十四、反射操作注解

模拟ORM的类注解和属性注解

 

//模拟ORM
public class Demo11 {
    public static void main(String[] args) {
        Class clazz = Role.class;

        //获取类的注解信息
        Annotation[] classAnnotations = clazz.getAnnotations();
        for (Annotation classAnnotation : classAnnotations) {
            System.out.println(classAnnotation);
        }

        //单独打印name的值
        Table table = (Table) clazz.getAnnotation(Table.class);
        System.out.println(table.name());

        System.out.println("==================");

        //获取属性的注解信息
        Field[] fields = clazz.getDeclaredFields();
        for (Field field : fields) {
            Annotation[] fieldAnnotations = field.getAnnotations();
            for (Annotation fieldAnnotation : fieldAnnotations) {
                System.out.println(fieldAnnotation);
            }
        }
        
        //单独获取
        for (Field field : fields) {
            Column column = (Column) field.getAnnotation(Column.class);
            System.out.println("name="+column.name()+",type="+column.type()+",length="+column.length());;
        }
    }
}

@Table(name = "user")
class Role {

    @Column(name = "id",type = "int",length = 10)
    Integer id;

    @Column(name = "name",type = "char",length = 255)
    String name;

    @Column(name = "type",type = "char",length = 2)
    String type;

}


@Target(ElementType.TYPE)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@interface Table {

    String name();
}


@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@Documented
@Inherited
@interface Column {

    String name();

    String type();

    int length();

}