项目中常量的定义方式

方式一
在常量个数少的时候，通常情况下使用这种方式。

public class MqConstants {public static final String EXCHANGE_1 = "exchange1";public static final String EXCHANGE_2 = "exchange2";public static final String EXCHANGE_3 = "exchange3";public static final String KEY_1 = "key1";public static final String KEY_2 = "key1";public static final String KEY_3 = "key1";
}//使用常量
System.out.println(MqConstants.EXCHANGE_1);

方式二
在一的基础上，当常量个数变多的时，且为了分类，采用如下内部类方式。

public class MqConstants {public static class Exchange{public static final String EXCHANGE_1 = "exchange1";public static final String EXCHANGE_2 = "exchange2";public static final String EXCHANGE_3 = "exchange3";}public static class Key{public static final String KEY_1 = "key1";public static final String KEY_2 = "key1";public static final String KEY_3 = "key1";}
}//使用常量
System.out.println(MqConstants.Exchange.EXCHANGE_1);

方式三
在二的基础上，为了简略写修饰符，即为了不写public static final和public static final，可以把class换成interface。
即采用如下方式

public interface MqConstants {interface Exchange{String EXCHANGE_1 = "exchange1";String EXCHANGE_2 = "exchange2";String EXCHANGE_3 = "exchange3";}interface Key{String KEY_1 = "key1";String KEY_2 = "key1";String KEY_3 = "key1";}
}//使用常量
System.out.println(MqConstants.Exchange.EXCHANGE_1);

以RabbitMq涉及常量为示例

public interface MqConstants {interface Exchange{/*课程有关的交换机*/String COURSE_EXCHANGE = "course.topic";/*订单有关的交换机*/String ORDER_EXCHANGE = "order.topic";/*学习有关的交换机*/String LEARNING_EXCHANGE = "learning.topic";/*信息中心短信相关的交换机*/String SMS_EXCHANGE = "sms.direct";/*异常信息的交换机*/String ERROR_EXCHANGE = "error.topic";/*支付有关的交换机*/String PAY_EXCHANGE = "pay.topic";/*交易服务延迟任务交换机*/String TRADE_DELAY_EXCHANGE = "trade.delay.topic";/*点赞记录有关的交换机*/String LIKE_RECORD_EXCHANGE = "like.record.topic";}interface Queue {String ERROR_QUEUE_TEMPLATE = "error.{}.queue";}interface Key{/*课程有关的 RoutingKey*/String COURSE_NEW_KEY = "course.new";String COURSE_UP_KEY = "course.up";String COURSE_DOWN_KEY = "course.down";String COURSE_EXPIRE_KEY = "course.expire";String COURSE_DELETE_KEY = "course.delete";/*订单有关的RoutingKey*/String ORDER_PAY_KEY = "order.pay";String ORDER_REFUND_KEY = "order.refund";/*积分相关RoutingKey*//* 写回答 */String WRITE_REPLY = "reply.new";/* 签到 */String SIGN_IN = "sign.in";/* 学习视频 */String LEARN_SECTION = "section.learned";/* 写笔记 */String WRITE_NOTE = "note.new";/* 笔记被采集 */String NOTE_GATHERED = "note.gathered";/*点赞的RoutingKey*/String LIKED_TIMES_KEY_TEMPLATE = "{}.times.changed";/*问答*/String QA_LIKED_TIMES_KEY = "QA.times.changed";/*笔记*/String NOTE_LIKED_TIMES_KEY = "NOTE.times.changed";/*短信系统发送短信*/String SMS_MESSAGE = "sms.message";/*异常RoutingKey的前缀*/String ERROR_KEY_PREFIX = "error.";String DEFAULT_ERROR_KEY = "error.#";/*支付有关的key*/String PAY_SUCCESS = "pay.success";String REFUND_CHANGE = "refund.status.change";String ORDER_DELAY_KEY = "delay.order.query";}
}