Android topics — 08: מבקשת HTTP למודל Java

package com.example.topics;

/** The small typed subset of a JSONPlaceholder todo that this screen needs. */
public final class Todo {
    public int userId;
    public int id;
    public String title;
    public boolean completed;
}

package com.example.topics;

import retrofit2.Call;
import retrofit2.http.GET;
import retrofit2.http.Path;

/** Maps one HTTP GET route to a typed response. */
public interface TodoApi {
    @GET("todos/{id}")
    Call<Todo> getTodo(@Path("id") int id);
}

package com.example.topics;

import java.io.IOException;
import java.util.concurrent.TimeUnit;

import com.google.gson.JsonParseException;
import com.google.gson.stream.MalformedJsonException;

import okhttp3.OkHttpClient;
import retrofit2.Call;
import retrofit2.Callback;
import retrofit2.Response;
import retrofit2.Retrofit;
import retrofit2.converter.gson.GsonConverterFactory;

/** Owns HTTP, JSON conversion, and response classification outside the Activity. */
public final class TodoRepository {
    public enum Kind { SUCCESS, HTTP_ERROR, NETWORK_ERROR, DECODE_ERROR, INVALID_BODY }

    public static final class Result {
        public final Kind kind;
        public final Todo todo;
        public final int status;
        public final String contentType;
        public final String detail;

        private Result(Kind kind, Todo todo, int status, String contentType, String detail) {
            this.kind = kind;
            this.todo = todo;
            this.status = status;
            this.contentType = contentType;
            this.detail = detail;
        }
    }

    public interface Listener {
        void onResult(Result result);
    }

    private final TodoApi api;

    public TodoRepository() {
        this("https://jsonplaceholder.typicode.com/");
    }

    /** Package-visible endpoint override lets a local HTTP server exercise the same code. */
    TodoRepository(String baseUrl) {
        OkHttpClient client = new OkHttpClient.Builder()
                .connectTimeout(5, TimeUnit.SECONDS)
                .readTimeout(5, TimeUnit.SECONDS)
                .retryOnConnectionFailure(false)
                .build();
        api = new Retrofit.Builder()
                .baseUrl(baseUrl)
                .client(client)
                .addConverterFactory(GsonConverterFactory.create())
                .build()
                .create(TodoApi.class);
    }

    /** Enqueues a GET and returns its cancellable call to the screen owner. */
    public Call<Todo> load(int id, Listener listener) {
        Call<Todo> call = api.getTodo(id);
        call.enqueue(new Callback<>() {
            @Override
            public void onResponse(Call<Todo> ignored, Response<Todo> response) {
                String type = response.headers().get("Content-Type");
                if (!response.isSuccessful()) {
                    listener.onResult(new Result(Kind.HTTP_ERROR, null, response.code(), type, ""));
                } else if (response.body() == null || response.body().id <= 0
                        || response.body().title == null || response.body().title.isBlank()) {
                    listener.onResult(new Result(Kind.INVALID_BODY, null, response.code(), type, ""));
                } else {
                    listener.onResult(new Result(Kind.SUCCESS, response.body(), response.code(), type, ""));
                }
            }

            @Override
            public void onFailure(Call<Todo> failedCall, Throwable error) {
                if (!failedCall.isCanceled()) {
                    boolean badJson = error instanceof MalformedJsonException
                            || error instanceof JsonParseException;
                    listener.onResult(new Result(badJson || !(error instanceof IOException)
                            ? Kind.DECODE_ERROR : Kind.NETWORK_ERROR, null, 0, null,
                            error.getClass().getSimpleName()));
                }
            }
        });
        return call;
    }
}

private final TodoRepository repository = new TodoRepository();
private Call<Todo> activeCall;
private int generation;
private int lastRequestedId = 1;

// Inside onCreate, after the insets listener:
binding.loadTodo.setOnClickListener(v -> load(1));
binding.loadMissing.setOnClickListener(v -> load(999999));
binding.cancelRequest.setOnClickListener(v -> cancel());
binding.retryRequest.setOnClickListener(v -> load(lastRequestedId));

private void load(int id) {
    lastRequestedId = id;
    generation++;
    if (activeCall != null) {
        activeCall.cancel();
    }
    int expectedGeneration = generation;
    binding.loadTodo.setEnabled(false);
    binding.loadMissing.setEnabled(false);
    binding.cancelRequest.setVisibility(View.VISIBLE);
    binding.retryRequest.setVisibility(View.GONE);
    binding.loading.setVisibility(View.VISIBLE);
    binding.status.setText(getString(R.string.http_loading, id));
    binding.todoDetail.setText("");

    activeCall = repository.load(id, result -> runOnUiThread(() -> {
        if (expectedGeneration != generation || isDestroyed()) {
            return;
        }
        activeCall = null;
        binding.loadTodo.setEnabled(true);
        binding.loadMissing.setEnabled(true);
        binding.cancelRequest.setVisibility(View.GONE);
        binding.loading.setVisibility(View.GONE);
        binding.retryRequest.setVisibility(result.kind == TodoRepository.Kind.NETWORK_ERROR
                || (result.kind == TodoRepository.Kind.HTTP_ERROR && result.status >= 500)
                ? View.VISIBLE : View.GONE);
        switch (result.kind) {
            case SUCCESS:
                binding.status.setText(getString(R.string.http_success, result.status, result.contentType));
                Todo todo = result.todo;
                binding.todoDetail.setText(getString(R.string.todo_detail,
                        todo.id, todo.userId, todo.title, todo.completed));
                break;
            case HTTP_ERROR:
                binding.status.setText(getString(R.string.http_error, result.status, result.contentType));
                break;
            case NETWORK_ERROR:
                binding.status.setText(getString(R.string.http_network_error, result.detail));
                break;
            case DECODE_ERROR:
                binding.status.setText(getString(R.string.http_decode_error, result.detail));
                break;
            case INVALID_BODY:
                binding.status.setText(getString(R.string.http_invalid_body, result.status));
                break;
        }
    }));
}

private void cancel() {
    generation++;
    if (activeCall != null) {
        activeCall.cancel();
        activeCall = null;
    }
    binding.loadTodo.setEnabled(true);
    binding.loadMissing.setEnabled(true);
    binding.cancelRequest.setVisibility(View.GONE);
    binding.loading.setVisibility(View.GONE);
    binding.status.setText(R.string.http_cancelled);
}

@Override
protected void onDestroy() {
    generation++;
    if (activeCall != null) {
        activeCall.cancel();
    }
    super.onDestroy();
}