Firebase Rest Api reading data from my model classes using interface callback return null-CodePudding

I am trying to run a Get method in java Restful API. I have tried naming my model classes similar to my real-time firebase. I have tried using interface callback, and it has printed to my console but it still return null in my postman,

My interface callback class

public interface CallBack {
    void onCallBack(DeviceTest value);

}

my model class

public class DeviceTest implements Serializable {
    private String LightSwitch;
    private String DoorSwitch;

    // empty COnstructor
    public DeviceTest() { }

    public DeviceTest(String lightSwitch, String doorSwitch) {
        this.LightSwitch = lightSwitch;
        this.DoorSwitch = doorSwitch;
    }

    public String getLightSwitch() {
        return LightSwitch;
    }

    public void setLightSwitch(String lightSwitch) {
        LightSwitch = lightSwitch;
    }

    public String getDoorSwitch() {
        return DoorSwitch;
    }

    public void setDoorSwitch(String doorSwitch) {
        DoorSwitch = doorSwitch;
    }

    @Override
    public String toString() {
        return "DeviceTest{"  
                "LightSwitch='"   LightSwitch   '\''  
                ", DoorSwitch='"   DoorSwitch   '\''  
                '}';
    }
}

The FireBase Connection class and the method I use.

public static void  handleLight(CallBack callback) {
        FireBaseService fbs = null;
        fbs = new FireBaseService();
        device = new DeviceTest();
        mylist = new ArrayList<Map<String, Object>>();
        DatabaseReference ref = fbs.getDb()
                .getReference("/Devices/Lamp/Ambient");
        Map<String, Object> chemainChild = new HashMap<>();
        // chemainChild.put("server/user/",array);

        ref.addValueEventListener(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {

           callback.onCallBack(dataSnapshot.getValue(DeviceTest.class));
            }


            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

//mylist.add(device);


    }

The Get method i use to print to postman

  DeviceTest deviceTest = new DeviceTest();
    @GET
    @Produces(MediaType.APPLICATION_JSON)
    public DeviceTest getCustomers() {


        //System.out.println(device.toString());
        FireBaseService.handleLight(new CallBack() {

            @Override
            public void onCallBack(DeviceTest value) {

                // this one will print to my console
                System.out.println("Should work "   value.toString());

                // this value does not seem to be added to my deviceTest, likely a asynchronous issue again. 
                deviceTest = new DeviceTest(value.getLightSwitch(),value.getDoorSwitch());
            }

        });

        // this is here i get my null value
        return deviceTest ;
    }

This is what i got in my postman:

What i got in my console:

My question is how can I print this value DeviceTest{LightSwitch='LIGHT', DoorSwitch='CLOSED'} in my console to my postman? The issue seems to be in my GET Method.

CodePudding user response：

You're right, sorry for misunderstanding the question. It is because you return deviceTest immediately before its actually value was resolved.

You probably want to use a CompletableFuture.
Try something like this:

CompletableFuture<DeviceTest> deviceTestFut = new CompletableFuture<>();

 //System.out.println(device.toString());
    FireBaseService.handleLight(new CallBack() {

        @Override
        public void onCallBack(DeviceTest value) {

            // this one will print to my console
            System.out.println("Should work "   value.toString());

            // this value does not seem to be added to my deviceTest, likely a asynchronous issue again. 
            deviceTestFut.complete(new DeviceTest(value.getLightSwitch(),value.getDoorSwitch());
        })

    });

    // this is here i get my null value
    return deviceTestFut;

The you can call:

deviceTestFut.thenAccept(value -> System.out.println("Should work "   value.toString()););

CodePudding user response：

Solved Edit my GET Method to this


        CompletableFuture<DeviceTest> deviceTestFut = new CompletableFuture<>();
        //System.out.println(device.toString());

        FireBaseService.handleLight(new CallBack() {
                                               @Override
                                               public DeviceTest onCallBack(DeviceTest value) {
                                                   deviceTest = new DeviceTest(value.getLightSwitch(),value.getDoorSwitch());

                                                   System.out.println("Here is the value"    deviceTest.toString());

                                                  deviceTestFut.complete(new DeviceTest(value.getLightSwitch(),value.getDoorSwitch()));
                                                   return deviceTest;
                                               }
                                           });


                // this is here i get my null value
       deviceTestFut.thenAccept(value -> System.out.println("Should work "   value.toString()));
 return deviceTestFut.get();
    }