Firebase Rest Api 使用接口回调 return 从我的模型类读取数据 null

Question

我正在尝试运行 java Restful API 中的 Get 方法。我尝试将我的模型 classes 命名为类似于我的实时 firebase。我试过使用接口回调，它已经打印到我的控制台，但它在我的邮递员中仍然 return null，

我的界面回调class

public interface CallBack {
    void onCallBack(DeviceTest value);

}

我的模型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 + '\'' +
                '}';
    }
}

FireBase 连接 class 和我使用的方法。

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);


    }

我用来打印给邮递员的 Get 方法

  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 ;
    }

这是我在邮递员那里得到的：

我在控制台中获得的内容：

我的问题是如何在我的控制台中将这个值 DeviceTest{LightSwitch='LIGHT', DoorSwitch='CLOSED'} 打印给我的邮递员？问题似乎出在我的 GET 方法中。

Answer 1

你是对的，抱歉误解了问题。这是因为你 return deviceTest 就在它的实际值被解析之前。

您可能想使用 CompletableFuture。
尝试这样的事情：

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;

您可以拨打：

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

Answer 2

已解决 将我的 GET 方法编辑为此


        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();
    }

Firebase Rest Api 使用接口回调 return 从我的模型类读取数据 null

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Firebase Rest Api 使用接口回调 return 从我的模型类读取数据 null