java - 如何从 Paho MQTT 消息中解析 JSON

Question

编辑我已经使用 Volley 添加了 pars 函数。这是功能代码：

private void pars(){

    JsonObjectRequest request = new JsonObjectRequest(Request.Method.GET, String.valueOf(txt), null,
            new Response.Listener<JSONObject>() {
                @Override
                public void onResponse(JSONObject response) {
                    try {
                        JSONArray jsonArray = response.getJSONArray("employees");
                        for(int i = 0; i<jsonArray.length(); i++){
                            JSONObject employee = jsonArray.getJSONObject(i);
                            String firstName = employee.getString("firstname");
                            int age = employee.getInt("age");
                            String mail = employee.getString("mail");
                            txt.append(firstName + ", " + String.valueOf(age) + ", " + mail + "\n\n");
                        }
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                }
            }, new Response.ErrorListener() {
        @Override
        public void onErrorResponse(VolleyError error) {
            error.printStackTrace();
        }
    });
     mQueue.add(request);}

如您所见，我为 URL 端编写了“String.valueOf(txt)。但它现在不起作用。”添加此 txt 代码后，新的 Response.Listener() 变为灰色。

---------编辑结束----

我在解析来自 MQTT 的 JSON 数据时遇到问题。我正在使用 PAHO MQTT 服务器连接和订阅我在 android studio 中的主机和主题。

我正在使用 textInput 获取用户想要订阅的主题数据，就像这样：

               topic = topicInput.getEditText().getText().toString();

订阅主题后，我将在 TextView 中显示消息，方法如下：

                txt.setText(new String(message.getPayload()));

这些代码适用于从 MQTT 获取消息。但是，当我从 mqtt 推送 JSON 数据时，我的 textView 不显示解析的数据。我怎样才能解析这个字符串？我搜索了每个网站，他们通常使用普通的 url 来解析 json 数据。但是有一些不同的问题。我没有“正常”的网址，我有一个主题。

我怎样才能做到这一点？

这是我的 MainActivity.java 的完整代码：

public class MainActivity extends AppCompatActivity {
private Button btn1;
private Button btn2;
private TextView txt;
private static final String TAG="MyTag";
private MqttAndroidClient client;
private TextInputLayout topicInput;


@Override
protected void onCreate(Bundle savedInstanceState) {

    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_main);
    

    btn1 = (Button) findViewById(R.id.btn1);
    btn2 = (Button) findViewById(R.id.btn2);
    txt = (TextView)findViewById(R.id.txt);
    topicInput = (TextInputLayout) findViewById(R.id.topicInput);

    String clientId = MqttClient.generateClientId();

    final  MqttAndroidClient client =
            new MqttAndroidClient(MainActivity.this, "tcp://broker.mqttdashboard.com:1883",
                    clientId);

    //Connection
    btn1.setOnClickListener(new View.OnClickListener() {
        AlarmManager alarmManager = (AlarmManager)getSystemService(ALARM_SERVICE);
        @Override
        public void onClick(View v) {

            try {
                IMqttToken token = client.connect();
                token.setActionCallback(new IMqttActionListener() {
                    @Override
                    public void onSuccess(IMqttToken asyncActionToken) {
                        Toast.makeText(MainActivity.this, "MQTT Bağlantısı Kuruldu", Toast.LENGTH_SHORT).show();
                    }

                    @Override
                    public void onFailure(IMqttToken asyncActionToken, Throwable exception) {
                        Toast.makeText(MainActivity.this, "MQTT Bağlantısı BAŞARISIZ!", Toast.LENGTH_SHORT).show();
                    }
                });
            } catch (MqttException e) {
                e.printStackTrace();
            }
        }

    });

    //Subscribe settings
    btn2.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            String topic;
           topic = topicInput.getEditText().getText().toString();


            int qos = 1;
            try {
                IMqttToken subToken = client.subscribe(topic, qos);
                subToken.setActionCallback(new IMqttActionListener() {
                    @Override
                    public void onSuccess(IMqttToken asyncActionToken) {
                        Toast.makeText(MainActivity.this, "Topic'e Bağlanıldı", Toast.LENGTH_SHORT).show();
                    }

                    @Override
                    public void onFailure(IMqttToken asyncActionToken,
                                          Throwable exception) {
                        Toast.makeText(MainActivity.this, "Topic'e Bağlantı Kurulamadı", Toast.LENGTH_SHORT).show();


                    }
                });
            } catch (MqttException e) {
                e.printStackTrace();
            }

        }
    });

    //Text
    client.setCallback(new MqttCallback() {
        @Override
        public void connectionLost(Throwable cause) {

        }

        @Override
        public void messageArrived(String topic, MqttMessage message) throws Exception {
            txt.setText(new String(message.getPayload()));
        }
        @Override
        public void deliveryComplete(IMqttDeliveryToken token) {

        }
    });
}

}

标签： javaandroidjsonmqttpaho