java - 如何从服务器获得响应？

Question

我正在编写一个包含对 rest API(Yandex 磁盘)请求的类。我使用 Volley 抽射，但我在从中获得回应时确实遇到了一些问题。您可以查看其余 API here .

我使用 volley，我可以在调试器中得到响应，但在我的 Activity 中没有。

这是我的请求类

class Requests {
    private String response_of_server, token;
    private String url = "https://cloud-api.yandex.net/v1/disk";
    private Context context;

    Requests (String token, Context context) {
        this.token = token;
        this.context = context;
    }

    private void set_response_of_server(String response) {
        this.response_of_server = response;
    }

    String get_response() {
        return response_of_server;
    }

    void get_metadata_of_user() {

        try {
            /*Request*/

            RequestQueue queue = Volley.newRequestQueue(this.context);


            Response.ErrorListener error_listener = new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    error.printStackTrace();
                }
            };
            Response.Listener<String> response_listener = new Response.Listener<String>()
            {
                @Override
                public void onResponse(String response) {
                    set_response_of_server(response);
                }
            };

            StringRequest getRequest = new StringRequest(Request.Method.GET, url+"?fields=user", response_listener, error_listener) {
                @Override
                public Map<String, String> getHeaders() {
                    Map<String, String>  params = new HashMap<>();
                    params.put("Host", "cloud-api.yandex.net");
                    params.put("Authorization", token);
                    return params;
                }
            };
            queue.add(getRequest);
            /*Request end*/

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

还有我想要响应的 MainActivity。

public class MainActivity extends AppCompatActivity {

    private final String ID_OF_APP = "Your token of app";
    private final String URL_FOR_CODE_QUERY = "https://oauth.yandex.com/authorize?response_type=token&client_id=" + ID_OF_APP;
    private String SAVED_TOKEN = "";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        Button btn_get_code = findViewById(R.id.btn_get_code); // send to get code page (yandex)
        btn_get_code.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                    Intent i = new Intent(Intent.ACTION_VIEW);
                    i.setData(Uri.parse(URL_FOR_CODE_QUERY));
                    startActivity(i);
            }
        });

        Button btn_sign_in = findViewById(R.id.btn_sign_in);
        btn_sign_in.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                EditText code_field = findViewById(R.id.code_field);
                String token = code_field.getText().toString();
                save_token(token);
                try {
                    if(check_token()) {
                        //Toast.makeText(MainActivity.this, "You are successfully signed in", Toast.LENGTH_SHORT).show();
                        // TODO change activity
                    }
                    else {}
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                //Toast.makeText(MainActivity.this, "Something went wrong. Please, check your connection and try again later", Toast.LENGTH_SHORT).show();
            }
        });
    }

    private void save_token(String token) {
        SharedPreferences sPref = getPreferences(MODE_PRIVATE);
        SharedPreferences.Editor ed = sPref.edit();
        ed.putString(SAVED_TOKEN, token);
        ed.apply();
    }

    private String load_token() {
        SharedPreferences sPref = getPreferences(MODE_PRIVATE);
        return sPref.getString(SAVED_TOKEN, "");
    }

    private boolean check_token() throws InterruptedException {
        String token = load_token();
        String result;
        Requests request = new Requests(token, this);
        request.get_metadata_of_user();
        result = request.get_response();
        Toast.makeText(MainActivity.this, result, Toast.LENGTH_SHORT).show();
        return !(result.equals("-1"));
    }
}

check_token() 函数此刻应该只是为服务器的响应干杯。但是，我无法获得 Toast 或服务器返回的任何响应。

Answer 1

您有一个Requests 类，它具有调用异步 服务器API 的功能。因此，在 check_token() 函数中调用 request.get_metadata_of_user(); 后，您不会立即获得 result。

因此，我建议您修改您的 Request 类，如下所示。

public class Requests {
    private String response_of_server, token;
    private String url = "https://cloud-api.yandex.net/v1/disk";
    private Context context;
    private HttpListener listener; // Add a listener to get the callback functionality

    Requests (String token, Context context, HttpListener listener) {
        this.token = token;
        this.context = context;
        this.listener = listener; // initialize the listener here
    }

    private void set_response_of_server(String response) {
        this.response_of_server = response;
        listener.onResponseReceived(response); // Send the response back to the calling class
    }

    String get_response() {
        return response_of_server;
    }

    void get_metadata_of_user() {

        try {
            RequestQueue queue = Volley.newRequestQueue(this.context);
            Response.ErrorListener error_listener = new Response.ErrorListener() {
                @Override
                public void onErrorResponse(VolleyError error) {
                    error.printStackTrace();
                }
            };

            Response.Listener<String> response_listener = new Response.Listener<String>()
            {
                @Override
                public void onResponse(String response) {
                    set_response_of_server(response);
                }
            };

            StringRequest getRequest = new StringRequest(Request.Method.GET, url+"?fields=user", response_listener, error_listener) {
                @Override
                public Map<String, String> getHeaders() {
                    Map<String, String>  params = new HashMap<>();
                    params.put("Host", "cloud-api.yandex.net");
                    params.put("Authorization", token);
                    return params;
                }
            };

            queue.add(getRequest);
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
}

现在 HttpListener 类可能如下所示。创建 HttpListener.java 并添加以下代码以将其创建为接口(interface)。

public interface HttpListener {
    public void onResponseReceived();
}

因此您需要在您的MainActivity 中实现此接口(interface)，如下所示。

public class MainActivity extends AppCompatActivity implements HttpListener {

    private final String ID_OF_APP = "Your token of app";

    // I fixed this part too. Please change if that is not useful
    private final String URL_FOR_CODE_QUERY = "https://oauth.yandex.com/authorize?response_type=" + SAVED_TOKEN + "&client_id=" + ID_OF_APP;
    private String SAVED_TOKEN = "";

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);

        // ... I omitted some code

        Button btn_sign_in = findViewById(R.id.btn_sign_in);
        btn_sign_in.setOnClickListener(new View.OnClickListener() {
            @Override
            public void onClick(View v) {
                EditText code_field = findViewById(R.id.code_field);
                String token = code_field.getText().toString();
                save_token(token);

                try {
                    // if(check_token()) {
                        // The check_token function call is Async. This will not return immediately. Hence you might consider removing this if part. Simply just call the function and listen to the callback function when the response is received
                    // }

                    check_token(); // Simply call the function here
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
            }
        });
    }

    private void save_token(String token) {
        SharedPreferences sPref = getPreferences(MODE_PRIVATE);
        SharedPreferences.Editor ed = sPref.edit();
        ed.putString(SAVED_TOKEN, token);
        ed.apply();
    }

    private String load_token() {
        SharedPreferences sPref = getPreferences(MODE_PRIVATE);
        return sPref.getString(SAVED_TOKEN, "");
    }

    // I changed the return type as this is not returning anything.
    private void check_token() throws InterruptedException {
        String token = load_token();
        String result;
        Requests request = new Requests(token, this);
        request.get_metadata_of_user();

        // You will not get the response immediately here. So omit these codes.
        // result = request.get_response();
        // Toast.makeText(MainActivity.this, result, Toast.LENGTH_SHORT).show();
        // return !(result.equals("-1"));
    }

    @Override
    public void onResponseReceived(String response) {
        // Here is your response. Now you can use your response
        // and can perform the next action here. 
    }
}

请注意，代码未经测试。请根据您的要求进行修改。我希望这可以帮助您理解问题。