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用法1:注解的属性互为别名
简介
它可以注解到自定义注解的两个属性上,表示这两个互为别名,也就是说这两个属性其实同一个含义。
其中一个属性名必须是"value"
无论指明设置哪个属性名设置属性值,另一个属性名也是同样属性值,也可以缺省属性名。
若两个都指明属性值,要求值必须相同,否则会报错。
使用简洁。这样使用之后,@MyAnno(location="shanghai")可以直接写为:@MyAnno("shanghai");
这个功能产生的原因:
若自定义注解有一个属性,且该属性命名上为了体现其含义,调用方必须每次使用自定义注解的时候,都必须写明属性 ,然后设置,这样稍微麻烦。
实例
注解
package com.example.annotation; import org.springframework.core.annotation.AliasFor; import java.lang.annotation.*; @Retention(RetentionPolicy.RUNTIME)@Target({ElementType.METHOD, ElementType.TYPE})@Documented@Inheritedpublic @interface MyAnnotation { @AliasFor(attribute = "location") String value() default ""; @AliasFor(attribute = "value") String location() default "";}
控制器
package com.example.controller; import com.example.annotation.MyAnnotation;import org.springframework.core.annotation.AnnotationUtils;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController; @RestController@RequestMapping("/hello")public class HelloController { @MyAnnotation(value = "location") @RequestMapping("/test1") public String test1() { MyAnnotation myAnnotation = null; try { myAnnotation = AnnotationUtils.getAnnotation(this.getClass().getMethod("test1"), MyAnnotation.class); } catch (NoSuchMethodException e) { e.printStackTrace(); } return "value:" + myAnnotation.value() + ";loation:" + myAnnotation.location(); }}
测试
前端访问:http://localhost:8080/hello/test1
前端结果(value和location都是同一个值)
value:location;loation:location
用法2.继承父注解的属性,不重写属性名
简介
子注解的属性值的读写,其实是对父注解的属性值的读写。(对继承的属性来说)
此时,只能读写继承了的属性值。
代码
注解
package com.example.annotation; import org.springframework.core.annotation.AliasFor; import java.lang.annotation.*; @Retention(RetentionPolicy.RUNTIME)@Target({ElementType.METHOD, ElementType.TYPE})@Documented@Inheritedpublic @interface MyAnnotation { @AliasFor(attribute = "location") String value() default ""; @AliasFor(attribute = "value") String location() default "";}
package com.example.annotation; import org.springframework.core.annotation.AliasFor; import java.lang.annotation.*; @Retention(RetentionPolicy.RUNTIME)@Target({ElementType.METHOD, ElementType.TYPE})@Documented@Inherited@MyAnnotationpublic @interface SubMyAnnotation { @AliasFor(annotation = MyAnnotation.class) String location() default ""; // 这个不能写,只能有一个与父属性名同名的属性,否则报错// @AliasFor(annotation = MyAnnotation.class)// String value() default "";}
控制器
package com.example.controller; import com.example.annotation.MyAnnotation;import com.example.annotation.SubMyAnnotation;import org.springframework.core.annotation.AnnotatedElementUtils;import org.springframework.core.annotation.AnnotationUtils;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController; @RestController@RequestMapping("/hello")public class HelloController { @SubMyAnnotation(location = "location(my)") @RequestMapping("/test") public String test() { SubMyAnnotation subMyAnnotation = null; MyAnnotation myAnnotation = null; MyAnnotation myAnnotation1 = null; try { subMyAnnotation = AnnotationUtils.getAnnotation(this.getClass().getMethod("test"), SubMyAnnotation.class); myAnnotation = AnnotationUtils.getAnnotation(this.getClass().getMethod("test"), MyAnnotation.class); myAnnotation1 = AnnotatedElementUtils.getMergedAnnotation(this.getClass().getMethod("test"), MyAnnotation.class); } catch (NoSuchMethodException e) { e.printStackTrace(); } return "loation(sub):" + subMyAnnotation.location() + "\n" + "location:" + myAnnotation.location() + "\n" + "location:" + myAnnotation1.location(); }}
测试
前端访问:http://localhost:8080/hello/test
结果
loation(sub):location(my)
location:
location:location(my)
用法3:继承父注解的属性,并重写属性名
简介
子注解的属性值的读写,其实是对父注解的属性值的读写。(对重写的属性来说)
无论指明设置哪个属性名设置属性值,另一个属性名也是同样属性值,不可以缺省属性名。
若两个都指明属性值,要求值必须相同,否则会报错。
代码
注解
package com.example.annotation; import org.springframework.core.annotation.AliasFor; import java.lang.annotation.*; @Retention(RetentionPolicy.RUNTIME)@Target({ElementType.METHOD, ElementType.TYPE})@Documented@Inheritedpublic @interface MyAnnotation { @AliasFor(attribute = "location") String value() default ""; @AliasFor(attribute = "value") String location() default "";}
package com.example.annotation; import org.springframework.core.annotation.AliasFor; import java.lang.annotation.*; @Retention(RetentionPolicy.RUNTIME)@Target({ElementType.METHOD, ElementType.TYPE})@Documented@Inherited@MyAnnotationpublic @interface SubMyAnnotation { @AliasFor(attribute = "value", annotation = MyAnnotation.class) String subValue() default ""; @AliasFor(attribute = "location", annotation = MyAnnotation.class) String subLocation() default ""; // subLocation属性写成下边这两种结果是一样的// @AliasFor(attribute = "value", annotation = MyAnnotation.class)// String subLocation() default ""; // @AliasFor(value = "location", annotation = MyAnnotation.class)// String subLocation() default "";//}
控制器
package com.example.controller; import com.example.annotation.MyAnnotation;import com.example.annotation.SubMyAnnotation;import org.springframework.core.annotation.AnnotatedElementUtils;import org.springframework.core.annotation.AnnotationUtils;import org.springframework.web.bind.annotation.RequestMapping;import org.springframework.web.bind.annotation.RestController; @RestController@RequestMapping("/hello")public class HelloController { @SubMyAnnotation(subValue = "subLocation")// @SubMyAnnotation(subLocation = "subLocation") //这个与上边结果相同// @SubMyAnnotation("subLocation") //缺省属性名会报错 @RequestMapping("/test") public String test() { SubMyAnnotation subMyAnnotation = null; MyAnnotation myAnnotation = null; MyAnnotation myAnnotation1 = null; try { subMyAnnotation = AnnotationUtils.getAnnotation(this.getClass().getMethod("test"), SubMyAnnotation.class); myAnnotation = AnnotationUtils.getAnnotation(this.getClass().getMethod("test"), MyAnnotation.class); myAnnotation1 = AnnotatedElementUtils.getMergedAnnotation(this.getClass().getMethod("test"), MyAnnotation.class); } catch (NoSuchMethodException e) { e.printStackTrace(); } return "subValue:" + subMyAnnotation.subValue() + ";subLoation:" + subMyAnnotation.subLocation() + "\n" + "value:" + myAnnotation.value() + ";location:" + myAnnotation.location() + "\n" + "value:" + myAnnotation1.value() + ";location:" + myAnnotation1.location(); }}
测试
前端访问:http://localhost:8080/hello/test
结果
subValue:subLocation;subLoation:subLocation
value:;location:
value:subLocation;location:subLocation
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