Retrofit自定義解析器

某些情況下，從服務器返回過來的json無法自動解析，只能通過手動解析（比如json某些字段的key是不固定的），如果項目中又正在用Retrofit作爲網絡庫的話，就會比較頭疼，因爲Retrofit一般都只需要調用.addConverterFactory()傳一個GsonConverterFactory對象就可以用Gson完成自動解析。然而網絡上對於Retrofit的資源相當有限，摸索了一段時間終於知道如何用Retrofit自定義解析器了，寫下來做個備忘，也爲了方便後來人。

通常情況下Retrofit的代碼會是這樣：

private static OkHttpClient.Builder sOkHttpClient = new OkHttpClient.Builder();
private static Converter.Factory sGsonConverterFactory = GsonConverterFactory.create();
private static CallAdapter.Factory sRxJavaCallAdapterFactory = RxJavaCallAdapterFactory.create();

public static HotApi getHotApi(){
    if(sHotApi == null){
        Retrofit retrofit = new Retrofit.Builder()
                .client(sOkHttpClient.build())
                .baseUrl(BASE_URL)
                .addConverterFactory(sGsonConverterFactory)//這裏一般傳個GsonConverterFactory對象就可以用gson完成自動解析
                .addCallAdapterFactory(sRxJavaCallAdapterFactory)
                .build();
        sHotApi = retrofit.create(HotApi.class);
    }
    return sHotApi;
}

但是如果不想用Gson完成自動解析則需要自定義解析器了，總共分爲四步。
步驟一：

public abstract class BaseResponseConverter<T> implements Converter<ResponseBody,T> {

    @Override
    public T convert(ResponseBody value) throws IOException {
        return parserJson(value.string());
    }

    public abstract T parserJson(String json);
}

public abstract class BaseConverterFactory<T> extends Converter.Factory {
    @Override
    public Converter<ResponseBody, T> responseBodyConverter(Type type, Annotation[] annotations, Retrofit retrofit) {
        return responseConverter();
    }

    public abstract BaseResponseConverter<T> responseConverter();

    @Override
    public Converter<?, RequestBody> requestBodyConverter(Type type, Annotation[] parameterAnnotations, Annotation[] methodAnnotations, Retrofit retrofit) {
        return super.requestBodyConverter(type, parameterAnnotations, methodAnnotations, retrofit);
    }
}

步驟二：

public class HotResponseConverter extends BaseResponseConverter<HotListBean>{

    @Override
    public HotListBean parserJson(String json) {
        HotListBean bean = new HotListBean();
        try {
            JSONObject jsonRoot = new JSONObject(json);
            String status = jsonRoot.getString("status");
            bean.setStatus(status);
            if ("ok".equals(status)) {
                JSONObject jsonPkg = jsonRoot.getJSONObject("list");
                bean.setId(jsonPkg.getString("id"));
                bean.setName(jsonPkg.getString("name"));
                bean.setType(jsonPkg.getString("type"));

                JSONArray JAcontents = jsonPkg.getJSONArray("contents");
                List<String> contents = new ArrayList<>();
                for (int i = 0; i < JAcontents.length(); i++) {
                    contents.add(JAcontents.getString(i));
                }
                bean.setContents(contents);

                bean.setTimestamp(jsonPkg.getLong("timestamp"));
                bean.setCount(jsonPkg.getInt("count"));

                JSONObject jsonDetails = jsonPkg.getJSONObject("details");
                List<EmoticonBean> details = new ArrayList<>();
                for (String emoId:contents) {
                    details.add(new Gson().fromJson(jsonDetails.getJSONObject(emoId).toString(), EmoticonBean.class));
                }
                bean.setDetails(details);
            }
        } catch (JSONException e) {
            e.printStackTrace();
        }
        return bean;
    }
}

步驟三：

public interface HotApi {
    @GET("v2_5/lists/hot")
    Observable<HotListBean> getHots(@Query("auth_token") String authToken,@Query("user_id")String userId,@Query("limit")int limit,@Query("page") int page);
}

步驟四：

public static HotApi getHotApi(){
    if(sHotApi == null){
        Retrofit retrofit = new Retrofit.Builder()
                .client(sOkHttpClient.build())
                .baseUrl(BASE_URL)
                .addConverterFactory(new BaseConverterFactory() {
                    @Override
                    public BaseResponseConverter responseConverter() {
                        return new HotResponseConverter();
                    }
                })
                .addCallAdapterFactory(sRxJavaCallAdapterFactory)
                .build();
        sHotApi = retrofit.create(HotApi.class);
    }
    return sHotApi;
}