继承关系下怎样使用Builder 模式

以微信图文消息推送为例

需要组装的消息体

 

{
"touser" : "UserID1|UserID2|UserID3",
"toparty" : "PartyID1|PartyID2",
"totag" : "TagID1 | TagID2",
"msgtype" : "text",
"agentid" : 1,
"text" : {
"content" : "你的快递已到，请携带工卡前往邮件中心领取。\n出发前可查看<a href=\"http://work.weixin.qq.com\">邮件中心视频实况</a>，聪明避开排队。"
},
"safe":0
}

一、基础的字段放到父类 BaseMessage 中

public class BaseMessage {
    /**
     * 消息类型:text、textcard、
     */
    private String msgtype;
    /**
     * 应用id
     */
    private Integer agentid;
    /**
     * 加密方式。默认不传或传0传2不进行任何解密处理直接发送文本 。传1对整个文本内容将进行base64解密。传3对整个文本内容进行UrlEncode编码
     */

    private String touser;
    /**
     * 部门ID列表，多个接收者用‘|’分隔，最多支持100个。部门id请查询OA接口获取部门id。注：使用该参数会对整个部门的全部人员进行群发，请慎重使用
     */
    private String toparty;
    /**
     * 标签ID列表，多个接收者用‘|’分隔，最多支持100个。当touser为@all时忽略本参数。
     */
    private String totag;
    /**
     * 表示是否是保密消息，0表示否，1表示是，默认0
     */
    private Integer safe;

    public BaseMessage(String msgtype) {
        this.msgtype = msgtype;
    }


    public BaseMessage() {
    }

    public <T extends BaseMessageBuilder> BaseMessage(BaseMessageBuilder builder) {
        this.msgtype = builder.msgtype;
        this.agentid = builder.agentid;
        this.touser = builder.touser;
        this.toparty = builder.toparty;
        this.totag = builder.totag;
        this.safe = builder.safe;
    }

    public String getMsgtype() {
        return msgtype;
    }

    public Integer getAgentid() {
        return agentid;
    }

    public String getTouser() {
        return touser;
    }

    public String getToparty() {
        return toparty;
    }

    public String getTotag() {
        return totag;
    }

    public Integer getSafe() {
        return safe;
    }

    /**
     * 在父类中使用泛型 根据调用的子类不同 返回子类对应的Builder
     */
    public static class BaseMessageBuilder<T extends BaseMessageBuilder> {
        private String msgtype;
        private Integer agentid;
        private String touser;
        private String toparty;
        private String totag;
        private Integer safe;

        public BaseMessageBuilder(String msgtype) {
            this.msgtype = msgtype;
        }

        public T agentid(Integer agentid) {
            this.agentid = agentid;
            return (T) this;
        }

        public T touser(String touser) {
            this.touser = touser;
            return (T) this;
        }

        public T toparty(String toparty) {
            this.toparty = toparty;
            return (T) this;
        }

        public T totag(String totag) {
            this.totag = totag;
            return (T) this;
        }

        public T safe(Integer safe) {
            this.safe = safe;
            return (T) this;
        }
    }
}

二、 不同种类型的消息只需要继承父类 然后加上独有字段

public class WorkWeiXinContentText extends BaseMessage {

    private static final String MSGTYPE = "text";
    private Text text;

    public WorkWeiXinContentText(String content) {
        super(MSGTYPE);
        this.text = new Text(content);
    }

    public WorkWeiXinContentText(WorkWeiXinContentTextBuilder builder) {
        /**
         * 调用的是父类的构造方法  public <T extends BaseMessageBuilder> BaseMessage(BaseMessageBuilder builder)
         */
        super(builder);
        this.text = builder.text;
    }

    public static WorkWeiXinContentTextBuilder builder() {
        return new WorkWeiXinContentTextBuilder(MSGTYPE);
    }

    public Text getText() {
        return text;
    }

    /**
     * 如果先赋值子类的属性 则返回的是子类的WorkWeiXinContentTextBuilder ,如果先赋值父类的属性 不加泛型的话  返回的是父类的 BaseMessageBuilder 无法转换为子类对象 WorkWeiXinContentText
     */
    public static class WorkWeiXinContentTextBuilder extends BaseMessageBuilder<WorkWeiXinContentTextBuilder> {
        private Text text;

        WorkWeiXinContentTextBuilder(String msgtype) {
            super(msgtype);
        }

        public WorkWeiXinContentTextBuilder text(Text text) {
            this.text = text;
            return this;
        }

        public WorkWeiXinContentText build() {
            return new WorkWeiXinContentText(this);
        }
    }

}

public class Text {
    private String content;

    public Text(String content) {
        this.content = content;
    }

    public Text() {
    }

    public String getContent() {
        return content;
    }

    public void setContent(String content) {
        this.content = content;
    }

}

三、使用

    public static void main(String[] args) {
        String content="你的快递已到，请携带工卡前往邮件中心领取。\n出发前可查看<a href=\"http://work.weixin.qq.com\">邮件中心视频实况</a>，聪明避开排队。";
        WorkWeiXinContentText msgBody =WorkWeiXinContentText.builder()
                .touser("UserID1|UserID2|UserID3")
                .toparty("PartyID1|PartyID2")
                .totag("TagID1 | TagID2")
                .agentid(1)
                .safe(0)
                .text(new Text(content))
                .build();
        // do something

    }