设计模式之观察者模式

被观察者

/**
 * @Author: chuan.bai
 * @Description  邮件发送人
 * @Date: Created on 15:03 2021/4/1
 * @Modified By:
 */
public interface EmailSender {

    /**
     * 新增需要发送邮件的人
     * @param emailReceiver
     */
    void addUser(EmailReceiver emailReceiver);

    /**
     * 删除需要发送邮件的人
     * @param emailReceiver
     */
    void removeUser(EmailReceiver emailReceiver);

    /**
     * 通知收件人接收邮件
     * @param msg
     */
    void sendMsgToUser(String msg);
}

观察者抽象

/**
 * @Author: chuan.bai
 * @Description  邮件收件人
 * @Date: Created on 15:03 2021/4/1
 * @Modified By:
 */
public interface EmailReceiver {


    /**
     * 接收邮件
     * @param msg
     */
    void receiveEmailMsg(String name,String msg);
}

观察者的实现类

/**
 * @Author: chuan.bai
 * @Description   收件人
 * @Date: Created on 15:20 2021/4/1
 * @Modified By:
 */
public class ReceiverUser implements EmailReceiver{

    /**
     * 收件人姓名
     */
    private String name;

    public ReceiverUser(String name) {
        this.name = name;
    }


    @Override
    public void receiveEmailMsg(String name, String msg) {
        System.out.println("用户" + this.name + "收到"+name+"的邮件内容为：" + msg);
    }
}

被观察者的实现

/**
 * @Author: chuan.bai
 * @Description
 * @Date: Created on 15:15 2021/4/1
 * @Modified By:
 */
public class SenderUser implements EmailSender{

    /**
     * 声明收件人列表
     */
    private List<EmailReceiver> receiverList;
    /**
     * 发件人姓名
     */
    private String name;

    public SenderUser(String name) {
        this.receiverList = new ArrayList<>();
        this.name = name;
    }

    @Override
    public void addUser(EmailReceiver emailReceiver) {
        receiverList.add(emailReceiver);
    }

    @Override
    public void removeUser(EmailReceiver emailReceiver) {
        receiverList.remove(emailReceiver);
    }

    @Override
    public void sendMsgToUser(String msg) {
        //遍历收件人列表 ，向他们群发邮件
        for (EmailReceiver emailReceiver : receiverList) {
            emailReceiver.receiveEmailMsg(this.name,msg);
        }
    }
}

客户端

/**
 * @Author: chuan.bai
 * @Description  邮件客户端
 * @Date: Created on 15:26 2021/4/1
 * @Modified By:
 */
public class EmailClient {

    public static void main(String[] args) {
        SenderUser senderUser = new SenderUser("系统用户");
        ReceiverUser receiverUser1 = new ReceiverUser("jack");
        senderUser.addUser(receiverUser1);
        senderUser.sendMsgToUser("发的第一邮件");
        ReceiverUser receiverUser2 = new ReceiverUser("lucy");
        //加入收件人2 也作为收件人列表
        senderUser.addUser(receiverUser2);
        senderUser.sendMsgToUser("发的第二封邮件");


    }
}

结果

用户jack收到系统邮箱的邮件内容为：发的第一邮件
用户jack收到系统邮箱的邮件内容为：发的第二封邮件
用户lucy收到系统邮箱的邮件内容为：发的第二封邮件

同时是观察者和被观察者

/**
 * @Author: chuan.bai
 * @Description  邮件收发人 （既能收邮件又能发邮件）
 * @Date: Created on 15:36 2021/4/1
 * @Modified By:
 */
public class ReceiverAndSender implements EmailSender,EmailReceiver{



    private List<EmailReceiver> receiverUserList;
    private String name;



    public ReceiverAndSender(String name) {
        this.receiverUserList = new ArrayList<>();
        this.name = name;
    }

    @Override
    public void receiveEmailMsg(String name, String msg) {
        System.out.println("用户" + this.name + "收到"+name+"的邮件内容为：" + msg);
    }

    @Override
    public void addUser(EmailReceiver emailReceiver) {
        receiverUserList.add(emailReceiver);
        System.out.println("收件人增加");
    }

    @Override
    public void removeUser(EmailReceiver emailReceiver) {
        receiverUserList.remove(emailReceiver);
        System.out.println("收件人剔除");
    }

    @Override
    public void sendMsgToUser(String msg) {
        //遍历收件人列表 ，向他们群发邮件
        for (EmailReceiver emailReceiver : receiverUserList) {
            emailReceiver.receiveEmailMsg(this.name,msg);
        }
    }


}

客户端

/**
 * @Author: chuan.bai
 * @Description
 * @Date: Created on 15:50 2021/4/1
 * @Modified By:
 */
public class EmailClient2 {

    public static void main(String[] args) {
        ReceiverAndSender jack = new ReceiverAndSender("jack");
        ReceiverAndSender bill = new ReceiverAndSender("bill");
        ReceiverAndSender lucy = new ReceiverAndSender("lucy");
        jack.addUser(bill);
        jack.addUser(lucy);
        jack.sendMsgToUser("aaa");

        bill.addUser(jack);
        bill.addUser(lucy);
        bill.sendMsgToUser("cc");

        lucy.addUser(bill);
        lucy.addUser(jack);
        lucy.sendMsgToUser("dd");

    }
}

执行结果

收件人增加
收件人增加
用户bill收到jack的邮件内容为：aaa
用户lucy收到jack的邮件内容为：aaa
收件人增加
收件人增加
用户jack收到bill的邮件内容为：cc
用户lucy收到bill的邮件内容为：cc
收件人增加
收件人增加
用户bill收到lucy的邮件内容为：dd
用户jack收到lucy的邮件内容为：dd