Develop Reference

How to inject pojo class in spring?

I have a pojo class which i need to inject in component. how to inject pojo object in spring?
For example
RestClass is under Module(like one microservice). Pojo Value should be injected here only. service class and pojo is different module.
#Controller
public class RestClass {
#Autowired
private ServiceClass serviceClass;
// How to apply MyConfig pojo object into ServiceClass
//like MyConfig.Builder().limit(100).build();
#PostMapping("/business")
private void callDoBusiness(){
serviceClass.doBusiness();
}
}
//// ServiceClass and Pojo class is under one module. Pojo object should not construct here. should be passed from another module
#Service
public class ServiceClass {
#Autowired
private MyConfig myConfig;
public void doBusiness(){
System.out.println(myConfig.getLimit())
}
}
#Builder
#Getter
public class MyConfig {
private int limit;
.
.
}

#Bean annotation is used in your case. For example:
Create some configuration file with #Configuration annotation. It doesn't matter where you create your Config configuration class or how you name it. You can even have multiple #Configuration classes across your project.
import org.springframework.context.annotation.Bean;
import org.springframework.context.annotation.Configuration;
#Configuration
class Config {
// configure your MyConfig class here as a bean
#Bean
public MyConfig myConfig() {
return MyConfig.Builder().limit(100).build();
}
}
Now you can autowire it wherever you use it as in you example.

You can use #Configuration and #Bean. Something like this
AppConfig.java
#Configuration
public class AppConfig {
#Bean
public PojoClass getBean(){ return new PojoClass();}
}

You can use #Bean
#Configuration
public class Config {
#Bean
public MyConfig MyConfig() {
return new MyConfig();
}
}

Spring boot dependency injection of an interface

I have 2 spring boot microservice let's say core and persistence. where persistence has a dependency on core.
I have defined an interface in core whose implementation is inside persistence as below:
core
package com.mine.service;
public interface MyDaoService {
}
Persistence
package com.mine.service.impl;
#Service
public class MyDaoServiceImpl implements MyDaoService {
}
I am trying to inject MyDaoService in another service which is in core only:
core
package com.mine.service;
#Service
public class MyService {
private final MyDaoService myDaoService;
public MyService(MyDaoService myDaoService) {
this.myDaoService = myDaoService;
}
}
while doing this i am getting this weird error:
***************************
APPLICATION FAILED TO START
***************************
Description:
Parameter 0 of constructor in com.mine.service.MyService required a bean of type 'com.mine.service.MyDaoService' that could not be found.
Action:
Consider defining a bean of type 'com.mine.service.MyDaoService' in your configuration.
can anyone explain me why ?
NOTE: i have already included com.mine.service in componentscan of springbootapplication as below
package com.mine.restpi;
#SpringBootApplication
#EnableScheduling
#ComponentScan(basePackages = "com.mine")
public class MyRestApiApplication {
public static void main(String[] args) {
SpringApplication.run(MyRestApiApplication.class, args);
}
}

Try adding the #Service annotation to your impl classes and the #Autowired annotation to the constructor.
// Include the #Service annotation
#Service
public class MyServiceImpl implements MyService {
}
// Include the #Service annotation and #Autowired annotation on the constructor
#Service
public class MyDaoServiceImpl implements MyDaoService {
private final MyService myService ;
#Autowired
public MyDaoServiceImpl(MyService myService){
this.myService = myService;
}
}

As stated in the error message hint: Consider defining a bean of type 'com.mine.service.MyDaoService' in your configuration to solve this problem you can define in your package com.mine a configuration class named MyConfiguration annotated with #Configuration including a bean named myDaoService like below:
#Configuration
public class MyConfiguration {
#Bean
public MyDaoService myDaoService() {
return new MyDaoServiceImpl();
}
}

Try the following, move MyRestApiApplication class to com.mine package and remove #ComponentScan annotation.
package com.mine;
#SpringBootApplication
#EnableScheduling
public class MyRestApiApplication {
public static void main(String[] args) {
SpringApplication.run(MyRestApiApplication.class, args);
}
}

How using spring-boot-starter-jpa in custom spring-boot-starter?

I have my custom starter. Inside it, I define a repository. How should I define it in the configuration? This is how I did the usual bean before.
#Bean
#ConditionalOnMissingBean(HelloWorldController.class)
public HelloWorldController helloWorldController() {
return new HelloWorldController();
}
Repository:
#Repository
public interface CarRepository extends JpaRepository<Car, Long> {
}
And configuration
#Configuration
#EnableJpaRepositories
public class DomainConfiguration {
}
If you use this starter, context will not see the repository bean. Because I did not declare it in the configuration.I don't know how to declare it.

Turn POJO to #Configuration programmatically Spring

Given a class:
class MyConfiguration {
#Bean
String bean() {
return new String();
}
}
as you may notice it does not have #Configuration annotation.
How can I make it behave like it has #Configuration annotation, but not adding it?
#Bean annotation should not work in Lite Mode, https://docs.spring.io/spring/docs/current/javadoc-api/org/springframework/context/annotation/Bean.html
Something like:
#Configuration
class MainConfiguration {
#Bean
MyConfiguration myConfiguration() {
MyConfiguration myConfiguration = do_some_spring_magic();
// myConfiguration behaving like it's having #Configuration here
return myConfiguration;
}
}

I dont understand what is the use case you are trying to achieve here.. But if you are looking for programatically registering beans into the Spring Context then you can do it as below.
#Configuration
public class MyBeanRegisterFactory implements BeanDefinitionRegistryPostProcessor, PriorityOrdered {
#Override
public void postProcessBeanDefinitionRegistry(BeanDefinitionRegistry beanRegistry) throws BeansException {
//depending on some condition you can do the below line
beanRegistry.registerBeanDefinition("myBeanClass", new RootBeanDefinition("com.mybean.MyBeanClass"));
}
#Override
public int getOrder() {
return Ordered.HIGHEST_PRECEDENCE;
}
}
In Your case, the bean definitions inside the class MyConfiguration can be programatically registered as below into to the spring context.
http://docs.spring.io/spring-framework/docs/current/javadoc-api/org/springframework/beans/factory/support/BeanDefinitionRegistryPostProcessor.html

Spring Bean Alias in JavaConfig

I have a #Service annotated class which provides core functionality which I can use in all my projects:
#Service
public class MyService {}
and another one which extends it to implement project specific stuff:
#Service
public class ExtendedMyService extends MyService {}
Now I would like to configure a bean alias to be able to use #Qualifier("MyServiceAlias") when autowiring it using a property:
# MyService qualifier (default: myService)
myService.qualifier=extendedMyService
In XML it would look like:
<alias name="${myService.qualifier}" alias="MyServiceAlias" />
It is also discussed here, but I need to do it w/o XML, JavaConfig only.
Is it possible and how to realize?

There is an open Jira for this: https://jira.spring.io/browse/SPR-6736
The workaround is to use #Bean in #Configuration class:
#Configuration
public class AppConfig {
#Bean(name = { "dataSource", "subsystemA-dataSource", "subsystemB-dataSource" })
public MyService myService() {}
}

If you want to use the placeholder, another workaround is to use #Bean in a #Configuration class using #Value and the Spring applicationContext.
#Configuration
public class AppConfig {
#Autowired
private ApplicationContext context;
#Bean
public MyService myService(#Value("${myService.qualifier}") String qualifier) {
return (MyService) context.getBean(qualifier);
}
}
NB : special consideration must be taken for the placeholder bean which must be loaded at the beginning (cf javadoc)

With small amount of configuration and one ImportBeanDefinitionRegistrar you can configure bean aliases via Java configuration. You can check bean-alias library project for reference - developed for the needs of my projects. Feel free to modify and/or copy the source into your own project in case the spring version used in it does not work with your setup.
Once you have the library on your path, you declare an alias through the annotation:
#Configuration
#BeanAlias(name = "fromName", alias = "toName")
public class ExampleConfiguration {
}
That's it.
How it works is that with the annotation we import a ImportBeanDefinitionRegistrar implementation
#Import(BeanAliasBeanRegistrar.class)
public #interface BeanAlias {
}
which registers the alias in the BeanDefinitionRegistry
class BeanAliasBeanRegistrar implements ImportBeanDefinitionRegistrar, PriorityOrdered {
#Override
public void registerBeanDefinitions(AnnotationMetadata metadata, BeanDefinitionRegistry registry) {
...
registerAlias(registry, metadata.getAnnotationAttributes(BeanAlias.class.getName()));
}
private void registerAlias(BeanDefinitionRegistry registry, Map<String, Object> attributes) {
...
registry.registerAlias(name, alias);
}
}