问题
I'm trying to parse this json response yahoo yql with Retrofit,but the problem is that the response begins(as you can see in the link above) with the following characters: "finance_charts_json_callback(".
Therefore i get the following error: com.google.gson.JsonSyntaxException: java.lang.IllegalStateException: Expected BEGIN_OBJECT but was STRING at line 1 column 1 path $ .
Is posible to parse this json file with Retrofit? Thanks in advance
回答1:
It returns a json that's invoked by a callback function(jsonp). Strip out the function wrapper and parse it or invoke an endpoint that's not jsonp based if one available.
Update1:
The following is a sample of how we can convert the jsonp response to json using regex:
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);
}
}
Update 2:
I have extended the existing GsonConverterFactory to support 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);
}
}
Now while building the service, register the above converter to retrofit as converter like below:
Retrofit retrofit = new Retrofit.Builder()
.setEndpoint("<yahoo api url>").setConverter(JsonpGsonConverterFactory.create())
.build();
Update 3:
The class "GsonRequestBodyConverter" already comes with the following dependency, but I am adding it here for the sake of completeness:
"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());
}
}
And finally the missing piece '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) {
}
}
}
来源：https://stackoverflow.com/questions/34421851/retrofit-how-to-parse-this-response