SpringBoot通知机制的实现

1. 快速创建maven管理的SpringBoot项目

• 1、访问 http://start.spring.io/
• 2、 选择构建工具Maven Project、Spring Boot版本1.3.6以及一些工程基本信息，点击“Switch to the full version.”java版本选择1.7；
• 3、点击Generate Project下载项目压缩包；
• 4、解压后，使用eclipse，Import -> Existing Maven Projects -> Next ->选择解压后的文件夹-> Finsh，OK done!
• 使用IDEA的话，按如下步骤导入项目： File -> New -> Project fron Existing Sourses -> 选择解压后的直接包含pom.xml文件的demo文件夹，OK -> 选第二项Import project from external model, 选maven，Next -> Next -> 勾选左下角Open Project Structure after import, Next -> Next -> Finish -> 选Yes -> OK -> 大功告成！
  （记录自己踩过的坑：一定要选直接包含pom.xml的demo文件夹，一开始选择直接解压后的demo文件夹，结果找不到可以导入的maven项目。 ）
  
• 5、 运行刚导入的项目，访问localhost:8080/hello, 看到页面显示Hello World。
• 6、 在这个demo的基础上进行开发。

2. 通知机制的流程

1、客户端向server订阅通知，订阅信息包括通知类型（notificationTypes）、过滤条件（filteringCriteria）、订阅者地址（subscriberUri）和 managerId。

• 请求数据以json格式发送，因此在服务端用@RequestBody Map request 来处理请求中的json数据，创建JSONObject 对象，从而根据参数名获取请求中传入的参数值。
  服务端代码如下：

@RequestMapping("/notifications")
    public void subscribeNotification(@RequestBody Map request, HttpServletResponse response)
            throws ServletException, IOException, JSONException {

        System.out.println("Enter localhost:8083/notifications. " );

        JSONObject jsonObject = new JSONObject(request);  
        String subscriptionId = (String) jsonObject.get("subscriptionId");  // 通过JSONObject 对象获取请求中传入的参数值
        String notificationType = (String) jsonObject.get("notificationType");
        String filteringCriteria = (String) jsonObject.get("filteringCriteria");
        String managerId = (String) jsonObject.get("managerId");

        System.out.println("subscriptionId=" + subscriptionId + ", notificationType=" + notificationType + ", filteringCriteria=" + filteringCriteria + ", managerId=" + managerId );

        // some code... 省略了存数据库的操作

        response.setHeader("Location", "http://localhost:8083/notifications/0101");  // 通过response.setHeader()方法设置响应头
        PrintWriter out = response.getWriter();
        String result = "Success to Subscribe a notification! ";
        out.write(result);
    }

• 服务端端口设为8083，默认是8080，可以通过在resources 下的application.properties文件里加一条语句server.port=8083 修改为其他端口号。

Postman的接口测试结果如下：

2、服务端将通知发送给客户端。请求信息包括订阅Id(subscriptionId)、通知类型（NotificationType）、发送者Id(producerId)、消息（message）。首先根据subscriptionId 从数据库查找到该订阅的通知类型、过滤条件和订阅者地址，然后判断该通知是否符合订阅条件，符合则将该通知发送给订阅者。

服务端代码如下：

@RequestMapping("/sendNotification")
    public void sendNotification(@RequestBody Map request, HttpServletResponse response)
            throws ServletException, IOException, JSONException {

        System.out.println("request:" + request);

        JSONObject jsonObject = new JSONObject(request);
        System.out.println("jsonObject:" + jsonObject);
        String subscriptionId = (String) jsonObject.get("subscriptionId");
        String notificationType = (String) jsonObject.get("notificationType");
        String producerId = (String) jsonObject.get("producerId");
        String alarmType = (String) jsonObject.getJSONObject("message").get("alarmType");
        System.out.println("subscriptionId=" + subscriptionId + ", notificationType=" + notificationType + ", producerId=" + producerId + ", alarmType=" + alarmType );

        //  some code...  查询数据库（省略）

        // 模拟数据库查询结果
        String getNotificationType = "";
        String getAlarmType = "";
        String getsubscriberUri = "";
        if(subscriptionId.equals("http://localhost:8081/notifications/0101")){
            getNotificationType = "alarm";
            getAlarmType = "01";
            getsubscriberUri = "http://localhost:8081/notifications/001";
        }
        if(subscriptionId.equals("http://localhost:8081/notifications/0102")){
            getNotificationType = "alarm";
            getAlarmType = "02";
            getsubscriberUri = "http://localhost:8082/notifications/001";
        }

        // 判断该通知是否符合订阅条件
        String subscribeURL = "";
        if(notificationType.equals(getNotificationType) && alarmType.equals(getAlarmType)){
            subscribeURL = getsubscriberUri;
        } else return;

        // 建立连接，将通知发送给订阅者
        HttpURLConnection subscribeConnection = null;
        StringBuffer responseBuffer = new StringBuffer();
        try{
            URL getsubscribeURL = new URL(subscribeURL);
            subscribeConnection = (HttpURLConnection) getsubscribeURL.openConnection(); // 建立连接
            subscribeConnection.setDoOutput(true);
            subscribeConnection.setDoInput(true);
            subscribeConnection.setRequestMethod("POST");
            subscribeConnection.setRequestProperty("Accept-Charset", "utf-8");
            subscribeConnection.setRequestProperty("Content-Type", "application/json");
            subscribeConnection.setRequestProperty("Charset", "UTF-8");
            byte[] data = (jsonObject.toString()).getBytes();
            subscribeConnection.setRequestProperty("Content-Length", String.valueOf(data.length));

            // 开始连接请求
            subscribeConnection.connect();
            OutputStream out = subscribeConnection.getOutputStream();
            // 写入请求的字符串
            out.write((jsonObject.toString()).getBytes()); // 发送json数据
            out.flush();
            out.close();
        }catch (IOException e) {
        }
        if (subscribeConnection.getResponseCode() == 200) {    // 若响应码为200，则通知订阅成功
            System.out.println("Success to send the notification." );
            String readLine;
            BufferedReader responseReader = new BufferedReader(new InputStreamReader(
                    subscribeConnection.getInputStream(), "utf-8"));
            while ((readLine = responseReader.readLine()) != null) {
                responseBuffer.append(readLine);
            }
            System.out.println("Http Response:" + responseBuffer);
            subscribeConnection.disconnect();

            PrintWriter out = response.getWriter();
            out.write(responseBuffer.toString());
        }else return;
    }

订阅者(8081端口)接收通知，代码如下：

@RequestMapping("/notifications/001")
    public void receiveNotification(@RequestBody Map request, HttpServletResponse response)
            throws ServletException, IOException{
        System.out.println("Receive a new notification." );
        System.out.println("request:" + request);

        PrintWriter out = response.getWriter();
        String result = "Success to Subscribe a notification! ";
        out.write(result);
    }

3. 运行过程及结果

首先，用Postman 向服务端（8083端口）发送通知：

服务端结果如下：

订阅者（8081端口）结果如下：

• 附上demo源码地址： https://github.com/bupt-lxl/SpringBoot-Notification