两步让Retrofit使用FastJson解析：解决返回String报错：Expected a string but was BEGIN_OBJECT at line 1 column 2 path

博主最近遇到一个项目需求，需要对一个JSONString数据进行判断，根据type字段解析成不同的Object。

    @POST("v1/recharge/new")
    Call payNewPhone(@Body PayNewPhoneReq payNewPhoneReq);

然而，就在我自信的完成了返回类型的修改后，Retrofit毫不留情的给了我一个异常。

其实这个报错并不是来自Retrofit，而是来自Gson，它只会将"anything"这样的数据解析成String。博主也尝试了将返回类型替换为JSONObject，添加Scalars Converter等等等等……最终全部以失败告终。

于是博主决定更换掉不完善的Gson库，换成FastJson。

相信很多朋友在使用Retrofit的时候，为了图方便，使用的都是Gson解析，因为Retrofit官方并没有提供FastJson的解析库。不过不要紧，伟大的阿里爸爸早就帮我们写好了，他就在这里：

https://github.com/alibaba/fastjson/blob/master/src/main/java/com/alibaba/fastjson/support/retrofit/Retrofit2ConverterFactory.java

import com.alibaba.fastjson.JSON;
import com.alibaba.fastjson.parser.Feature;
import com.alibaba.fastjson.parser.ParserConfig;
import com.alibaba.fastjson.serializer.SerializeConfig;
import com.alibaba.fastjson.serializer.SerializerFeature;
import okhttp3.MediaType;
import okhttp3.RequestBody;
import okhttp3.ResponseBody;
import retrofit2.Converter;
import retrofit2.Retrofit;

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

/**
 * @author ligboy, wenshao
 */
public class Retrofit2ConverterFactory extends Converter.Factory {
    private static final MediaType MEDIA_TYPE = MediaType.parse("application/json; charset=UTF-8");
    private static final Feature[] EMPTY_SERIALIZER_FEATURES = new Feature[0];

    private ParserConfig parserConfig = ParserConfig.getGlobalInstance();
    private int featureValues = JSON.DEFAULT_PARSER_FEATURE;
    private Feature[] features;

    private SerializeConfig serializeConfig;
    private SerializerFeature[] serializerFeatures;

    public Retrofit2ConverterFactory() {
    }

    @Override
    public Converter responseBodyConverter(Type type, //
                                                            Annotation[] annotations, //
                                                            Retrofit retrofit) {
        return new ResponseBodyConverter(type);
    }

    @Override
    public Converter requestBodyConverter(Type type, //
                                                          Annotation[] parameterAnnotations, //
                                                          Annotation[] methodAnnotations, //
                                                          Retrofit retrofit) {
        return new RequestBodyConverter();
    }

    public ParserConfig getParserConfig() {
        return parserConfig;
    }

    public Retrofit2ConverterFactory setParserConfig(ParserConfig config) {
        this.parserConfig = config;
        return this;
    }

    public int getParserFeatureValues() {
        return featureValues;
    }

    public Retrofit2ConverterFactory setParserFeatureValues(int featureValues) {
        this.featureValues = featureValues;
        return this;
    }

    public Feature[] getParserFeatures() {
        return features;
    }

    public Retrofit2ConverterFactory setParserFeatures(Feature[] features) {
        this.features = features;
        return this;
    }

    public SerializeConfig getSerializeConfig() {
        return serializeConfig;
    }

    public Retrofit2ConverterFactory setSerializeConfig(SerializeConfig serializeConfig) {
        this.serializeConfig = serializeConfig;
        return this;
    }

    public SerializerFeature[] getSerializerFeatures() {
        return serializerFeatures;
    }

    public Retrofit2ConverterFactory setSerializerFeatures(SerializerFeature[] features) {
        this.serializerFeatures = features;
        return this;
    }

    final class ResponseBodyConverter implements Converter {
        private Type type;

        ResponseBodyConverter(Type type) {
            this.type = type;
        }

        public T convert(ResponseBody value) throws IOException {
            try {
                return JSON.parseObject(value.string()
                        , type
                        , parserConfig
                        , featureValues
                        , features != null
                                ? features
                                : EMPTY_SERIALIZER_FEATURES
                );
            } finally {
                value.close();
            }
        }
    }

    final class RequestBodyConverter implements Converter {
        RequestBodyConverter() {
        }

        public RequestBody convert(T value) throws IOException {
            byte[] content = JSON.toJSONBytes(value
                    , serializeConfig == null
                            ? SerializeConfig.globalInstance
                            : serializeConfig
                    , serializerFeatures == null
                            ? SerializerFeature.EMPTY
                            : serializerFeatures
            );

            return RequestBody.create(MEDIA_TYPE, content);
        }
    }
}

只需要将它拷贝下来，新建一个Retrofit2ConverterFactory.java，粘贴，官方提供的Converter就有了，现成的~

然后就可以大刀阔斧的删掉Gson的ProGuard-Rule和implementation，导入FastJsonForAndroid：

implementation 'com.alibaba:fastjson:1.1.70.android'

在初始化Retrofit的地方，更换ConvertFactory：

Retrofit retrofit = new Retrofit.Builder().baseUrl(HttpArgs.BASE_URL)

                //更换ConvertFactory

                .addConverterFactory(new Retrofit2ConverterFactory())

再次运行APP，OK问题解决~

你看，国外的月亮也不比中国的圆。

最后是国际惯例，如果觉得有帮助的话，就打赏博主一个红包吧~