一、背景 为什么要自定义Converter

Retrofit官方给了以下几个常用的转换库

    Gson: com.squareup.retrofit2:converter-gson
    Jackson: com.squareup.retrofit2:converter-jackson
    Moshi: com.squareup.retrofit2:converter-moshi
    Protobuf: com.squareup.retrofit2:converter-protobuf
    Wire: com.squareup.retrofit2:converter-wire
    Simple XML: com.squareup.retrofit2:converter-simplexml
    Scalars (primitives, boxed, and String): com.squareup.retrofit2:converter-scalars

这对于一般的使用来说确实够用了，但是如果我们对安全性要求比较高，或者编码不太一样的话，这些库就没法使用了，于是我们就需要自定义ConverterFactory。Retrofit已经为我们提供了自定义ConverterFactory的接口，我们只需要实现它给的接口即可，首先新建一个类继承Converter.Factory,这里也用到了Gson是因为项目需要解密之后是json字符串。

public final class DecodeConverterFactory extends Converter.Factory {

    public static DecodeConverterFactory create() {
        return create(new Gson());
    }

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

    private final Gson gson;

    private DecodeConverterFactory(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 DecodeResponseBodyConverter<>(adapter);
    }

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

然后我们需要自定义responseBodyConverter和requestBodyConverter，这里我们发送请求的时候不需要加密，接收请求的时候需要解密，具体代码如下

public class DecodeResponseBodyConverter<T> implements Converter<ResponseBody, T> {
    private final TypeAdapter<T> adapter;

    DecodeResponseBodyConverter(TypeAdapter<T> adapter) {
        this.adapter = adapter;
    }

    @Override
    public T convert(ResponseBody value) throws IOException {
        //解密字符串
        return adapter.fromJson(EncryptUtils.decode(value.string()));
    }
}

public class DecodeRequestBodyConverter<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;
    DecodeRequestBodyConverter(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);
        adapter.write(jsonWriter,value);
        jsonWriter.flush();
        return RequestBody.create(MEDIA_TYPE,buffer.readByteString());
    }
}