反射和自定义标注

参考：https://blog.csdn.net/qq_42025798/article/details/119422105

package com.bj58;

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

public class TestAnnotation {
    public static void main(String[] args) throws Exception {
        Class c1 = Class.forName("com.bj58.Student");//通过反射获取注解

//        Class c1 = Class.forName("Student");//通过反射获取 类注解数组
        Annotation[] annotations = c1.getAnnotations();
        for (Annotation annotation : annotations) {
            System.out.println(annotation);
        }

        Tabel annotation = c1.getAnnotation(Tabel.class);//获得Student的类注解
        String value = annotation.value();
        System.out.println("类注解："+value);

        //获取类的成员变量的注解
//        Field name = c1.getField("name");//报错 因为权限是private
        Field name = c1.getDeclaredField("name");
        Annotation[] fieldAnnotations = name.getAnnotations();
        for (Annotation fieldAnnotation : fieldAnnotations) {
            System.out.println("Student的 name成员变量的标注："+fieldAnnotation);
        }

        TabelColumn tabelColumn = name.getAnnotation(TabelColumn.class);
        System.out.println(tabelColumn.columnName());
        System.out.println(tabelColumn.type());
        System.out.println(tabelColumn.length());


    }


    //类名注解
    @Target(ElementType.TYPE)
    @Retention(value = RetentionPolicy.RUNTIME)
    @interface Tabel{
        String value();
    }

    //类名注解
    @Target(ElementType.FIELD)
    @Retention(value = RetentionPolicy.RUNTIME)
    @interface TabelColumn{
        String columnName();
        String type();
        int length();
    }


}

@TestAnnotation.Tabel(value = "db_student")
class Student{//这个类不能
    @TestAnnotation.TabelColumn(columnName = "id",type = "int",length = 10)
    private  int id;
    @TestAnnotation.TabelColumn(columnName = "age",type = "age",length = 10)
    private  int age;
    @TestAnnotation.TabelColumn(columnName = "name",type = "varchar",length = 5)
    private String name;

    public Student() {
    }

    public Student(int id, int age, String name) {
        this.id = id;
        this.age = age;
        this.name = name;
    }

    @Override
    public String toString() {
        return "Student{" +
                "id=" + id +
                ", age=" + age +
                ", name='" + name + ''' +
                '}';
    }

    public int getId() {
        return id;
    }

    public void setId(int id) {
        this.id = id;
    }

    public int getAge() {
        return age;
    }

    public void setAge(int age) {
        this.age = age;
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }
}