#Component
public class SpringApplicationContext implements ApplicationContextAware{
private static ApplicationContext CONTEXT;
public static Object getBean(String beanName) {
return CONTEXT.getBean(beanName);
}
#Override
public void setApplicationContext(ApplicationContext context)
throws BeansException {
CONTEXT = context;
}
}
Then I created a AppProperties class for reading the decrypt token from application.properties.
#Component
public class AppProperties {
#Autowired
private Environment env;
public String getTokenSecret() {
return env.getProperty("tokenSecret");
}
}
Then, I try to get the AppProperties instance as bean like this, which SecurityConstants.getTokenSecret() are used as parameter by manually inject in another method like this:
public class SecurityConstants {
...
public static String getTokenSecret() {
//Fail to get bean in this line
AppProperties appProperties = (AppProperties)SpringApplicationContext.getBean("AppProperties");
return appProperties.getTokenSecret();
}
}
but fail with below exception:
org.springframework.beans.factory.NoSuchBeanDefinitionException: No bean named 'AppProperties' available
After that, I add getAppProperties() with #Bean to make it register as a bean and it worked.
#SpringBootApplication
public class RegAppApplication {
public static void main(String[] args) {
SpringApplication.run(RegAppApplication.class, args);
}
#Bean(name="AppProperties")
public AppProperties getAppProperties() {
return new AppProperties();
}
}
The question is:
Why SpringApplicationContext is run on application start and AppProperties does not?
Why cannot get AppProperties as bean? Isn't adding #Component above the class will make it a component scan target, thus being treated as a bean?
How adding getAppProperties() with #Bean making it different with adding #Component above the class?
Thank you.

Application Context not injected in an `#Configuration` annotated class

I have a setup like:
#Configuration
public class MyConfig {
#Autowired
ApplicationContext applicationContext;
#Bean
public MyBean myBean() {
return applicationContext.getAutowireCapableBeanFactory().createBean(MyBean.class);
}
}
Soon as I launch my Application, Spring tries to create myBean even before injecting applicationContext. As the latter is null, it will cause a NullPointerException in the method myBean().
Strangely, injecting the Application Context works in some other #Configuration classes, but not in the one mentioned above.
Is there a way force the injection of applicationContext before the method myBean() is called?

I don't think that you have the guarantee that the fields declared with #Autowired be always loaded before the invocation of the methods declared with #Bean .
To ensure that the ApplicationContext object is valued, you could make your configuration class implement ApplicationContextAware.
#Configuration
public class MyConfig implements ApplicationContextAware {
private ApplicationContext context;
public void setApplicationContext(ApplicationContext context) {
this.context = context;
}
...
}

How to get bean using application context in spring boot

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()
}

Spring / Accessing the current applicationContext in one bean's factory-method

Is there a possibility to get the actual reference to the current ApplicationContext ? :
package myPackage;
public class AFactory {
public static A createA() {
// I need to access to the current instance of ApplicationContext here, passing it to another object's method for example
}
}
In my applicationContext.xml:
<bean id="myBeanA" class="myPackage.AFactory" factory-method="createA">
</bean>
UPDATE --------------------------------------------------------
I thought an example with Java would be more popular and would work in Scala but it's trickier in Scala due to the fact that "static" method are defined outside the class:
object ActorSystemFactory {
var applicationContext: ApplicationContext = _
def createActorSystem = {
val system = ActorSystem("AkkaScalaSpring")
SpringExtensionImpl(system)(applicationContext)
system
}
}
class ActorSystemFactory extends ApplicationContextAware {
def setApplicationContext(context: ApplicationContext) {
ActorSystemFactory.applicationContext = context
}
}
For those who know Scala, here Spring warns logically about the fact that there isn't createActorSystem static method in the class.
Has someone ever handled this case?

Make your bean implements ApplicationContextAware
public class AFactory implements ApplicationContextAware {
private static ApplicationContext applicationContext = null;
public static ApplicationContext getApplicationContext() {
return applicationContext;
}
public void setApplicationContext(ApplicationContext applicationContext) throws BeansException {
this.applicationContext = applicationContext;
}
}

How to get an object with transaction in Spring?

I have a Service class like this:
#Service
public class CompanyServiceImpl implements CompanyService {
#Autowired
private CompanyDAO companyDAO;
#Transactional
public void addOrUpdateCompany(Company company) {
companyDAO.addOrUpdateCompany(company);
}
}
Normally, I can have an instance of CompanyService from Spring by:
#Autowired
CompanyService companyService;
But, in some cases, I want to create/get an instalce of CompanyService without #Autowired like this:
CompanyService companyService = XXX.getxxx("CompanyService");
Is there any ways I can do this?

Other way is
#Component
public class ContextHolder implements ApplicationContextAware {
private static ApplicationContext CONTEXT;
public void setApplicationContext(ApplicationContext applicationContext) {
CONTEXT = applicationContext;
}
public static ApplicationContext getContext() {
return CONTEXT;
}
}
And then
CompanyService service = ContextHolder.getContext().getBean(CompanyService.class);

If I understand you correctly, you mean something like - ServiceLocatorFactoryBean
with it you can call somthing like MyService getService(String id)).
Another way, will be to implement some kind of a controller service that will have all other services autowired to it, and will hold a map from their string id to actual instances.
In my opinion the second option is better, since it's more manageable and clear.
Hope that helps you.

You can do it. You need to instancate the application context and then get your been.
Resource res = new FileSystemResource("beans.xml");
XmlBeanFactory factory = new XmlBeanFactory(res);
or
ClassPathResource res = new ClassPathResource("beans.xml");
XmlBeanFactory factory = new XmlBeanFactory(res);
or
ClassPathXmlApplicationContext appContext = new ClassPathXmlApplicationContext(
new String[] {"applicationContext.xml", "applicationContext-part2.xml"});
// of course, an ApplicationContext is just a BeanFactory
BeanFactory factory = (BeanFactory) appContext;
and use:
MyObject my = (MyObject)factory.getBean(NAME_OF_YOUR_BEAN);

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