Retrofit2使用CallAdapterFactory的错误处理

概述

在使用Retrofit1的时候有一个类叫ErrorHandler,可以方便的定义自己的异常处理，但是在Retrofit2中是没有这个类的，详情见讨论：How do we create ErrorHandler in retrofit 2.0? #1102

总结

在相关讨论之下发现了一种好的解决方案,详情见： Retrofit 2 and Rx Java call adapter error handling，主要通过CallAdapter.Factory 来实现，核心代码

• 定义CallAdapter

public class RxErrorHandlingCallAdapterFactory extends CallAdapter.Factory {
    private final RxJavaCallAdapterFactory original;

    private RxErrorHandlingCallAdapterFactory() {
        original = RxJavaCallAdapterFactory.create();
    }

    public static CallAdapter.Factory create() {
        return new RxErrorHandlingCallAdapterFactory();
    }

    @Override
    public CallAdapter<?> get(Type returnType, Annotation[] annotations, Retrofit retrofit) {
        return new RxCallAdapterWrapper(retrofit, original.get(returnType, annotations, retrofit));
    }

    private static class RxCallAdapterWrapper implements CallAdapter<Observable<?>> {
        private final Retrofit retrofit;
        private final CallAdapter<?> wrapped;

        public RxCallAdapterWrapper(Retrofit retrofit, CallAdapter<?> wrapped) {
            this.retrofit = retrofit;
            this.wrapped = wrapped;
        }

        @Override
        public Type responseType() {
            return wrapped.responseType();
        }

        @SuppressWarnings("unchecked")
        @Override
        public <R> Observable<?> adapt(Call<R> call) {
            return ((Observable) wrapped.adapt(call)).onErrorResumeNext(new Func1<Throwable, Observable>() {
                @Override
                public Observable call(Throwable throwable) {
                    return Observable.error(asRetrofitException(throwable));
                }
            });
        }

        private RetrofitException asRetrofitException(Throwable throwable) {
            // We had non-200 http error
            if (throwable instanceof HttpException) {
            // A network error happened
            }
            if (throwable instanceof IOException) {
            }
            // We don't know what happened. We need to simply convert to an unknown error
            return RetrofitException.unexpectedError(throwable);
        }
    }
}

• 定义Exception

public class RetrofitException extends RuntimeException {
    public static RetrofitException httpError(String url, Response response, Retrofit retrofit) {
        String message = response.code() + " " + response.message();
        return new RetrofitException(message, url, response, Kind.HTTP, null, retrofit);
    }

    public static RetrofitException networkError(IOException exception) {
        return new RetrofitException(exception.getMessage(), null, null, Kind.NETWORK, exception, null);
    }

    public static RetrofitException unexpectedError(Throwable exception) {
        return new RetrofitException(exception.getMessage(), null, null, Kind.UNEXPECTED, exception, null);
    }
}

• 设置到Builder

new Retrofit.Builder()
        .baseUrl("your base url")
        .addConverterFactory(GsonConverterFactory.create(new Gson()))
        .addCallAdapterFactory(RxErrorHandlingCallAdapterFactory.create())
        .build();

• 错误处理

public void onError(Throwable throwable) {
    if (throwable instanceof HttpException) {
       // We had non-2XX http error
    }
    if (throwable instanceof IOException) {
       // A network or conversion error happened
    }

    // We don't know what happened. We need to simply convert to an unknown error
    // ...
  }