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Can I define a Spring #bean as a #Repository or #Service?

I'm wiring a third party library into a Spring Boot application and I'd like to both control its lifecycle and benefit from exception transform/translation capability of #Repository.
I can inherit from the type in the third party library and use #Repository on the inherited type, but that would not work for final classes and I want the lifecycle flexibility of #bean.
Is there any way I can declare a bean to also act like a stereotype?

As far as I know there's no way you can add stereotype information to an existing class. There's a workaround as seen in this SO answer, however it seems kind of complicated.
I'd suggest a more straightfoward approach: favor composition over inheritance. This way you can create your own class that wraps the third party library class functionality, annotate it as #Repository and define it as a ´#Bean´:
#Repository
public class LibWrapper {
private TrirdPartyClass wrapped;
public void insert() {
wrappped.insert();
}
}
#Configuration
public class LibWrapperConfiguration {
#Bean
public LibWrapper libWrapper(){
return new LibWrapper();
}
}

How to call Spring Framework repositories methods

I know that there are questions similar to this one, but none of them have helped me. I'm following along this tutorial, and the part I can't wrap my mind around is:
#SpringBootApplication
public class Application {
private static final Logger log =
LoggerFactory.getLogger(Application.class);
public static void main(String[] args) {
SpringApplication.run(Application.class);
}
#Bean
public CommandLineRunner demo(CustomerRepository repository) {
return (args) -> {
// save a couple of customers
...
// more lines, etc...
What I don't understand is where the repository passed into demo comes from. I know that the Autowired annotation can do something like that, but it isn't used at all here.
The more specific reason I ask is because I'm trying to adapt what they do here to an application I'm working on. I have a class, separate from all of the persistence/repository stuff, and I want to call repository methods like save and findAll. The issue is that the repository is an interface, so I can't instantiate an object of it to call the methods. So do I have to make a new class that implements the interface and create an object of that? Or is there an easier way using annotations?

When creating a #Bean, adding the repository in the parameters of the bean is enough to wire the repos in your bean. This works pretty much like adding #Autowired annotation inside a class that is annotated as #Component or something similar.
Spring works mostly with interface, since that is simplier to wire vs wiring concrete classes.

Can you try #Repository before the declaration of class? Worked for me in a Spring MVC structure.
#Repository
public class EntityDAOImpl implements EntityDAO{
...
}

The thing to wrap your head around is a Spring Boot application at startup time aims to resolve its dependancy tree. This means discovering and instantiating Beans that the application defines, and those are classes annotated with #Service, #Repository, etc.
This means the default constructor (or the one marked with #Autowire) of all beans is invoked, and after all beans have been constructed the application starts to run.
Where the #Bean annotation comes into play is if you have a bean which does not know the values of it's constructor parameters at compile time (e.g. if you want to wire in a "started at" timestamp): then you would define a class with an #Configuration annotation on it, and expose an #Bean method in it, which would return your bean and have parameters that are the beans dependencies. In it you would invoke the beans constructor and return the bean.
Now, if you want a certain method of some class to be invoked after the application is resolved, you can implement the CommandLineRunner interface, or you can annotate a method with #PostConstruct.
Some useful links / references:
https://docs.spring.io/spring-javaconfig/docs/1.0.0.m3/reference/html/creating-bean-definitions.html
https://www.baeldung.com/spring-inject-prototype-bean-into-singleton
Running code after Spring Boot starts
Execute method on startup in Spring

Spring Injecting Beans from src folder in test folders

I have utility classes exposed as beans in my source folders. I want to use some of those utilities in my test classes written in junit 4. For example , I have a utility class that has methods which marshal an object into JSON string. I want to inject this utility bean in my test class. I am unable to inject these beans using Autowired annotation. Should I copy all these classes over to test folder?
Edit:
I am trying to inject jsonUtil. Below is how my code looks like.
import static org.junit.Assert.*;
import java.math.BigDecimal;
#RunWith(MockitoJUnitRunner.class)
#SpringApplicationConfiguration(classes = ProxyApplicationMock.class)
public class ProxyApplicationMock {
#Mock
public SoapClient soapClientMock;
private JsonUtil jsonUtil;
Main Class
public class ProxyApplication {
public static void main(String[] args) {
SpringApplication.run(ProxyApplication.class, args);
}
}

Your main classes can be seen by your test classes, but not the other way around. So no, you don't need to copy them.
If your utility class is declared as a Spring managed bean in your test Spring context configuration (the class -or XML file- declared in the #ContextConfiguration) which may and probably should be different from your main configuration.
Then you can inject it in any Spring managed class, which includes your test classes if it's using the SpringJUnit4ClassRunner.
EDIT:
To sum up what we discussed in the comments, the main problem is that your test runner is not a SpringRunner (alias for SpringJUnit4ClassRunner), and thus JUnit is not running your test in a Spring context. Have a look at a test example here.
The simplest test case will look like this.
#RunWith(SpringRunner.class)
#SpringBootTest
public class CityRepositoryIntegrationTests {
#Autowired
private MySpringBean springBean;
//...
}
But as often with Spring Boot, there's some magic happening behind. #SpringBootTest is a convenient annotation that will detect automatically a class annotated with #SpringBootConfiguration, meaning if you don't have a specific Spring configuration for your test, it will use your main Spring configuration, and thus include and instanciate all the beans for your main app, and that's not usually what we want in a unit test cause we want to test a class independently by mocking its dependencies.
What you can do, is provide the Spring compenent classes you want to include in your tests, as such:
#RunWith(SpringRunner.class)
#SpringBootTest(classes = MySpringBean.class)
public class CityRepositoryIntegrationTests {
#Autowired
private MySpringBean springBean;
#Mock
private MyMockedSpringBeanDependency mocked;
//...
}

This question is to Matt, since adding comment is throwing error saying only one additional use can be notified.
NOTE: Not an Answer
I have an Application class & many config classes which are imported in Application class. Earlier it was #Configuration, which I converted to #SpringBootConfiguration in Application class and the actual Config class, whos bean I am trying to mock. Ended up in
java.lang.NoSuchMethodError: org.springframework.boot.SpringApplication.<init>([Ljava/lang/Object;)V
at org.springframework.boot.test.context.SpringBootContextLoader.getSpringApplication(SpringBootContextLoader.java:121)
at org.springframework.boot.test.context.SpringBootContextLoader.loadContext(SpringBootContextLoader.java:84)
Please suggest How do I mock, I have the same setup as specified in the ticket.
#Bean
public CacheManager cacheManager()
{
EhCacheManagerFactoryBean factoryBean = new EhCacheManagerFactoryBean();
factoryBean.setConfigLocation(new ClassPathResource("ehcache.xml"));
factoryBean.setShared(true);
return new EhCacheCacheManager(factoryBean.getObject());
}
}

NoSuchBeanDefinitionException when implementing a new interface

I had the following set-up which worked perfectly fine:
#Service
public class MyService {
}
public class Test {
#Autowired
MyService service;
}
I changed MyService to implement a new interface, like this
#Service
public class MyService implements NewInterface {
}
There's nothing special in this interface, it's just a normal Java interface without any annotation and 2 very simple methods.
Now, Spring is not able to autowire this bean anymore, it gives a NoSuchBeanDefinitionException. I also tried to define it explicitly in the XML but it gave the same exception.
In case it's relevant, I'm using Spring 2.5 and build with Maven, the class Test is a unit test class. When I try to run the real application, it's using applicationContext.getBean() to get this service, and it gives the following exception: java.lang.ClassCastException: $Proxy81 cannot be cast to MyService.
What am I missing and what should I do?

When you see a class with a name like $Proxy81, it's telling you that Spring has auto-generated a proxy object for one of your beans, in this case a proxy object for the MyService bean. This uses java.lang.reflect.Proxy to generate the proxy object. This proxy object will implement the same interfaces as the class that's being proxied, but it will not be type-compatible with the target class itself.
Now, if the target class doesn't implement any interfaces, then Spring will instead use CGLIB to generate the proxy. This proxy will be a subclass of the target class, so the proxy object can be safely cast to the original type of the target object.
Now, when using the lower-level proxy-generation stuff in Spring, you can often override this behaviour, and tell it to always use CGLIB proxies, but I'm assuming that since you're using #Service, then you're also using <context:component-scan>, in which case I think you have to stick with the default behaviour.
It's not bad thing, though. This encourages you to not couple your classes together, but instead to program to interfaces. Any interaction with MyService should be expressible via interfaces, although this concept can get a little fuzzy when talking about unit testing.

It looks like you're autowiring by interface instead of autowiring by class name.
I'd simply code my test against the Interface:
public class Test {
#Autowired
NewInterface service;
}
Also, check this bug, it might be relevant to you since it appears like your class is being proxied.

How to inject dependencies into a self-instantiated object in Spring?

Let's say we have a class:
public class MyClass {
#Autowired private AnotherBean anotherBean;
}
Then we created an object of this class (or some other framework have created the instance of this class).
MyClass obj = new MyClass();
Is it possible to still inject the dependencies? Something like:
applicationContext.injectDependencies(obj);
(I think Google Guice has something like this)

You can do this using the autowireBean() method of AutowireCapableBeanFactory. You pass it an arbitrary object, and Spring will treat it like something it created itself, and will apply the various autowiring bits and pieces.
To get hold of the AutowireCapableBeanFactory, just autowire that:
private #Autowired AutowireCapableBeanFactory beanFactory;
public void doStuff() {
MyBean obj = new MyBean();
beanFactory.autowireBean(obj);
// obj will now have its dependencies autowired.
}

You can also mark your MyClass with #Configurable annotation:
#Configurable
public class MyClass {
#Autowired private AnotherClass instance
}
Then at creation time it will automatically inject its dependencies. You also should have <context:spring-configured/> in your application context xml.

Just got the same need and in my case it was already the logic inside non Spring manageable java class which had access to ApplicationContext. Inspired by scaffman.
Solved by:
AutowireCapableBeanFactory factory = applicationContext.getAutowireCapableBeanFactory();
factory.autowireBean(manuallyCreatedInstance);

I used a different approach. I had spring loaded beans that I wanted to call from my extended classes of a third-party library that created its own threads.
I used approach I found here https://confluence.jaytaala.com/display/TKB/Super+simple+approach+to+accessing+Spring+beans+from+non-Spring+managed+classes+and+POJOs
In the non-managed class:
{
[...]
SomeBean bc = (SomeBean) SpringContext.getBean(SomeBean.class);
[...]
bc.someMethod(...)
}
And then as a helper class in the main application:
import org.springframework.beans.BeansException;
import org.springframework.context.ApplicationContext;
import org.springframework.context.ApplicationContextAware;
import org.springframework.stereotype.Component;
#Component
public class SpringContext implements ApplicationContextAware
{
private static ApplicationContext context;
public static <T extends Object> T getBean(Class<T> beanClass)
{
return context.getBean(beanClass);
}
#Override
public void setApplicationContext(ApplicationContext context) throws BeansException
{
SpringContext.context = context;
}
}

I wanted to share my solution that follows the #Configurable approach as briefly mentioned in #glaz666 answer because
The answer by #skaffman is nearly 10 years old, and that does not mean not good enough or does not work
The answer by #glaz666 is brief and didn't really help me solve my problem but, did point me in the right direction
My setup
Spring Boot 2.0.3 with Spring Neo4j & Aop starts (which is irrelevant anyway)
Instantiate a bean when Spring Boot is ready using #Configurable approach (using ApplicationRunner)
Gradle & Eclipse
Steps
I needed to follow the steps below in order to get it working
The #Configurable(preConstruction = true, autowire = Autowire.BY_TYPE, dependencyCheck = false) to be placed on top of your Bean that is to be manually instantiated. In my case the Bean that is to be manually instantiated have #Autowired services hence, the props to above annotation.
Annotate the Spring Boot's main XXXApplicaiton.java (or the file that is annotated with #SpringBootApplication) with the #EnableSpringConfigured and #EnableLoadTimeWeaving(aspectjWeaving=AspectJWeaving.ENABLED)
Add the dependencies in your build file (i.e. build.gradle or pom.xml depending on which one you use) compile('org.springframework.boot:spring-boot-starter-aop') and compile('org.springframework:spring-aspects:5.0.7.RELEASE')
New+up your Bean that is annotated with #Configurable anywhere and its dependencies should be autowired.
*In regards to point #3 above, I am aware that the org.springframework.boot:spring-boot-starter-aop transitively pulls the spring-aop (as shown here mavencentral) but, in my case the Eclipse failed to resolve the #EnableSpringConfigured annotations hence, why I explicitly added the spring-aop dependency in addition to the starter. Should you face the same issue, just declare the dependency or go on adventure of figuring out
Is there a version conflict
Why the org.springframework.context.annotation.aspect.* is not available
Is your IDE setup properly
Etc etc.

This worked for me:
#Configuration
public class AppConfig {
#Bean
public TransferService transferService() {
return new TransferServiceImpl();
}
}
See more information: https://docs.spring.io/spring-javaconfig/docs/1.0.0.m3/reference/html/creating-bean-definitions.html

Found the following way useful for my use case. Sharing here for reference, credit goes to the blogger entirely. This creates a static field and populates that from Spring and then provides a public static method which returns the field populated above.
https://sultanov.dev/blog/access-spring-beans-from-unmanaged-objects/