1.  添加本地缓存时，post 方式的请求不缓存。

2. @Body 方式提交数据时，会转成 json 形式提交， 而不是键值对。

自定义 GsonConverterFactory ,主要是 GsonRequestBodyConverter 类。

final class GsonRequestBodyConverter<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;

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

  @Override public RequestBody convert(T value) throws IOException {
    Buffer buffer = new Buffer();
    buffer.read(UrlFormedUtils.getFormUrlEncoded(value).getBytes());
    return RequestBody.create(MEDIA_TYPE, buffer.readByteString());
  }
}

// 把对象转为url 键值对。

public static <T> String getFormUrlEncoded(T t){
    String cls1 = t.getClass().getName();
    StringBuffer sb = new StringBuffer();
    try {
        Class<?> cls = Class.forName(cls1);
        Field[] fields = cls.getDeclaredFields();
        for(Field field:fields){
            if (field.isSynthetic()) {
                continue;
            }
            if (field.getName().equals("serialVersionUID")) {
                continue;
            }
            field.setAccessible(true);
            if(field.get(t)!=null && !TextUtils.isEmpty(field.get(t).toString())){
                sb.append("&").append(field.getName()).append("=").append(field.get(t));
            }
        }
        Class<?> superCls = cls.getSuperclass();
        if(!superCls.getSimpleName().equals("Object")){
            fields = superCls.getDeclaredFields();
            for(Field field:fields){
                if (field.isSynthetic()) {
                    continue;
                }
                if (field.getName().equals("serialVersionUID")) {
                    continue;
                }
                field.setAccessible(true);
                if(field.get(t)!=null  && !TextUtils.isEmpty(field.get(t).toString())){
                    sb.append("&").append(field.getName()).append("=").append(field.get(t));
                }
            }
        }
        return sb.toString();
    } catch (Exception e) {
        e.printStackTrace();
    }
    return "";
}

Retrofit 使用过程中遇到的坑