定義一個類名的註解

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

定義一個屬性的註解

//屬性的註解
@Target(ElementType.FIELD)
@Retention(RetentionPolicy.RUNTIME)
@interface FieldLite {
    String colunName();

    String type();

    int length();
}

定義一個Student實體類 模擬資料庫

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

測試反射獲取註解資訊

public class Demo4 {

    public static void main(String[] args) throws ClassNotFoundException, NoSuchFieldException {
        Class c1 = Class.forName("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
        TableLite tableLite = (TableLite) c1.getAnnotation(TableLite.class);
        String value = tableLite.value();
        System.out.println(value);

        // 獲得類指定的註解
        Field f = c1.getDeclaredField("name");
        FieldLite annotation = f.getAnnotation(FieldLite.class);
        System.out.println(annotation.colunName());
        System.out.println(annotation.type());
        System.out.println(annotation.length());
    }

}

控制檯結果輸出