如何使用Retrofit从异步回调返回String或JSONObject？

Question

例如

api.getUserName(userId, new Callback<String>() {...});

原因:

retrofit.RetrofitError: retrofit.converter.ConversionException:
com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: 
Expected a string but was BEGIN_OBJECT at line 1 column 2

我想我必须禁用gson解析到POJO中，但不知道如何做到这一点。

Answer 1

匿名用户

翻新2.0.0-beta3增加了一个< code >转换器-标量模块，提供了一个< code >转换器。Factory，用于将< code>String、8种基本类型和8种装箱的基本类型转换为< code>text/plain主体。在普通转换器之前安装它，以避免将这些简单的标量传递给例如JSON转换器。

因此，首先将转换器标量模块添加到构建中。gradle文件，用于您的应用程序。

dependencies {
    ...
    // use your Retrofit version (requires at minimum 2.0.0-beta3) instead of 2.0.0
    // also do not forget to add other Retrofit module you needed
    compile 'com.squareup.retrofit2:converter-scalars:2.0.0'
}

然后，像这样创建改造实例：

new Retrofit.Builder()
        .baseUrl(BASE_URL)
        // add the converter-scalars for coverting String
        .addConverterFactory(ScalarsConverterFactory.create())
        .addConverterFactory(GsonConverterFactory.create())
        .addCallAdapterFactory(RxJavaCallAdapterFactory.create())
        .build()
        .create(Service.class);

现在您可以像这样使用API声明：

interface Service {

    @GET("/users/{id}/name")
    Call<String> userName(@Path("userId") String userId);

    // RxJava version
    @GET("/users/{id}/name")
    Observable<String> userName(@Path("userId") String userId);
}

Answer 2

一种可能的解决方案是使用jsonement作为回调类型（回调）

api.getUserName(userId, new Callback<JsonElement>() {...});

在成功方法中，您可以将jsonement转换为字符串，或JsonObject。

JsonObject jsonObj = element.getAsJsonObject();
String strObj = element.toString();

Answer 3

我想通了。这很尴尬，但很简单...临时解决办法可能是这样的:

 public void success(Response response, Response ignored) {
            TypedInput body = response.getBody();
            try {
                BufferedReader reader = new BufferedReader(new InputStreamReader(body.in()));
                StringBuilder out = new StringBuilder();
                String newLine = System.getProperty("line.separator");
                String line;
                while ((line = reader.readLine()) != null) {
                    out.append(line);
                    out.append(newLine);
                }

                // Prints the correct String representation of body. 
                System.out.println(out);
            } catch (IOException e) {
                e.printStackTrace();
            }
        }

但是，如果您想直接获得回调，更好的方法是使用转换器。

public class Main {
public interface ApiService {
    @GET("/api/")
    public void getJson(Callback<String> callback);
}

public static void main(String[] args) {
    RestAdapter restAdapter = new RestAdapter.Builder()
            .setClient(new MockClient())
            .setConverter(new StringConverter())
            .setEndpoint("http://www.example.com").build();

    ApiService service = restAdapter.create(ApiService.class);
    service.getJson(new Callback<String>() {
        @Override
        public void success(String str, Response ignored) {
            // Prints the correct String representation of body.
            System.out.println(str);
        }

        @Override
        public void failure(RetrofitError retrofitError) {
            System.out.println("Failure, retrofitError" + retrofitError);
        }
    });
}

static class StringConverter implements Converter {

    @Override
    public Object fromBody(TypedInput typedInput, Type type) throws ConversionException {
        String text = null;
        try {
            text = fromStream(typedInput.in());
        } catch (IOException ignored) {/*NOP*/ }

        return text;
    }

    @Override
    public TypedOutput toBody(Object o) {
        return null;
    }

    public static String fromStream(InputStream in) throws IOException {
        BufferedReader reader = new BufferedReader(new InputStreamReader(in));
        StringBuilder out = new StringBuilder();
        String newLine = System.getProperty("line.separator");
        String line;
        while ((line = reader.readLine()) != null) {
            out.append(line);
            out.append(newLine);
        }
        return out.toString();
    }
}

public static class MockClient implements Client {
    @Override
    public Response execute(Request request) throws IOException {
        URI uri = URI.create(request.getUrl());
        String responseString = "";

        if (uri.getPath().equals("/api/")) {
            responseString = "{result:\"ok\"}";
        } else {
            responseString = "{result:\"error\"}";
        }

        return new Response(request.getUrl(), 200, "nothing", Collections.EMPTY_LIST,
                new TypedByteArray("application/json", responseString.getBytes()));
    }
  }
}

如果你知道如何改进这段代码，请随意写。