Zmodernizuj datę serializacji GSON z łańcucha json do java.util.date

Używam biblioteki Retrofit dla moich wywołań REST. Większość tego, co zrobiłem, była gładka jak masło, ale z jakiegoś powodu mam problemy z konwersją ciągów datowników JSON na java.util.Dateobiekty. Wygląda na to, że nadchodzący JSON.

{
    "date": "2013-07-16",
    "created_at": "2013-07-16T22:52:36Z",
} 

How can I tell Retrofit or Gson to convert these strings into java.util.Date objects?

Gson gson = new GsonBuilder()
    .setDateFormat("yyyy-MM-dd'T'HH:mm:ss")
    .create();

RestAdapter restAdapter = new RestAdapter.Builder()
    .setEndpoint(API_BASE_URL)
    .setConverter(new GsonConverter.create(gson))
    .build();

Or the Kotlin equivalent:

val gson = GsonBuilder().setDateFormat("yyyy-MM-dd'T'HH:mm:ss").create()
RestAdapter restAdapter = Retrofit.Builder()
    .baseUrl(API_BASE_URL)
    .addConverterFactory(GsonConverterFactory.create(gson))
    .build()
    .create(T::class.java)

You can set your customized Gson parser to retrofit. More here: Retrofit Website

Look at Ondreju's response to see how to implement this in retrofit 2.

@gderaco's answer updated to retrofit 2.0:

Gson gson = new GsonBuilder()
.setDateFormat("yyyy-MM-dd'T'HH:mm:ss")
.create();

Retrofit retrofitAdapter = new Retrofit.Builder()
.baseUrl(API_BASE_URL)
.addConverterFactory(GsonConverterFactory.create(gson))
.build();

Here is how I did it:

Create DateTime class extending Date and then write a custom deserializer:

public class DateTime extends java.util.Date {

    public DateTime(long readLong) {
        super(readLong);
    }

    public DateTime(Date date) {
        super(date.getTime());
    }       
}

Now for the deserializer part where we register both Date and DateTime converters:

public static Gson gsonWithDate(){
    final GsonBuilder builder = new GsonBuilder();

    builder.registerTypeAdapter(Date.class, new JsonDeserializer<Date>() {  

        final DateFormat df = new SimpleDateFormat("yyyy-MM-dd");  
        @Override  
        public Date deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {  
            try {  
                return df.parse(json.getAsString());  
            } catch (final java.text.ParseException e) {  
                e.printStackTrace();  
                return null;  
            }  
        }
    });

    builder.registerTypeAdapter(DateTime.class, new JsonDeserializer<DateTime>() {  

        final DateFormat df = new SimpleDateFormat("yyyy-MM-dd HH:mm:ss");  
        @Override  
        public DateTime deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {  
            try {  
                return new DateTime(df.parse(json.getAsString()));  
            } catch (final java.text.ParseException e) {
                e.printStackTrace();  
                return null;  
            }  
        }
    });

    return builder.create();
}

And when you create your RestAdapter, do the following:

new RestAdapter.Builder().setConverter(gsonWithDate());

Your Foo should look like this:

class Foo {
    Date date;
    DateTime created_at;
}

Gson can handle only one datetime format (those specified in builder) plus the iso8601 if parsing with custom format is not possible. So, a solution could be to write your custom deserializer. To solve your problem I defined:

package stackoverflow.questions.q18473011;

import java.util.Date;

public class Foo {

    Date date;
    Date created_at;

    public Foo(Date date, Date created_at){
       this.date = date;
       this.created_at = created_at;
    }

    @Override
    public String toString() {
       return "Foo [date=" + date + ", created_at=" + created_at + "]";
    }

}

with this deserializer:

package stackoverflow.questions.q18473011;

import java.lang.reflect.Type;
import java.text.*;
import java.util.Date;

import com.google.gson.*;

public class FooDeserializer implements JsonDeserializer<Foo> {

     public Foo deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {

        String a = json.getAsJsonObject().get("date").getAsString();
        String b = json.getAsJsonObject().get("created_at").getAsString();

        SimpleDateFormat sdfDate = new SimpleDateFormat("yyyy-MM-dd");
        SimpleDateFormat sdfDateWithTime = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'");

        Date date, created;
        try {
           date = sdfDate.parse(a);
           created = sdfDateWithTime.parse(b);
        } catch (ParseException e) {
           throw new RuntimeException(e);
        }

        return new Foo(date, created);
    }

}

Final step is to create a Gson instance with right adapter:

package stackoverflow.questions.q18473011;

import com.google.gson.*;

public class Question {

    /**
     * @param args
     */
    public static void main(String[] args) {
      String s = "{ \"date\": \"2013-07-16\",    \"created_at\": \"2013-07-16T22:52:36Z\"}";


      GsonBuilder builder = new GsonBuilder();
      builder.registerTypeAdapter(Foo.class, new FooDeserializer());

      Gson gson = builder.create();
      Foo myObject = gson.fromJson(s, Foo.class);

      System.out.println("Result: "+myObject);
    }

}

My result:

Result: Foo [date=Tue Jul 16 00:00:00 CEST 2013, created_at=Tue Jul 16 22:52:36 CEST 2013]

Quite literally if you already have an Date object with the name "created_at" in the class you are creating then it is this easy:

Gson gson = new GsonBuilder().setDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'").create();
YourObject parsedObject1 = gson.fromJson(JsonStringYouGotSomehow, YourObject.class);

And you're done. no complicated overriding needed.

You can define two new classes like this:

import java.util.Date;

public class MyDate extends Date {
}

and

import java.util.Date;

public class CreatedAtDate extends Date {
}

Your POJO will be like this:

import MyDate;
import CreatedAtDate;

public class Foo {
    MyDate date;
    CreatedAtDate created_at;
}

Finally set your custom deserializer:

public class MyDateDeserializer implements JsonDeserializer<Date> {

    public static final SimpleDateFormat sServerDateDateFormat = new SimpleDateFormat("yyyy-MM-dd");

    @Override
    public MyDate deserialize(JsonElement json, Type typeOfT, JsonDeserializationContext context) throws JsonParseException {
         if (json != null) {
            final String jsonString = json.getAsString();
            try {
                return (MyDate) sServerDateDateFormat.parse(jsonString);
            } catch (ParseException e) {
                e.printStackTrace();
            }
        }
        return null;
    }
}

and

GsonBuilder builder = new GsonBuilder();
builder.registerTypeAdapter(MyDate.class, new MyDateDeserializer());

This doesn't answer directly the question asked, but is in my opinion the "state of the art" if the coder has the full freedom of choice on how to solve the problem.

First of all, it's not best solution to use java.util.Date. Reason is that those classes had no ideal behaviour in some corner cases so where superseeded by the Java Instant class etc. check the answer of Basil Bourque in this S.O. question: Creating Date objects in Kotlin for API level less than or equal to 16

So I used the Instant class of ThreeTenABP, and using Kotlin, on Android:

val gson = GsonBuilder().registerTypeAdapter(Instant::class.java,
    JsonDeserializer<Instant> { json: JsonElement, _: Type?, _: JsonDeserializationContext? ->
        ZonedDateTime.parse(
            json.asJsonPrimitive.asString
        ).toInstant()
    }
).create()

val retrofit = Retrofit.Builder()
    .baseUrl(baseUrl)
    .addConverterFactory(GsonConverterFactory.create(gson))
    .build()