获取注解信息(重点）

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package com.kuang.reflection;
// 练习反射操作注解

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

public class Test12 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
        Class c1 = Class.forName("com.kuang.reflection.Student2");

        // 通过反射获得注解
        Annotation[] annotations = c1.getAnnotations();
        for (Annotation annotation : annotations) {
            System.out.println(annotation);
        }

        // 获得注解value的值
        Tablekuang tablekuang= (Tablekuang)c1.getAnnotation(Tablekuang.class);
        String value = tablekuang.value();
        System.out.println(value);

        // 获得指定注解
        Field f = c1.getDeclaredField("name");  // 一个属性
        Fieldkuang annotation = f.getAnnotation(Fieldkuang.class); // 获得属性注解
        System.out.println(annotation.columnNam());
        System.out.println(annotation.type());
        System.out.println(annotation.length());


    }
}

@Tablekuang("db_student")
class Student2{
    @Fieldkuang(columnNam = "db_name",type = "varchar",length = 3)
    private String name;
    @Fieldkuang(columnNam = "db_id", type = "int", length = 10)
    private  int id;
    @Fieldkuang(columnNam = "db_age", type = "int", length = 3)
    private  int age;

    public Student2() {
    }

    public Student2(String name, int id, int age) {
        this.name = name;
        this.id = id;
        this.age = age;
    }

    public String getName() {
        return name;
    }

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

    @Override
    public String toString() {
        return "Student2{" +
                "name='" + name + '\'' +
                ", id=" + id +
                ", age=" + age +
                '}';
    }
}

// 类名的注解
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.TYPE)
@interface Tablekuang{
    String value();
}

// 属性的注解
@Retention(RetentionPolicy.RUNTIME)
@Target(ElementType.FIELD)
@interface Fieldkuang{
    String columnNam();
    String type();
    int length();
}