SpringBoot注解随用随记
@SpringBootApplication
Indicates a configuration class that declares one or more @Bean methods and also triggers auto-configuration and component scanning. This is a convenience annotation that is equivalent to declaring @Configuration, @EnableAutoConfiguration and @ComponentScan.
@RestController
A convenience annotation that is itself annotated with @Controller and @ResponseBody.
Types that carry this annotation are treated as controllers where @RequestMapping methods assume @ResponseBody semantics by default.
@Controller
Indicates that an annotated class is a "Controller" (e.g. a web controller).
This annotation serves as a specialization of @Component, allowing for implementation classes to be autodetected through classpath scanning. It is typically used in combination with annotated handler methods based on the org.springframework.web.bind.annotation.RequestMapping annotation.
@RequestMapping
Annotation for mapping web requests onto methods in request-handling classes with flexible method signatures.
Both Spring MVC and Spring WebFlux support this annotation through a RequestMappingHandlerMapping and RequestMappingHandlerAdapter in their respective modules and package structure.
@RequestParam
Annotation which indicates that a method parameter should be bound to a web request parameter.
Supported for annotated handler methods in Servlet and Portlet environments.
If the method parameter type is Map and a request parameter name is specified, then the request parameter value is converted to a Map assuming an appropriate conversion strategy is available.
If the method parameter is Map<String, String> or MultiValueMap<String, String> and a parameter name is not specified, then the map parameter is populated with all request parameter names and values.
@Autowired
Marks a constructor, field, setter method or config method as to be autowired by Spring's dependency injection facilities.
Only one constructor (at max) of any given bean class may carry this annotation, indicating the constructor to autowire when used as a Spring bean. Such a constructor does not have to be public.
Fields are injected right after construction of a bean, before any config methods are invoked. Such a config field does not have to be public.
Config methods may have an arbitrary name and any number of arguments; each of those arguments will be autowired with a matching bean in the Spring container. Bean property setter methods are effectively just a special case of such a general config method. Such config methods do not have to be public.
In the case of a multi-arg constructor or method, the 'required' parameter is applicable to all arguments. Individual parameters may be declared as Java-8-style java.util.Optional, overriding the base required semantics.
In case of a java.util.Collection or java.util.Map dependency type, the container autowires all beans matching the declared value type. For such purposes, the map keys must be declared as type String which will be resolved to the corresponding bean names. Such a container-provided collection will be ordered, taking into account org.springframework.core.Ordered/org.springframework.core.annotation.Order values of the target components, otherwise following their registration order in the container. Alternatively, a single matching target bean may also be a generally typed Collection or Map itself, getting injected as such.
Note that actual injection is performed through a BeanPostProcessor which in turn means that you cannot use @Autowired to inject references into BeanPostProcessor or BeanFactoryPostProcessor types. Please consult the javadoc for the AutowiredAnnotationBeanPostProcessor class (which, by default, checks for the presence of this annotation).
@Qualifier
This annotation may be used on a field or parameter as a qualifier for candidate beans when autowiring. It may also be used to annotate other custom annotations that can then in turn be used as qualifiers.
@Value
Annotation at the field or method/constructor parameter level that indicates a default value expression for the affected argument.
Typically used for expression-driven dependency injection. Also supported for dynamic resolution of handler method parameters, e.g. in Spring MVC.
A common use case is to assign default field values using "#{systemProperties.myProp}" style expressions.
Note that actual processing of the @Value annotation is performed by a BeanPostProcessor which in turn means that you cannot use @Value within BeanPostProcessor or BeanFactoryPostProcessor types. Please consult the javadoc for the AutowiredAnnotationBeanPostProcessor class (which, by default, checks for the presence of this annotation).
