How to use the @AliasFor annotation in SpringBoot

Usage 1: The attributes of the annotation are aliases for each other

Introduction

It can be annotated to two attributes of the custom annotation, indicating that the two attributes are aliases for each other, that is to say, this The two attributes actually have the same meaning.

• One of the attribute names must be "value"

• No matter which attribute name is specified to set the attribute value, the other attribute name is also the same attribute value, or the default attribute name.

• If both specify attribute values, the required values ​​must be the same, otherwise an error will be reported.

• Use concisely. After using it like this, @MyAnno(location="shanghai") can be written directly as: @MyAnno("shanghai");

The reason for this function:

If the custom annotation has an attribute, and the attribute is named to reflect its meaning, the caller must write the attribute and then set it every time he uses the custom annotation, which is a little troublesome.

Example

Annotation

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 "";
}

Controller

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();
    }
}

Test

Front-end access: http://localhost:8080/hello/test1

Front-end result (value and location are both the same value)

value:location; loation:location

Usage 2. Inherit the attributes of the parent annotation without rewriting the attribute name

Introduction

The reading and writing of the attribute value of the child annotation is actually Read and write the attribute value of the parent annotation. (For inherited properties)

At this time, only inherited property values ​​can be read and written.

Code

Annotations

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 "";
}

Controller

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();
    }
}

Test

Front-end access: http://localhost:8080/hello/test

Result

##loation(sub):location(my)

location:
location:location(my)

Usage 3: Inherit the attributes of the parent annotation and rewrite the attribute name

Introduction

The reading and writing of the attribute value of the child annotation is actually the reading and writing of the attribute value of the parent annotation. (For overridden attributes)

No matter which attribute name is specified to set the attribute value, the other attribute name also has the same attribute value, and the default attribute name cannot be used.

If both specify attribute values, the required values ​​must be the same, otherwise an error will be reported.

Code

Annotations

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 "";
//
}

Controller

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();
    }
}

Test

Front-end access: http://localhost:8080/hello/test

Result

##subValue:subLocation;subLoation:subLocation

value:;location:

value:subLocation;location:subLocation

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