Spring core : Annotations when to use what

 @Configuration: 
Annotation based configuration alternative to xml based configuration .This will be mostly used with @Bean to define bean at run time 
 for annotation-based configuration, as opposed to xml-based configuration. 

 @Bean:
 define bean at run time, should be under class annotated with @configuration 
 It is used to explicitly declare a single bean, rather letting spring to do it while classpath scanning.
 It decouple declaration from the class definition
 When we don't own the class, it might make sense to use @bean wherever its being used

 @Component:
Define bean at run time, should be under class annotated with @configuration 
 Requires @ComponentScan to allow autoscanning

By default, the bean instances of this class have the same name as the class name with a lowercase initial. On top of that, we can specify a different name using the optional value argument of this annotation.

@ConditionalOnMissingBean:
 conditional that only matches when the specified bean / with name is not already in the bean container.Typically available in spring boot applciation

@ConditionalOnClass:
Will create bean if com.thetechiehouse.MyServiceClass class exist in the class path.To be used in Spring boot env.
@Bean
@ConditionalOnClass(name ="com.thetechiehouse.MyServiceClass")

@ConditionalOnProperty:

@ConditionalOnProperty("app.somekey") // Bean registration hapen only when app.somekey is present
@ConditionalOnProperty(name='com.myproperty',  havingValue = "true")

@ConditionalOnProperty(prefix = "notification", name = "service", havingValue = "sms") 

    //notification.service=sms
@Bean
Create bean only if a specific  property value is true.To be used in Spring boot env.
@ConditionalOnExpression("${xxx.YYY.enabled:true}")
similar to @ConditionalOnProperty but it's a bit slower

Uses 
//@Resources

@Resource (name="myBean")

//@Bean

@Bean(name = "myBean")

    public SomeClass someMethod() {

        return new SomeClass();

    }

//@ Autowired

@Autowired

or

@Autowired

@Qualifier("myBean")

What are differences among @Autowired vs @Inject vs @Resource

Annotataion              package

@Resource	javax.annotation
@Inject	javax.inject
@Qualifier	javax.inject
@Autowired	org.springframework.bean.factory

@Resource:
annotation based on JSR-250. @Resource is quite similar to @Autowired 
 @Autowired (Spring specific)

 @Autowired:
It is fundamentally about type-driven injection ie  that  a resource by-type,
with optional semantic qualifiers.
The bean name is considered a default qualifier value.
 It does  have the required field so this can be used if the field is null and required so.

@Inject:
Annotation based on JSR-330
replacement for Spring’s @Autowired annotation
It  does not have the required field so if it does not find a suitable object it will fail.
It has @Named similar to qualifier in case of autowired.

@Resource will narrow down the search first by name then by type and finally by Qualifiers (ignored if match is found by name). @Autowired and @Inject will narrow down the search first by type then by qualifier and finally by the name.

Since @Repository, @Service, @Configuration, and @Controller are all meta-annotations of @Component, they share the same bean naming behaviour