这是一个 Retrofit2 的 byte[] 转换器，基于 Java 8 编写的。如果你使用了其他版本的 Java，得不到预期结果，可能与 type == byte[].class 判断语句有关。

• ByteArrayConverterFactory.java

package retrofit2.converter.bytearray;

import okhttp3.MediaType;
import okhttp3.RequestBody;
import okhttp3.ResponseBody;
import retrofit2.Converter;
import retrofit2.Retrofit;

import java.lang.annotation.Annotation;
import java.lang.reflect.Type;

public class ByteArrayConverterFactory extends Converter.Factory {

    private static final MediaType MEDIA_TYPE = MediaType.get("application/octet-stream");

    public static ByteArrayConverterFactory create() {
        return new ByteArrayConverterFactory();
    }

    private ByteArrayConverterFactory() {
    }

    @Override
    public Converter<ResponseBody, ?> responseBodyConverter(
            Type type, Annotation[] annotations, Retrofit retrofit) {
        if (!(type instanceof Class)) {
            return null;
        }
        return (type == byte[].class) ? ResponseBody::bytes : null;
    }

    @Override
    public Converter<?, RequestBody> requestBodyConverter(
            Type type, Annotation[] parameterAnnotations,
            Annotation[] methodAnnotations, Retrofit retrofit) {
        if (!(type instanceof Class)) {
            return null;
        }
        return (type == byte[].class) ? (Converter<byte[], RequestBody>)
                value -> RequestBody.create(MEDIA_TYPE, value) : null;
    }

}

简单测试

    private static interface TestApi {

        @POST("/")
        public Call<ResponseBody> post(@Body byte[] body);

    }

    public static void main(String[] args) throws IOException {
        Retrofit retrofit = new Retrofit.Builder()
                .baseUrl("http://github.com/")
                .addConverterFactory(ByteArrayConverterFactory.create())
                .build();
        TestApi api = retrofit.create(TestApi.class);
        api.post(new byte[]{(byte) 0xab, 0x01, 0x02, (byte) 0xcd}).execute();
    }

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