我知道我可以使用 TypeAdapter，但我想使用同一个 Retrofit 客户端来执行不同的调用，并且 JSON 结构可能会因 API 端点而有很大不同。
嗯，你可以做到，而且使用 Retrofit 2 比普通的 Gson 更容易。
例如
final class User {
final String name = null;
final String lastname = null;
}
interface IService {
@GET("/")
@Unwrap
Call<List<User>> getUsers();
}
注意上面的@Unwrap 注释。这是一个可选的自定义注释，标记调用响应正文应“展开”：
@Retention(RUNTIME)
@Target(METHOD)
@interface Unwrap {
}
现在您可以创建一个 Retrofit 转换器工厂来分析注释。当然，这并不能涵盖所有情况，但它是可扩展的，您可以对其进行改进：
final class UnwrappingGsonConverterFactory
extends Converter.Factory {
private final Gson gson;
private UnwrappingGsonConverterFactory(final Gson gson) {
this.gson = gson;
}
static Converter.Factory create(final Gson gson) {
return new UnwrappingGsonConverterFactory(gson);
}
@Override
public Converter<ResponseBody, ?> responseBodyConverter(final Type type, final Annotation[] annotations, final Retrofit retrofit) {
if ( !needsUnwrapping(annotations) ) {
return super.responseBodyConverter(type, annotations, retrofit);
}
final TypeAdapter<?> typeAdapter = gson.getAdapter(TypeToken.get(type));
return new UnwrappingResponseConverter(typeAdapter);
}
private static boolean needsUnwrapping(final Annotation[] annotations) {
for ( final Annotation annotation : annotations ) {
if ( annotation instanceof Unwrap ) {
return true;
}
}
return false;
}
private static final class UnwrappingResponseConverter
implements Converter<ResponseBody, Object> {
private final TypeAdapter<?> typeAdapter;
private UnwrappingResponseConverter(final TypeAdapter<?> typeAdapter) {
this.typeAdapter = typeAdapter;
}
@Override
public Object convert(final ResponseBody responseBody)
throws IOException {
try ( final JsonReader jsonReader = new JsonReader(responseBody.charStream()) ) {
// Checking if the JSON document current value is null
final JsonToken token = jsonReader.peek();
if ( token == JsonToken.NULL ) {
return null;
}
// If it's an object, expect `{`
jsonReader.beginObject();
Object value = null;
// And iterate over all properties
while ( jsonReader.hasNext() ) {
final String name = jsonReader.nextName();
// I'm assuming apiVersion and otherData should be skipped
switch ( name ) {
case "apiVersion":
case "otherData":
jsonReader.skipValue();
break;
// But any other is supposed to contain the required value (or null)
default:
value = typeAdapter.read(jsonReader);
break;
}
}
// Consume the object end `}`
jsonReader.endObject();
return value;
} finally {
responseBody.close();
}
}
}
}
我已经用以下代码对其进行了测试：
for ( final String filename : ImmutableList.of("usersA.json", "usersB.json") ) {
// Mocking the HTTP client to return a JSON document always
final OkHttpClient client = new Builder()
.addInterceptor(staticResponse(Q43921751.class, filename))
.build();
// Note the order of converter factories
final Retrofit retrofit = new Retrofit.Builder()
.baseUrl("http://whatever")
.client(client)
.addConverterFactory(UnwrappingGsonConverterFactory.create(gson))
.addConverterFactory(GsonConverterFactory.create(gson))
.build();
final IService service = retrofit.create(IService.class);
service.getUsers()
.execute()
.body()
.forEach(user -> System.out.println(user.name + " " + user.lastname));
}
输出：
美食吧
富吧