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Spring注解–@AliasFor的使用

简介

本文用示例介绍Spring的@AliasFor(别名)注解的用法。

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。

  1. 其中一个属性名必须是”value”
  2. 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。
  3. 若两个都指明属性值,要求值必须相同,否则会报错。
  4. 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
@Inherited
public @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")
    /*//下边这两种写法结果与上边是相同的
    @MyAnnotation("location")
    @MyAnnotation(location = "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
@Inherited
public @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
@MyAnnotation
public @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

  1. 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)
  2. 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。
  3. 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
@Inherited
public @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
@MyAnnotation
public @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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