修改响应体改造2.2拦截器

我正在开发一个使用 Retrofit 2 来请求 API 的应用程序。该API位于ASP.NET中，使用GZip进行压缩并编码为Base64，如下代码所示：

private static string Compress(string conteudo)
{
    Encoding encoding = Encoding.UTF8;
    byte[] raw = encoding.GetBytes(conteudo);

    using (var memory = new MemoryStream())
    {
        using (GZipStream gzip = new GZipStream(memory, CompressionMode.Compress, true))
        {
            gzip.Write(raw, 0, raw.Length);
        }
        return Convert.ToBase64String(memory.ToArray());
    }
}

private static string Decompress(string conteudo)
{
    Encoding encoding = Encoding.UTF8;
    var gzip = Convert.FromBase64String(conteudo);

    using (GZipStream stream = new GZipStream(new MemoryStream(gzip), CompressionMode.Decompress))
    {
        int size = gzip.Length;
        byte[] buffer = new byte[size];
        using (MemoryStream memory = new MemoryStream())
        {
            int count = 0;
            do
            {
                count = stream.Read(buffer, 0, size);
                if (count > 0)
                {
                    memory.Write(buffer, 0, count);
                }
            }
            while (count > 0);
            return encoding.GetString(memory.ToArray());
        }
    }
}

现在，我需要在 Android 应用程序中获取来自 Retrofit 的响应，从 Base64 进行解码并解压缩。我尝试使用Interceptor，但我没有成功。

这是我从服务收到的回报H4sIAAAAAAAEACspKk0FAI1M/P0EAAAA，解码并解压缩响应，我们有true.

有人知道该怎么做吗？

这很容易。下面的代码使用 Google Guava 来解码 Base64 字符流，并使用 Google Gson 来反序列化 JSON 内容。

考虑以下测试服务接口：

interface IService {

    @GET("/")
    Call<String> get();

}

现在您可以使用模板方法设计模式来实现拦截器响应输入流转换器基础：

abstract class AbstractTransformingDecodingInterceptor
        implements Interceptor {

    protected abstract InputStream transformInputStream(InputStream inputStream)
            throws IOException;

    @Override
    @SuppressWarnings("resource")
    public final Response intercept(final Chain chain)
            throws IOException {
        final Request request = chain.request();
        final Response response = chain.proceed(request);
        final ResponseBody body = response.body();
        return response.newBuilder()
                .body(ResponseBody.create(
                        body.contentType(),
                        body.contentLength(),
                        Okio.buffer(Okio.source(transformInputStream(body.byteStream())))
                ))
                .build();
    }

}

此实现还应该检测内容 MIME 类型，以免进行错误的转换，但您可以轻松地自己实现。因此，这里还有两个适用于 Base64 和 GZip 的转换拦截器：

final class Base64DecodingInterceptor
        extends AbstractTransformingDecodingInterceptor {

    private static final Interceptor base64DecodingInterceptor = new Base64DecodingInterceptor();

    private Base64DecodingInterceptor() {
    }

    static Interceptor getBase64DecodingInterceptor() {
        return base64DecodingInterceptor;
    }

    @Override
    protected InputStream transformInputStream(final InputStream inputStream) {
        return BaseEncoding.base64().decodingStream(new InputStreamReader(inputStream));
    }

}

final class GzipDecodingInterceptor
        extends AbstractTransformingDecodingInterceptor {

    private static final Interceptor gzipDecodingInterceptor = new GzipDecodingInterceptor();

    private GzipDecodingInterceptor() {
    }

    static Interceptor getGzipDecodingInterceptor() {
        return gzipDecodingInterceptor;
    }

    @Override
    protected InputStream transformInputStream(final InputStream inputStream)
            throws IOException {
        return new GZIPInputStream(inputStream);
    }

}

并测试一下：

private static final OkHttpClient okHttpClient = new OkHttpClient.Builder()
        .addInterceptor(getGzipDecodingInterceptor())
        .addInterceptor(getBase64DecodingInterceptor())
        .addInterceptor(getFakeContentInterceptor())
        .build();

private static final Retrofit retrofit = new Retrofit.Builder()
        .baseUrl("http://whatever")
        .client(okHttpClient)
        .addConverterFactory(GsonConverterFactory.create())
        .build();

private static final IService service = retrofit.create(IService.class);

public static void main(final String... args)
        throws IOException {
    final String body = service.get().execute().body();
    System.out.println(body);
}

注意getFakeContentInterceptor返回一个总是返回的假拦截器H4sIAAAAAAAEACspKk0FAI1M/P0EAAAA以便baseUrl甚至没有真正的 URL。输出：

true