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How to access the same instance of a bean from HttpServlet?

I am somewhat new to Spring Framework. I have a web application written with Spring (4.2.1). I'm trying to expose metrics using Micrometer library and will be scraping with Prometheus.
The relevant structure of the application is this:
- core-module (JAR)
- webservice-module (WAR)
I created a PrometheusService class which is a bean defined in core-module. Defined inside the bean is the PrometheusMeterRegistry and Counter:
#Service
public class PrometheusService {
private static PrometheusMeterRegistry registry = new PrometheusMeterRegistry(PrometheusConfig.DEFAULT);
private static Counter newAssetCounter = Counter
.builder("new_asset_counter")
.description("count of created assets")
.tags("region", "na")
.register(registry);
public PrometheusService() {
new JvmMemoryMetrics().bindTo(registry);
new DiskSpaceMetrics(new File("/")).bindTo(registry);
new ProcessorMetrics().bindTo(registry);
new UptimeMetrics().bindTo(registry);
}
public static PrometheusMeterRegistry getRegistry() {
return registry;
}
public Counter getNewAssetCounter() {
return this.newAssetCounter;
}
}
I created MetricsResource which is an HttpServlet that exposes the /metrics endpoint. When trying to #Autowire the PrometheusService bean, it was always null here. A quick search told me that HttpServlet isn't managed by Spring. If I wanted to #Autowire, I needed to add something like this:
SpringBeanAutowiringSupport.processInjectionBasedOnCurrentContext(webApplicationContext);
Now, I was able to #Autowire the PrometheusService bean within the Servlet.
The Counter defined in the bean gets incremented within the core-module. The MetricsResource doGet method writes the metrics stored in the PrometheusMeterRegistry.
#WebServlet("/metrics")
public class MetricsResource extends HttpServlet {
private PrometheusService promService; // #Autowired
private PrometheusMeterRegistry registry;
#Override
public void init() throws ServletException {
super.init();
// SpringBeanAutowiringSupport.processInjectionBasedOnCurrentContext(webApplicationContext);
// promService = (PrometheusService) getServletContext().getAttribute("prometheusService");
// WebApplicationContext context = WebApplicationContextUtils.getWebApplicationContext(getServletContext());
// AutowireCapableBeanFactory ctx = context.getAutowireCapableBeanFactory();
// ctx.autowireBean(this);
}
#Override
protected void doGet(final HttpServletRequest req, final HttpServletResponse resp) throws IOException {
resp.setStatus(HttpServletResponse.SC_OK);
resp.setContentType(TextFormat.CONTENT_TYPE_004);
registry = promService.getRegistry();
Writer writer = resp.getWriter();
try {
registry.scrape(writer);
writer.flush();
} finally {
writer.close();
}
}
}
The problem though, is that the value of the Counter is always 0 at the /metrics endpoint.
No matter if it's #Autowired or if I'm manually trying to get the bean.
How could this be? My PrometheusService bean is a singleton. Even the PrometheusMeterRegistry and the Counter are marked static, so why am I getting a different object in my servlet? After some more searching, I found that Spring will create one singleton bean per container. So what I'm assuming is happening here is there are two containers or contexts. A main application context and a servlet context.
Some things I've tried:
Making PrometheusService implement ApplicationContextAware
Using a ServiceLocator class that implements ApplicationContextAware and returns beans
Adding context-params to web.xml
Using ServletContextAttributeExporter in app-context.xml
Using WebApplicationContextUtils.getRequiredWebApplicationContext(config.getServletContext())
I continue to get a new instance of the object. All I want to do is be able to create and expose custom metrics with Micrometer. Is my approach flawed? How can I access the correct bean from within my HttpServlet?
Spring dependency injection to other instance
http://senthadev.com/sharing-spring-container-between-modules-in-a-web-application.html
Spring dependency injection to other instance
ApplicationContext and ServletContext

Try processInjectionBasedOnServletContext(Object target, ServletContext servletContext).

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

Spring integration test with context hierarchy child context bean as application listener

I am new to Spring, forgive me if I am doing something silly. I am trying to write an integration test for my application which uses spring.
I am creating a context hierarchy, as follows
#Before
public void setup(){
parentContext = new AnnotationConfigApplicationContext(TestConfig.class);
// some more setup stuff here
}
In my test method, I am trying to create a new child context that has just one bean which is an application listener, that depends on beans in parent method.
public void test(){
childContext = new AnnotationConfigApplicationContext();
childContext.setParent(ctx);
register(TestConfig2.class);
childContext.refresh();
// some testing stuff here that generates events
}
The problem I am facing is that my bean from the child context is not getting notified on application events also my #Value annotations are not processed.
what am I doing wrong here?

Actually I figured out what was going wrong. My event publisher was in the parent context. I read on the spring forum, that spring context hierarchies work like class loaders. As in any beans loaded by the child Context are not visible to the parent context.
So I had to manually add the applicationlistener to the parent context.
parentContext.addApplicationListener(messageListener);
If want my childContext beans to get properties from parentContext I had to add the parentContext's PropertyPlaceholderConfigurer as a beanFactoryPostProcessor.
configurer = parentContext.getBean(PropertyPlaceholderConfigurer.class);
childContext.addBeanFactoryPostProcessor(configurer);
to sum it up, I had to do the following in my test method
public void test(){
childContext = new AnnotationConfigApplicationContext();
childContext.setParent(parentContext);
register(TestConfig2.class);
configurer = parentContext.getBean(PropertyPlaceholderConfigurer.class);
childContext.addBeanFactoryPostProcessor(configurer);
childContext.refresh();
MessageListener messageListener = childContext.getBean(MessageListener.class);
parentContext.addApplicationListener(messageListener);
// some testing stuff here that generates events
}

Declare
private static ClassPathXmlApplicationContext context;
at the method #Before
#BeforeClass
public static void setUpBeforeClass() throws Exception {
context = new ClassPathXmlApplicationContext("/WEB-INF/application-Context.xml");
}
at the methode #After
#AfterClass
public static void tearDownAfterClass() throws Exception {
context.close();
}
your method test
#Test
public void Test() {
//Your Code Here
}
I am also starting in spring

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.

Insert bean from applicationContext into POJO

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.