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Initiate object via constructor through #AutoWired during runtime

I was new to Springboot application using the #Autowired to perform the dependency injection. We can use #Autowired directly by initiate that class object for class that has none or default parameterless constructor. But what if a class has some parameter in its constructor, and I would like to initiate it during runtime conditionally and automatically, is it possible to do that?
For example
#Component
public class SomeContext {
private String name;
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
}
#Component
public class SomeBuilder {
private final SomeContext ctx;
#Autowired
public SomeBuilder(SomeContext ctx) {
this.ctx = ctx;
}
public void test() {
System.out.println("ctx name: " + ctx.getName());
}
}
#Service
public class SomeService {
#Autowired
SomeBuilder someBuilder;
public void run(SomeContext ctx) {
if (ctx != null) {
// I want someBuilder to be initiated here in someway with my input ctx
// but NOT doing through new with constructor like below
// someBuilder = new SomeBuilder(ctx);
someBuilder.test(); // ctx name: null, I would expect to see "ctx name: someUser", while ctx was injected into someBuilder in any possible way
}
}
}
#RestController
public class HelloWorldController
{
#Autowired
SomeService someService;
#RequestMapping("/")
public String hello() {
SomeContext someContext = new SomeContext();
someContext.setName("someUser");
someService.run(someContext);
return "Hello springboot";
}
}

I'm not sure I've got your question right, but from the code it looks like you really want to create a new instance of SomeBuilder every time you call the run method of SomeService.
If so, I think the first thing to understand is that in general the injection magic happens only if the class is managed by Spring by itself. Read, if spring creates the object of the class - it will inject stuff into it otherwise you're on your own here.
The next thing to understand is that, if you have a object of class SomeBuilder managed by spring and you want to inject SomeContext into it, this SomeContext instance has to be managed by spring as well.
Bottom line, spring can deal only with objects that it manages. These objects are stored in a 'global registry' of all the objects called ApplicationContext in spring.
Now Spring has a concept of prototype scope vs. singleton scope. By Default all the beans are singletons, however you can easily alter this behavior. This has two interesting consequences:
You Can create prototype objects being injected into the singleton upon each invocatino (of method run in your case, so the SomeBuilder can and I believe should be a prototype)
Prototype objects are not stored in the application contexts so the capabilities of injecting stuff in there during the runtime are rather limited
With all this in mind:
If you want to create SomeContext like you do in the controller, its not managed by spring, so you can't use Injection of spring as is into the builder.
The builder is a singleton, so if you inject it with a regular #Autowire into another singleton (SomeService in your case), you'll have to deal with the same instance of the builder object - think about concurrent access to the method run of SomeService and you'll understand that this solution is not really a good one.
So these are the "inaccuracies" in the presented solution.
Now, in terms of solution, you can:
Option 1
Don't manage builders in Spring, not everything should be managed by spring, in this case you'll keep your code as it is now.
Option 2
and this is a the solution, although pretty advanced one:
Use Java Configuration to create prototype beans in runtime with an ability to inject parameters into the bean.
Here is an example:
// Note, I've removed all the annotations, I'll use java configurations for that, read below...
public class SomeBuilder {
private final SomeContext ctx;
public SomeBuilder(SomeContext ctx) {
this.ctx = ctx;
}
public void test() {
System.out.println("ctx name: " + ctx.getName());
}
}
Now the class SomeService will also slightly change:
public class SomeService {
private Function<SomeContext, SomeBuilder> builderFactory;
public void run(SomeContext ctx) {
SomeBuilder someBuilder = builderFactory.apply(ctx);
someBuilder.test();
}
}
And now you should "glue" it to spring in an advanced way with Java Configurations:
#Configuration
public class MyConfiguration {
#Bean
public Function<SomeContext, SomeBuilder> builderFactory() {
return ctx -> someBuilder(ctx);
}
#Bean
#Scope(value = "prototype")
public SomeBuilder someBuilder(SomeContext ctx) {
return new SomeBuilder(ctx);
}
#Bean
public SomeService someService() {
return new SomeService(builderFactory());
}
}
For more details with a really similar example, see this tutorial

Not able to get application context object using ApplicationContextAware

i have a microservice application developed using spring boot. i also have a project under under the same application which contains some java classes (non spring classes). i am trying to use some of the beans which are available in the spring container in this non java class using the ApplicationContextAware approach. when i debug the code during the bootrun, i can see the setApplicationContext(ApplicationContext ctx) is getting call and the context is getting set.
when from inside my non spring java class when i tried to get the instance of the context using the public static getApplicationContext(), i am getting null for context.
below is the sample example i had used.
#Component
public class ApplicationContextProvider implements ApplicationContextAware {
private static ApplicationContext context;
public ApplicationContext getApplicationContext() {
return context;
}
#Override
public void setApplicationContext(ApplicationContext ctx) {
context = ctx;
}
}
this is how i try to get the instance
ApplicationContext c = ApplicationContextProvider.getApplicationContext();
i am not able to figure it out what is missing here, as i am using spring boot, i dont think there is a need to configure any bean in xml.

This worked for me with your code. I could get the application start time after fetching the provider from the context.
#RestController
public class SampleController {
#Inject
ApplicationContextProvider provider;
#RequestMapping(value = "..", method = RequestMethod.GET)
public ResponseEntity<String> someMethod() throws IOException {
ApplicationContext c = provider.getApplicationContext();
System.out.println(c.getApplicationName());
c.getStartupDate()
}
}

Why is programmatically created bean not available in the application context

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

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()
}

How does ApplicationContextAware work in Spring?

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.