For the basic use of Retrofit2, please refer to Java Retrofit2 uses

Custom converter
By default, the supported conversions of retrofit are Gson,Jackson,Moshi

1. Build infrastructure
   Here, we will customize a FastJsonConverterFactory to parse the returned data, which internally uses Alibaba's fastjson (depends on adding compile 'com.alibaba:fastjson:1.2.37').
   First, we need to build the use architecture of Retrofit2, and then add an instance of Retrofit2 when creating an instance

        // 3. Get an example
        Retrofit retrofit = new Retrofit.Builder()
                // Set OKHttpClient. If it is not set, a default
                .client(new OkHttpClient())
                //Set baseUrl
                .baseUrl(url)
                //Add Gson converter
                .addConverterFactory(FastJsonConverterFactory.create())
                .build();

1. Create the FastJsonConverterFactory class inherited from Converter.Factory, and implement the create(), requestBodyConverter(),responseBodyConverter().

/**
 * fastjson Analytic factory
 * @author mazaiting
 */
public class FastJsonConverterFactory extends Converter.Factory{

    public static Factory create() {
        return new FastJsonConverterFactory();
    }
    
    @Override
    public Converter<Info, RequestBody> requestBodyConverter(Type type, Annotation[] parameterAnnotations,
            Annotation[] methodAnnotations, Retrofit retrofit) {
        return new FastJsonRequestConverter();
    }
    
    
    @Override
    public Converter<ResponseBody, Info> responseBodyConverter(Type type, Annotation[] annotations, Retrofit retrofit) {
        return new FastJsonResponseConverter(type);
    }

}

1. Implement FastJsonRequestConverter class

/**
 * Request conversion class, converting Info object to RequestBody object
 * @author mazaiting
 */
public class FastJsonRequestConverter implements Converter<Info, RequestBody> {
    private static final MediaType MEDIA_TYPE = MediaType.parse("application/json; charset=UTF-8");
    private static final Charset UTF_8 = Charset.forName("UTF-8");

    public FastJsonRequestConverter() {
    }

    public RequestBody convert(Info value) throws IOException {
        Buffer buffer = new Buffer();
        Writer writer = new OutputStreamWriter(buffer.outputStream(), UTF_8);
        writer.write(value.toString());
        writer.close();         
        return RequestBody.create(MEDIA_TYPE, buffer.readByteString());
    }

}

1. Implement FastJsonResponseConverter class

/**
 * fastjson Response converter, converting ResponseBody object to Info object
 * @author Administrator
 *
 */
public class FastJsonResponseConverter implements Converter<ResponseBody, Info> {
    /**
     * Reflection type
     */
    private Type type;
    public FastJsonResponseConverter(Type type) {
        this.type = type;
    }

    public Info convert(ResponseBody value) throws IOException {
        try {
            /**
             * fastjson Analytical data
             * Special note here: Info should be an external class and its members in the class should be set to public,
             * Otherwise, the Info object cannot be created, resulting in parsing exception
             */
            Info info = JSON.parseObject(value.string(), type);
            System.out.println(info);
            return info;
        } finally {
            value.close();
        }
    }

}