java - 线程不会自动关闭

Question

即使从 run() 返回后，启动的线程看起来也没有关闭。在 Netbeans 的左侧面板中，它显示了许多“pool-xx-thread-1-running”的数量，并且每次执行线程时都会增加。下面是我的代码:

//监听操作 client.subscribe("/location/#", new IMqttMessageListener() { public void messageArrived(最终字符串主题，最终MqttMessage消息)抛出异常{ 最终字符串有效负载 = new String(message.getPayload());

            System.out.println("Received operation " + payload);
            if (payload.startsWith("{\"location\":")) {
                // execute the operation in another thread to allow the MQTT client to
                // finish processing this message and acknowledge receipt to the server
                Executors.newSingleThreadScheduledExecutor().execute(new Runnable() {
                    public void run() {
                        if(payload.equals("")) return;

                        try {
                            JsonObject jsonObject = new Gson().fromJson(payload, JsonObject.class);
                            String fixTime="", vehicleid="", deviceTime="", lat="", lon="", speed="",alt="", accuracy="", bearing="";
                            try{
                                String locationStr=jsonObject.get("location").toString();
                                locationStr=locationStr.substring(1, locationStr.length()-1).trim();
                                locationStr=locationStr.replace("\\", "");
                                JsonObject locationJson = new Gson().fromJson(locationStr, JsonObject.class);
                                try{
                                    long millis = Long.parseLong(locationJson.get("mTime").toString());
                                    Calendar cal = Calendar.getInstance();
                                    cal.setTimeInMillis(millis);
                                    fixTime = df.format(cal.getTime());
                                }catch(Exception ex){

                                }

                                lat=locationJson.get("mLatitude").toString();
                                lon=locationJson.get("mLongitude").toString();
                                alt=locationJson.get("mAltitude").toString();
                                speed=locationJson.get("mSpeed").toString();
                                accuracy=locationJson.get("mAccuracy").toString();
                                bearing=locationJson.get("mBearing").toString();
                            }catch(Exception ex){
                                ex.printStackTrace();
                            }

                            try{
                                String entityStr = jsonObject.get("entity").toString();
                                JsonObject entityJson = new Gson().fromJson(entityStr, JsonObject.class);
                                vehicleid = entityJson.get("id").toString();
                                vehicleid = vehicleid.replace("\"", "");
                            }catch(Exception ex){
                                ex.printStackTrace();
                            }

                            try{
                                String headerStr=jsonObject.get("header").toString();
                                JsonObject headerJson = new Gson().fromJson(headerStr, JsonObject.class);
                                String deviceTimeMsStr = headerJson.get("timestamp").toString();
                                long msTime = Long.parseLong(deviceTimeMsStr);
                                Calendar cal = Calendar.getInstance();
                                cal.setTimeInMillis(msTime);
                                deviceTime = df.format(cal.getTime());
                            }catch(Exception ex){
                                ex.printStackTrace();
                            }

                            Connection conn = null;
                            Statement stmt = null;
                            try{
                                String SQL = "INSERT INTO positions(protocol, deviceid, devicetime, fixtime, valid, latitude, longitude, altitude, speed, course, address, attributes, accuracy, network)";
                                SQL += " VALUES('osmand',(SELECT id FROM devices WHERE uniqueid = '" + vehicleid + "'),'" + deviceTime + "','" + fixTime + "',1," + lat + "," + lon + "," + alt + "," + speed + "," + bearing + ",'',''," + accuracy + ",'')";

                                Class.forName("com.mysql.jdbc.Driver");
                                conn =DriverManager.getConnection(MYSQL_SERVERURL, MYSQL_USERID, MYSQL_PASSWORD);
                                stmt = conn.createStatement();
                                stmt.executeUpdate(SQL);
                                System.out.println("Executed " + SQL);
                                return;
                            }catch(Exception ex){
                                ex.printStackTrace();
                            }finally {
                                try {
                                    if(stmt != null)
                                        conn.close();
                                } catch(SQLException se) {
                                }
                                try {
                                    if(conn != null)
                                        conn.close();
                                } catch(SQLException se) {
                                    se.printStackTrace();
                                }
                            }
                        }catch(Exception ex){
                            ex.printStackTrace();
                        }
                        finally{
                            return;
                        }
                    }
                });
            }
        }
    });

screenshot

Answer 1

我建议您学习 Oracle 的执行器教程。并在 Stack Overflow 上搜索有关此主题的许多现有问题和解答。

仅创建执行器服务一次

不要重复调用Executors.newSingleThreadScheduledExecutor()。每次调用都会创建一个线程池。你永远不会关闭它们。即使您的应用程序终止，线程也会继续运行。

您应该在应用中仅实例化执行程序服务一次(通常)。然后将返回的 ScheduledExecutorService 对象保存在应用中的某个位置。

当您有一个任务要在后台线程上运行时，检索现有对象并安排该任务。

最终您必须关闭执行程序(及其支持线程池)。

有关更多讨论，请参阅this Answer我的一个非常类似的问题。

ScheduledExecutorService 用于调度

您没有延迟安排任务。所以你不需要 ScheduledExecutorService。

您只需要一个具有 submit 方法的 ExecutorService 。