获取注解信息

练习：ORM

Object relationship Mapping 对象关系映射

• 类和表对应
• 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

代码

/**
 * @Description 反射操作注解
 * @Author Administrator
 * @Date 2020/12/2 13:39
 */
public class Test12 {

    public static void main(String[] args) throws Exception {

        Class c1 = Class.forName("com.hejin.reflection.Student2");

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

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

        /**
         * 获得类指定的注解
         */
        System.out.println("===================================");
        Field f = c1.getDeclaredField("id");
        Fieldkuang annotation = f.getAnnotation(Fieldkuang.class);
        System.out.println(annotation.columnName());
        System.out.println(annotation.length());
        System.out.println(annotation.type());

    }

}

@Tablekuang("db_student")
class Student2{
    @Fieldkuang(columnName = "db_id",type = "int", length = 10)
    private int id;
    @Fieldkuang(columnName = "db_age",type = "int", length = 10)
    private int age;
    @Fieldkuang(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 + '\'' +
                '}';
    }
}


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

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

结果

@com.hejin.reflection.Tablekuang(value=db_student)
===================================
db_student
===================================
db_id
10
int

Process finished with exit code 0