android - RETROFIT 如何解析这个响应

Question

我正在尝试解析此 json 响应 yahoo yql使用 Retrofit，但问题是响应以以下字符开始(如您在上面的链接中所见):“finance_charts_json_callback(”。

因此我得到以下错误:com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: 应为 BEGIN_OBJECT 但在第 1 行第 1 列路径 $ 中为 STRING。

可以用 Retrofit 解析这个 json 文件吗？提前致谢

Answer 1

它返回一个由回调函数 (jsonp) 调用的 json。剥离函数包装器并解析它或调用一个不基于 jsonp 的端点(如果可用)。

更新1:

以下是我们如何使用正则表达式将 jsonp 响应转换为 json 的示例:

import java.util.regex.Matcher;
import java.util.regex.Pattern;

/**
 * Created by jamesanto on 12/22/15.
 */
public class JsonpParser {

    private static final Pattern JSONP = Pattern.compile("(?s)\\w+\\((.*)\\).*");

    public static String jsonpToJson(String jsonStr) {
        Matcher matcher = JSONP.matcher(jsonStr);
        if(matcher.find()) {
            return matcher.group(1);
        } else {
            throw new IllegalArgumentException("Unknown jsonp format");
        }
    }

    public static void main(String[] args) {
        String sampleJson = "finance_charts_json_callback({\n" +
                "    \"base\": \"cmc stations\",\n" +
                "    \"clouds\": {\n" +
                "        \"all\": 75\n" +
                "    },\n" +
                "    \"cod\": 200,\n" +
                "    \"coord\": {\n" +
                "        \"lat\": 51.51,\n" +
                "        \"lon\": -0.13\n" +
                "    },\n" +
                "    \"dt\": 1450807548,\n" +
                "    \"id\": 2643743,\n" +
                "    \"main\": {\n" +
                "        \"humidity\": 82,\n" +
                "        \"pressure\": 1011,\n" +
                "        \"temp\": 286.94,\n" +
                "        \"temp_max\": 287.59,\n" +
                "        \"temp_min\": 286.15\n" +
                "    },\n" +
                "    \"name\": \"London\",\n" +
                "    \"sys\": {\n" +
                "        \"country\": \"GB\",\n" +
                "        \"id\": 5091,\n" +
                "        \"message\": 0.0136,\n" +
                "        \"sunrise\": 1450771468,\n" +
                "        \"sunset\": 1450799652,\n" +
                "        \"type\": 1\n" +
                "    },\n" +
                "    \"weather\": [\n" +
                "        {\n" +
                "            \"description\": \"light rain\",\n" +
                "            \"icon\": \"10n\",\n" +
                "            \"id\": 500,\n" +
                "            \"main\": \"Rain\"\n" +
                "        },\n" +
                "        {\n" +
                "            \"description\": \"light intensity drizzle rain\",\n" +
                "            \"icon\": \"09n\",\n" +
                "            \"id\": 310,\n" +
                "            \"main\": \"Drizzle\"\n" +
                "        }\n" +
                "    ],\n" +
                "    \"wind\": {\n" +
                "        \"deg\": 210,\n" +
                "        \"gust\": 14.9,\n" +
                "        \"speed\": 9.8\n" +
                "    }\n" +
                "});";


        String json = jsonpToJson(sampleJson);
        System.out.println(json);
    }
}

更新 2:

我扩展了现有的 GsonConverterFactory 以支持 jsonp。

//JsonpGsonResponseBodyConverter.java

package retrofit;

import com.google.gson.Gson;
import com.squareup.okhttp.ResponseBody;
import java.io.IOException;
import java.io.Reader;
import java.lang.reflect.Type;

final class JsonpGsonResponseBodyConverter<T> implements Converter<ResponseBody, T> {
  private final Gson gson;
  private final Type type;

  JsonpGsonResponseBodyConverter(Gson gson, Type type) {
    this.gson = gson;
    this.type = type;
  }

  private static String readerToString(Reader reader) throws IOException {
    StringBuilder builder = new StringBuilder();
    int charsRead = -1;
    char[] chars = new char[100];
    do{
      charsRead = reader.read(chars,0,chars.length);
      //if we have valid chars, append them to end of string.
      if(charsRead>0)
        builder.append(chars,0,charsRead);
    }while(charsRead>0);
    return builder.toString();
  }

  @Override public T convert(ResponseBody value) throws IOException {
    Reader reader = value.charStream();
    try {
      String jsonp = readerToString(reader);
      String json = JsonpParser.jsonpToJson(jsonp);
      return gson.fromJson(json, type);
    } finally {
      Utils.closeQuietly(reader);
    }
  }
}

//JsonpGsonConverterFactory.java

package retrofit;

import com.google.gson.Gson;
import com.squareup.okhttp.RequestBody;
import com.squareup.okhttp.ResponseBody;
import java.lang.annotation.Annotation;
import java.lang.reflect.Type;

/**
 * A {@linkplain Converter.Factory converter} which uses Gson for JSON.
 * <p>
 * Because Gson is so flexible in the types it supports, this converter assumes that it can handle
 * all types. If you are mixing JSON serialization with something else (such as protocol buffers),
 * you must {@linkplain Retrofit.Builder#addConverterFactory(Converter.Factory) add this instance}
 * last to allow the other converters a chance to see their types.
 */
public final class JsonpGsonConverterFactory extends Converter.Factory {
  /**
   * Create an instance using a default {@link Gson} instance for conversion. Encoding to JSON and
   * decoding from JSON (when no charset is specified by a header) will use UTF-8.
   */
  public static JsonpGsonConverterFactory create() {
    return create(new Gson());
  }

  /**
   * Create an instance using {@code gson} for conversion. Encoding to JSON and
   * decoding from JSON (when no charset is specified by a header) will use UTF-8.
   */
  public static JsonpGsonConverterFactory create(Gson gson) {
    return new JsonpGsonConverterFactory(gson);
  }

  private final Gson gson;

  private JsonpGsonConverterFactory(Gson gson) {
    if (gson == null) throw new NullPointerException("gson == null");
    this.gson = gson;
  }

  @Override
  public Converter<ResponseBody, ?> fromResponseBody(Type type, Annotation[] annotations) {
    return new JsonpGsonResponseBodyConverter<>(gson, type);
  }

  @Override public Converter<?, RequestBody> toRequestBody(Type type, Annotation[] annotations) {
    return new GsonRequestBodyConverter<>(gson, type);
  }
}

现在在构建服务时，注册上述转换器以改造为如下转换器:

Retrofit retrofit = new Retrofit.Builder()
                    .setEndpoint("<yahoo api url>").setConverter(JsonpGsonConverterFactory.create())
                    .build();

更新 3:

“GsonRequestBodyConverter”类已经带有以下依赖项，但为了完整起见，我将其添加到这里:

"com.squareup.retrofit"% "converter-gson"% "2.0.0-beta2"

package retrofit;

import com.google.gson.Gson;
import com.squareup.okhttp.MediaType;
import com.squareup.okhttp.RequestBody;
import java.io.IOException;
import java.io.OutputStreamWriter;
import java.io.Writer;
import java.lang.reflect.Type;
import java.nio.charset.Charset;
import okio.Buffer;

final class GsonRequestBodyConverter<T> implements Converter<T, RequestBody> {
  private static final MediaType MEDIA_TYPE = MediaType.parse("application/json; charset=UTF-8");
  private static final Charset UTF_8 = Charset.forName("UTF-8");

  private final Gson gson;
  private final Type type;

  GsonRequestBodyConverter(Gson gson, Type type) {
    this.gson = gson;
    this.type = type;
  }

  @Override public RequestBody convert(T value) throws IOException {
    Buffer buffer = new Buffer();
    Writer writer = new OutputStreamWriter(buffer.outputStream(), UTF_8);
    try {
      gson.toJson(value, type, writer);
      writer.flush();
    } catch (IOException e) {
      throw new AssertionError(e); // Writing to Buffer does no I/O.
    }
    return RequestBody.create(MEDIA_TYPE, buffer.readByteString());
  }
}

最后是缺少的部分“Utils”:

package retrofit;

import java.io.Closeable;
import java.io.IOException;

/**
 * Created by jamesanto on 12/23/15.
 */
public final class Utils {
    static void closeQuietly(Closeable closeable) {
        if (closeable == null) return;
        try {
            closeable.close();
        } catch (IOException ignored) {
        }
    }
}