如何在android应用程序中提供后台服务，即使当app关闭时，也应该继续运行？

Service

public class MyTestService extends IntentService {

private ServerSocket serverSocket;
private Socket tempClientSocket;
Thread serverThread = null;
public static final int SERVER_PORT = 3001;

public MyTestService() {
    // Used to name the worker thread, important only for debugging.
    super("test-service");
}

@Override
public void onCreate() {
    super.onCreate(); // if you override onCreate(), make sure to call super().
    // If a Context object is needed, call getApplicationContext() here.
}

@Override
protected void onHandleIntent(Intent intent) {
    Socket socket;
    try {
        serverSocket = new ServerSocket(SERVER_PORT);
    } catch (IOException e) {
        e.printStackTrace();
    }
    if (null != serverSocket) {
        while (true) {
            try {
                socket = serverSocket.accept();
                try {
                    BufferedReader input = new BufferedReader(new InputStreamReader(socket.getInputStream()));
                    String mess = input.readLine();
                    BufferedWriter bf = new BufferedWriter(new OutputStreamWriter(socket.getOutputStream()));
                    PrintWriter out = new PrintWriter(bf,true);
                    out.println("message recieve");
                    input.close();
                    bf.close();
                    serverSocket.close();

                    NotificationCompat.Builder mBuilder = new NotificationCompat.Builder(this, "asdsadasd")
                            .setSmallIcon(R.drawable.ic_launcher_background)
                            .setContentTitle("Title")
                            .setContentText(mess)
                            .setPriority(NotificationCompat.PRIORITY_DEFAULT)
                            .setAutoCancel(true);

                    NotificationManagerCompat notificationManager = NotificationManagerCompat.from(this);
                    notificationManager.notify(1, mBuilder.build());
                } catch (IOException e) {
                e.printStackTrace();
            }
        }
        catch (Exception e){
            }
        }
    }
  }
}

JobScheduler

可以在Android框架使用JobScheduler在Android框架中，API用于调度任务或在后台工作。还可以指定网络类型或要运行作业的期间或少量其他参数,创建一个扩展JobService类并重写onStartJobs和onStopJobs方法

public class myJob extends JobService {
      public boolean onStartJob(JobParameters jobParameters) {
      }
       public boolean onStopJob(JobParameters jobParameters) {
      }
 }

在OnStartJob中编写要在后台运行的代码，将此添加到JobInfo

JobInfo.Builder builder = new JobInfo.Builder(jobID, new ComponentName(context, Myjob.service));

在JobInfo.Builder上，可以包含调度条件

builder.setPeriodic(10000);
builder.setRequiredNetworkType(JobInfo.NETWORK_TYPE_ANY);

创建一个Jobscheduler并通过JobInfo根据您指定的调度参数调用JobService：

JobScheduler jobScheduler = (JobScheduler) context.getSystemService(Context.JOB_SCHEDULER_SERVICE);
jobScheduler.schedule(builder.build());