This annotation is an annotation that allows you to create an alias for an attribute in an annotation. These attributes have the same function. The idea is to avoid confusion when multiple attributes can be used for the same purpose
Maybe this is the first time you have seen it.
Spring uses this annotation in places like @Bean
, @ComponentScan
, @Scope
, @RequestMapping
, etc.
So it’s more used internally. And maybe you are already using its functionality and don’t even know.
Let’s take a look at how @RequestMapping
is using this annotation:
@Target({ElementType.TYPE, ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Mapping
@Reflective({ControllerMappingReflectiveProcessor.class})
public @interface RequestMapping {
String name() default "";
@AliasFor("path")
String[] value() default {};
@AliasFor("value")
String[] path() default {};
RequestMethod[] method() default {};
String[] params() default {};
String[] headers() default {};
String[] consumes() default {};
String[] produces() default {};
}
The attributes path
and value
have the same purpose, they define the URL pattern for your request mappings.
The scenario below shows how the effect is the same and you can choose the alias you want.
@Controller
public class AlisForController {
@RequestMapping(value = "/home", method = RequestMethod.GET)
public String homePage() {
return "home";
}
// Equivalent to the above using 'path'
@RequestMapping(path = "/home", method = RequestMethod.GET)
public String homePage2() {
return "home";
}
}
Have you ever seen this before?
Have some dev defined the path
and in another controller, you found that it’s using a value
for the same purpose, and somehow everything works, now you know why it works.
Conclusion
So, pay attention to your project, have you found any places where this happened? Open the annotation’s code and see the @AliasFor
there.
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