构建后端第3篇之---springb @Alias注解使用

write by 张艳涛 in 202210210,after today i will write aritles by english,because english is so diffent from chiness that i can't

understand english in java,spring doc notice ,so i begin to use english for a lifelong time. atthought is hard for me ,but i am a man would like learn little by little , yes is the only way to learn language by use it in common daily time

Tody I would lile recode usage of spring annotion @Aliasfor

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ToIntroduce @Aliasfor , you master kown the @SpringBootApplication ,it uses start Main Class, then show the context

@Target(ElementType.TYPE)

@Retention(RetentionPolicy.RUNTIME)

@Documented

@Inherited

@SpringBootConfiguration

@EnableAutoConfiguration

@ComponentScan(excludeFilters = {

        @Filter(type = FilterType.CUSTOM, classes = TypeExcludeFilter.class),

        @Filter(type = FilterType.CUSTOM, classes = AutoConfigurationExcludeFilter.class) })

public @interface SpringBootApplication {

    /**

     * Exclude specific auto-configuration classes such that they will never be applied.

     * @return the classes to exclude

     */

    @AliasFor(annotation = EnableAutoConfiguration.class)

    Class<?>[] exclude() default {};

    /**

     * Exclude specific auto-configuration class names such that they will never be

     * applied.

     * @return the class names to exclude

     * @since 1.3.0

     */

    @AliasFor(annotation = EnableAutoConfiguration.class)

    String[] excludeName() default {};

    /**

     * Base packages to scan for annotated components. Use {@link #scanBasePackageClasses}

     * for a type-safe alternative to String-based package names.

     * @return base packages to scan

     * @since 1.3.0

     */

    @AliasFor(annotation = ComponentScan.class, attribute = "basePackages")

    String[] scanBasePackages() default {};

    /**

     * Type-safe alternative to {@link #scanBasePackages} for specifying the packages to

     * scan for annotated components. The package of each class specified will be scanned.

     * <p>

     * Consider creating a special no-op marker class or interface in each package that

     * serves no purpose other than being referenced by this attribute.

     * @return base packages to scan

     * @since 1.3.0

     */

    @AliasFor(annotation = ComponentScan.class, attribute = "basePackageClasses")

    Class<?>[] scanBasePackageClasses() default {};

}

and with

@SpringBootApplication(scanBasePackages ={ "com.zyt" } )//这个是rouyi的方案

public class ZytAuthApplication {

    public static void main(String[] args) {

        SpringApplication.run(ZytAuthApplication.class, args);

        System.out.println("(◠‿◠)ﾉﾞ  授权认证中心启动成功   ლ(´ڡ`ლ)ﾞ  \n" );

    }

}

you can know the attibute (scanBasePackages ={ "com.zyt" } ) is for

    @AliasFor(annotation = ComponentScan.class, attribute = "basePackages")

    String[] scanBasePackages() default {};

then the SpringBootApplication Annotation attibute scanBasePackages ={ "com.zyt" } , so we can undestand

@AliasFor isfor give scanBasePackages ={ "com.zyt" } to ComponentScan.class ,

ComponentScan overrite its attibute  with {"com.zyt"}

In One World like  meta-annotation get attibute value from Top Annotation 's attibute
this is call Explicit alias for attribute in meta-annotation:

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Explicit aliases within an annotation:

 public @interface ContextConfiguration {

      @AliasFor("locations")

      String[] value() default {};

      @AliasFor("value")

      String[] locations() default {};

      // ...

   }

for more

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Example: Implicit Aliases within an Annotation

 @ContextConfiguration

   public @interface MyTestConfig {

      @AliasFor(annotation = ContextConfiguration.class, attribute = "locations")

      String[] value() default {};

      @AliasFor(annotation = ContextConfiguration.class, attribute = "locations")

      String[] groovyScripts() default {};

      @AliasFor(annotation = ContextConfiguration.class, attribute = "locations")

      String[] xmlFiles() default {};

   }

 @MyTestConfig

   public @interface GroovyOrXmlTestConfig {

      @AliasFor(annotation = MyTestConfig.class, attribute = "groovyScripts")

      String[] groovy() default {};

      @AliasFor(annotation = ContextConfiguration.class, attribute = "locations")

      String[] xml() default {};

   }

for more

巴特西

构建后端第3篇之---springb @Alias注解使用

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