反射操作注解

反射操作注解

• getAnnotations

• getAnnotation

练习：ORM

• 了解什么是ORM?

  • Object relationship Mapping--> 对象关系映射

  • 类和表结构对应

  • 属性和字段对应

  • 对象和记录对应

• 要求：利用注解和反射完成类和表结构的映射关系

package com.hua.reflection;

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

//练习反射操作注解
public class Test12 {
    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
        //通过反射获取注解
        Class c1 = Class.forName("com.hua.test08.Cat");
        Annotation[] annotations = c1.getAnnotations();
        for (Annotation annotation : annotations) {
            System.out.println(annotation);
        }

        //获得注解的value的值
        Tablehua tablehua = (Tablehua)c1.getAnnotation(Tablehua.class);
        String value = tablehua.value();
        System.out.println(value);

        //获得类指定的注解
        Field f = c1.getDeclaredField("name");
        Fieldhua annotation = f.getAnnotation(Fieldhua.class);
        System.out.println(annotation.columnName());
        System.out.println(annotation.type());
        System.out.println(annotation.length());
    }
}
@Tablehua("db_cat")
class Cat{
    @Fieldhua(columnName = "db_name",type = "varchar",length = 10)
    private String name;
    @Fieldhua(columnName = "db_id",type = "int",length = 10)
    private int id;
    @Fieldhua(columnName = "db_age",type = "int",length = 10)
    private int age;

    public Cat() {
    }

    public Cat(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 "Cat{" +
                "name='" + name + '\'' +
                ", id=" + id +
                ", age=" + age +
                '}';
    }
}

//类名的注解
@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@interface Tablehua{
    String value();
}
//属性的注解
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@interface Fieldhua{
    String columnName();
    String type();
    int length();
}