加密代理和Retrofit解密Converter

最近在做后台数据加密，然后遇到这样一个问题，服务器的数据全部用加密算法加密了，发现无法使用“com.squareup.retrofit2:converter-gson:2.1.0”Jar包了。

自定义ConverterFactory

现在安卓流行Retrofit+Okhttp+Converter-gson，不过如果数据如果加密了，使用Converter-gson进行解析的时候会出现问题。字符串被加密了，自然不能直接使用Gson进行解析，这样我们就需要自己写一个Converter架包了。

其中Retrofit.Builder中有一个addConverterFactory，我们最后要将自己的ConverterFactory作为参数写入，通过这个ConverterFactory接口，实现我们自己的解析类即可。

//添加ConverterFactory
Retrofit client = new Retrofit.Builder()                  .addConverterFactory(ConverterAesJsonFactory.create())

ConverterFactory

要实现这个ConverterFactory需要重写三部分代码：

public class ConverterAesJsonFactory extends Converter.Factory {
    private final Gson gson;
    public static ConverterAesJsonFactory create() {
        return create(new Gson());
    }


    public static ConverterAesJsonFactory create(Gson gson) {
        return new ConverterAesJsonFactory(gson);
    }


    private ConverterAesJsonFactory(Gson gson) {
        if (gson == null) throw new NullPointerException("gson == null");
        this.gson = gson;
    }


    @Override
    public Converter<ResponseBody, ?> responseBodyConverter(Type type,
                                                            Annotation[] annotations,
                                                            Retrofit retrofit) {
        TypeAdapter<?> adapter = gson.getAdapter(TypeToken.get(type));
        return new AesGsonResponseBodyConverter(gson, adapter);
    }

    @Override
    public Converter<?, RequestBody> requestBodyConverter(Type type,
                                                          Annotation[] parameterAnnotations,
                                                          Annotation[] methodAnnotations,
                                                          Retrofit retrofit) {
        TypeAdapter<?> adapter = gson.getAdapter(TypeToken.get(type));
        return new AesJsonRequestBodyConverter<>(gson, adapter);
    }
}

ResponseBodyConverter

这个类负责处理服务端的响应数据，除了解密算法，还有Json解析的代码。

/**
 * 响应体
 * Created by ChenSS on 2016/12/26.
 */
final class AesGsonResponseBodyConverter<T> implements Converter<ResponseBody, T> {
    private final Gson gson;
    private final TypeAdapter<T> adapter;

    AesGsonResponseBodyConverter(Gson gson, TypeAdapter<T> adapter) {
        this.gson = gson;
        this.adapter = adapter;
    }

    @Override
    public T convert(ResponseBody responseBody) throws IOException {
        try {
             // TODO: 2016/12/26 设计你自己的响应体解密算法，下面使用了Base64解码
            String decodeBody = Base64.decode(responseBody.string());
            //Base64解码就上面一行，大家可以自行设计算法
            Log.e("AesJsonFactory:", decodeBody);
            JsonReader jsonReader = gson.newJsonReader(new StringReader(decodeBody));
            try {
                return adapter.read(jsonReader);
            } finally {
                responseBody.close();
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
        return null;
    }
}

RequestBodyConverter

如果需要对请求数据加密，需要改造一部分的代码

/**
 * 请求体
 * Created by ChenSS on 2016/12/26.
 */
final class AesJsonRequestBodyConverter<T> implements Converter<T, RequestBody> {
    private static final MediaType MEDIA_TYPE = MediaType.parse("application/json; charset=UTF-8");
    private static final Charset UTF_8 = Charset.forName("UTF-8");

    private final Gson gson;
    private final TypeAdapter<T> adapter;

    AesJsonRequestBodyConverter(Gson gson, TypeAdapter<T> adapter) {
        this.gson = gson;
        this.adapter = adapter;
    }

    @Override public RequestBody convert(T value) throws IOException {
        Buffer buffer = new Buffer();
        Writer writer = new OutputStreamWriter(buffer.outputStream(), UTF_8);
        JsonWriter jsonWriter = gson.newJsonWriter(writer);
        // TODO: 2016/12/26 网络请求，这里我没修改，这和Converter-gson是一样的
        adapter.write(jsonWriter, value);
        jsonWriter.close();
        return RequestBody.create(MEDIA_TYPE, buffer.readByteString());
    }
}