Java自學-註解與反射(4)

1、獲取註解資訊

package lesson01;

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

/**
 * Author: Gu Jiakai
 * Date: 2021/9/4 21:19
 * FileName: Test12
 * Description:
 */
//練習反射操作註解
public class Test12 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
        Class c1 = Class.forName("lesson01.Student2");
        //通過反射獲得註解
        Annotation[] annotations = c1.getAnnotations();
        for (Annotation annotation : annotations) {
            System.out.println(annotation);
        }

        //獲得註解的value的值。
        TableKai annotation = (TableKai)c1.getAnnotation(TableKai.class);
        String value = annotation.value();
        System.out.println(value);

        //獲得類指定的註解
        Field f = c1.getDeclaredField("name");
        FieldKai annotation1 = f.getAnnotation(FieldKai.class);
        System.out.println(annotation1.columnName());
        System.out.println(annotation1.type());
        System.out.println(annotation1.length());

    }
}

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

    public Student2() {
    }

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

    public String getName() {
        return name;
    }

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

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

//類名的註解。
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@interface TableKai{
    String value();
}

//屬性的註解
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@interface FieldKai{
    String columnName();
    String type();
    int length();
}
 

2、本章小結

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