深入学习java笔记-19.注解与反射

从JDK5加入注解和反射后，java的编程方式具有了动态性，有了一点python语言那种编码的快感，来一个小Demo

MyAnnotationClass.java

package spring_annotation.annotation;

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

@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotationClass {
//    String name();
    String name() default "";
//    String type();
    String type() default "";
}

MyAnnotationFiled.java

package spring_annotation.annotation;


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

@Target(value = ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
public @interface MyAnnotationFiled {

    String value() default "";

    String type() default "";

    int length() default 0;

}

TestObject.java

package spring_annotation.pojo;

import lombok.*;
import lombok.experimental.Accessors;
import spring_annotation.annotation.MyAnnotationClass;
import spring_annotation.annotation.MyAnnotationFiled;


@Data
@AllArgsConstructor
@NoArgsConstructor
@Accessors(chain = true)
@Builder
@MyAnnotationClass(name = "t_object", type = "innodb")
public class TestObject {

    @MyAnnotationFiled(value = "id", type = "int", length = 10)
    private Integer id;

    @MyAnnotationFiled(value = "name", type = "varchar", length = 20)
    private String name;

    @MyAnnotationFiled(value = "age", type = "int", length = 10)
    private Integer age;

}

Annotation.java

import org.junit.jupiter.api.Test;
import spring_annotation.annotation.MyAnnotationClass;
import spring_annotation.annotation.MyAnnotationFiled;
import spring_annotation.pojo.TestObject;

import java.lang.annotation.Annotation;
import java.lang.reflect.Field;

public class AnnotationTest {

    @Test
    public void test01() throws ClassNotFoundException, IllegalAccessException,
            InstantiationException, NoSuchFieldException {
        String path = "spring_annotation.pojo.TestObject";
        Class clazz = Class.forName(path);
        TestObject testObject = (TestObject) clazz.newInstance();
        System.out.println(testObject.setId(1).setName("zzz").setAge(20));

        Annotation[] declaredAnnotations = clazz.getDeclaredAnnotations();
        for (Annotation declaredAnnotation : declaredAnnotations) {
            System.out.println(declaredAnnotation);
        }

        MyAnnotationClass annotation = (MyAnnotationClass) clazz.getAnnotation(MyAnnotationClass.class);
        System.out.println(annotation.name()+"--->"+annotation.type());

        Field f = clazz.getDeclaredField("id");
        MyAnnotationFiled af = f.getAnnotation(MyAnnotationFiled.class);
        System.out.println(af.value()+"--->"+af.type()+"--->"+af.length());
    }
}