反射与注解

package cn.notfound945;

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

public class Main {

    public static void main(String[] args) {
        Class user = null;
        try {
            user = Class.forName("cn.notfound945.User");
            Annotation[] annotations = user.getAnnotations();
            for (Annotation annotation : annotations) {
                System.out.println(annotation);
            }
//            获取的注解 value
            table annotation = (table)user.getAnnotation(table.class);
            System.out.println(annotation.value());
//            获取指定类的注解
            Field userDeclaredField = user.getDeclaredField("id");
            field annotation1 = userDeclaredField.getAnnotation(field.class);
            
            System.out.println(annotation1.col());
            System.out.println(annotation1.type());
            System.out.println(annotation1.length());

        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

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

@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@interface field {
    String col();
    String type();
    int length();
}

@table("db_tab")
class User {
    @field(col = "db_id", type = "int", length = 10)
    private int id;
    @field(col = "db_id", type = "varchar", length = 10)
    private String name;
    @field(col = "db_password", type = "varchar", length = 6)
    private String password;

    public User(int id, String name, String password) {
        this.id = id;
        this.name = name;
        this.password = password;
    }

    public int getId() {
        return id;
    }

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

    public String getName() {
        return name;
    }

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

    public String getPassword() {
        return password;
    }

    public void setPassword(String password) {
        this.password = password;
    }

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