Java基础之理解Annotation

Java基础之理解Annotation

学习了：https://www.cnblogs.com/mandroid/archive/2011/07/18/2109829.html

学习了：https://www.jianshu.com/p/ca7f22b4b751

@Retetion决定运行的事件；

@Target说明注解针对的对象；

jdk方面的说明：https://docs.oracle.com/javase/tutorial/java/annotations/predefined.html

可以查看@HystrixCommand源码，

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package com.netflix.hystrix.contrib.javanica.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Inherited;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Inherited
@Documented
public @interface HystrixCommand {
    String groupKey() default "";

    String commandKey() default "";

    String threadPoolKey() default "";

    String fallbackMethod() default "";

    HystrixProperty[] commandProperties() default {};

    HystrixProperty[] threadPoolProperties() default {};

    Class<? extends Throwable>[] ignoreExceptions() default {};

    ObservableExecutionMode observableExecutionMode() default ObservableExecutionMode.EAGER;
}

Annotation可以包含默认值，字符串默认值是“”，对象默认值是{}；

而且Annotation中可以包含Annotation数组，HystrixProperty也是一个Annotation；

//
// Source code recreated from a .class file by IntelliJ IDEA
// (powered by Fernflower decompiler)
//

package com.netflix.hystrix.contrib.javanica.annotation;

import java.lang.annotation.Documented;
import java.lang.annotation.ElementType;
import java.lang.annotation.Retention;
import java.lang.annotation.RetentionPolicy;
import java.lang.annotation.Target;

@Target({ElementType.METHOD})
@Retention(RetentionPolicy.RUNTIME)
@Documented
public @interface HystrixProperty {
    String name();

    String value();
}