如何使用 Retrofit2 下载文件？

Question

我怎样才能下载一个文件（图像/视频）从我的PHP服务器使用Retrofit2？

我无法在网上找到有关如何进行的任何资源或教程；我发现这篇文章处理了SO上的某个下载错误，但我不太清楚。有人能指出我正确的方向吗？

更新：

这是我的代码：

文件下载服务.java

public interface FileDownloadService {
    @GET(Constants.UPLOADS_DIRECTORY + "/{filename}")
    @Streaming
    Call<ResponseBody> downloadRetrofit(@Path("filename") String fileName);
}

MainActivity.java（@Blackbelt的解决方案）

private void downloadFile(String filename) {
    FileDownloadService service = ServiceGenerator
            .createService(FileDownloadService.class, Constants.SERVER_IP_ADDRESS);
    Call<ResponseBody> call = service.downloadRetrofit("db90408a4bb1ee65d3e09d261494a49f.jpg");

    call.enqueue(new Callback<ResponseBody>() {
        @Override
        public void onResponse(final Response<ResponseBody> response, Retrofit retrofit) {
            try {
                InputStream is = response.body().byteStream();
                FileOutputStream fos = new FileOutputStream(
                        new File(Environment.getExternalStorageDirectory(), "image.jpg")
                );
                int read = 0;
                byte[] buffer = new byte[32768];
                while ((read = is.read(buffer)) > 0) {
                    fos.write(buffer, 0, read);
                }

                fos.close();
                is.close();
            } catch (Exception e) {
                Toast.makeText(MainActivity.this, "Exception: " + e.toString(), Toast.LENGTH_LONG).show();
            }
        }

        @Override
        public void onFailure(Throwable t) {
            Toast.makeText(MainActivity.this, "Failed to download file...", Toast.LENGTH_LONG).show();
        }
    });
}

当 USB 调试处于活动状态时，我会收到FileNotFoundException 异常，否则会收到NetworkOnMainThreadException。

MainActivity.java： （@Emanuel的溶液）

private void downloadFile(String filename) {
    FileDownloadService service = ServiceGenerator
            .createService(FileDownloadService.class, Constants.SERVER_IP_ADDRESS);
    Call<ResponseBody> call = service.downloadRetrofit("db90408a4bb1ee65d3e09d261494a49f.jpg");

    call.enqueue(new Callback<ResponseBody>() {
        @Override
        public void onResponse(final Response<ResponseBody> response, Retrofit retrofit) {
            Log.i(TAG, "external storage = " + (Environment.getExternalStorageState() == null));
            Toast.makeText(MainActivity.this, "Downloading file... " + Environment.getExternalStorageDirectory(), Toast.LENGTH_LONG).show();

            File file = new File(Environment.getDataDirectory().toString() + "/aouf/image.jpg");
            try {
                file.createNewFile();
                Files.asByteSink(file).write(response.body().bytes());
            } catch (Exception e) {
                Toast.makeText(MainActivity.this,
                        "Exception: " + e.toString(),
                        Toast.LENGTH_LONG).show();
            }
        }

        @Override
        public void onFailure(Throwable t) {
            Toast.makeText(MainActivity.this, "Failed to download file...", Toast.LENGTH_LONG).show();
        }
    });
}

我得到一个FileNotFoundException。

Answer 1

这是一个展示如何下载 Retrofit JAR 文件的小例子。您可以根据自己的需要进行调整。

这是界面：

import com.squareup.okhttp.ResponseBody;
import retrofit.Call;
import retrofit.http.GET;
import retrofit.http.Path;

interface RetrofitDownload {
    @GET("/maven2/com/squareup/retrofit/retrofit/2.0.0-beta2/{fileName}")
    Call<ResponseBody> downloadRetrofit(@Path("fileName") String fileName);
}

这是一个使用接口的 Java 类：

import com.google.common.io.Files;
import com.squareup.okhttp.ResponseBody;
import retrofit.Call;
import retrofit.Callback;
import retrofit.Response;
import retrofit.Retrofit;

import java.io.File;
import java.io.IOException;

public class Main {

    public static void main(String... args) {
        Retrofit retrofit = new Retrofit.Builder().
                baseUrl("http://repo1.maven.org").
                build();

        RetrofitDownload retrofitDownload = retrofit.create(RetrofitDownload.class);

        Call<ResponseBody> call = retrofitDownload.downloadRetrofit("retrofit-2.0.0-beta2.jar");

        call.enqueue(new Callback<ResponseBody>() {
            @Override
            public void onResponse(Response<ResponseBody> response, Retrofit retrofitParam) {
                File file = new File("retrofit-2.0.0-beta2.jar");
                try {
                    file.createNewFile();
                    Files.asByteSink(file).write(response.body().bytes());
                } catch (IOException e) {
                    e.printStackTrace();
                }
            }

            @Override
            public void onFailure(Throwable t) {
            }
        });
    }
}